JP5640569B2 - Power module substrate manufacturing method - Google Patents

Description

The present invention provides a power module base used in a semiconductor device that controls a large current and a high voltage.
The present invention relates to a method for manufacturing a plate .

Among semiconductor elements, a power element for supplying power has a relatively high calorific value. Therefore, as a substrate on which the power element is mounted, for example, as shown in Patent Document 1, an Al (AlN (aluminum nitride)) ceramic substrate is made of Al ( A power module substrate in which a metal plate of (aluminum) is bonded via a brazing material is used.
The metal plate is formed as a circuit layer, and a power element (semiconductor element) is mounted on the metal plate via a solder material.
In addition, a metal plate made of Al or the like is bonded to the lower surface of the ceramic substrate to form a metal layer for heat dissipation, and the entire power module substrate is bonded to the heat sink via this metal layer. Yes.

  As a means for forming a circuit layer, in addition to a method of forming a circuit pattern on a metal plate after bonding the metal plate to a ceramic substrate, for example, as disclosed in Patent Document 2, a circuit pattern is previously provided. There has been proposed a method of joining a metal piece formed in a shape to a ceramic substrate.

  Here, in order to obtain good bonding strength between the circuit layer and the metal plate as the metal layer and the ceramic substrate, for example, the following Patent Document 3 discloses a technique in which the surface roughness of the ceramic substrate is less than 0.5 μm. Has been.

JP 2003-086744 A JP 2008-311294 A Japanese Patent Laid-Open No. 3-234045

However, when the metal plate is bonded to the ceramic substrate, there is a disadvantage that a sufficiently high bonding strength cannot be obtained even if the surface roughness of the ceramic substrate is simply reduced, and the reliability cannot be improved. For example, even if the surface of the ceramic substrate is subjected to a honing process with Al ₂ O ₃ particles in a dry manner and the surface roughness is set to Ra = 0.2 μm, interface peeling may occur in the peeling test. I understood. Further, even when the surface roughness was set to Ra = 0.1 μm or less by the polishing method, there was a case where the interface peeling occurred in the same manner.

  In particular, recently, power modules have become smaller and thinner, and the usage environment has become harsh, and the amount of heat generated from electronic components tends to increase. It is necessary to dispose a module substrate. In this case, since the power module substrate is constrained by the heat radiating plate, a large shearing force acts on the bonding interface between the metal plate and the ceramic substrate at the time of thermal cycle loading. There is a demand for improvement in bonding strength and reliability between the metal plate and the metal plate.

The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a method for manufacturing a power module substrate in which a metal plate and a ceramic substrate are securely bonded and the thermal cycle reliability is high. .

In order to solve the above problems and achieve the above object, a method for manufacturing a power module substrate according to the present invention is for a power module in which a metal plate made of aluminum is laminated and bonded to the surface of a ceramic substrate. A method for manufacturing a substrate, wherein at least one of a bonding surface of the ceramic substrate and a bonding surface of the metal plate is selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li in addition to Si and Cu. And fixing the ceramic substrate and the metal plate via the fixing layer, fixing one or two or more additional elements, and forming a fixing layer containing Si, Cu and the additional element. A laminating step, and pressurizing and heating the laminated ceramic substrate and the metal plate in a laminating direction, and a molten metal region is formed at an interface between the ceramic substrate and the metal plate. And a solidifying step of joining the ceramic substrate and the metal plate by solidifying the molten metal region, and in the fixing step, the ceramic substrate and the metal plate Si, Cu, and the additive element are interposed in the interface within a range of 0.1 mg / cm ² or more and 10 mg / cm ² or less, and the element of the fixed layer is diffused to the metal plate side in the heating step. By forming the molten metal region at the interface between the ceramic substrate and the metal plate, and maintaining the temperature constant in the state where the molten metal region is formed in the solidification step, By further diffusing Si, Cu and the additive element to the metal plate side, solidification of the molten metal region is allowed to proceed while maintaining a constant temperature. It is a feature.

According to the method for manufacturing a power module substrate having this configuration, in addition to Si and Cu, Zn, Ge, Ag, Mg, Ca, at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate, The metal plate and the ceramic substrate are provided with a fixing step of fixing one or more additive elements selected from Ga and Li and forming a fixing layer containing Si, Cu and the additional element. In addition to Si and Cu, one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li are present at the bonding interface. Here, since elements such as Si and Cu, and Zn, Ge, Ag, Mg, Ca, Ga, and Li are elements that lower the melting point of aluminum, the metal plate and the ceramic substrate can be bonded at a relatively low temperature. A molten metal region can be formed at the interface. In addition, since Cu is an element highly reactive with Al, the presence of Cu in the vicinity of the bonding interface activates the surface of the metal plate made of aluminum.
Therefore, it is possible to firmly bond the ceramic substrate and the metal plate even if they are bonded under relatively low temperature and short time bonding conditions.

  Further, in the heating process, Si, Cu, and one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li are diffused to the metal plate side. By forming the molten metal region at the interface between the ceramic substrate and the metal plate, and solidifying the molten metal region, the metal plate and the ceramic substrate are joined. It is not necessary to use a Si-based brazing material foil or the like, and a power module substrate in which a metal plate and a ceramic substrate are reliably bonded can be manufactured at low cost.

  Thus, since the ceramic substrate and the metal plate can be joined without using a brazing material foil, it is not necessary to perform an alignment operation or the like of the brazing material foil. Even when the formed metal piece is bonded to the ceramic substrate, troubles due to misalignment can be prevented in advance.

Further, in the fixing step, the fixing amount of Si, Cu and the additive element interposed at the interface between the ceramic substrate and the metal plate is 0.1 mg / cm ² or more. A molten metal region can be reliably formed at the interface, and the ceramic substrate and the metal plate can be firmly bonded.
Furthermore, since the fixed amount of Si, Cu and the additive element interposed at the interface between the ceramic substrate and the metal plate is 10 mg / cm ² or less, it is possible to prevent the fixed layer from cracking. The molten metal region can be reliably formed at the interface between the ceramic substrate and the metal plate. Furthermore, it can be prevented that Si, Cu and the additive element are excessively diffused to the metal plate side and the strength of the metal plate near the interface is excessively increased. Therefore, when a cooling cycle is loaded on the power module substrate, the thermal stress can be absorbed by the metal plate, and cracking of the ceramic substrate can be prevented.

Further, in the fixing step, Si, Cu and the additive element are interposed in the range of 0.1 mg / cm ² or more and 10 mg / cm ² or less at the interface between the ceramic substrate and the metal plate. Producing a power module substrate in which the total concentration of Si, Cu and the additive element in the vicinity of the interface with the ceramic substrate in the metal plate is in the range of 0.05 mass% to 5 mass%. it can.

  Moreover, since the fixing layer is formed directly on the metal plate and the ceramic substrate, the oxide film is formed only on the surface of the metal plate, and the total thickness of the oxide film existing at the interface between the metal plate and the ceramic substrate. Therefore, the yield of initial bonding is improved.

  In addition, although it is set as the structure which adheres Si, Cu, and the said additional element directly to at least one among the joint surface of the said ceramic substrate and the said metal plate, from a viewpoint of productivity, Si, It is preferable to fix Cu and the additive element. When Si, Cu, and the additive element are fixed to the bonding surface of the ceramic substrate, Si, Cu, and the additive element must be fixed to each ceramic substrate. On the other hand, when Si, Cu and the additive element are fixed to the joint surface of the metal plate, Si is continuously applied from one end to the other end of the long metal strip wound in a roll shape. Cu and the additive element can be fixed, and the productivity is excellent.

  Alternatively, the Cu layer, the Si layer, and the additive element layer may be formed by fixing Si, Cu, and the additive element individually to at least one of the joint surface of the ceramic substrate and the joint surface of the metal plate. Good. Alternatively, Si, Cu, and the additional element may be simultaneously fixed to at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate to form a fixed layer of Si, Cu, and the additional element.

Here, in the fixing step, it is preferable that Al is fixed together with Si, Cu and the additive element.
In this case, since Al is fixed together with Si, Cu and the additive element, the fixed layer to be formed contains Al, and in the heating process, the fixed layer is preferentially melted and molten metal region. Can be reliably formed, and the ceramic substrate and the metal plate can be firmly bonded. Moreover, oxidation of oxidation active elements, such as Mg, Ca, Li, can be prevented. In order to fix Al together with Si, Cu and the additive element, Si, Cu and the additive element and Al may be vapor-deposited simultaneously, or an alloy of Si, Cu and the additive element and Al may be used as a target. Sputtering may be performed. Furthermore, Si, Cu, an additive element, and Al may be stacked.

Further, the fixing step may include at least one of a bonding surface of the ceramic substrate and a bonding surface of the metal plate by plating, vapor deposition, CVD, sputtering, cold spray, or application of paste and ink in which powder is dispersed. It is preferable to fix Si, Cu, and the additional element on one side.
In this case, Si, Cu, and the additive element are bonded to the bonding surface of the ceramic substrate and the metal plate by plating, vapor deposition, CVD, sputtering, cold spray, or application of paste and ink in which powder is dispersed. Since it is securely fixed to at least one of the surfaces, Si, Cu, and the additive element can be reliably interposed at the bonding interface between the ceramic substrate and the metal plate. In addition, it is possible to accurately adjust the amount of Si, Cu, and the additive element, and it is possible to securely form the molten metal region and firmly bond the ceramic substrate and the metal plate.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the board | substrate for power modules with which a metal plate and a ceramic substrate are reliably joined and heat cycle reliability is high.

It is a schematic explanatory drawing of the power module using the board | substrate for power modules which is the 1st Embodiment of this invention. It is explanatory drawing which shows Si density | concentration, Cu density | concentration, and additive element density | concentration of the circuit layer and metal layer of the board | substrate for power modules which are the 1st Embodiment of this invention. It is a schematic diagram of the joining interface of the circuit layer of the board | substrate for power modules which is the 1st Embodiment of this invention, a metal layer (metal plate), and a ceramic substrate. It is a flowchart which shows the manufacturing method of the board | substrate for power modules which is the 1st Embodiment of this invention. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules which is the 1st Embodiment of this invention. It is explanatory drawing which shows the joining interface vicinity of the metal plate and ceramic substrate in FIG. It is explanatory drawing which shows Si density | concentration, Cu density | concentration, and additive element density | concentration of the circuit layer and metal layer of the board | substrate for power modules which are the 2nd Embodiment of this invention. It is the schematic diagram of the joining interface of the circuit layer of the board | substrate for power modules which is the 2nd Embodiment of this invention, a metal layer (metal plate), and a ceramic substrate. It is a flowchart which shows the manufacturing method of the board | substrate for power modules which is the 2nd Embodiment of this invention. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules which is the 2nd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a power module substrate and a power module according to the first embodiment of the present invention.
The power module 1 includes a power module substrate 10 on which a circuit layer 12 is disposed, a semiconductor chip 3 bonded to the surface of the circuit layer 12 via a solder layer 2, and a heat sink 4. Here, the solder layer 2 is made of, for example, a Sn—Ag, Sn—In, or Sn—Ag—Cu solder material. In the present embodiment, a Ni plating layer (not shown) is provided between the circuit layer 12 and the solder layer 2.

The power module substrate 10 has a ceramic substrate 11, a circuit layer 12 disposed on one surface (the upper surface in FIG. 1) of the ceramic substrate 11, and the other surface (lower surface in FIG. 1) of the ceramic substrate 11. And a disposed metal layer 13.
The ceramic substrate 11 prevents electrical connection between the circuit layer 12 and the metal layer 13, and is made of highly insulating AlN (aluminum nitride). In addition, the thickness of the ceramic substrate 11 is set within a range of 0.2 to 1.5 mm, and in this embodiment is set to 0.635 mm. In the present embodiment, as shown in FIG. 1, the width of the ceramic substrate 11 (the length in the left-right direction in FIG. 1) is set wider than the width of the circuit layer 12 and the metal layer 13.

  As shown in FIG. 5, the circuit layer 12 is formed by bonding a conductive metal plate 22 to one surface of the ceramic substrate 11. In the present embodiment, the circuit layer 12 is formed by joining a metal plate 22 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more to the ceramic substrate 11.

  As shown in FIG. 5, the metal layer 13 is formed by bonding a metal plate 23 to the other surface of the ceramic substrate 11. In the present embodiment, the metal layer 13 is formed by joining a metal plate 23 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more, like the circuit layer 12, to the ceramic substrate 11. Is formed.

The heat sink 4 is for cooling the power module substrate 10 described above, and the top plate portion 5 joined to the power module substrate 10 and the flow path 6 for circulating a cooling medium (for example, cooling water). And. The heat sink 4 (top plate portion 5) is preferably made of a material having good thermal conductivity, and in this embodiment, is made of A6063 (aluminum alloy).
In the present embodiment, a buffer layer 15 made of aluminum, an aluminum alloy, or a composite material containing aluminum (for example, AlSiC) is provided between the top plate portion 5 of the heat sink 4 and the metal layer 13. .

As shown in FIG. 2, the circuit layer 12 (metal plate 22) is formed at the center in the width direction of the bonding interface 30 between the ceramic substrate 11, the circuit layer 12 (metal plate 22), and the metal layer 13 (metal plate 23). ) And the metal layer 13 (metal plate 23), in addition to Si and Cu, one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga and Li are in solid solution. . In the vicinity of the bonding interface 30 between the circuit layer 12 and the metal layer 13, a concentration gradient layer 33 is formed in which the Si concentration, the Cu concentration, and the concentration of the additive element gradually decrease as they are separated from the bonding interface 30 in the stacking direction. . Here, the total concentration of Si, Cu and the additive element on the bonding interface 30 side of the concentration gradient layer 33 (near the bonding interface 30 of the circuit layer 12 and the metal layer 13) is 0.05 mass% or more and 5 mass%. It is set within the following range.
The concentrations of Si, Cu, and the additive element in the vicinity of the bonding interface 30 between the circuit layer 12 and the metal layer 13 are average values measured at five points at a position 50 μm from the bonding interface 30 by EPMA analysis (spot diameter 30 μm). is there. The graph of FIG. 2 is obtained by performing line analysis in the stacking direction in the central portion of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23), and obtaining the above-mentioned concentration at the 50 μm position as a reference. It is.

  Here, in this embodiment, Ge is used as an additive element, the Ge concentration in the vicinity of the junction interface 30 between the circuit layer 12 and the metal layer 13 is 0.05 mass% or more and 1 mass% or less, and the Si concentration is 0.05. The Cu concentration is set within the range of 0.05% by mass or more and 1% by mass or less.

Further, at the end portion in the width direction of the bonding interface 30 between the ceramic substrate 11 and the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23), a Cu-containing compound is precipitated in the aluminum matrix. A precipitation portion 35 is formed. Here, Cu concentration in this Cu precipitation part 35 is set in the range of 0.5 mass% or more and 5.0 mass% or less, and Cu exceeding the amount of solid solution in aluminum is contained. .
Note that the Cu concentration of the Cu precipitation portion 35 is an average value measured at five points by EPMA analysis (spot diameter of 30 μm).

Further, when the bonding interface 30 between the ceramic substrate 11 and the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) is observed with a transmission electron microscope, as shown in FIG. A Si high concentration portion 32 enriched with Si is formed. In the high Si concentration portion 32, the Si concentration is 5 times or more higher than the Si concentration in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23). The thickness H of the high Si concentration portion 32 is 4 nm or less.
Here, as shown in FIG. 3, the bonding interface 30 to be observed is an interface side end of the lattice image of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) and the lattice image of the ceramic substrate 11. A center between the interface side end portion is defined as a reference plane S.

  Below, the manufacturing method of the board | substrate 10 for power modules of the above-mentioned structure is demonstrated with reference to FIGS.

(Fixing step S1)
First, as shown in FIGS. 5 and 6, 1 is selected from Si and Cu, and Zn, Ge, Ag, Mg, Ca, Ga, and Li by sputtering on the respective joint surfaces of the metal plates 22 and 23. The seeds or two or more additional elements are fixed to form the fixed layers 24 and 25.
Here, in the present embodiment, using the Ge as an additional element, Si amount in the pinned layer 24 and 25 are 0.002 mg / cm ² or more 1.2 mg / cm ² or less, Cu amount is 0.08 mg / cm ² The above is set to 2.7 mg / cm ² or less and the Ge amount is set to 0.002 mg / cm ² or more and 2.5 mg / cm ² or less.

(Lamination process S2)
Next, as shown in FIG. 5, the metal plate 22 is laminated on one surface side of the ceramic substrate 11, and the metal plate 23 is laminated on the other surface side of the ceramic substrate 11. At this time, as shown in FIGS. 5 and 6, the metal plates 22 and 23 are laminated so that the surfaces on which the fixing layers 24 and 25 are formed face the ceramic substrate 11. That is, the fixing layers 24 and 25 (Si, Cu and the additive elements) are interposed between the metal plates 22 and 23 and the ceramic substrate 11, respectively. In this way, the laminate 20 is formed.

(Heating step S3)
Next, the stacked body 20 formed in the stacking step S2 is charged in the stacking direction (pressure 1 to 35 kgf / cm ² ) in a heating furnace and heated, as shown in FIG. The molten metal regions 26 and 27 are formed at the interfaces between the metal plates 22 and 23 and the ceramic substrate 11, respectively. As shown in FIG. 6, the molten metal regions 26 and 27 are formed by fixing the Si and Cu in the fixing layers 24 and 25 and the additive element to the metal plates 22 and 23, thereby causing the fixing layers of the metal plates 22 and 23. It is formed by increasing the Si concentration in the vicinity of 24 and 25, the Cu concentration, and the concentration of the additive element (in this embodiment, the Ge concentration) to lower the melting point. When the pressure is less than 1 kgf / cm ² , there is a possibility that the ceramic substrate 11 and the metal plates 22 and 23 cannot be bonded well. Moreover, when the above-mentioned pressure exceeds 35 kgf / cm < ² >, there exists a possibility that the metal plates 22 and 23 may deform | transform. Therefore, the above-mentioned pressurizing pressure is preferably in the range of 1 to 35 kgf / cm ² .
Here, in this embodiment, the atmosphere in the heating furnace is an N ₂ gas atmosphere, and the heating temperature is set in a range of 550 ° C. or more and 650 ° C. or less.

(Coagulation step S4)
Next, the temperature is kept constant with the molten metal regions 26 and 27 formed. Then, Si, Cu and additive elements (Ge in this embodiment) in the molten metal regions 26 and 27 are further diffused toward the metal plates 22 and 23. As a result, the Si concentration, the Cu concentration, and the concentration of the additive element (Ge concentration in the present embodiment) in the portions that were the molten metal regions 26 and 27 gradually decrease, and the melting point increases. Coagulation proceeds in a state where is kept constant. That is, the ceramic substrate 11 and the metal plates 22 and 23 are bonded by so-called isothermal diffusion bonding (Transient Liquid Phase Diffusion Bonding). After solidification progresses in this way, cooling is performed to room temperature.

  In this way, the metal plates 22 and 23 to be the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 are joined, and the power module substrate 10 according to the present embodiment is manufactured.

  In the power module substrate 10 and the power module 1 according to the present embodiment configured as described above, Si, Cu, and the additive element (Ge in the present embodiment) are added to the joint surfaces of the metal plates 22 and 23. Since the fixing step S <b> 1 for fixing is provided, Si, Cu, and the additive element are present in the bonding interface 30 between the metal plates 22 and 23 and the ceramic substrate 11. Here, since Cu is an element highly reactive with Al, the presence of Cu at the bonding interface 30 activates the surfaces of the metal plates 22 and 23 made of aluminum. Therefore, the ceramic substrate 11 and the metal plates 22 and 23 can be firmly bonded.

  Further, the ceramic substrate 11, the circuit layer 12 (metal plate 22), and the metal layer 13 (metal plate 23) are formed on the bonding surfaces of the metal plates 22 and 23, and a fixing layer containing Si, Cu, and the additive element. The molten metal regions 26 and 27 are formed by diffusing 24, 25 Si, Cu and the additive element toward the metal plates 22 and 23, and Si, Cu and the additive element in the molten metal regions 26 and 27 are formed. Since the metal plates 22 and 23 are solidified by being diffused and bonded, the ceramic substrate 11 and the metal plates 22 and 23 can be firmly bonded even if bonded under relatively low temperature and short time bonding conditions. Is possible. In particular, since elements such as Si, Cu, Zn, Ge, Ag, Mg, Ca, Ga, and Li lower the melting point of aluminum, bonding under low temperature conditions is possible.

Further, at the center portion in the width direction of the bonding interface 30 between the ceramic substrate 11 and the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23), the circuit layer 12 (metal plate 22) and the metal layer 13 (metal) In the plate 23), Si, Cu and the additive element are dissolved, and the total concentration of Si, Cu and the additive element on the bonding interface 30 side of the circuit layer 12 and the metal layer 13 is 0.05 mass. In the present embodiment, Ge is used as an additive element, and the Ge concentration in the vicinity of the junction interface 30 between the circuit layer 12 and the metal layer 13 is 0.05% by mass. 1% by mass or less, Si concentration of 0.05% by mass or more and 0.5% by mass or less, and Cu concentration of 0.05% by mass or more and 1% by mass or less. Plate 22) and metal layer 13 (metal plate 2) Joint interface 30 side portions solid solution strengthening of), it is possible to prevent the occurrence of cracks in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23).
Further, in the heating step S3, Si, Cu and the additive element are sufficiently diffused to the metal plates 22 and 23 side, and the metal plates 22 and 23 and the ceramic plate 11 are firmly bonded.

  Furthermore, in the present embodiment, the ceramic substrate 11 is made of AlN, and the Si concentration at the bonding interface 30 between the metal plates 22 and 23 and the ceramic substrate 11 is the circuit layer 12 (metal plate 22) and the metal layer 13. Since the Si high concentration portion 32 having a Si concentration of 5 times or more of the (metal plate 23) is formed, the bonding strength between the ceramic substrate 11 and the metal plates 22 and 23 is increased by Si present at the bonding interface 30. Improvements can be made.

  In addition, a fixing step S1 is provided in which Si, Cu and the additive element are fixed to the bonding surface of the metal plate to form the fixing layers 24, 25. In the heating step S3, the Si, Cu and the fixing layers 24, 25 Since the molten metal regions 26 and 27 are formed at the interface between the ceramic substrate 11 and the metal plates 22 and 23 by diffusing the additive element toward the metal plates 22 and 23, Al-Si which is difficult to manufacture is formed. It is not necessary to use a brazing material foil, and the power module substrate 10 in which the metal plates 22 and 23 and the ceramic substrate 11 are reliably bonded can be manufactured at low cost.

In the present embodiment, in the fixing step S1, the Si amount, the Cu amount, and the Ge amount interposed at the interface between the ceramic substrate 11 and the metal plates 22, 23 are set to Si: 0.002 mg / cm ² or more, Cu; Since 0.08 mg / cm ² or more and Ge; 0.002 mg / cm ² or more, the molten metal regions 26 and 27 can be reliably formed at the interface between the ceramic substrate 11 and the metal plates 22 and 23, It becomes possible to firmly bond the ceramic substrate 11 and the metal plates 22 and 23.

Furthermore, Si amount is interposed in the interface between the ceramic substrate 11 and the metal plates 22 and 23, the Cu amount and amount of Ge, Si; 1.2mg / cm ² or less, Cu; 2.7 mg / cm ² or less, Ge; Since it is 2.5 mg / cm ² or less, the occurrence of cracks in the fixing layers 24 and 25 can be prevented, and the molten metal regions 26 and 27 are surely provided at the interface between the ceramic substrate 11 and the metal plates 22 and 23. Can be formed. Furthermore, it is possible to prevent the Si and Cu and the additive element from excessively diffusing to the metal plates 22 and 23 side and excessively increasing the strength of the metal plates 22 and 23 in the vicinity of the interface. Therefore, when the cooling cycle is applied to the power module substrate 10, the thermal stress can be absorbed by the circuit layer 12 and the metal layer 13 (metal plates 22 and 23), and cracking of the ceramic substrate 11 can be prevented. .

Further, since the fixing layers 24 and 25 are formed directly on the joint surfaces of the metal plates 22 and 23 without using the brazing material foil, it is not necessary to perform the alignment work of the brazing material foil, and the ceramics can be surely used. The board | substrate 11 and the metal plates 22 and 23 can be joined.
In addition, since the fixing layers 24 and 25 are formed on the joining surfaces of the metal plates 22 and 23, the oxide film interposed at the interface between the metal plates 22 and 23 and the ceramic substrate 11 is formed on the surfaces of the metal plates 22 and 23. Therefore, bonding can be performed in an N ₂ atmosphere. Therefore, this power module substrate 10 can be produced efficiently, and the manufacturing cost can be greatly reduced.

Next, a second embodiment of the present invention will be described with reference to FIGS.
In the power module substrate according to the second embodiment, the ceramic substrate 111 is made of Si ₃ N ₄ .

As shown in FIG. 7, the circuit layer 112 (metal plate 122) and the ceramic substrate 111, the circuit layer 112 (metal plate 122), and the metal layer 113 (metal plate 123) In addition to Si and Cu, one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li are dissolved in the metal layer 113 (metal plate 123). Here, the total concentration of Si, Cu and the additive element in the vicinity of the bonding interface 130 between the circuit layer 112 and the metal layer 113 is set within a range of 0.05 mass% or more and 5 mass% or less.
The concentrations of Si, Cu, and the additive element in the vicinity of the bonding interface 130 between the circuit layer 112 and the metal layer 113 are average values measured at five points from the bonding interface 130 by the EPMA analysis (spot diameter 30 μm). is there. In addition, the graph of FIG. 7 is obtained by performing line analysis in the stacking direction in the central portion of the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123), and obtaining the concentration at the above-mentioned 50 μm position as a reference. It is.

  Here, in this embodiment, Ag is used as an additive element, the Ag concentration in the vicinity of the bonding interface 130 between the circuit layer 112 and the metal layer 113 is 0.05 mass% or more and 1.5 mass% or less, and the Si concentration is 0. 0.05 mass% or more and 0.5 mass% or less, and Cu concentration is set within the range of 0.05 mass% or more and 1 mass% or less.

When the bonding interface 130 between the ceramic substrate 111 and the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123) is observed with a transmission electron microscope, as shown in FIG. An oxygen high concentration portion 132 in which oxygen is concentrated is formed. In the oxygen high concentration portion 132, the oxygen concentration is higher than the oxygen concentration in the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123). Note that the thickness H of the high oxygen concentration portion 132 is 4 nm or less.
As shown in FIG. 8, the bonding interface 130 observed here is a lattice image of the ceramic substrate 111 and the interface side end of the lattice image of the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123). The reference plane S is the center between the end of the bonding interface side.

  Below, the manufacturing method of the board | substrate for power modules of the above-mentioned structure is demonstrated with reference to FIG.9 and FIG.10. In the present embodiment, the fixing step is separated into a Cu fixing step S10, a Si fixing step S11, and an additive element fixing step S12.

(Cu fixing step S10)
First, as shown in FIG. 10, Cu is fixed to the respective joint surfaces of the metal plates 122 and 123 by sputtering to form Cu layers 124A and 125A. Here, the amount of Cu in the Cu layers 124A and 125A is set to 0.08 mg / cm ² or more and 2.7 mg / cm ² or less. Moreover, it is preferable to set the thickness of the Cu layers 124A and 125A within the range of 0.1 μm or more and 3 μm or less.

(Si fixing step S11)
Next, Si is fixed on the Cu layers 124A and 125A formed on the joint surfaces of the metal plates 122 and 123 by sputtering to form Si layers 124B and 125B. Here, Si layer 124B, Si amount in the 125B is set to 0.002 mg / cm ² or more 1.2 mg / cm ² or less. The thickness of the Si layers 124B and 125B is preferably set within a range of 0.01 μm to 5 μm.

(Additive element fixing step S12)
Next, one or more additional elements selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li are fixed on the Si layers 124B and 125B by sputtering, and the additional element layer 124C is obtained. , 125C. Here, in the present embodiment uses the Ag as an additional element, the additional element layer 124C, Ag amount in the 125C is set to 0.08 mg / cm ² or more 5.4 mg / cm ² or less. The thickness of the additive element layers 124C and 125C is preferably set within a range of 0.01 μm to 5 μm.

(Lamination process S13)
Next, the metal plate 122 is laminated on one surface side of the ceramic substrate 111, and the metal plate 123 is laminated on the other surface side of the ceramic substrate 111. At this time, as shown in FIG. 10, the metal plates 122 and 123 are stacked so that the surfaces on which the Cu layers 124A and 125A, the Si layers 124B and 125B, and the additive element layers 124C and 125C are formed face the ceramic substrate 111. . That is, Cu layers 124A and 125A, Si layers 124B and 125B, and additive element layers 124C and 125C are interposed between the metal plates 122 and 123 and the ceramic substrate 111, respectively. In this way, a laminate is formed.

(Heating step S14)
Next, the stack formed in the stacking step S13 is charged in the stacking direction (pressure 1 to 35 kgf / cm ² ) in a heating furnace and heated, as shown in FIG. Molten metal regions 126 and 127 are formed at the interfaces between the metal plates 122 and 123 and the ceramic substrate 111, respectively. As shown in FIG. 10, in the molten metal regions 126 and 127, the Cu layers 124A and 125A, the Si layers 124B and 125B, and the additive element layers 124C and 125C have Si, Cu, and the additive element (Ag in this embodiment) made of metal. By diffusing toward the plates 122 and 123, the Si concentration, the Cu concentration and the concentration of the additive element in the vicinity of the Cu layers 124A and 125A, the Si layers 124B and 125B and the additive element layers 124C and 125C of the metal plates 122 and 123 are increased. Thus, the melting point is lowered.
Here, in this embodiment, the atmosphere in the heating furnace is an N ₂ gas atmosphere, and the heating temperature is set in a range of 550 ° C. or more and 650 ° C. or less.

(Coagulation step S15)
Next, the temperature is kept constant with the molten metal regions 126 and 127 formed. Then, Si, Cu and additive elements in the molten metal regions 126 and 127 are further diffused to the metal plates 122 and 123 side. As a result, the Si concentration, the Cu concentration, and the concentration of the additive element in the portions that were the molten metal regions 126 and 127 are gradually decreased and the melting point is increased, and solidification proceeds while the temperature is kept constant. Will do. That is, the ceramic substrate 111 and the metal plates 122 and 123 are bonded by so-called isothermal diffusion bonding (Transient Liquid Phase Diffusion Bonding). After solidification progresses in this way, cooling is performed to room temperature.

  In this way, the metal plates 122 and 123 to be the circuit layer 112 and the metal layer 113 are bonded to the ceramic substrate 111, and the power module substrate according to this embodiment is manufactured.

  In the power module substrate according to the present embodiment configured as described above, the Cu fixing step S10 for fixing Cu to the joint surfaces of the metal plates 122 and 123, the Si fixing step S11 for fixing Si, Since the additive element fixing step S12 for fixing the additive element (Ag in the present embodiment) is provided, Si, Cu, and the additive element are interposed in the bonding interface 130 between the metal plates 122 and 123 and the ceramic substrate 111. Will do. Here, since Cu is a highly reactive element with respect to Al, the presence of Cu at the bonding interface 130 activates the surfaces of the metal plates 122 and 123 made of aluminum, and the ceramic substrate 111. And the metal plates 122 and 123 can be firmly bonded.

  Further, the ceramic substrate 111, the circuit layer 112 (metal plate 122), and the metal layer 113 (metal plate 123) are formed by Cu layers 124A and 125A and Si layers 124B and 125B formed on the joining surfaces of the metal plates 122 and 123, respectively. Molten metal regions 126 and 127 are formed by diffusing Cu, Si and additive elements of the additive element layers 124C and 125C toward the metal plates 122 and 123, and Si, Cu and additive elements in the molten metal regions 126 and 127 are formed. Is bonded to the metal plates 122 and 123 by solidification, so that the ceramic substrate 111 and the metal plates 122 and 123 are firmly bonded even when bonded under relatively low temperature and short time bonding conditions. It becomes possible. In particular, since elements such as Si, Cu, Zn, Ge, Ag, Mg, Ca, Ga, and Li lower the melting point of aluminum, bonding under low temperature conditions is possible.

In the present embodiment, the ceramic substrate 111 is made of Si ₃ N ₄ , and the oxygen concentration is present at the bonding interface 130 between the metal plates 122 and 123 to be the circuit layer 112 and the metal layer 113 and the ceramic substrate 111. Since the oxygen high concentration part 132 made higher than the oxygen concentration in the metal plates 122 and 123 constituting the layer 112 and the metal layer 113 is generated, the oxygen bonds between the ceramic substrate 111 and the metal plates 122 and 123. The strength can be improved. Further, since the thickness of the high oxygen concentration portion 132 is set to 4 nm or less, the occurrence of cracks in the high oxygen concentration portion 132 due to stress when a thermal cycle is loaded is suppressed.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
For example, the metal plate constituting the circuit layer and the metal layer has been described as a rolled plate of pure aluminum having a purity of 99.99%, but is not limited to this, and aluminum having a purity of 99% (2N aluminum) It may be.

Further, in the fixing process, it has been described that Si, Cu and the additive element are fixed to the bonding surface of the metal plate, but the present invention is not limited thereto, and Si, Cu and the bonding surface of the ceramic substrate are not limited thereto. The additive element may be fixed, or Si, Cu, and the additive element may be fixed to the bonding surface of the ceramic substrate and the bonding surface of the metal plate, respectively.
Further, in the fixing step, Al may be fixed together with Si, Cu and the additive element.
Further, although it has been described that Si, Cu and the additive element are fixed by sputtering in the fixing step, the present invention is not limited to this, and plating, vapor deposition, CVD, cold spray, or powder is dispersed. Si, Cu, and the additive element may be fixed by applying paste, ink, or the like.

Further, in the second embodiment, the fixing process is described as performing the Si fixing process S11 after the Cu fixing process S10, and further performing the additive element fixing process S12, but is not limited thereto. There is no restriction on the order of the Si fixing step, the Cu fixing step, and the additive element fixing step.
Further, an alloy layer of Cu and an additive element or Si and an additive element may be formed using an alloy such as an additive element and Cu or an additive element and Si.
Further, the bonding between the ceramic substrate and the metal plate has been described as being performed using a heating furnace of an N ₂ atmosphere, it is not limited thereto, bonding between the ceramic substrate and the metal plate using a vacuum furnace May be performed. In this case, the degree of vacuum is preferably in the range of 10 ⁻⁶ to 10 ⁻³ Pa.

Moreover, although demonstrated as what provided the buffer layer which consists of aluminum, the aluminum alloy, or the composite material containing aluminum (for example, AlSiC etc.) between the top-plate part of a heat sink and a metal layer, even if this buffer layer is not provided Good.
Furthermore, although the heat sink has been described as being made of aluminum, it may be made of an aluminum alloy or a composite material containing aluminum. Furthermore, although the description has been made with the heat sink having the flow path of the cooling medium, the structure of the heat sink is not particularly limited, and heat sinks having various configurations can be used.

Further, the ceramic substrate AlN, has been described as being composed of Si ₃ N _4, it is not limited thereto, but may be composed of other ceramic such as Al ₂ O _3.

A comparative experiment conducted to confirm the effectiveness of the present invention will be described.
A power module substrate is fabricated by bonding a circuit layer made of 4N aluminum having a thickness of 0.6 mm and a metal layer made of 4N aluminum having a thickness of 0.6 mm to a ceramic substrate made of AlN having a thickness of 0.635 mm. did.
Here, a bonding layer is formed by bonding Si, Cu and additive elements to the bonding surface of an aluminum plate (4N aluminum) to be a circuit layer and a metal layer, and the metal plate and the ceramic substrate are stacked and pressurized and heated. Then, the metal plate and the ceramic substrate were joined.

And various test pieces which changed the adhering additive element were produced, and joining reliability was evaluated using these test pieces. As an evaluation of the bonding reliability, the bonding rates after 2000 times of the thermal cycle (−45 ° C.-125 ° C.) were compared. The results are shown in Tables 1 to 3.
In addition, the joining rate was computed with the following formula | equation. Here, the initial bonding area is an area to be bonded before bonding.
Bonding rate = (initial bonding area-peeling area) / initial bonding area

  Moreover, about these test pieces, the density | concentration of Si, Cu, and an additional element of the metal board vicinity of the joining interface (50 micrometers from a joining interface) of a ceramic substrate was measured by EPMA analysis (spot diameter of 30 micrometers). The total concentration of Si, Cu and additive elements is shown in Table 1-3.

The amount of Si in the fixing layer is 0.001 mg / cm ² (0.0043 μm in terms of thickness), the amount of Cu is 0.005 mg / cm ² (0.0056 μm in terms of thickness), and the amount of fixing of the additive element (Li) is 0 It is the .05mg / cm ² (thickness in terms of 0.935μm), the total fixed amount in Comparative example 1 was set to 0.056 mg / cm ^2, was repeated 2000 times a thermal cycle (-45 ° C. -125 ° C.) The subsequent bonding rate was a very low value of 52.1%. This is presumably because the amount of Si, Cu, and additive element (Li) present at the interface was small, and the molten metal region could not be sufficiently formed at the interface between the metal plate and the ceramic substrate.

The fixed layer has an Si amount of 0.9 mg / cm ² (thickness conversion: 3.86 μm), a Cu amount of 2.2 mg / cm ² (thickness conversion: 2.47 μm), and an additional element (Ag) fixing amount of 5 .2mg / cm ² (thickness in terms of 4.96μm), the amount fixation of the additive element (Ge) is a 2.2 mg / cm ² (thickness in terms of 4.13μm), a total of fixed amount 10.5 mg / cm ^In Comparative Example 2, which was set to 2, the joining rate after 2000 times of the cooling / heating cycle (−45 ° C. to 125 ° C.) was 65.3%. This is presumably because the amount of Si, Cu, and additive elements (Ag, Ge) is so large that the metal plate becomes too hard and thermal stress due to the thermal cycle is applied to the bonding interface.

On the other hand, in Inventive Example 1-60, the joining rate after repeating the cooling / heating cycle (-45 ° C.-125 ° C.) 2000 times was 93% or more.
Further, Si amount is 0.002 mg / cm ² (thickness conversion 0.0086Myuemu) of the pinned layer, Cu amount is 0.008 mg / cm ² (thickness in terms of 0.009), and added sticking amount of the element (Li) Is 0.09 mg / cm ² (thickness conversion 1.68 μm), and the total amount of fixing is 0.1 mg / cm ² of the present invention example 61 and the fixing layer Si amount is 0.9 mg / cm ² ( (Thickness conversion: 3.86 μm), Cu amount: 2.2 mg / cm ² (thickness conversion: 2.47 μm), and additional element (Ag) sticking amount: 5.0 mg / cm ² (thickness conversion: 4.77 μm) In the present invention example 62 in which the fixed amount of the additive element (Ge) was 1.9 mg / cm ² (thickness conversion 3.57 μm) and the total fixed amount was 10 mg / cm ² , the cooling cycle (− 45 ° C.-125 ° C.) 0% was over.
From this result, according to the example of the present invention, it becomes possible to reliably form a molten metal region at the interface between the metal plate and the ceramic substrate by diffusion of Si, Cu and various additive elements. It is judged that the material was able to be firmly joined.

  In Invention Example 1-62, the total concentration of Si, Cu and various additive elements in the vicinity of the bonding interface of the ceramic substrate (50 μm from the bonding interface) of the metal plate is 0.05% by mass or more and 5% by mass or less. It was confirmed to be within the range.

1 Power module 3 Semiconductor chip (electronic component)
10 Power module substrate 11, 111 Ceramic substrate 12, 112 Circuit layer 13, 113 Metal layer 22, 23, 122, 123 Metal plate 24, 25 Adhering layer 26, 27, 126, 127 Molten metal region 30, 130 Bonding interface 124A 125A Cu layer 124B, 125B Si layer 124C, 125C additive element layer

Claims (3)

A method for manufacturing a power module substrate in which a metal plate made of aluminum is laminated and bonded to the surface of a ceramic substrate,
In addition to Si and Cu, at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate is one or more selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li. A fixing step of fixing the additive element and forming a fixing layer containing Si, Cu and the additive element;
A laminating step of laminating the ceramic substrate and the metal plate via the fixing layer;
Heating and pressurizing and heating the laminated ceramic substrate and the metal plate in a laminating direction to form a molten metal region at the interface between the ceramic substrate and the metal plate;
A solidification step of joining the ceramic substrate and the metal plate by solidifying the molten metal region;
In the fixing step, Si, Cu and the additive element are interposed in an interface between the ceramic substrate and the metal plate within a range of 0.1 mg / cm ² or more and 10 mg / cm ² or less,
In the heating step, the molten metal region is formed at the interface between the ceramic substrate and the metal plate by diffusing the elements of the fixed layer toward the metal plate.
In the solidification step, the temperature is kept constant with the molten metal region formed, and the temperature is kept constant by further diffusing Si, Cu and the additive element in the molten metal region to the metal plate side. A method for manufacturing a power module substrate, wherein solidification of the molten metal region is allowed to proceed in a state where the molten metal region is held. The method for manufacturing a power module substrate according to claim 1 , wherein in the fixing step, Al is fixed together with Si, Cu, and the additive element. The fixing step may be performed on at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate by plating, vapor deposition, CVD, sputtering, cold spray, or application of a paste and ink in which powder is dispersed. , Si and Cu, as well as, Zn, Ge, Ag, Mg , Ca, according to claim 1 or claim 2, characterized in that to fix the one or more additive elements selected from Ga and Li Of manufacturing a power module substrate.

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