Bonded body, ceramic copper circuit board, and semiconductor device

Abstract

This joined body according to one embodiment comprises a ceramic substrate, a copper plate, and a joining layer disposed at least on one surface of the ceramic substrate to join the ceramic substrate and the copper plate together. The joining layer contains titanium. The joining layer includes a layer in which titanium is a main component. This layer has a first region and a second region, the first region being formed at the interface between the joining layer and the ceramic substrate, and the second region being located between the first region and the copper plate. When the concentrations of titanium in the first region and in the second region, within a region of 200 µm × the thickness of each of the measurement regions, are measured by the EDX, the joined body is characterized by having a ratio M1 / M2 of the titanium concentration in the first region, M1 at%, to the titanium concentration in the second region, M2 at%, of 0.1-5.

Description

Technical Field

[0001] The embodiments described below relate to a bonded body, a ceramic copper 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 for mounting semiconductor elements and the like. 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. Further, by controlling the nanoindentation hardness of the bonding layer, the temperature cycle test (TCT) characteristics are improved. In Patent Document 1, the nanoindentation hardness is controlled by making AgTi crystals or TiC present in the bonding layer. In Patent Document 1, the bonding strength and TCT characteristics are improved by controlling the nanoindentation hardness. On the other hand, when the bonded body becomes large, there are cases where the TCT characteristics deteriorate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Upon investigating the cause, it was found that the Ti distribution in the bonding layer was the culprit. Patent No. 4077888 (Patent Document 2) discloses a bonded body using Ag-Cu-Ti brazing material. In Patent Document 2, a titanium nitride (TiN) layer is formed in the bonding layer. This titanium nitride layer is a hard layer with a Vickers hardness of about 1100 to 1300. It was found that the difference in hardness between the TiN layer and the AgCu layer was the cause. The present invention aims to provide a bonded body in which the Ti distribution in the bonding layer is controlled to address such problems. [Means for solving the problem]

[0005] The bonded body according to the embodiment comprises a ceramic substrate, a copper plate, and a bonding layer disposed on at least one surface of the ceramic substrate and bonding the ceramic substrate and the copper plate. The bonding layer contains titanium. The bonding layer includes a layer mainly composed of titanium and has a first region formed at the interface of the bonding layer with the ceramic substrate, and a second region located between the first region and the copper plate. The bonded body is characterized in that, when the Ti concentration in a 200 μm × thickness range of each measurement area of ​​the first region and the second region is measured by EDX, the ratio M1 / M2 of the titanium concentration M1 at% in the first region to the titanium concentration M2 at% in the second region is 0.1 or more and 5 or less. [Brief explanation of the drawing]

[0006] [Figure 1] A diagram showing an example of a joint according to an embodiment. [Figure 2] A diagram showing an example of a bonding layer of a joint according to an embodiment. [Figure 3] A diagram showing an example of a ceramic copper circuit board according to an embodiment. [Figure 4] Another example of a ceramic copper circuit board according to the embodiment is shown. [Figure 5] A diagram showing an example of a semiconductor device according to an embodiment. [Modes for carrying out the invention]

[0007] The bonded body according to the embodiment comprises a ceramic substrate, a copper plate, and a bonding layer disposed on at least one surface of the ceramic substrate and bonding the ceramic substrate and the copper plate. The bonding layer contains titanium. The bonding layer includes a layer mainly composed of titanium and has a first region formed at the interface of the bonding layer with the ceramic substrate, and a second region located between the first region and the copper plate. The bonded body is characterized in that, when the Ti concentration in a 200 μm × thickness range of each measurement area of ​​the first region and the second region is measured by EDX, the ratio M1 / M2 of the titanium concentration M1 at% in the first region to the titanium concentration M2 at% in the second region is 0.1 or more and 5 or less. Figure 1 shows an example of a bonded body according to the embodiment. Figure 2 shows an example of a bonding layer of a bonded body according to the embodiment. In Figures 1 and 2, 1 is the bonded body. 2 is a ceramic substrate. 3 is a copper plate. 4 is a bonding layer. 5 is the first region. 6 is the second region. Figure 1 shows a bonded body 1 in which two copper plates 3 are arranged on both sides of a ceramic substrate 2, with bonding layers 4 in between. In the illustrated example, the length and width dimensions of the ceramic substrate 2 and the two copper plates 3 are the same. The bonded body according to this embodiment is not limited to this form, and may have a structure in which the copper plate is provided on only one side of the ceramic substrate 2. Also, the length and width dimensions of the ceramic substrate 2 may differ from the length and width dimensions of the copper plates 3.

[0008] The bonded body 1 comprises a ceramic substrate 2, a copper plate 3, and a bonding layer 4. The bonding layer 4 is disposed on at least one surface of the ceramic substrate and bonds the ceramic substrate 2 and the copper plate 3. The bonding layer 4 also contains Ti and has a first region 5 and a second region 6. The first region 5 includes a layer mainly composed of titanium. The layer mainly composed of titanium is formed at the interface between the bonding layer 4 and the ceramic substrate 2. The second region 6 is located between the first region 5 and the copper plate. Figure 2 shows a conceptual diagram of the bonding layer 4. The bonding layer 4 has a laminated structure consisting of a first region 5 and a second region 6.

[0009] Region 5 is the region containing a layer primarily composed of titanium. A layer primarily composed of titanium refers to a region where titanium is present at a concentration of 30 at% or more. Furthermore, a layer primarily composed of titanium refers to a layer containing one or more of the following: elemental titanium, oxides, nitrides, silicides, and oxynitrides. For example, if titanium silicide is formed on a titanium nitride layer in contact with the titanium nitride layer, the layer primarily composed of titanium is the titanium silicide and the titanium nitride layer. In other words, if titanium silicide is in direct contact with the titanium nitride layer, both the titanium nitride layer and the titanium silicide are counted as layers primarily composed of titanium. Furthermore, the first region 5 is located along the interface between the ceramic substrate 2 and the bonding layer 4. Therefore, the layer mainly composed of titanium is formed along the surface of the ceramic substrate 2. The layer primarily composed of titanium is formed continuously in the thickness direction from the ceramic substrate 2. For example, titanium nitride located at a distance from the titanium-primary layer is counted as a second region 6. If elemental titanium, oxides, or oxynitrides are located at a distance from the titanium-primary layer, they are also counted as second region 6. Examples of titanium oxides include TiO2 (titanium oxide). Examples of titanium nitrides include TiN (titanium nitride) and Ti2N (titanium dinitride). Examples of titanium oxynitride include TiON (titanium oxynitride). The examples of titanium oxides, titanium nitrides, and titanium oxynitrides are not limited to those listed above. For example, while TiN (titanium nitride) has a stable stoichiometry with a titanium-to-nitrogen atomic ratio of 1:1, it may deviate from this stoichiometry. Also, a layer with titanium as the main component may be a layer containing two or more of the materials listed above. "Titanium nitride" refers to a compound of titanium and nitrogen. When written as TiN, the titanium-to-nitrogen atomic ratio is not limited to 1:1, and it refers to a compound of titanium and nitrogen. Furthermore, in the case of a nitride-based ceramic substrate, the titanium-based layer contains titanium nitride as its main component. In the case of a nitride-based ceramic substrate, titanium nitride containing 30 at% or more titanium constitutes the titanium-based layer. In addition, the titanium nitride may be in one or more forms selected from cubic, hexagonal, and tetragonal crystals. Furthermore, in the case of a nitride-based ceramic substrate, the first region 5 can be determined based on the titanium nitride layer formed on the surface of the ceramic substrate 2. That is, the amount of titanium M1 in the first region 5 can be determined using the maximum thickness of the titanium nitride layer. If bonding layer 4 contains Ag, the layer mainly composed of titanium nitride contains Ti2N and Ti 0.83 N 0.17 And one or more types selected from metallic Ti may be present. Ti2N, Ti 0.83 N 0.17 Alternatively, metallic Ti will form a Ti-rich phase with a high Ti content. The presence of a Ti-rich phase in a layer mainly composed of titanium nitride allows for control over the amount of Ti present in the second region 6. Furthermore, if the bonding layer does not contain Ag, it is preferable that the Ti-rich phase be present in the layer mainly composed of titanium nitride within a range of 0 at% to 10 at%. Note that 0 at% of the Ti-rich phase means that it is below the detection limit. The Ti-rich phase contains more Ti than the region where the atomic ratio of Ti to N is 1:1. By increasing the amount of Ti in the first region 5, the ratio of the titanium concentration in the first region 5 to the titanium concentration in the second region 6 can be controlled. Furthermore, when the ceramic substrate is an oxide-based ceramic, the titanium-based layer primarily contains titanium oxide. Examples of titanium oxide include TiO2, TiO, and Ti3O2. For this reason, the titanium-based layer may be identified based on the titanium oxide layer. The titanium-based layer is formed on the surface of the ceramic substrate 2. The titanium-based layer does not need to have a constant thickness in the surface direction. Furthermore, the titanium-based layer only needs to be present in 90% or more of the interface between the bonding layer 4 and the ceramic substrate 2. The interface of the ceramic substrate 2 refers to the region of the surface of the ceramic substrate 2 where the bonding layer 4 is provided. Even on the surface of the ceramic substrate 2, regions where the bonding layer 4 is not provided are not included in the count. A layer primarily composed of titanium can be confirmed by EDX (energy-dispersive X-ray) analysis. An arbitrary cross-section of the bonded body 1 is subjected to EDX analysis. In the EDX analysis, an area analysis is performed within the measurement region of the bonded layer 4. The measurement region is a range of 200 μm in length and thickness. If a layer primarily composed of titanium is observed on the surface of the ceramic substrate 2 over a distance of 180 μm (= 200 μm × 90%) or more within the measurement region, it can be considered that a layer primarily composed of titanium exists. Furthermore, area analysis using EDX analysis allows for the analysis of components other than Ti contained in the titanium-based layer. For example, if nitrogen is detected by area analysis, it can be assumed that the titanium-based layer contains Ti nitride. When the boundary between the ceramic substrate 2 and the bonding layer 4 is difficult to distinguish, TEM (transmission electron microscopy) analysis is used. Based on the results of the TEM analysis, EDX point analysis of the bonding layer 4 is an effective method for detecting Ti and N. Other elements can be detected in a similar manner.

[0010] The thickness of the first region 5 is determined by the width between the point closest to the ceramic substrate 2 with the titanium-based layer and the point furthest from it within the measurement area. The titanium-based layer is formed along the surface of the ceramic substrate 2. The surface of the ceramic substrate 2 has minute irregularities. Therefore, the thickness of the first region 5 is determined by the method described above. Because the thickness of the first region 5 is determined by this method, the first region 5 also includes areas other than the titanium-based layer. Furthermore, within the measurement area, a line passing through the nearest point and parallel to the plane direction is defined as the boundary line between the ceramic substrate 2 and the first region 5. The plane direction is perpendicular to the thickness direction connecting the ceramic substrate 2 and the bonding layer 4. The boundary line between the ceramic substrate 2 and the first region 5 is called the first boundary line. Within the measurement area, a line passing through the furthest point and parallel to the plane direction is defined as the boundary line between the first region 5 and the second region 6. This boundary line between the first region 5 and the second region 6 is called the second boundary line. Therefore, the thickness of the first region 5 is the width between the first boundary line and the second boundary line. The thickness of the second region 6 is the width from the second boundary line to the boundary between the bonding layer 4 and the copper plate 3. The boundary between the bonding layer 4 and the copper plate 3 is the point furthest from the point where the components of the bonding layer connect and contact the copper plate 3 within the measurement region (the point furthest from the ceramic substrate 2). From near the interface between the second region 6 and the copper plate 3 across the copper plate 3, the amount of detected components of the bonding layer decreases sharply, and the components of the bonding layer become discontinuous. Within the measurement region, the line passing through the point furthest from the point where the components of the bonding layer connect and contact the copper plate 3, and parallel to the plane direction, is called the third boundary line. Therefore, the thickness of the second region 6 is the width from the second boundary line to the third boundary line. Within the measurement region, there is a region where the components constituting the bonding layer 4 connect up to the first region 5. The point where this region contacts the copper plate 3 is the point where the components of the bonding layer 4 connect and contact the copper plate 3.

[0011] For example, let's explain using the case where the components constituting the bonding layer 4 are Ag (silver), Cu (copper), Sn (tin), and Ti (titanium). "Connected" in the bonding layer 4 means that one or more mixed components selected from Ag, Cu, Sn, and Ti are connected from the first region 5 to the copper plate 3. Mixed components refer to a state where Ag, Cu, Sn, and Ti are mixed as individual components or as alloys. Therefore, even if the components constituting the bonding layer 4 diffuse into the copper plate 3, if they are not connected, they are not counted as the third boundary line. "Not connected" means that the components of the bonding layer are distributed in a discontinuous state. Furthermore, if the Cu constituting the bonding layer 4 and the Cu in the copper plate 3 cannot be distinguished, the third boundary line is counted using another component.

[0012] For the bonded body according to the embodiment, when the Ti concentration in the range of 200 μm × thickness of each measurement region of the first region 5 and the second region 6 is measured by EDX, the ratio M1 / M2 of the Ti concentration M1 at% in the first region 5 to the Ti concentration M2 at% in the second region 6 is 0.1 or more and 5 or less. The fact that M1 / M2, which is the ratio of the Ti concentration, is 0.1 or more and 5 or less indicates that Ti is relatively abundantly distributed in the second region 6. Among bonding techniques using Ti, there is an active metal bonding method. As shown in Patent Document 1 and Patent Document 2, the active metal bonding method forms a titanium nitride (TiN) layer. This titanium nitride layer corresponds to a layer mainly composed of titanium. Conventionally, since Ti was concentrated in the titanium nitride layer, the Ti concentration in the region corresponding to the second region 6 was low. For this reason, conventionally, M1 / M2 was 20 or more. The titanium nitride layer is a hard layer. It has been found that a difference in hardness between the first region and the second region can adversely affect the TCT characteristics. Also, when M1 / M2 is less than 0.1, the amount of Ti in the first region 5 is small. When the amount of Ti in the first region 5 is small, the amount of titanium nitride is insufficient, and thus the bonding strength may decrease. In Patent Document 1 and Patent Document 2, the layer mainly composed of titanium contains titanium nitride (TiN). This is because the nitride ceramic substrate reacted with Ti. Therefore, when an oxide ceramic substrate is used, titanium oxide is formed. In the active metal bonding method, an active metal brazing filler mainly composed of Ag or Cu and containing Ti as an active metal is used. Also, Sn (tin) or In (indium) may be added to the active metal brazing filler. Among the active metal brazing fillers, Ti is a relatively hard material. Therefore, by controlling the Ti concentration in the bonding layer, the hardness in the bonding layer can be made more uniform. Accordingly, M1 / M2 is preferably 0.1 or more and 5 or less, and more preferably 0.5 or more and 4 or less.

[0013] For EDX analysis, SEM-EDX is used. For the SEM, a device manufactured by JEOL, JSM-IT100 or a device with equivalent performance is used. Also, for the EDX, a device manufactured by JEOL, EX-9440IT4L11 or a device with equivalent performance is used. First, area analysis is performed by EDX within a range of 200 μm × thickness in the measurement area. The reason for setting the measurement area to 200 μm × thickness is that it is a suitable range for examining the distribution of the bonding layer components. If the measurement area is smaller than 200 μm, it is likely to be affected by the diffusion state of the materials contained in the bonding layer into the copper plate. The particle size of the copper particles contained in the copper plate is about 10 to 1000 μm. The grain boundaries of the copper plate serve as the routes for the diffusion of the materials contained in the bonding layer. To suppress the influence on the analysis of the areas where diffusion is easy and difficult, it is preferable that the measurement area is 200 μm. If the measurement area is larger than 200 μm, the variation in Ti concentration cannot be measured. Also, as described later, in order to measure the variation in Ti concentration within the second region, it is preferable that the measurement area is 200 μm. M1 / M2 is obtained by the average value of any three locations.

[0014] The variation in Ti concentration within the second region 6 is preferably within ±20%. The variation in Ti concentration within the second region 6 is the difference between the Ti concentration of the second region 6 in the first measurement area and the Ti concentration of the second region 6 in another measurement area. Let the Ti concentration in the first measurement area be M2a and the Ti concentration in another measurement area be M2b. The variation in Ti concentration V within the second region 6 is calculated by V(%) = [(M2a - M2b) / M2a] × 100. By suppressing not only the Ti concentration of the first region 5 and the second region 6 but also the variation in Ti concentration within the second region 6, the TCT characteristics can be improved. Therefore, the variation in Ti concentration within the second region 6 is preferably within ±20%, and more preferably within ±10%.

[0015] The thickness of the first region is preferably 5 μm or less. The first region 5 contains a layer mainly composed of titanium. If the first region 5 is thicker than 5 μm, too much titanium accumulates in the first region 5, and there is a possibility that M1 / M2 exceeds 5. The thickness of the second region is preferably 5 μm or more and 70 μm or less. It is preferable to control the Ti concentration of the second region 6 having a predetermined thickness.

[0016] It is preferable that the Ti concentration in the second region be within the range of 0.5 at% to 15 at%. If the Ti concentration in the second region 6 is less than 0.5 at%, there is a possibility that the amount of Ti in the second region 6 will be insufficient. If the amount of Ti is low, the variation in Ti concentration within the second region 6 tends to increase. Also, if the Ti concentration is high, exceeding 15 at%, the M1 / M2 ratio tends to be less than 0.1. For this reason, it is preferable that the Ti concentration in the second region 6 be between 0.5 at% and 15 at%, and moreover, between 1 at% and 10 at%. When measuring the Ti concentration in the second region 6 in at%, the value should be obtained excluding O (oxygen), N (nitrogen), and C (carbon). As will be described later, metallic components such as Ag and Cu exist in the M2 region. at% is effective for controlling the abundance ratio of metallic components other than Ti.

[0017] The thickness of the copper plate is preferably 0.6 mm or more. The ceramic substrate is preferably one selected from a silicon nitride substrate and an aluminum nitride substrate. The copper plate 3 can be made of copper or a copper alloy plate. Preferably, the copper plate 3 is made of oxygen-free copper. Oxygen-free copper has a copper purity of 99.96 wt% or higher, as indicated in JIS-H-3100 (ISO1337, etc.). The copper plate 3 is used as a circuit board or a heat sink. Increasing the thickness of the copper plate 3 can improve current conductivity and heat dissipation. For this reason, the thickness of the copper plate 3 is preferably 0.6 mm or more, and more preferably 0.8 mm or more.

[0018] As the ceramic substrate 2, silicon nitride substrates, aluminum nitride substrates, aluminum oxide substrates, argil substrates, etc., can be used. 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, it may lead to a decrease in strength. Also, if it is thicker than 1 mm, the ceramic substrate will act as a thermal resistor, which may reduce the heat dissipation of the bonded structure. The three-point bending strength of the silicon nitride substrate is preferably 600 MPa or higher. The thermal conductivity is preferably 80 W / m·K or higher. 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 higher, and more preferably 700 MPa or higher. This allows the thickness of the silicon nitride substrate to be reduced to 0.40 mm or less, and more preferably 0.30 mm or less. The three-point bending strength of the aluminum nitride substrate is approximately 300-450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or higher. Due to the low strength of the aluminum nitride substrate, a substrate thickness of 0.60 mm or more is preferable. The three-point bending strength of aluminum oxide substrates is approximately 300-450 MPa, and they are inexpensive. On the other hand, while the three-point bending strength of argil substrates is high at approximately 550 MPa, their thermal conductivity is only about 30-50 W / m·K. The ceramic substrate 2 is preferably either a silicon nitride substrate or an aluminum nitride substrate. Both the silicon nitride substrate and the aluminum nitride substrate are nitride ceramic substrates. Nitride ceramics react with an active metal brazing material containing Ti to form titanium nitride. This makes it easier to form a layer mainly composed of titanium nitride in the first region 5. Furthermore, oxide ceramics react with active metal brazing materials containing Ti to form titanium oxide. This makes it easier to form a layer mainly composed of titanium oxide in the first region 5. Examples of oxide ceramics include aluminum oxide substrates and argyl substrates.

[0019] It is preferable that copper plates 3 are arranged on both sides of the ceramic substrate 2. By joining copper plates to both sides, warping of the joined body can be suppressed. The second region preferably contains one or two selected from silver and copper. Furthermore, the second region preferably contains one or two selected from tin and indium. To include silver or copper in the second region 6, it is effective to include silver or copper in the active metal brazing material. To include tin or indium in the second region 6, it is effective to include tin or indium in the active metal brazing material. The active metal brazing material composition preferably contains 0% to 70% by mass of Ag (silver), 15% to 85% by mass of Cu (copper), and 1% to 15% by mass of Ti (titanium) or TiH2 (titanium hydride). When both Ti and TiH2 are used, their total amount should be within the range of 1 to 15% by mass. When both Ag and Cu are used, it is preferable that Ag is 20 to 60% by mass and Cu is 15 to 40% by mass. If necessary, the activated metal brazing material may contain one or two elements selected from Sn (tin) and In (indium) in an amount of 1% to 50% by mass. The Ti or TiH2 content is preferably 1 to 15% by mass. If necessary, the activated metal brazing material may contain C (carbon) in an amount of 0.1% to 2 wt% by mass. The ratio of the active metal brazing alloy composition is calculated by considering the total value of the raw materials to be mixed as 100% by mass. For example, if the active metal brazing alloy is composed of three types of materials: Ag, Cu, and Ti, then Ag + Cu + Ti = 100% by mass. If the active metal brazing alloy is composed of four types of materials: Ag, Cu, TiH2, and In, then Ag + Cu + TiH2 + In = 100% by mass. If the active metal brazing alloy is composed of five types of materials: Ag, Cu, Ti, Sn, and C, then Ag + Cu + Ti + Sn + C = 100% by mass.

[0020] Ag or Cu are components that form the base material of the brazing material. Sn or In have the effect of lowering the melting point of the brazing material. C (carbon) have the effect of controlling the fluidity of the brazing material and controlling the structure of the bonded layer by reacting with other components. For this reason, examples of brazing material components include Ag-Cu-Ti, Ag-Cu-Sn-Ti, Ag-Cu-Ti-C, Ag-Cu-Sn-Ti-C, Ag-Ti, Cu-Ti, Ag-Sn-Ti, Cu-Sn-Ti, Ag-Ti-C, Cu-Ti-C, Ag-Sn-Ti-C, and Cu-Sn-Ti-C. In may be used instead of Sn. Both Sn and In may be used. Low-melting-point metals such as Bi (bismuth), Sb (antimony), and Ga (gallium) may be used instead of Sn or In.

[0021] The melting point of the active metal brazing material is preferably 700°C or lower. Lowering the melting point of the brazing material allows for a reduction in the bonding temperature. Lowering the bonding temperature allows for control of the Ti concentration in the first region 5 and the Ti concentration in the second region 6. In the DSC curve of the activated metal brazing material, it is preferable that the largest endothermic peak occurs within the range of 550°C to 700°C. The temperature at which the largest endothermic peak occurs in the DSC curve is defined as the melting point of the activated metal brazing material.

[0022] DSC curves are obtained by measuring the peaks of endothermic and exothermic reactions using a differential scanning calorimeter (DSC). Peaks in the negative direction represent endothermic reactions, and peaks in the positive direction represent exothermic reactions. The DSC curve is measured using a temperature profile consisting of a heating process, a holding process at a constant temperature, and a cooling process. Regarding the temperature profile, the heating process involves raising the temperature from room temperature to 500°C at a heating rate of 5°C / min. Next, the heating process involves holding the temperature at 500°C for 60 minutes. After that, the heating process continues at a heating rate of 5°C / min to 845°C. The holding process involves holding the temperature at 845°C for 30 minutes. The cooling process involves cooling the temperature from 845°C to room temperature at a cooling rate of 5°C / min. For DSC, a NETZSCH TGA-DSC simultaneous thermal analyzer STA449-F3-Jupiter or an instrument with equivalent performance is used. The measurement is performed in an argon (Ar) flow by dropping an appropriate amount of brazing material into an alumina container. It is necessary to prevent the brazing material from reacting with the atmosphere by performing the measurement in an Ar atmosphere.

[0023] In the heating process of the DCS curve, the melting point is defined as the temperature at which the largest endothermic peak is detected within the temperature range of 550°C to 800°C. A melting point of 700°C or lower means that the largest endothermic peak is within the range of 550°C to 700°C. Note that even if there is a negative peak below 550°C, it does not need to be counted as an endothermic peak. Endothermic reactions are caused by the melting and decomposition of the active metal brazing material. For example, when titanium hydride (TiH2) is used as the active metal, a negative peak is detected around 500°C. This peak represents the decomposition of TiH2 into Ti and H.

[0024] The above-described bonded structure is suitable for a ceramic copper circuit board. A circuit structure is provided on a copper plate placed on at least one surface of the ceramic substrate. This yields a ceramic copper circuit board using the bonded structure according to the embodiment. Figure 3 shows an example of a ceramic copper circuit board according to an embodiment. In Figure 3, 7 is a circuit section, 8 is a heat sink, and 10 is a ceramic copper circuit board. The circuit section 7 is formed by applying a circuit structure to the front copper plate 3. The heat sink 8 is formed by processing the back copper plate 3. In Figure 3, two circuit sections 7 are provided. The ceramic copper circuit board according to the embodiment is not limited to the illustrated structure. The number and shape of the circuit sections 7 are arbitrary. The circuit sections 7 may also be formed by applying a circuit structure to both copper plates 3. The side surfaces of the circuit sections 7 or the heat sink 8 may be inclined with respect to the thickness direction. A bonding layer overhang may be provided, where the bonding layer 4 protrudes from the end of the circuit section 7 or the end of the heat sink 8. In the ceramic copper circuit board 10 according to the embodiment, the Ti distribution within the bonding layer 4 is controlled, so the TCT characteristics can be improved.

[0025] Figure 4 shows another example of a ceramic copper circuit board according to the embodiment. The ceramic substrate may have through holes. The copper plate on the front side and the copper plate on the back side may be electrically connected through the through holes. Figure 4 shows an example of a ceramic copper circuit board having through holes. Figure 4 is a cross-sectional view of the portion where the through holes are provided. In Figure 4, 10 is a ceramic copper circuit board. 2 is a silicon nitride substrate. 4 is a bonding layer. 7a is the circuit portion on the front side. 7b is the circuit portion on the back side. 9 is a through hole. In Figure 4, the circuit portions 7a and 7b are electrically connected through the through holes 9. In Figure 4, multiple through holes 9 connect multiple circuit portions 7a and multiple circuit portions 7b, respectively. The embodiment is not limited to this structure. In the ceramic copper circuit board 10, through holes 9 may be provided only for a portion of the multiple circuit portions 7a. Through holes 9 may be provided only for a portion of the circuit portions 7b. It is preferable that the inside of the through holes 9 be filled with the same material as the bonding layer 4. The internal structure of the through-hole 9 is not particularly limited, as long as it allows electrical conductivity between the circuit section on the front side and the circuit section on the back side. For this reason, a thin metal film may be provided only on the inner wall of the through-hole 9. On the other hand, the bonding strength can be improved by filling it with the same material as the bonding layer 4.

[0026] Figure 5 shows an example of a semiconductor device according to an embodiment. The ceramic copper circuit board according to this embodiment is suitable for semiconductor devices. In a semiconductor device, semiconductor elements are mounted on the copper plate of the ceramic copper circuit board via a bonding layer. Figure 5 shows an example of a semiconductor device. In Figure 5, 10 is a ceramic copper circuit board. 7 is a circuit section. 8 is a heat sink. 20 is a semiconductor device. 21 is a semiconductor element. 22 is a bonding layer. 23 is wire bonding. 24 is a metal terminal. In Figure 5, a semiconductor element 21 is bonded to the circuit section of the ceramic copper circuit board 10 via a bonding layer 22. Similarly, a metal terminal 24 is bonded via a bonding layer 22. Adjacent circuit sections are electrically connected by wire bonding 23. In Figure 5, in addition to the semiconductor element 21, wire bonding 23 and metal terminal 24 are bonded to the ceramic copper circuit board 10. The semiconductor device according to this embodiment is not limited to this structure. For example, only one of the wire bonding 23 or the metal terminal 24 may be provided. Multiple semiconductor elements 21, wire bonding 23, and metal terminals 24 may be provided in the circuit portion on the front side. A circuit structure may be provided on the copper plate on the back side, and the semiconductor elements 21, wire bonding 23, and metal terminals 24 may be joined to it. Various shapes such as lead frame shape and convex shape can be applied to the metal terminals 24. By using the bonded structure according to this embodiment in the ceramic copper circuit board or semiconductor device described above, the TCT characteristics can be improved.

[0027] Next, a method for manufacturing the joint according to the embodiment will be described. The method for manufacturing the joint according to the embodiment is not limited as long as it has the above configuration. Here, an example of a method for obtaining the joint according to the embodiment with good yield will be described. First, prepare the ceramic substrate 2. The ceramic substrate 2 can be a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, or an argil substrate. Note that the argil substrate is a substrate made of a mixture of aluminum oxide and zirconium oxide. The copper plate 3 can be a copper plate or a copper alloy plate. Furthermore, the copper plate 3 is preferably oxygen-free copper. Oxygen-free copper has a copper purity of 99.96 wt% or higher, as specified in JIS-H-3100.

[0028] Next, an activated metal brazing paste containing Ti is prepared. It is preferable to add one or two components selected from Ag and Cu as components other than Ti to the activated metal brazing paste containing Ti. It is also preferable to add one or two components selected from Sn and In to the activated metal brazing paste. C (carbon) may also be added to the activated metal brazing paste. Furthermore, compounds such as TiH2 may be added to the activated metal brazing paste as Ti. The composition ratio (mass%) of each component is as described above. To control the melting point of activated metal brazing materials, it is effective to control the composition and particle size of the raw material powders. As mentioned above, Sn or In has the effect of lowering the melting point of the brazing material. Among the components that make up the brazing material, it is effective to make the particle size of Sn or In the largest. For example, when using Ag-Cu-Sn-Ti brazing material, the particle size of Sn powder should be the largest among Ag powder, Cu powder, Sn powder, and Ti powder. Sn powder reacts readily with other brazing material components. By increasing the particle size of Sn powder, the Sn powder comes into contact with other components more easily. This can lower the melting point of the brazing material. The same effect can be obtained by using In instead of Sn. It is effective to increase the particle size of the component that has the effect of lowering the melting point. In addition, lowering the joining temperature can reduce the load on the joining equipment.

[0029] The powders of the constituent components of the activated metal brazing material are mixed to prepare a uniformly dispersed mixed powder. The mixing process of the constituent powders is preferably carried out for 10 hours or more. Next, the mixed powder is mixed with a binder and a solvent to prepare an activated metal brazing paste. It is also preferable to carry out the mixing process of the mixed powder and the binder for 10 hours or more. An activated metal brazing paste is applied to at least one of a ceramic substrate or a copper plate. The thickness of the activated metal brazing paste layer is preferably 5 μm to 80 μm. The thickness of the activated metal brazing paste layer is the thickness after the applied paste has dried. If the thickness is less than 5 μm, the bonding strength may decrease. If it is thicker than 80 μm, the thermal stress during the bonding process will increase, which may lead to greater warping of the bonded body. For this reason, the thickness of the activated metal brazing paste layer is preferably 5 μm to 80 μm, and more preferably 10 μm to 50 μm.

[0030] After the step of applying the activated metal brazing paste, the step of placing a component that does not have the paste applied onto the component that does have the paste applied is performed. For example, if the activated metal brazing paste is applied to a ceramic substrate, a copper plate is placed on the ceramic substrate. The activated metal brazing paste may be applied to both sides of the ceramic substrate, and copper plates may be placed on each side. Alternatively, the activated metal brazing paste may be applied to a copper plate, and the ceramic substrate may be placed on the copper plate.

[0031] Next, a bonding process is performed at a bonding temperature of 800°C or lower. The bonding temperature is the highest temperature that can be maintained for a certain period of time. Higher bonding temperatures promote the growth of copper crystal grains that make up the copper plate. In conventional activated metal bonding methods, the bonding temperature was around 850°C. When the bonding temperature exceeds 800°C, the grain growth of the copper plate increases. When the grain growth of the copper plate is large, large crystal grains with a major axis exceeding 400 μm are more likely to form. The bonding temperature is preferably 800°C or lower, and more preferably 700°C or lower. While there is no particular lower limit to the bonding temperature, 500°C or higher is preferred. A low bonding temperature may reduce the reliability of the bond. Therefore, a bonding temperature of 500°C to 800°C, and more preferably 550°C to 700°C, is preferred. Furthermore, the holding time at the bonding temperature is preferably 100 minutes or less, and more preferably 30 minutes or less. When joining at temperatures exceeding 800°C, it is preferable to set the heating rate to 20°C / min or higher. By increasing the heating rate, the amount of heat required to rise from room temperature to the joining temperature can be reduced. This allows for achieving the same effect as joining at temperatures below 800°C. The joining temperature can range from above 800°C to below 950°C. There is no particular upper limit to the heating rate, but it is preferably 100°C / min or lower. A heating rate of 20 to 100°C / min, and more preferably 30 to 70°C / min, from room temperature to the joining temperature is preferable. If the heating rate exceeds 100°C / min, control may become difficult. Similarly, a cooling rate of 20 to 100°C / min from the joining temperature to room temperature is also preferable. By increasing both the heating and cooling rates, the amount of heat required can be equivalent to that at temperatures below 800°C. Furthermore, the atmosphere during the bonding process is preferably a vacuum or a nitrogen atmosphere. The pressure in a vacuum is 10 -3 A vacuum of Pa or less is preferable. In a vacuum, the nitridation of Ti in the brazing material before it reacts with the ceramic substrate can be suppressed. A nitrogen atmosphere refers to an atmosphere containing 90 vol% to 100 vol% nitrogen. If nitrogen is present in the atmosphere during the bonding process, it is possible that the Ti will become titanium nitride before it can react with the ceramic substrate. If the Ti content in the brazing material is 6 mass% or more, the Ti and ceramic substrate can react sufficiently even in a nitrogen atmosphere. The joining process can be either batch-type or continuous-type. The batch-type method involves placing ceramic substrates and copper plates in a storage container and subjecting them to heat treatment. The continuous-type method involves placing ceramic substrates and copper plates on a conveyor belt and subjecting them to heat treatment while they are moved. The batch-type method is suitable for joining processes in a vacuum. The continuous-type method is suitable for joining processes in a nitrogen atmosphere. In the batch-type method, the holding time at the joining temperature can be shortened. In the continuous-type method, the holding time at the joining temperature is longer, but continuous heat treatment is possible, improving mass production efficiency. Batch-type joining equipment is sometimes called a batch furnace, and continuous-type joining equipment is sometimes called a continuous furnace.

[0032] The Ti concentration within the bonded layer 4 can be controlled by lowering the bonding temperature or shortening the holding time at the bonding temperature. As mentioned above, the components of the activated metal brazing material are uniformly mixed. Therefore, at the stage of the activated metal brazing material paste layer, Ti is uniformly dispersed. Furthermore, at the stage of the activated metal brazing material paste layer, no layer mainly composed of titanium is formed. The bonding process forms a layer primarily composed of titanium. If the bonding temperature is as high as 850°C as in conventional methods, Ti will accumulate in the titanium-primarily composed layer. As a result, Ti aggregates in the first region 5, and the M1 / M2 ratio becomes approximately 10. The M1 / M2 ratio can be controlled by setting the bonding temperature to 800°C or lower, or even between 550°C and 700°C. Lowering the bonding temperature reduces the amount of Ti that accumulates in the titanium-dominant layer, allowing Ti to remain in the second region 6. Similarly, by setting the bonding temperature holding time to 60 minutes or less, or even 30 minutes or less, the amount of Ti that accumulates in the titanium-dominant layer can be reduced, allowing Ti to remain in the second region 6. Furthermore, it is possible to increase the amount of Ti in the second region by increasing the content of Ti or TiH2 as a component of the active metal brazing material (for example, 5% by mass or more). As a result, the M1 / M2 ratio can be set within the range of 0.1 to 5. Furthermore, by uniformly mixing the active metal brazing powder, the variation in Ti concentration within the second region 6 can be reduced to within ±20%. In other words, in the case of batch processing performed in a vacuum, it is effective to lower the bonding temperature to 800°C or even below, and even to 700°C or below. In the case of continuous bonding performed in a nitrogen atmosphere, temperatures exceeding 800°C may be used. By increasing the heating or cooling rate, the holding time of the bonding temperature can be shortened. This reduces the amount of Ti that accumulates in the titanium-dominant layer, allowing Ti to remain in the second region 6. Furthermore, for continuous bonding performed in a nitrogen atmosphere, activated metal brazing materials that do not contain Ag are effective. Furthermore, in the bonded body after the bonding process, TiSi, CuSn, and TiSn are formed in the second region 6. TiSi is formed by the reaction of titanium and silicon. CuSn is formed by the reaction of copper and tin. TiSn is formed by the reaction of titanium and tin. Note that the atomic ratio of each compound is not limited to 1:1. When the bonding process is performed in a vacuum, it is preferable that the mass ratio of the compounds in the second region 6 satisfies TiSi > TiSn and CuSn > TiSn. Among TiSi, CuSn, and TiSn, CuSn has the lowest melting point. The bonding process in a vacuum has a slow heating rate of about 1-2°C / min. By increasing the amount of CuSn formed during the slow heating process, the amount of Ti in the second region 6 can be controlled.

[0033] Regarding the bonded structure, it is preferable that the length and width dimensions of the ceramic substrate 2 and the copper plate 3 are the same. The thermal conductivity of the ceramic substrate 2 is preferably 60 W / m·K or higher. It is preferable to bond the copper plates 3 to both sides of the ceramic substrate 2. The theoretical thermal conductivity of copper is approximately 398 W / m·K. By making the length and width dimensions of the ceramic substrate 2 the same as those of the copper plate 3, the heat transfer to the activated metal brazing paste layer becomes uniform. Similarly, the heat transfer can also be made uniform by increasing the thermal conductivity of the ceramic substrate 2 or by placing copper plates 3 on both sides. This allows the variation in Ti concentration within the second region 6 to be reduced to within ±20%, and even within ±10%. Even if the size of the bonded body 1 increases, the variation in Ti concentration can be suppressed. Therefore, even if the size of the bonded body increases to 200 mm in length and 200 mm in width, the variation in Ti concentration can be suppressed. Furthermore, even if the vertical or horizontal dimensions of the joint exceed 200 mm, the amount of warping of the joint can be kept to 0.1 mm or less. Also, even if the thickness of the copper plate on the front side and the copper plate on the back side are different, the amount of warping of the joint can be kept to 0.1 mm or less.

[0034] Through the above process, a bonded body in which a ceramic substrate and a copper plate are joined can be manufactured. If necessary, a circuit section 7 or a heat sink 8 structure is added to the copper plate 3. By adding the circuit section 7, the bonded body 1 becomes a ceramic copper circuit board 10. Because the Ti concentration in the first region 5 and the second region 6 is controlled, the TCT characteristics can be improved. In addition, since the size of the bonded body 1 can be increased, it is a bonded body suitable for multi-cavity production. Multi-cavity production is a method of obtaining smaller bonded bodies by cutting a large bonded body. There are also methods of dividing the bonded body or dividing the ceramic copper circuit board. Scribing may be performed to facilitate division.

[0035] (Examples) (Examples 1-15, Comparative Examples 1-3) As ceramic substrates, we prepared silicon nitride substrates and aluminum nitride substrates as shown in Table 1.

[0036] [Table 1]

[0037] Next, we prepared the copper plates shown in Table 2. All of the copper plates were made of oxygen-free copper.

[0038] [Table 2]

[0039] Next, the activated metal brazing materials shown in Table 3 were prepared. For activated metal brazing materials 1-3, the particle size of the Sn powder was the largest. For activated metal brazing material 4, the particle size of the Ag powder was the largest. The mixing time for the components of brazing materials 1-3 and 5-6 was 10 hours or more. The mixing time for the components of brazing material 4 was 5 hours. The melting point of the brazing materials was determined by measuring the DSC curve as described above.

[0040] [Table 3]

[0041] Next, a bonding process was carried out using a ceramic substrate, a copper plate, and an activated metal brazing material. The length and width of the copper plate were matched to the length and width of the ceramic substrate. Table 4 shows the atmosphere of the bonding process. -3 Processes performed in a vacuum of Pa or less were indicated as "vacuum." Processes performed in a nitrogen atmosphere of 98 vol% or higher were indicated as "nitrogen." For bonding processes with a bonding temperature of 800°C or lower, the heating rate from room temperature to the bonding temperature and the cooling rate from the bonding temperature to room temperature were set within the range of 1 to 10°C / min. For Examples 13 and 14, where the bonding temperature exceeded 800°C, the heating rate from room temperature to the bonding temperature and the cooling rate from the bonding temperature to room temperature were set within the range of 30 to 70°C / min. Bonding processes in a vacuum were performed in a batch furnace. Bonding processes in a nitrogen atmosphere were performed in a continuous furnace. The combinations of materials are shown in Table 4.

[0042] [Table 4]

[0043] The joints according to the examples and comparative examples were fabricated using the above procedure. EDX analysis was performed on any cross-section of each joint. This allowed for the analysis of the thickness of the first region, the thickness of the second region, and the Ti concentration in each region. For EDX analysis, an area analysis was performed using a measurement area of ​​200 μm length × thickness. The average values ​​of three arbitrary locations are shown as M1 and M2. Ti concentration was calculated in at%. For the at% calculation, the sum of components excluding O (oxygen), N (nitrogen), and C (carbon) was set to 100 at%. Other conditions were as described above. The results are shown in Table 5.

[0044] [Table 5]

[0045] As can be seen from the analysis results of Examples 1 to 15 shown in Table 5, the M1 / M2 ratio in the bonded bodies of the examples was within the range of 0.1 to 5. In addition, a layer mainly composed of titanium with a TiN content of 65% to 100% was observed in the first region. In the second region 6 of the bonded material formed in a vacuum, the mass ratios TiSi > TiSn and CuSn > TiSn were satisfied. On the other hand, in the bonded material formed in a nitrogen atmosphere, some bonded materials were observed that did not necessarily satisfy these relationships. Furthermore, the amount of warpage of the joints in the examples and comparative examples was measured. The amount of warpage was measured on the longer side. Joints with a warpage of 0.1 mm or less on the longer side were classified as good products (○), and those with a warpage exceeding 0.1 mm were classified as defective products (×). Each joint was fabricated, and the worst value among 50 joints was displayed. The results are shown in the table. 6 As shown.

[0046] [Table 6]

[0047] As can be seen from Table 6, the warp of the joints in the examples was small, less than 0.1 mm. Even when the thickness of the copper plates on the front and back sides were different, as in Examples 7, 8, 10, and 12, the warp of the joints could be kept small. In contrast, the warp of the joints in the comparative examples exceeded 0.1 mm.

[0048] Next, each joint was etched to form the circuit section and heat sink. Furthermore, each joint was divided into four sections, and numerous ceramic copper circuit boards were obtained. The shapes of the circuit section and heat sink were the same between the example and the comparative example. Twelve joints were prepared after division. The TCT characteristics were investigated for each ceramic copper circuit board. For the TCT test, one cycle consisted of -40°C for 30 minutes → room temperature for 10 minutes → 170°C for 30 minutes → room temperature for 10 minutes. Bonded structures using silicon nitride substrates were tested for 2000 and 3000 cycles. Bonded structures using aluminum nitride substrates were tested for 300 and 600 cycles. In each test, joints that showed no defects in any of the 12 were classified as the best product (◎), joints with one defect were classified as good (〇), and joints with two or more defects were classified as poor (×). The results are shown in Tables 7 and 8.

[0049] [Table 7]

[0050] [Table 8]

[0051] The ceramic copper circuit boards used in the examples exhibited good TCT characteristics. It was found that controlling the Ti concentration in the bonding layer improved the TCT characteristics. Furthermore, even when the size of the bonded body was increased, the Ti concentration could be controlled, resulting in good reliability even when multiple pieces were produced. In contrast, in the comparative example, the ratio of Ti concentrations M1 / M2 in the bonding layer was outside the range of 0.1 to 5, resulting in variability in TCT characteristics. This is thought to be due to the influence of Ti concentration variations as the size of the bonded body increased. Therefore, it was found that this method is not suitable for multi-piece molding.

[0052] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Modifications of these embodiments are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

Claims

1. Ceramic substrate and Copper plate and A bonding layer is provided on at least one surface of the ceramic substrate and joins the ceramic substrate and the copper plate, Equipped with, The aforementioned bonding layer contains titanium, The aforementioned bonding layer is A first region comprising a layer mainly composed of titanium, wherein the layer is formed at the interface between the bonding layer and the ceramic substrate, A second region located between the first region and the copper plate, It has, When the Ti concentration in a 200 μm × thickness range of each measurement area of ​​the first region and the second region is measured by EDX, the ratio M1 / M2 of the titanium concentration M1 at% in the first region to the titanium concentration M2 at% in the second region is 0.5 or more and 5 or less. The titanium concentration M2 in the second region is in the range of 0.5 at% or more and 15 at% or less. The joint is characterized in that the second region contains one or two selected from silver and copper, and one or two selected from tin and indium.

2. The bonded body according to claim 1, characterized in that the variation in Ti concentration between the measurement regions in the second region is within ±20%.

3. The bonded body according to any one of claims 1 to 2, characterized in that the thickness of the first region is 5 μm or less.

4. The joint according to any one of claims 1 to 3, characterized in that the thickness of the copper plate is 0.6 mm or more.

5. The bonded body according to any one of claims 1 to 4, characterized in that the ceramic substrate is one selected from a silicon nitride substrate and an aluminum nitride substrate.

6. The bonded body according to any one of claims 1 to 5, characterized in that the copper plates are arranged on both sides of the ceramic substrate.

7. The joint comprises the one described in any one of claims 1 to 6, A ceramic copper circuit board characterized in that a circuit structure is provided on the copper plate disposed on at least one surface of the ceramic substrate.

8. A ceramic copper circuit board according to claim 7, A semiconductor element mounted on the copper plate on which the circuit structure is provided, A semiconductor device characterized by having the following features.

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