Bonded body, ceramic circuit board, and semiconductor device

Abstract

A bonded body according to the present embodiment is provided with a ceramic substrate, a copper plate, and a bonding layer. The bonding layer is disposed on at least one surface of the ceramic substrate and bonds the ceramic substrate and the copper plate. The bonding layer includes a Ti reaction layer and a plurality of first alloys. The Ti reaction layer contains titanium nitride or titanium oxide as a main component. The plurality of first alloys are located between the Ti reaction layer and the copper plate. Each of the plurality of first alloys contains at least one selected from a Cu-Sn alloy and a Cu-In alloy. The plurality of first alloys have mutually differing Sn concentrations or In concentrations. The amount of warping can be reduced by using the present embodiment. Furthermore, the speed of heating and the speed of cooling in a joining process can be increased. In the present embodiment, a silicon nitride substrate is suitable as the ceramic substrate.

Description

Technical Field

[0001] The embodiments described below relate to a bonded body, a ceramic circuit board, and a semiconductor device.

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, heating 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. Also, 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, bonding is performed in a vacuum in order to prevent Ti from being nitrided or oxidized before bonding. To bond in a vacuum, the inside of the bonding apparatus must be evacuated. After evacuating to a vacuum and then raising the temperature, only batch processing could be performed in the heating bonding process. In the heating bonding process, there are four processes of evacuation, heating, bonding, and cooling per batch. It took more than 24 hours per batch. For this reason, the mass productivity is not good. On the other hand, International Publication No. 2018 / 199060 (Patent Document 2) discloses performing a heating bonding process in a continuous furnace. In the examples of Patent Document 2, bonding is performed at a furnace length of 3 m and a conveyance speed of 10 cm / min. Including the holding time in the middle, heating bonding can be performed in about 2 hours.

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, an Ag-Cu-Ti based brazing filler metal containing 40 mass% or more of Ag is used. Ag and Cu are components that form a eutectic. The solidification temperature of the AgCu eutectic is about 780°C. The bonding temperature in the active metal bonding method is 800°C to 950°C. Since the solidification temperature of the AgCu eutectic is about 780°C, solidification starts during the bonding process. In the bonding process, after maintaining the bonding temperature, it is cooled to room temperature. When the solidification temperature of the compound present in the bonding layer is high, the thermal stress increases during the cooling process. The increase in thermal stress has led to an increase in the amount of warpage of the bonded body. In order to address such problems, the present invention provides a bonded body in which a compound having a low solidification temperature or phase change temperature is present in the bonding layer.

MEANS FOR SOLVING THE PROBLEMS

[0005] The bonded body according to the embodiment includes a ceramic substrate, a copper plate, and a bonding layer. The bonding layer is disposed on at least one surface of the ceramic substrate and bonds the ceramic substrate and the copper plate. The bonding layer includes a Ti reaction layer and a plurality of first alloys. The Ti reaction layer contains titanium nitride or titanium oxide as a main component. The plurality of first alloys are located between the Ti reaction layer and the copper plate. Each of the plurality of first alloys contains one or more selected from a Cu-Sn alloy and a Cu-In alloy. The plurality of first alloys have different Sn concentrations or In concentrations from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0007] The joined body according to the embodiment includes a ceramic substrate, a copper plate, and a joining layer. The joining layer is disposed on at least one surface of the ceramic substrate and joins the ceramic substrate and the copper plate. The joining layer includes a Ti reaction layer and a plurality of first alloys. The Ti reaction layer contains titanium nitride or titanium oxide as a main component. The plurality of first alloys are located between the Ti reaction layer and the copper plate. Each of the plurality of first alloys contains one or more selected from a Cu-Sn alloy and a Cu-In alloy. The plurality of first alloys have different Sn concentrations or In concentrations from each other. FIG. 1 is a schematic diagram showing an example of a joined body according to an embodiment. FIG. 2 is a schematic cross-sectional view showing an example of the joining layer of the joined body according to the embodiment. In FIGS. 1 and 2, 1 is the joined body, 2 is the ceramic substrate, 3 is the copper plate, 4 is the joining layer, 5 is the Ti reaction layer, 6 is the first alloy, 7 is the second alloy, and 8 is titanium silicide particles. In FIG. 2, the first alloy 6 is indicated by a dotted line. The second alloy 7 is indicated by a dotted hatching. The titanium silicide particles 8 are indicated by blackening. In the joined body 1 illustrated in FIG. 1, copper plates 3 are respectively provided on both surfaces of the ceramic substrate 2 via the joining layer 4. Also, the vertical and horizontal sizes of the ceramic substrate 2 are the same as the vertical and horizontal sizes of the copper plate 3, respectively. The joined body according to the embodiment is not limited to such a form. The joined body may have a structure in which the copper plate 3 is provided only on one side of the ceramic substrate 2. The vertical and horizontal sizes of the ceramic substrate 2 may be different from the vertical and horizontal sizes of the copper plate 3.

[0008] Examples of the ceramic substrate 2 include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and an aludur substrate. The aludur substrate is a ceramic substrate in which aluminum oxide and zirconium oxide are mixed. 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 may decrease. Also, if the substrate thickness is greater than 1 mm, the ceramic substrate may become a heat resistor, possibly reducing the heat dissipation of the bonded body. Also, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more. Also, 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. Therefore, 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 aludur substrate is as high as about 550 MPa, but the thermal conductivity is about 30 - 50 W / m·K. As the ceramic substrate 2, it 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 ceramic reacts with an active metal brazing material containing Ti to form a reaction layer mainly composed of titanium nitride. Also, the oxide ceramic reacts with an active metal brazing material containing Ti to form a reaction layer mainly composed of titanium oxide. The oxide ceramic is an aluminum oxide substrate, an aludur substrate, etc. The Ti reaction layer 5 is a layer mainly composed of titanium nitride or a layer mainly composed of titanium oxide. The layer mainly composed of titanium nitride or the layer mainly composed of titanium oxide is formed by the reaction of Ti of the ceramic substrate 2 and the active metal brazing material.

[0009] It is preferable that copper plates 3 are arranged on both sides of the ceramic substrate 2. By joining copper plates on both sides, warpage of the joined body can be suppressed. As 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. As shown in JIS-H-3100 (such as ISO1337), the copper purity of oxygen-free copper is 99.96 mass% or more. Oxygen-free copper is a kind of pure copper. The copper plate 3 is used as a circuit part or a heat sink. By increasing the thickness of the copper plate 3, the capacitance and heat dissipation can be improved. Therefore, the thickness of the copper plate 3 is preferably 0.6 mm or more, and more preferably 0.8 mm or more.

[0010] The bonding layer 4 includes a Ti reaction layer 5 mainly composed of titanium nitride or titanium oxide. The Ti reaction layer 5 is formed when the so-called active metal bonding method is used. When the ceramic substrate 2 is a nitride-based ceramic, the main component of the Ti reaction layer 5 is titanium nitride (TiN). The titanium nitride, which is the main component of the Ti reaction layer 5, may contain a compound other than the atomic ratio of titanium to nitrogen of 1:1. When the ceramic substrate 2 is an oxide-based ceramic, the main component of the Ti reaction layer 5 is titanium oxide (TiO2). The titanium oxide, which is the main component of the Ti reaction layer 5, may contain a compound other than the atomic ratio of titanium to oxygen of 1:2, such as TiO2, TiO, and Ti2O3. The Ti reaction layer 5 refers to a region with a Ti content of 50 mass% or more formed on the surface of the ceramic substrate 2. Also, the Ti reaction layer 5 preferably exists on the surface of the ceramic substrate 2 at 40% or more and 100% or less per 200 μm of the unit length. The phrase "40% or more per 200 μm of the unit length" means that when observing the cross-section of the bonding layer 4, on the surface of the ceramic substrate 2, the state where the Ti reaction layer 5 is formed over a total of 40 μm or more out of 200 μm.

[0011] The bonding layer 4 includes a plurality of first alloys 6 located between the Ti reaction layer 5 and the copper plate 3. The composition ratios of the plurality of first alloys 6 are different from each other. Specifically, the plurality of first alloys 6 have different Sn concentrations or In concentrations. Each of the plurality of first alloys contains one or more selected from Cu-Sn alloys and Cu-In alloys. Note that it is not necessary for all the Cu-Sn alloys or Cu-In alloys present in the bonding layer 4 to have different Sn concentrations or In concentrations from each other. It is sufficient that two or more first alloys 6 having different Sn concentrations or In concentrations are present in the bonding layer 4. Hereinafter, mainly, an example in which the first alloy 6 is a Cu-Sn compound will be described. In the following example, it is also possible to replace the Cu-Sn compound with a Cu-In compound. Note that different Sn concentrations means that when the total content of Cu and Sn is 100 atomic%, the Sn concentrations differ from each other by 2 atomic% or more. Different In concentrations means that when the total content of Cu and In is 100 atomic%, the In concentrations differ from each other by 2 atomic% or more. The atomic ratio of Cu and Sn can be measured by point analysis of Energy Dispersive X-ray Spectroscopy (EDX). EDX is sometimes also called EDS. Here, SEM-EDX is used as EDX. As the SEM, Field Emission SEM (FE-SEM) may be used. As the FE-SEM, a device manufactured by JEOL, JSM-7200F or a device having equivalent performance is used. As the EDX, a device manufactured by JEOL, EX-74600U4L2Q or a device having equivalent performance is used. In the FE-SEM, the cross-section of the bonding layer 4 is observed. The cross-section is a plane parallel to the thickness direction. The thickness direction is perpendicular to the surface of the ceramic substrate 2 and parallel to the direction connecting the ceramic substrate 2 and the copper plate 3. The measurement conditions of the FE-SEM are set to an acceleration voltage of 15 kV and a magnification of 3000 times. The field of view area is set to the thickness of the bonding layer × 40 μm in the width direction. The width direction is parallel to the surface of the ceramic substrate 2 and perpendicular to the thickness direction. The measurement conditions for EDX are set to 50 scanning times and a dwell time of 0.2 ms. The dwell time is the measurement speed per pixel. When performing area analysis of EDX, the number of captured pixels is set to 256 horizontally × 198 vertically, the detection count is set to 3700 - 4100 cps (Count Per Second), and the quantitative map is set to 5×5 bit / point. Point analysis is an analysis using the measurement result of 1 detection count (1 location). Area analysis is an analysis using the measurement results of multiple detection counts. Also, area analysis is sometimes referred to as surface analysis. Analysis by EDX may be performed after examining the elements constituting the bonding layer in advance to identify specific elements. For example, when Cu (copper), Sn (tin), Ti (titanium), Si (silicon), O (oxygen), and N (nitrogen) are detected as the elements constituting the bonding layer, these elements are set as specific elements. By performing mapping of specific elements using the results of area analysis, the area ratio can be obtained. When the thickness of the bonding layer is 30 μm, the field area is 30 μm in the thickness direction × 40 μm in the width direction. For SEM-EDX mapping, the functions attached to SEM-EDX are used. When the mapping function is not attached, image software is used for mapping. The area ratio is calculated using the average value obtained by performing EDX area analysis on three regions. The area (field area) of one region is the bonding layer thickness × 40 μm in the width direction. The measurement field of view is adjusted according to bonding layer 4. Any three adjacent regions are analyzed from the cross-section of bonding layer 4. Bonding layer 4 is the range from the boundary between ceramic substrate 2 and bonding layer 4 to the boundary between bonding layer 4 and copper plate 3. The boundary between ceramic substrate 2 and bonding layer 4 is the bonding interface between the surface of ceramic substrate 2 and Ti reaction layer 5. For example, when a silicon nitride substrate is used, the bonding interface between the silicon nitride substrate and the titanium nitride layer is the boundary between ceramic substrate 2 and bonding layer 4. For example, the dashed line BL1 shown in Figure 2 is the boundary between ceramic substrate 2 and bonding layer 4. The boundary between the bonding layer 4 and the copper plate 3 is defined based on the Ti content. In the vicinity of the boundary between the bonding layer 4 and the copper plate 3, the Ti content decreases from the bonding layer 4 toward the surface of the copper plate 3. The boundary is defined based on the location where a region with a Ti content of 1 atomic % or less is continuously formed in the width direction for 50 μm. When there are multiple such locations, the boundary between the bonding layer 4 and the copper plate 3 is defined based on the location closest to the bonding layer 4 (ceramic substrate 2) among the multiple locations. In FIG. 2, the solid line SL between the bonding layer 4 and the copper plate 3 indicates the set of points with a Ti content of 1 atomic %. As an example, in the vicinity of the solid line SL, in portions P1 and P2, regions with a Ti content of 1 atomic % or less are continuously formed in the width direction for 50 μm. Portion P1 is located closer to the ceramic substrate 2 side than portion P2. Therefore, the dashed line BL2 based on portion P1 is defined as the boundary between the bonding layer 4 and the copper plate 3. For the measurement of the Ti content for determining the boundary between the bonding layer 4 and the copper plate 3, EDX point analysis is used. Point analysis is performed at 5-μm intervals to obtain the Ti content. Also, the region with a Ti content of 1 atomic % or less includes the region with a Ti content of 0 atomic % (below the detection limit). The first alloy 6 refers to an alloy in which, when the total of Cu, the first element, and Ti is 100 atomic %, the total of Cu and the first element is 50 atomic % or more. The first element is one or two selected from Sn and In. For example, for a Cu-Sn alloy, when the total of Cu, Sn, and Ti is 100 atomic %, the total of Cu and Sn is 50 atomic % or more. For a Cu-In alloy, when the total of Cu, In, and Ti is 100 atomic %, the total of Cu and In is 50 atomic % or more. The composition of the first alloy 6 is determined by EDX point analysis. The second alloy 7 refers to an alloy in which, when the total of Cu, the first element, and Ti is 100 atomic %, the total of Ti and the first element is 50 atomic % or more. For example, for a Ti-Sn alloy, when the total of Cu, Sn, and Ti is 100 atomic %, the total of Ti and Sn is 50 atomic % or more. For a Ti-In alloy, when the total of Cu, In, and Ti is 100 atomic %, the total of Ti and In is 50 atomic % or more. The composition of the second alloy 7 is determined by EDX point analysis. The Cu-Sn alloy may have a state in which Cu and Sn are mixed, or may contain a compound of Cu and Sn. The compound includes an intermetallic compound. Ti may be mixed or dissolved in the Cu-Sn alloy. The first alloy 6 includes an alloy having a melting point of 400°C or higher and 600°C or lower. The melting point of the first alloy 6 can be examined from the solidification point of the alloy. The solidification point refers to the temperature at which a liquid becomes a solid. That is, it refers to the temperature at which the joining solder melts into a liquid phase and becomes a solid when cooled. Briefly, the solidification point of the compound may be examined using a phase diagram. Alternatively, the joining layer 4 may be cut out from the joined body 1 and the temperature at which it gradually heats up and melts may be measured.

[0012] The melting point of the first alloy 6 can be measured from the DSC curve. The DSC curve is the result of applying heat to a sample using a differential scanning calorimeter (DSC) and measuring the presence or absence of endothermic and exothermic reactions. When an endothermic or exothermic reaction occurs, a peak appears in the DSC curve. A negative-direction peak indicates the occurrence of an endothermic reaction. A positive-direction peak indicates the occurrence of an exothermic reaction. An endothermic reaction indicates that melting, decomposition, etc. of the sample are occurring. Also, an exothermic reaction indicates that the constituent elements of the sample are reacting to form a compound (including an alloy) or solidification is occurring. The larger the peak, the larger the heat of reaction. Here, the negative-direction peak is called the endothermic peak, and the positive-direction peak is called the exothermic peak. Also, the apex of the peak is called the peak top. The difference between the maximum and minimum points of the peak is called the peak height.

[0013] For example, since the endothermic peak is a negative-direction peak, in the vicinity of the endothermic peak, the DSC curve goes down and then up. In the vicinity of the endothermic peak, the maximum point → minimum point → maximum point of the DSC curve appears. This minimum point (the point that drops the most in the negative direction) is the peak top. Also, among the maximum points on the low-temperature side and high-temperature side of the minimum point, the larger value is taken as the most extreme maximum point (the point that rises the most in the positive direction). The peak height is the value obtained by subtracting the minimum point from the most extreme maximum point. Since the heat generation peak is a peak in the positive direction, near the heat generation peak, the DSC curve rises and then falls. Near the heat generation peak, the minimum point → maximum point → minimum point of the DSC curve appears. This maximum point (the point that rises the most in the positive direction) becomes the peak top. Also, among the minimum points on the low-temperature side and high-temperature side of the maximum point, the one with the smaller value is taken as the most extreme minimum point (the point that falls the most in the negative direction). 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). Here, this end point is also counted as the heat generation peak. Also, it is possible to draw a baseline and determine the respective peak heights. Further, in the DSC curve, a change of 0.02 mW / mg or more on the vertical axis is counted as a peak. That is, a change of less than 0.02 mW / mg is not counted as a peak.

[0014] In the DSC curve in the cooling process, it is preferable that an exothermic peak is detected in the range exceeding 600 °C and below 900 °C. The exothermic peak within this range is the main body of the solidification reaction. Moreover, it is preferable that there is also an exothermic peak in the range of 400 °C or higher and 600 °C or lower. As described above, the exothermic reaction indicates that the brazing material components react with each other to form a compound (including an alloy) or solidification occurs. That is, the exothermic peak in the range of 400 °C or higher and 600 °C or lower indicates that a compound formation or solidification reaction occurs within that temperature range. Solidification is a reaction accompanied by a phase change from a liquid to a solid. In addition, the formation of a compound may be accompanied by a phase change from a solid to a solid with a different crystal structure. By causing such phase changes in multiple stages, the stress during cooling can be relaxed. With a brazing material composition as described later, the phase change for forming a compound becomes the main factor for generating an exothermic peak. In other words, when the first alloy 6 is present, an exothermic peak can be generated in the range of 400 °C or higher and 600 °C or lower in the DSC curve in the cooling process. The presence of exothermic peaks in the ranges of 400 °C or higher and 600 °C or lower, and exceeding 600 °C and below 900 °C respectively, enables the reaction accompanied by a phase change to be in multiple stages. Here, the temperature at which a phase change from a liquid to a solid occurs is called the freezing point. The temperature at which a phase change to a solid with a different crystal structure occurs is called the phase change point. In addition, when there are a plurality of alloys (including compounds) with different composition ratios, the exothermic peaks of these alloys may overlap. In other words, even when only one exothermic peak is detected, a plurality of alloys (including compounds) with different composition ratios may exist. The freezing point is the temperature at which the liquid phase changes to the solid phase. The phase change point is the temperature at which it changes to a solid with a different crystal structure. By solidifying or undergoing a phase change within the range of 400 °C to 600 °C, the temperature at which thermal stress is generated can be lowered. The freezing point of the conventional AgCu eutectic compound is approximately 780 °C. In the cooling process, the compound solidified at 780 °C generates thermal stress until it returns to room temperature. The presence of the first alloy 6 with a freezing point or phase change point within the range of 400 °C to 600 °C can reduce the thermal stress until it returns to room temperature after solidification or phase change at 400 °C to 600 °C. Since the plurality of first alloys 6 have different composition ratios, their respective freezing points or phase change points are also different from each other. Within the range of 400°C to 600°C, there are a plurality of first alloys 6 with different freezing points or phase change points. Thereby, the solidification or phase change of the bonding layer can be performed in multiple stages. Thereby, the thermal stress is further reduced. The thermal stress is generated in the process where the brazing material melts into a liquid phase and solidifies and cools to room temperature. In particular, it is important to reduce the thermal stress from solidification to cooling to room temperature. The occurrence of the solidification or phase change of the first alloy 6 in multiple stages can reduce the thermal stress from solidification to cooling to room temperature. If the freezing point or phase change point of the first alloy 6 is less than 400°C, the freezing point or phase change point of the bonding layer 4 may decrease, and the temperature cycle test (TCT) characteristics may deteriorate. If the freezing point or phase change point of the first alloy 6 is higher than 600°C, the thermal stress may increase. For this reason, the freezing point or phase change point of the first alloy 6 is preferably 400°C or higher and 600°C or lower, and more preferably 450°C or higher and 550°C or lower. Also, even if the exothermic peaks at 400°C or higher and 600°C or lower in the DSC curve in the temperature decreasing process overlap, due to the presence of a plurality of first alloys 6 with different composition ratios, the effect of performing solidification or phase change in multiple stages can be obtained.

[0015] Also, the first alloy 6 preferably contains one or more selected from Cu-Sn compounds and Cu-In compounds. In a compound, the constituent elements are bonded at the atomic level. Examples of the compound include intermetallic compounds. Examples of the alloy include solid solutions and eutectics. A compound is distinguished from a solid solution and a eutectic. The phase structure can be specified by the crystal structure and the composition. For example, in a binary alloy of CuSn, when the Sn content is 9 atomic% or less, the alloy is mainly a solid solution. When the Sn content is 10 atomic% or more, the alloy is likely to form an intermetallic compound. Regarding at least a part of the plurality of first alloys 6, it is preferable that the Sn content is in the range of 3 atomic % or more and 30 atomic % or less. When the Sn content is in the range of 3 atomic % to 30 atomic %, it is easy to control the freezing point or the phase change point. If the Sn content is less than 3 atomic %, the freezing point or the phase change point will not drop sufficiently. Also, if the Sn content exceeds 30 atomic %, there is a possibility that the freezing point or the phase change point will drop too much. For this reason, the Sn content is preferably 3 atomic % or more and 30 atomic % or less. Also, the first alloy 6 with an Sn content of 3 atomic % or more and 30 atomic % or less is likely to form a Cu - Sn compound. When performing EDX point analysis on the region of the Cu - Sn alloy with a high Cu content by EDX area analysis, it is preferable that 80% or more of that region is a Cu - Sn alloy with an Sn content of 3 atomic % or more and 30 atomic % or less. The EDX point analysis is performed 10 times or more. The region with a high Cu content refers to the region where the atomic % of Cu is higher than that of Ti by comparing the atomic % of Cu and the atomic % of Ti by EDX area analysis.

[0016] Also, the first alloy 6 may contain a metal component other than Cu and Sn in an amount of 2 atomic % or less. The metal component other than Cu and Sn is a metal component or an impurity constituting the joining solder material. As the constituent components of the joining solder material other than Cu and Sn, Ti (titanium) and C (carbon) are mentioned as described later. For example, the freezing point of the TiSn alloy exceeds 600°C. If the amount of Ti in the Cu - Sn alloy increases, there is a possibility that the freezing point or the phase change point will not be in the range of 400°C or more and 600°C or less. For this reason, in at least a part of the plurality of first alloys 6, the amount of Ti is preferably 2 atomic % or less, and further preferably 1 atomic % or less. EDX point analysis is used to measure the amount of Ti in the Cu - Sn compound. Examples of components other than the metal component include oxygen and nitrogen. The first alloy 6 may contain Cu, Sn, and components other than the metal component in an amount of 10 atomic % or less. When Ag is contained in the brazing filler metal, an Ag-Cu eutectic is likely to be formed. The melting point of the Ag-Cu eutectic is about 780°C. Therefore, it is preferable that the brazing filler metal does not contain Ag. In other words, it is preferable that the bonding layer 4 does not contain Ag. As the brazing filler metal, Ag-Cu-Sn-Ti having Ag as the main component may be used. When Ag is the main component, Ag-Cu or Ag-Sn is formed. The proportion of the Cu-Sn alloy contained in the bonding layer 4 will decrease. Therefore, the possibility of forming Cu-Sn alloys with different compositions is reduced. Also from this point, it is preferable that the bonding layer 4 does not contain Ag.

[0017] Preferably, a part of the plurality of first alloys 6 is a Cu-Sn alloy with a Sn content of 3 atomic% or more and 9 atomic% or less, and another part of the plurality of first alloys 6 is a Cu-Sn alloy with a Sn content of 10 atomic% or more and 30 atomic% or less. Here, a Cu-Sn alloy with a Sn content of 3 atomic% or more and 9 atomic% or less is referred to as a first Cu-Sn alloy, and a Cu-Sn alloy with a Sn content of 10 atomic% or more and 30 atomic% or less is referred to as a second Cu-Sn alloy. The first Cu-Sn alloy is preferably a Cu-Sn compound. The second Cu-Sn alloy is preferably a Cu-Sn compound. This is because compounds are more likely to undergo solidification or phase change in multiple stages. The bonding layer 4 preferably contains a second alloy 7. The second alloy 7 contains one or two selected from a Ti-Sn alloy and a Ti-In alloy. The Ti-Sn alloy or the Ti-In alloy may contain an intermetallic compound. For example, as the intermetallic compound of the Ti-Sn alloy, one or more selected from SnTi3, Sn3Ti5, and Sn5Ti6 can be mentioned. In the average value measured at three locations of the bonding layer 4, it is preferable that the total area of the plurality of first alloys 6 is larger than the total area of the second alloy 7. That is, it is preferable that the total area of the Cu-Sn alloy or the Cu-In alloy is larger than the total area of the Ti-Sn alloy or the Ti-In alloy. The field of view area is set to the thickness of the bonding layer × 40 μm in the width direction. The measurement in one field of view area may be performed in multiple times. Also, when measuring in multiple times, each area is set so as not to overlap with each other. Also, at least a part of the Cu-Sn alloy and the Ti-Sn alloy detected by EDX point analysis of the bonding layer 4 preferably fall within the region surrounded by (97, 3, 0), (60, 40, 0), (2, 40, 58), and (39, 3, 58) in the ternary phase diagram of Cu, Sn, and Ti. Here, this region is referred to as the first composition region. Figure 3 is a ternary phase diagram of Cu, Sn, and Ti. In Figure 3, the concentration of each element is shown in atomic %. First, using the area analysis function of SEM-EDX, image data is obtained by elemental mapping. The locations determined to be the first alloy 6 and the second alloy 7 are subjected to EDX point analysis by the mapping function. According to elemental mapping, the difference in the concentration of a specific element can be indicated by brightness. The region with a high concentration has a high brightness, and the region with a low concentration has a low brightness. For example, if Ti is specified as a specific element, the light and dark of the Ti concentration can be visualized. By using this function, the first alloy 6 and the second alloy 7 present in the field of view area can be discriminated. That is, by specifying the first element as a specific element and visualizing the concentration of these elements, the first alloy 6 present in the field of view area can be discriminated. Also, by specifying Ti as a specific element and visualizing the concentration of these elements, the second alloy 7 present in the field of view area can be discriminated. When the locations determined to be the first alloy 6 and the second alloy 7 are each subjected to EDX point analysis, it is preferable that the composition is within the range of the first composition region. There may be an alloy outside the range of the first composition region, but the properties can be improved by the alloy composition being within the range of the first composition region. More preferably, when EDX point analysis is performed, at least a part of the composition of the Cu-Sn alloy is within the region surrounded by (97, 3, 0), (77, 23, 0), (52, 23, 25), and (72, 3, 25) in the ternary phase diagram of Cu, Sn, and Ti. This region is referred to as the second composition region. The bonding layer 4 may contain a first alloy 6 having a composition outside the second composition region. On the other hand, if there is a large amount of the first alloy 6 having the composition of the second composition region, the characteristics can be further improved. Also, when observing the Cu-Sn alloy by elemental mapping based on SEM-EDX area analysis and performing EDX point analysis on the Cu-Sn alloy, it is preferable that 80% or more of the analysis points have a composition within the range of the second composition region. In EDX point analysis, 10 or more points at positions separated from each other by 3 μm or more are analyzed. The Ti-Sn alloy detected by EDX point analysis of the bonding layer 4 is preferably within the region surrounded by (41, 23, 36), (24, 40, 36), (2, 40, 58), and (19, 23, 58) in the ternary phase diagram of Cu, Sn, and Ti. This region is referred to as the third composition region. When the bonding layer 4 contains a plurality of Ti-Sn alloys, it is sufficient that at least a part of the composition of the plurality of Ti-Sn alloys is within the range of the third composition region. On the other hand, if there is a large amount of the Ti-Sn alloy having the composition within the range of the third composition region, the characteristics can be further improved. Also, when observing the Ti-Sn alloy by elemental mapping based on SEM-EDX area analysis and performing EDX point analysis on the Ti-Sn alloy, it is preferable that 80% or more of the analysis points have a composition within the range of the third composition region. In EDX point analysis, 10 or more points at positions separated from each other by 3 μm or more are analyzed.

[0018] The Ti reaction layer 5 preferably contains titanium nitride particles with an average particle size of 50 nm or less. Further, it is preferable that Cu and the first element are present at the grain boundaries of the titanium nitride particles. The size of the titanium nitride particles in the Ti reaction layer 5 is analyzed using a scanning transmission electron microscope (STEM). By means of STEM, a magnified image of the cross-section of the bonding layer is obtained. At the outer edge of the titanium nitride particles shown in the magnified image, the distance between the two farthest points is taken as the particle size. The particle sizes are measured for any 30 particles. Their average value is taken as the average particle size. Since the average particle size is as small as 50 nm or less, it becomes easier for Cu and the first element to penetrate into the grain boundaries. The presence of Cu and the first element at the grain boundaries of the titanium nitride particles can cause the solidification or phase change of the bonding layer 4 to occur in more stages.

[0019] The amount of Cu in the Ti reaction layer 5 is preferably in the range of 0.5 atomic % or more and 5 atomic % or less. When the amount of Cu in the Ti reaction layer 5 is within this range, the thermal stress can be reduced without decreasing the bonding strength. If the amount of Cu in the Ti reaction layer 5 is less than 0.5 atomic %, the amount of Cu is too small and the effect of reducing the thermal stress may not be sufficiently obtained. If the amount of Cu exceeds 5 atomic %, the strength of the Ti reaction layer 5 may be insufficient and the bonding strength may decrease. The amount of the first element in the Ti reaction layer 5 is preferably 0.05 atomic % or more and 2 atomic % or less. When the amount of the first element in the Ti reaction layer 5 is within this range, the thermal stress can be reduced without decreasing the bonding strength. Also, Cu and Sn in the Ti reaction layer 5 are likely to alloy. By making Cu and Sn in the Ti reaction layer 5 into an alloy (preferably a compound), the generation of thermal stress can be suppressed. The amounts of Cu and the first element in the Ti reaction layer 5 refer to the amounts present at the grain boundaries of the titanium nitride particles. Both TiN and Ti2N may be present as the titanium nitride in the Ti reaction layer 5. The presence of both TiN and Ti2N can cause the solidification of the layer mainly composed of titanium nitride to occur in more stages. The thickness of the Ti reaction layer 5 is preferably 1 μm or less. More preferably, the thickness of the Ti reaction layer 5 is 0.3 μm or less. By making the Ti reaction layer 5 thinner, it becomes easier to have Cu and the first element present at the grain boundaries. In addition, the thickness of the Ti reaction layer 5 can be measured by a transmission electron microscope (TEM). The thickness of the Ti reaction layer 5 is measured with reference to the interface between the Ti reaction layer 5 and the ceramic substrate. TEM-EDX is used for the compositional analysis of the Ti reaction layer 5.

[0020] In the average value obtained by EDX area analysis of the three regions of the bonding layer 4, the total area of the first alloy 6 is preferably 50% or more and 95% or less of the areas of the three regions. The field area (the size of one region) is set to the bonding layer thickness × 40 μm in the width direction. When the total area ratio of the Cu-Sn alloy is within the range of 50% or more and 95% or less, the thermal stress of the bonding layer 4 can be reduced. When the total area ratio of the Cu-Sn alloy is less than 50%, since the proportion of the Cu-Sn alloy is small, the effect of reducing the thermal stress may be insufficient. Further, when the total area ratio of the Cu-Sn alloy exceeds 95% and is too large, the freezing point or the phase change point of the bonding layer 4 may drop too much. When the freezing point or the phase change point of the bonding layer 4 drops, the TCT characteristics of the joined body 1 may deteriorate. Therefore, the total area ratio of the Cu-Sn alloy is preferably 50% or more and 95% or less, and more preferably 70% or more and 90% or less. Also, no matter which three regions in the bonding layer 4 are measured, it is preferable that the total area of the Cu-Sn alloy is within the range of 50% or more and 95% or less. In the average value obtained by EDX area analysis of the three regions of the bonding layer 4, the total area of the Ti-Sn alloy is preferably within the range of 5% or more and 30% or less of the areas of the three regions. The total area of titanium silicide is preferably within the range of 0.5% or more and 15% or less of the areas of the three regions. Also, the area ratio of the rest is preferably within the range of 10% or less. Examples of the other material structures include the Ti reaction layer, carbides, and the like. In the measurement of the area ratio, the area analysis function of SEM-EDX is used to obtain image data by elemental mapping. Use the mapping function attached to the area analysis function of SEM-EDX. If there is no mapping function, an electron probe microanalyzer (EPMA) may be used. Also, the image data obtained by SEM-EDX may be processed using image analysis software. As the image analysis software, Image-J or equivalent software can be used. The field area is set to the bonding layer thickness × 40 μm in the width direction. The measurement conditions for area analysis are as described above. Using the elemental map obtained by area analysis, calculate the area ratio. For the elemental map, set the pinning size to 5 × 5 bit / point. When using image analysis software such as Image-J, perform binarization processing. The concept of binarization processing is as follows. First, let the area of the element x to be detected be Sx. Sx can be obtained by Sx = ((the number of pixels in the extraction region by binarization of the x element) / (the total number of pixels in the image)) × 100. By changing the element x to be detected to Ti, Si, N, C, the area can be obtained respectively. For example, the area ratio of the Ti-Sn alloy can be obtained as follows. As described above, in the second composition region of the Cu-Sn alloy (the first alloy 6), the Ti content is 0 atomic % or more and 25 atomic % or less. Therefore, exclude the region where the Ti content is 25 atomic % or less. The elemental map is shown with luminance according to the Ti concentration. Using this function, the region where the Ti content is 25 atomic % or less can be excluded. Binarize the image of the elemental map from which the region where the Ti content is 25 atomic % or less has been excluded, and measure the area of the Ti element and the area of the Si element. Let the area of the Ti-Sn alloy be S Sn-Ti , the area of the Ti element be S Ti , the area of the Si element be S Si , the area of the N element be S N , the area of the C element be S C . Let the area of the Ti-Sn alloy be S Sn-Ti = S Ti - (S Si + S N + S C) can be obtained. Si present in the bonding layer is titanium silicide. N (nitrogen) present in the bonding layer is titanium nitride. If the boundary between the silicon nitride substrate surface and the bonding layer is uneven, silicon nitride may be detected. Also, C (carbon) present in the bonding layer is either elemental carbon or titanium carbide. S Ti , S Si , S N , S C may be calculated using the binarized images obtained by mapping only Ti, Si, N, and C respectively. The area ratio of the Cu-Sn alloy is taken as S Cu-Sn . S Cu-Sn is obtained by excluding S Si , S N , S C from the region where the Ti content is 0 atomic % or more and 25 atomic %. The Ti element may be contained in both the Cu-Sn alloy and the Ti-Sn alloy. Based on the Ti content of 25 atomic %, the Cu-Sn alloy and the Ti-Sn alloy can be classified. The bonding layer 4 may contain carbon. The carbon present in the bonding layer 4 may be elemental carbon or a carbide. By adding carbon, the fluidity of the brazing material can be controlled. Thereby, it becomes easier to control the distribution of the Cu-Sn alloy in the bonding layer. Examples of materials other than the Cu-Sn alloy present in the bonding layer 4 include titanium nitride (TiN), Ti-Sn alloy, and titanium silicide. Also, when containing carbon, titanium carbide (TiC) may be present. Further, the components constituting the bonding layer 4 may exist as a single metal. Note that the alloy and the single metal can be distinguished from the electron diffraction pattern of the TEM.

[0021] The bonding layer 4 preferably contains titanium silicide particles 8 having a major axis of 0.5 μm or more and 6 μm or less. In the field area of the bonding layer 4 = bonding layer thickness × width direction 200 μm, the total area of the titanium silicide particles 8 having a major axis of 0.5 μm or more and 6 μm or less is preferably 1% or more and 15% or less of the field area. For measuring the major axis length of the titanium silicide particles 8, SEM photographs are used. At the outer edge of the titanium silicide particles 8 shown in the magnified cross-sectional photograph of the bonding layer 4, the distance between the two farthest points is defined as the major axis length. The titanium silicide particles 8 present in the bonding layer 4 can be identified by the mapping function included in the area analysis function of SEM-EDX. Specifically, Ti and Si are specified as specific elements, and the presence of these elements is visualized. The region where both Ti and Si are present corresponds to the titanium silicide particles 8. When the titanium silicide particles 8 are present, it is preferable that 80% or more and 100% or less of the titanium silicide particles 8 are present within 1 μm from the Ti reaction layer 5. When Ti that did not become the Ti reaction layer 5 or the Ti-Sn alloy reacts with the silicon nitride substrate, titanium silicide particles are formed. The presence of the titanium silicide particles 8 near the Ti reaction layer 5 makes it easier for Cu and the first element to enter the grain boundaries of the titanium nitride particles. If the major axis length of the titanium silicide particles 8 exceeds 6 μm or the area ratio exceeds 15%, the formation of the Ti reaction layer 5 may be insufficient.

[0022] The thickness of the bonding layer 4 is preferably 5 μm or more and 60 μm or less. Within this range, it is easy to control the area ratio of the Cu-Sn alloy. The thickness of the bonding layer 4 is the distance from the boundary between the ceramic substrate 2 and the Ti reaction layer 5 to the boundary between the bonding layer 4 and the copper plate 3. Let the concentration (atomic %) of the first element at the boundary between the bonding layer 4 and the copper plate 3 be the first concentration C1. Let the concentration (atomic %) of the first element in the region of the copper plate 3 10 μm away from the boundary between the bonding layer 4 and the copper plate 3 be the second concentration C2. The ratio C2 / C1 of the second concentration C2 to the first concentration C1 is preferably 0.60 or less. Also, let the concentration (atomic %) of the first element in the region of the copper plate 3 20 μm away from the boundary between the bonding layer 4 and the copper plate 3 be the third concentration C3. The ratio C3 / C1 of the third concentration C3 to the first concentration C1 is preferably 0.40 or less. When a pure copper plate is used as the copper plate 3, the second concentration C2 and the third concentration C3 indicate the diffusion amount of the first element into the copper plate 3. When Sn is used in the bonding layer 4, the concentration of Sn is used as the concentration of the first element. When In is used in the bonding layer 4, the concentration of In is used as the concentration of the first element. When both Sn and In are used in the bonding layer 4, the sum of the concentration of Sn and the concentration of In is used as the concentration of the first element. For example, when the bonding layer 4 contains a Cu-Sn alloy, the first concentration is C1 Sn , the second concentration is C2 Sn , and the third concentration is C3 Sn . C2 Sn / C1 Sn ≦0.60 or C3 Sn / C1 Sn ≦0.40 indicates that the diffusion of Sn into the copper plate is suppressed. By providing the first alloy 6 having different composition ratios in the bonding layer 4, the diffusion amount of the first element into the copper plate 3 can be reduced. Also, the diffusion distance of the first element from the boundary is preferably 50 μm or less. The diffusion region refers to the distance from the boundary to the point where the Sn amount is 0% by mass (below the detection limit). Also, in the case of the bonding method using a continuous furnace as described later, the first concentration can be reduced to 8 atomic % or less. The second concentration C2 and the third concentration C3 in the copper plate 3 are analyzed by EDX. Line analysis is used for the analysis. By reducing the diffusion amount of Sn into the copper plate 3, the heat resistance of the copper plate 3 can be improved. For example, when Sn diffuses into the copper plate 3, a CuSn alloy is formed in the copper plate. The CuSn alloy has a lower melting point than the copper plate. Therefore, as the amount of CuSn alloy in the copper plate increases, the copper plate becomes more likely to be deformed by heat. There is a possibility that the TCT characteristics of the bonded body deteriorate. Although Sn has been used for the explanation here, the same applies to In. By having the above configuration, the amount of voids in the bonding layer can be reduced. By reducing the amount of Sn diffusion (or In diffusion) into the copper plate, the amount of voids in the bonding layer can be made 0% or more and 3% or less by volume ratio. For calculating the amount of voids in the bonding layer, ultrasonic flaw detection inspection (SAT) is used. A probe for flaw detection inspection is brought into contact with the surface of the bonded body 1, and ultrasonic waves are transmitted toward the bonding layer 4. From the reception result of the reflected wave, the voids present in the bonding layer can be examined. Also, from the reception result, the volume ratio of the amount of voids can be calculated. By reducing the amount of voids in the bonding layer, the bonding strength of the copper plate can be improved. The bonding strength is measured by a peel test. The bonding strength of the copper plate can be made 15 kN / mm or more, and further 25 kN / mm or more.

[0023] A bonded body as described above is suitable for a ceramic circuit board. FIG. 4 is a schematic diagram showing an example of a ceramic circuit board according to an embodiment. In FIG. 4, 10 is a ceramic circuit board, 11 is a circuit portion, and 12 is a heat sink. The ceramic circuit board 10 shown in FIG. 4 is manufactured by processing the copper plate 3 on the front side of the bonded body 1 into the circuit portion 11 and processing the copper plate 3 on the back side into the heat sink 12. The copper plate 3 to which a circuit shape is imparted is used as the circuit portion 11. In FIG. 4, two circuit portions 11 are provided. Note that the ceramic circuit board 10 according to the embodiment is not limited to such a structure. The number and size of the circuit portions 11 can be appropriately changed as needed. Also, in FIG. 4, the copper plate 3 on the back side is used as the heat sink 12, but a circuit structure may be imparted to the copper plates 3 on both sides. As needed, an inclined shape may be imparted to the side surface of the circuit portion 11 or the side surface of the heat sink 12. As needed, a protruding portion protruding from the side end of the circuit portion 11 may be provided in the bonding layer 4 between the ceramic substrate 2 and the circuit portion 11. A protruding portion protruding from the side end of the heat sink 12 may be provided in the bonding layer 4 between the ceramic substrate 2 and the heat sink 12. For imparting the circuit structure and the inclined shape of the copper plate side surface, it is preferable to use an etching process.

[0024] The ceramic circuit board according to the embodiment is suitable for a semiconductor device. FIG. 5 is a schematic diagram showing an example of a semiconductor device according to an embodiment. In FIG. 5, reference numeral 20 denotes a semiconductor device, 21 denotes a semiconductor element, and 22 denotes a lead frame. In the semiconductor device 20 shown in FIG. 5, the semiconductor element 21 is mounted on one of the two circuit portions 11. The lead frame 22 is connected to the other of the two circuit portions 11. Note that the semiconductor device 20 according to the embodiment is not limited to such a structure. The number and size of the circuit portions 11, the number and size of the semiconductor elements 21, etc. can be appropriately changed as required.

[0025] Next, a method for manufacturing a joined body according to an embodiment will be described. If the joined body according to the embodiment has the above-described configuration, the manufacturing method is not limited. Hereinafter, an example of a method for favorably obtaining a joined body will be described. 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 aludur substrate. Note that the aludur substrate is a substrate formed by mixing aluminum oxide and zirconium oxide. As the copper plate 3, a pure copper plate or a copper alloy plate can be used. The copper plate is preferably oxygen-free copper. Oxygen-free copper is copper having a purity of 99.96 mass% or more as shown in JIS-H-3100. Next, a joining brazing material is prepared. The joining brazing material preferably contains 50 atomic% or more of Cu, 5 atomic% or more and 40 atomic% or less of Ti, 2 atomic% or more and 35 atomic% or less of a first element, and 0 atomic% or more and 12 atomic% or less of carbon. This is the ratio when the total of Cu, Ti, the first element, and C is 100 atomic%. Ti may be added as titanium hydride (TiH2). It is effective not to add Ag to the joining brazing material.

[0026] The characteristics of the joining brazing material used for manufacturing the joined body are preferably examined in advance by DSC. The DSC curve of the joining brazing material is measured by setting the heating rate in the heating process to 20°C / min and the cooling rate in the cooling process to 20°C / min. For DSC, a TGA-DSC simultaneous thermal analyzer STA449-F3-Jupiter manufactured by NETZSCH or a device with equivalent performance is used. The measurement is carried out in an Ar (argon) flow by dropping an appropriate amount of brazing filler metal into an alumina container. The measurement is performed with the lid of the alumina container closed. It is necessary to prevent the reaction between the brazing filler metal and the atmosphere by measuring in an Ar atmosphere. Note that the dropped amount (mg) is measured in advance with a balance. A sample of 15 mg or more is used. In the heating process, the temperature was raised from room temperature to 950 °C at a heating rate of 20 °C / min. Next, a holding process of holding at 950 °C for 20 minutes was performed. In the cooling process, the temperature was lowered from 950 °C to room temperature at a cooling rate of 20 °C / min. The temperature profile for obtaining the DSC curve consists of a heating process, a holding process, and a cooling process. Hereinafter, the DSC curve of the cooling process with a cooling rate of 20 °C / min may also be referred to as the DSC curve of the cooling process. Also, a peak was defined as a point where the heat flow difference is 0.02 mW / mg or more. When the first alloy 6 having a freezing point or phase change point in the range of 400 °C or more and 600 °C or less exists, an exothermic peak is detected within the range of 400 °C or more and 600 °C or less in the DSC curve of the cooling process. When a plurality of exothermic peaks are detected between 400 °C and 600 °C in the DSC curve of the cooling process, the temperature at which the largest peak appears is taken as the freezing point or phase change point of the bonding layer 4.

[0027] The average particle size D of the Cu powder used as the raw material of the brazing filler metal 50 is preferably 12.0 μm or less, and more preferably 10.0 μm or less. The average particle size D of the Ti powder or TiH2 powder 50 is preferably 6.0 μm or less, and more preferably 4.0 μm or less. The average particle size D of the Sn powder or In powder 50 is preferably 16.0 μm or less, and more preferably 14.0 μm or less. The average particle size D of the C powder 50 is preferably 6.0 μm or less, and more preferably 4.0 μm or less. The average particle size D of the Ag powder 50 is preferably 3.0 μm or less, and more 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 of the Cu powder 50is preferably smaller than the average particle size D of the Sn powder or In powder. As described above, Cu and the first element serve as the base material of the brazing material composition. The first element has a lower melting point than Cu. By increasing the particle size of the Sn powder or In powder, the reaction between the Cu powder and the first element powder can be made uniform. As a result, even if the heating rate or the cooling rate is increased, the ceramic substrate 2 and the copper plate 3 can be sufficiently joined. 50

[0028] A step of joining a ceramic substrate and a copper plate is performed using the brazing material as described above. The brazing material is mixed with an organic substance to prepare a brazing material paste. The brazing material paste is applied to the surface of the ceramic substrate 2 (or the copper plate 3) to form a brazing material paste layer. The copper plate 3 (or the ceramic substrate 2) is disposed on the brazing material paste layer. The heat joining step is performed in a nitrogen atmosphere. 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. Components other than nitrogen in the nitrogen atmosphere include an inert gas or air. The heat joining in the nitrogen atmosphere can be performed under various conditions such as normal pressure, reduced pressure, or increased pressure.

[0029] In the heating-up step of the heat joining step, the heating rate is set to 30 °C / min or more. The upper limit of the heating rate is not particularly limited, but is preferably 100 °C / min or less. If the heating rate is too fast exceeding 100 °C / min, the joinability may decrease. Therefore, the heating rate is preferably 30 °C / min or more and 100 °C / min or less, more preferably 40 °C / min or more and 70 °C / min or less. The joining temperature is set to 750 °C or more. The joining temperature is preferably 1000 °C or less. If the joining temperature is too high exceeding 1000 °C, the joining temperature is close to the melting point of copper (1085 °C). As a result, the copper plate may be deformed. Therefore, the joining temperature is preferably 750 °C or more and 1000 °C or less, more preferably 800 °C or more and 950 °C or less. In the heat bonding process, it is ensured that the temperature can be maintained for 10 minutes or more at the bonding temperature. The time maintained at the bonding temperature is referred to as the heat holding time. The heat holding time is preferably 10 minutes or more and 100 minutes or less. If the heat holding time is less than 10 minutes, there may be insufficient time for the solder material to melt and solidify. If the heat holding time is longer than 100 minutes, it may be difficult to control the distribution of the alloy in the bonding layer 4. After the heat holding time ends, a cooling process is performed. The cooling process is a process of cooling from the bonding temperature to room temperature. The cooling rate is set to 30°C / min or more. In the conventional active metal bonding method, the cooling rate was about 5°C / min. By using the bonding solder material having the DSC curve as described above, bonding is possible even if the cooling rate is increased. The upper limit of the cooling rate is not particularly limited, but is preferably 100°C / min or less. If it is faster than 100°C / min, the bondability may decrease. For this reason, the cooling rate is preferably 30°C / min or more and 100°C / min or less, and more preferably 30°C / min or more and 70°C / min or less. Also, it is preferable to use a continuous furnace to increase the heating rate and the cooling rate. The continuous furnace can perform heat treatment in a nitrogen atmosphere. Since there is no need to create a vacuum, the heating rate and the cooling rate can be increased.

[0030] By increasing the cooling rate, the distribution of the Cu-Sn alloy in the bonding layer 4 can be controlled. This is because after the bonding solder material melts, by quickly cooling, it becomes possible to form an alloy according to the freezing point or the phase change point. Also, by allowing the presence of Ti that does not become the Ti reaction layer 5, it is possible to form Ti-Sn alloy and titanium silicide particles. Quick cooling can suppress the unnecessary diffusion phenomenon to the copper plate. The difference between the heating rate and the cooling rate is preferably 20°C / min or less. That is, it is preferable to satisfy |heating rate - cooling rate| ≤ 20°C / min. In the solder layer, a melting reaction and a solidification reaction occur by heating. These reactions occur in the heating process and the cooling process. By reducing the difference between the heating rate and the cooling rate, the stress generated by the reaction can be made uniform. Thereby, defects such as warping can be suppressed. If necessary, the heat bonding process may be performed while placing a weight on the bonded body 1. Through the bonding process as described above, the bonded body 1 can be produced. Also, since the thermal stress of the bonding layer 4 can be reduced, the warpage of the bonded body 1 can be reduced. The obtained bonded body 1 is processed into the ceramic circuit board 10 by performing an etching process on it. If necessary, scribing may be performed on the bonded body 1 to produce multiple pieces.

[0031] (Example) (Examples 1 to 8, Comparative Example 1) The bonding solders shown in Tables 1 and 2 were prepared. Table 1 shows the particle size of the raw material powder, and Table 2 shows the composition ratio.

[0032]

Table 1

[0033]

Table 2

[0034] The bonding solder components according to the examples and comparative examples were mixed with an organic binder to prepare a solder paste. Using a differential scanning calorimeter, the DSC curve of each solder paste was measured. As the DSC, a TGA-DSC simultaneous thermal analyzer STA449-F3-Jupiter manufactured by NETZSCH was used. The measurement was performed by dropping an appropriate amount of solder into an alumina container in an Ar flow. The temperature program was set to a heating rate of 2°C / min, holding at 950°C for 20 minutes, and a cooling rate of 2°C / min. The temperature at which the exothermic peak in the DSC curve of the cooling process was detected was measured. Table 3 shows the temperature at which the largest peak among the exothermic peaks between 400°C and 600°C appeared in the DSC curve of the cooling process.

[0035]

Table 3

[0036] As can be seen from Table 3, for the brazing filler metal according to the examples, the temperature of the exothermic peak in the cooling process of the DSC curve was in the range of 400°C or higher and 600°C or lower. On the other hand, in Comparative Example 1, the temperature of the exothermic peak exceeded 600°C. No exothermic peak was detected in the range of 400°C or higher and 600°C or lower. Furthermore, for the brazing filler metal according to the examples, an exothermic peak was also detected in the range of exceeding 600°C and 900°C or lower. 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 300 mm × a width of 200 mm × a plate thickness of 0.32 mm was used as Silicon Nitride Substrate 1. Also, a silicon nitride substrate with a thermal conductivity of 85 W / m·K, a three-point bending strength of 650 MPa, a length of 300 mm × a width of 200 mm × a plate thickness of 0.25 mm was used as Silicon Nitride Substrate 2. Oxygen-free copper with a length of 300 mm × a width of 200 mm × a plate thickness of 0.5 mm was used as Copper Plate 1. Oxygen-free copper with a length of 300 mm × a width of 200 mm × a plate thickness of 0.8 mm was used as Copper Plate 2. A brazing filler metal paste was applied at 30 μm on both sides of the ceramic substrate, and copper plates were placed on each surface. Next, a heat joining process was carried out. The joining atmosphere was unified to a nitrogen atmosphere. Also, the joining conditions were in the range of 850°C to 920°C × 30 minutes to 50 minutes, and a continuous furnace was used. The heating rate and the cooling rate were set to the conditions shown in Table 4. The difference between the heating rate and the cooling rate was calculated by |heating rate - cooling rate|.

[0037]

Table 4

[0038] A joined body was manufactured through the above steps. The cross-section of the joined layer of the obtained joined body was observed, and the presence or absence of Cu-Sn alloys with different composition ratios, the average particle size of titanium nitride in the Ti reaction layer, and the amounts of Cu and Sn in the Ti reaction layer were examined. Also, when Cu-Sn alloys with different composition ratios were present, the presence or absence of the first Cu-Sn alloy with an Sn amount of 3 atomic % or more and 9 atomic % or less and the presence or absence of the second Cu-Sn alloy with an Sn amount of 10 atomic % or more and 30 atomic % or less were examined. In addition, the area ratios of the Cu-Sn alloy and the Ti-Sn alloy were also examined. Also, the major axis length and area ratio of titanium silicide were examined. To calculate the area ratio, the method of binarizing the EDX element map with image software was used. The detailed method is as described above. The results are shown in Tables 5 to 8.

[0039]

Table 5

[0040]

Table 6

[0041]

Table 7

[0042]

Table 8

[0043] As can be seen from Tables 5 to 8, the bonded body according to the example satisfied the preferable conditions. The Cu-Sn alloy was the main component of the bonding layer. Also, it was observed that the first Cu-Sn alloy and the second Cu-Sn alloy had become intermetallic compounds, respectively. EDX point analysis was performed at 10 arbitrary locations in the region of the Cu-Sn alloy. Also, EDX point analysis was performed at 10 arbitrary locations in the region of the Ti-Sn alloy. When the results were shown in the ternary phase diagram of Fig. 3, they were all within the range of the first composition region. Also, in the EDX point analysis results of the Cu-Sn alloy, the composition of the Cu-Sn alloy of 80% or more and 100% or less was within the range of the second composition region. In the EDX point analysis results of the Ti-Sn alloy of 80% or more and 100% or less, the composition of the Ti-Sn alloy of 80% or more and 100% or less was within the range of the third composition region. "Others" in the area ratio of Table 8 is a region where the Ti reaction layer, carbide, or metal component exists in a separated state in a simple substance. In the bonded body according to the example, the thickness of the Ti reaction layer was 1 μm or less. Also, in the Ti reaction layer, both TiN and Ti2N were observed. On the other hand, in Comparative Example 1, Cu-Sn alloys with different composition ratios were not confirmed. In Comparative Example 1, a trace amount of Cu-Sn alloy was observed, but Cu-Sn alloys with different compositions were not observed. This is presumably because the AgCu eutectic or AgSn was the main component of the bonding layer in Comparative Example 1. Next, 100 bonded bodies according to each example and comparative example were produced. The bonding strength and the amount of warpage were measured for each. The bonding strength was measured by a peel test. Specifically, in each example and comparative example, a sample for the peel test was prepared. The sample was prepared by bonding a strip-shaped copper plate to a ceramic substrate. At that time, one end of the copper plate was bonded so as to protrude from the ceramic substrate. The peel strength was measured by vertically pulling the protruding copper plate. Also, the amount of warpage was measured as the amount of warpage on the long side of the bonded body. For 90 or more bonded bodies, an example with a warpage amount of 0.3 mm or less was rated "best". For 70 to 89 bonded bodies, an example with a warpage amount of 0.3 mm or less was rated "good". An example in which 31 or more bonded bodies with a warpage amount exceeding 0.3 mm occurred was rated "poor". The results are shown in Table 9.

[0044]

Table 9

[0045] As can be seen from Table 9, for the bonded body according to the example, the bonding strength was equivalent to that of the bonded body according to Comparative Example 1 using an Ag-containing brazing filler metal. Even when the size of the bonded body was increased to 200 mm or more, the amount of warpage could be suppressed. Even when the heating rate and the cooling rate were increased, the amount of warpage could be suppressed. Therefore, it can be seen that the bonded body has good mass productivity. On the other hand, in Comparative Example 1, a large number of bonded bodies with a warpage amount exceeding 0.3 mm occurred. This is because Cu-Sn alloys with different composition ratios were not formed.

[0046] The amount of Sn in the copper plate of the bonded body according to the examples and comparative examples was examined. The amount of Sn was measured by analyzing the cross section of the bonded body with EDX. The boundary between the bonding layer and the copper plate was defined by the method described above. The amount of Sn at the boundary between the bonding layer and the copper plate was designated as Sn-1, the amount of Sn at a location 10 μm away from the boundary as Sn-2, and the amount of Sn at a location 20 μm away from the boundary as Sn-3. Sn-2 / Sn-1 and Sn-3 / Sn-1 were calculated. It was also confirmed whether the point farthest from the boundary among the regions where Sn was detected was within 50 μm. Examples within 50 μm were marked as "〇", and examples exceeding 50 μm were marked as "×". The presence or absence of voids in the bonding layer was also examined. The presence or absence of voids was examined by ultrasonic flaw detection (SAT). When the volume ratio of voids was 0% or more and 0.3% or less, it was marked as "◎", when it was 0.4% or more and 1% or less, it was marked as "〇", when it was 2% or more and 3% or less, it was marked as "△", and when it was 4% or more, it was marked as "×". The results are shown in Table 10.

[0047]

Table 10

[0048] As can be seen from Tables 9 and 10, it was found that in the bonded bodies according to the examples, the diffusion of Sn into the copper plate was suppressed. It was also found that the void area was small. In particular, in Examples 6 to 8 where the void area was reduced, the bonding strength was as high as 25 kN / mm or more. On the other hand, in the comparative examples, the diffusion amount of Sn into the copper plate was large and the void area ratio was also large.

[0049] As described above, several embodiments of the present invention have been illustrated, but 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 Symbols

[0050] 1…Bonded body 2…Ceramic substrate 3…Copper plate 4…Bonding layer 5…Ti reaction layer 6…Cu - Sn alloy or Cu - In alloy 7…Ti - Sn alloy or Ti - In alloy 8…Titanium silicide particles 10…Ceramic circuit board 11…Circuit section 12…Heat sink

Claims

1. A ceramic substrate, a copper plate, and a bonding layer disposed on at least one surface of the ceramic substrate for bonding the ceramic substrate and the copper plate, wherein the bonding layer comprises a Ti reaction layer containing titanium nitride or titanium oxide as a main component, and a plurality of first alloys located between the Ti reaction layer and the copper plate, each containing one or more selected from Cu—Sn alloys and Cu—In alloys and having different Sn concentrations or In concentrations, a bonded body.

2. The bonding layer further comprises a second alloy located between the Ti reaction layer and the copper plate, the second alloy containing one or more selected from Ti—Sn alloys and Ti—In alloys, and the total area of the plurality of first alloys is larger than the total area of the second alloy in the average value obtained by analyzing three regions each having a thickness×width of 40 μm in the bonding layer, the bonded body according to claim 1.

3. At least a part of the plurality of first alloys is a Cu—Sn alloy, the second alloy is a Ti—Sn alloy, and at least a part of the plurality of first alloys and the second alloy detected by EDX point analysis of the bonding layer are within a region surrounded by (97, 3, 0), (60, 40, 0), (2, 40, 58), and (39, 3, 58) in the ternary phase diagram of Cu, Sn, and Ti, the bonded body according to claim 2.

4. At least a part of the plurality of first alloys is a Cu—Sn alloy, and at least a part of the plurality of first alloys detected by EDX point analysis of the bonding layer are within a region surrounded by (97, 3, 0), (77, 23, 0), (52, 23, 25), and (72, 3, 25) in the ternary phase diagram of Cu, Sn, and Ti, the bonded body according to any one of claims 1 to 3.

5. The second alloy is a Ti—Sn alloy, and the second alloy detected by EDX point analysis of the bonding layer is within a region surrounded by (41, 23, 36), (24, 40, 36), (2, 40, 58), and (19, 23, 58) in the ternary phase diagram of Cu, Sn, and Ti, the bonded body according to any one of claims 2 or 3.

6. The bonded body according to any one of claims 1 to 5, wherein in one or more of the plurality of first alloys, the Ti content is 1 atomic% or less.

7. In a part of the plurality of first alloys, the Sn content is 3 atomic% or more and 9 atomic% or less, In another part of the plurality of first alloys, the Sn content is 10 atomic% or more and 30 atomic% or less, and the bonded body according to any one of claims 1 to 6 is characterized in that.

8. The bonded body according to any one of claims 1 to 7, wherein one or more freezing points or phase change points of the plurality of first alloys are 400 ° C or more and 600 ° C or less.

9. The Ti reaction layer contains titanium nitride particles having an average particle diameter of 50 nm or less, The bonded body according to any one of claims 1 to 8, wherein a first element containing Cu and one or two selected from Sn and In is present at the grain boundaries of the titanium nitride particles.

10. In the average value obtained by analyzing three regions in the thickness × width direction of 40 μm of each of the bonding layers, the total area of the plurality of first alloys is 50% or more and 95% or less of the areas of the three regions, and the bonding is characterized in that. The bonded body according to any one of claims 1 to 9

11. The bonded body according to any one of claims 1 to 10, wherein the bonding layer contains titanium silicide particles having a major axis of 0.5 μm or more and 6 μm or less.

12. The bonding layer contains a plurality of titanium silicide particles having a major axis of 0.5 μm or more and 6 μm or less, In a region of 200 μm in the thickness × width direction of the bonding layer, the area ratio of the plurality of titanium silicide particles is 1% or more and 15% or less, and the bonded body according to any one of claims 1 to 11 is characterized in that.

13. The bonded body according to any one of claims 1 to 12, wherein the bonding layer further contains carbon.

14. The bonded body according to any one of claims 1 to 13, wherein the thickness of the Ti reaction layer is 1 μm or less.

15. At the boundary between the bonding layer and the copper plate, a first element containing one or two selected from Sn and In is present, The ratio C2 / C1 of the second concentration C2 of the first element in the region in the copper plate 10 μm away from the boundary to the first concentration C1 of the first element at the boundary is 0.60 or less. The joined body according to any one of claims 1 to 14, characterized in that.

16. A ceramic circuit board comprising the joined body according to any one of claims 1 to 15.

17. The ceramic circuit board according to claim 16, A semiconductor element mounted on the ceramic circuit board, A semiconductor device comprising:

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