Patent Description:
The present application claims priority on <CIT>, and <CIT>,.

A power module, an LED module, and a thermoelectric module have a structure in which a power semiconductor element, an LED element, and a thermoelectric element are bonded to an insulating circuit substrate, and in the insulating circuit substrate, a circuit layer made of a conductive material is formed on one surface of an insulating layer.

For example, a power semiconductor element for high-power control used for controlling a wind power generation, an electric vehicle, a hybrid vehicle, or the like has a large amount of heat generated during operation. Therefore, as a substrate on which the power semiconductor element is mounted, an insulating circuit substrate including a ceramic substrate and a circuit layer formed by bonding a metal plate having excellent conductivity to one surface of the ceramic substrate has been widely used in the related art. As the insulating circuit substrate, one having a metal layer formed by bonding a metal plate to the other surface of the ceramic substrate is also provided.

Patent Document <NUM> proposes a substrate for a power module in which a first metal plate and the second metal plate constituting a circuit layer and a metal layer are made of a copper sheet, and the copper sheet is directly bonded to a ceramic substrate by a DBC method. In this DBC method, the copper sheet and the ceramic substrate are bonded to each other by forming a liquid phase at an interface between the copper sheet and the ceramic substrate by using a eutectic reaction of copper with a copper oxide.

Patent Document <NUM> proposes an insulating circuit substrate in which a circuit layer and a metal layer are formed by bonding a copper sheet to each of one surface and the other surface of a ceramic substrate. In Patent Document <NUM>, the copper sheet is disposed on each of one surface and the other surface of the ceramic substrate with an Ag-Cu-Ti-based brazing material interposed therebetween, and the copper sheet is bonded thereto by performing a heating treatment (so-called active metal brazing method). In the active metal brazing method, since the brazing material containing Ti as an active metal is used, the wettability between the molten brazing material and the ceramic substrate is improved, and the ceramic substrate and the copper sheet are satisfactorily bonded to each other.

Patent Document <NUM> proposes a substrate for a power module in which a copper sheet made of copper or a copper alloy and a ceramic substrate made of AlN or Al<NUM>O<NUM> are bonded to each other by using a bonding material containing Ag and Ti, and in which Ag particles are dispersed in a Ti compound layer formed at a bonded interface between the copper sheet and the ceramic substrate. Patent Document <NUM> discloses a copper/ceramic bonded body with an active metal compound interface layer between a copper member and a ceramic member.

However, as disclosed in Patent Document <NUM>, when the ceramic substrate and the copper sheet are bonded to each other by the DBC method, a bonding temperature needs to be set to <NUM> or higher (equal to or higher than eutectic point temperature of copper and copper oxide), so that there is a concern that the ceramic substrate deteriorates during bonding.

As disclosed in Patent Document <NUM>, when the ceramic substrate and the copper sheet are bonded to each other by the active metal brazing method, a bonding temperature is set to a relatively high temperature of <NUM>, so that there is a problem that the ceramic substrate deteriorates.

In Patent Document <NUM>, since a copper member made of copper or a copper alloy and a ceramic member made of AlN or Al<NUM>O<NUM> are bonded to each other by using the bonding material containing Ag and Ti, the ceramic member and the copper member can be bonded to each other under a relatively low temperature condition, and deterioration of the ceramic member during bonding can be suppressed.

Recently, depending on the application of the insulating circuit substrate, a thermal cycle that is more severe than in the related art is loaded.

Therefore, there is a demand for an insulating circuit substrate that has a high bonding strength and does not cause cracks even during loading of a thermal cycle, even in an application where a thermal cycle that is more severe than in the related art is loaded.

The present invention has been made in view of the above-described circumstances, and an objective of the present invention is to provide a copper/ceramic bonded body and an insulating circuit substrate, which have a high bonding strength and particularly excellent reliability of a thermal cycle.

In order to solve the above-described problem, a copper/ceramic bonded body according to one aspect of the present invention (hereinafter, referred to as a "copper/ceramic bonded body according to the present invention") includes a copper member made of copper or a copper alloy, and a ceramic member made of aluminum-containing ceramics, the copper member and the ceramic member are bonded to each other, in which, at a bonded interface between the copper member and the ceramic member, an active metal compound layer containing a compound of one or more active metals selected from Ti, Zr, Nb, and Hf is formed on a ceramic member side, and in the active metal compound layer, Al and Cu are present at a grain boundary of the active metal compound.

According to the copper/ceramic bonded body according to the present invention, in the active metal compound layer formed at the bonded interface between the copper member and the ceramic member, Al and Cu are present at the grain boundary of the active metal compound, so that the active metal contained in a bonding material sufficiently reacts with the ceramic member, and the ceramic member and the copper member are firmly bonded to each other. Since the active metal is sufficiently diffused to the ceramic member side via a liquid phase (Al-Cu eutectic liquid phase) formed during the reaction, a sufficient interfacial reaction can be promoted, and the ceramic member and the copper member can be firmly bonded to each other. Accordingly, reliability of a thermal cycle can be improved.

From the above, according to the copper/ceramic bonded body according to the present invention, it is possible to obtain a copper/ceramic bonded body having a high bonding strength and particularly excellent reliability of a thermal cycle.

In the copper/ceramic bonded body according to the present invention, it is preferable that in the active metal compound layer, Ag is present at the grain boundary of the active metal compound.

In this case, an Al-Ag-Cu eutectic liquid phase is present during the reaction. The Al-Ag-Cu eutectic has a lower eutectic temperature than Al-Cu eutectic, the Al-Ag-Cu eutectic lowers the energy of the system and thus further promotes the reaction.

In the copper/ceramic bonded body according to the present invention, a maximum indentation hardness in a region from <NUM> to <NUM> from the bonded interface between the copper member and the ceramic member to a copper member side is in a range of <NUM> mgf/µm<NUM> or more and <NUM> mgf/µm<NUM> or less.

In this case, since the maximum indentation hardness in the region from <NUM> to <NUM> from the bonded interface between the copper member and the ceramic member to the copper member side is set to <NUM> mgf/µm<NUM> or more, the copper at or in the vicinity of the bonded interface is sufficiently melted during bonding, to form a liquid phase, and the ceramic member and the copper member are firmly bonded to each other. On the other hand, since the maximum indentation hardness in the above-described region is suppressed to <NUM> mgf/µm<NUM> or less, the vicinity of the bonded interface is not harder than necessary, and the generation of cracks during loading of the thermal cycle can be suppressed.

In the copper/ceramic bonded body according to the present invention, it is preferable that the active metal is Ti.

In this case, a titanium nitride layer or a titanium oxide layer is formed as the active metal compound layer at the bonded interface between the ceramic member and the copper member, and the ceramic member and the copper member can be firmly bonded to each other.

In the copper/ceramic bonded body according to the present invention, it is preferable that a maximum particle size of particles of the active metal compound in the active metal compound layer is <NUM> or less.

In this case, a proportion of a grain boundary region (metal phase) having a relatively low hardness in the active metal compound layer increases, and impact resistance of the active metal compound layer is improved. As a result, it is possible to suppress the generation of cracks in the active metal compound layer, and to suppress peeling of the copper member and the ceramic member and the generation of cracks in the ceramic member.

An insulating circuit substrate according to another aspect of the present invention (hereinafter, referred to as an "insulating circuit substrate according to the present invention") includes a copper sheet made of copper or a copper alloy, and a ceramic substrate made of aluminum-containing ceramics, the copper sheet is bonded to a surface of the ceramic substrate, in which, at a bonded interface between the copper sheet and the ceramic substrate, an active metal compound layer containing a compound of one or more active metals selected from Ti, Zr, Nb, and Hf is formed on a ceramic substrate side, and in the active metal compound layer, Al and Cu are present at a grain boundary of the active metal compound.

According to the insulating circuit substrate according to the present invention, in the active metal compound layer formed at the bonded interface between the copper sheet and the ceramic substrate, Al and Cu are present at the grain boundary of the active metal compound, so that the active metal contained in a bonding material sufficiently reacts with the ceramic substrate, and the ceramic substrate and the copper sheet are firmly bonded to each other. Since the active metal is sufficiently diffused to the ceramic substrate side via a liquid phase (Al-Cu eutectic liquid phase) formed during the reaction, a sufficient interfacial reaction can be promoted, and the ceramic substrate and the copper sheet can be firmly bonded to each other. Accordingly, reliability of a thermal cycle can be improved.

From the above, according to the insulating circuit substrate according to the present invention, it is possible to obtain an insulating circuit substrate having a high bonding strength and particularly excellent reliability of a thermal cycle.

In the insulating circuit substrate according to the present invention, it is preferable that in the active metal compound layer, Ag is present at the grain boundary of the active metal compound.

In the insulating circuit substrate according to the present invention, it is preferable that a maximum indentation hardness in a region from <NUM> to <NUM> from the bonded interface between the copper sheet and the ceramic substrate to a copper sheet side is in a range of <NUM> mgf/µm<NUM> or more and <NUM> mgf/µm<NUM> or less.

In this case, since the maximum indentation hardness in the region from <NUM> to <NUM> from the bonded interface between the copper sheet and the ceramic substrate to the copper sheet side is set to <NUM> mgf/µm<NUM> or more, the copper at or in the vicinity of the bonded interface is sufficiently melted during bonding, to form a liquid phase, and the ceramic substrate and the copper sheet are firmly bonded to each other. On the other hand, since the maximum indentation hardness in the above-described region is suppressed to <NUM> mgf/µm<NUM> or less, the vicinity of the bonded interface is not harder than necessary, and the generation of cracks during loading of the thermal cycle can be suppressed.

In the insulating circuit substrate according to the present invention, it is preferable that the active metal is Ti.

In this case, a titanium nitride layer or a titanium oxide layer is formed as the active metal compound layer at the bonded interface between the ceramic substrate and the copper sheet, and the ceramic substrate and the copper sheet can be firmly bonded to each other.

In the insulating circuit substrate according to the present invention, it is preferable that a maximum particle size of particles of the active metal compound in the active metal compound layer is <NUM> or less.

In this case, a proportion of a grain boundary region (metal phase) having a relatively low hardness in the active metal compound layer increases, and impact resistance of the active metal compound layer is improved. As a result, it is possible to suppress the generation of cracks in the active metal compound layer, and to suppress peeling of the copper sheet and the ceramic substrate and the generation of cracks in the ceramic substrate.

According to the present invention, it is possible to provide a copper/ceramic bonded body and an insulating circuit substrate, which have a high bonding strength and particularly excellent reliability of a thermal cycle.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

A copper/ceramic bonded body according to the present embodiment is an insulating circuit substrate <NUM> formed by bonding a ceramic substrate <NUM> as a ceramic member made of ceramics to a copper sheet <NUM> (circuit layer <NUM>) and a copper sheet <NUM> (metal layer <NUM>) as a copper member made of copper or a copper alloy. <FIG> shows a power module <NUM> including the insulating circuit substrate <NUM> according to the present embodiment.

The power module <NUM> includes the insulating circuit substrate <NUM> on which the circuit layer <NUM> and the metal layer <NUM> are disposed, a semiconductor element <NUM> bonded to one surface (upper surface in <FIG>) of the circuit layer <NUM> with a bonding layer <NUM> interposed therebetween, and a heat sink <NUM> disposed on the other side (lower side in <FIG>) of the metal layer <NUM>.

The semiconductor element <NUM> is made of a semiconductor material such as Si. The semiconductor element <NUM> and the circuit layer <NUM> are bonded to each other with the bonding layer <NUM> interposed therebetween.

The bonding layer <NUM> is made of, for example, a Sn-Ag-based, Sn-ln-based, or Sn-Ag-Cu-based solder material.

The heat sink <NUM> dissipates heat from the above-mentioned insulating circuit substrate <NUM>. The heat sink <NUM> is made of copper or a copper alloy, and in the present embodiment, the heat sink <NUM> is made of phosphorus-deoxidized copper. The heat sink <NUM> is provided with a passage <NUM> through which a cooling fluid flows.

In the present embodiment, the heat sink <NUM> and the metal layer <NUM> are bonded to each other by a solder layer <NUM> made of a solder material. The solder layer <NUM> is made of, for example, a Sn-Ag-based, Sn-In-based, or Sn-Ag-Cu-based solder material.

As shown in <FIG>, the insulating circuit substrate <NUM> according to the present embodiment includes the ceramic substrate <NUM>, the circuit layer <NUM> disposed on one surface (upper surface in <FIG>) of the ceramic substrate <NUM>, and the metal layer <NUM> disposed on the other surface (lower surface in <FIG>) of the ceramic substrate <NUM>.

The ceramic substrate <NUM> is made of aluminum-containing ceramics having excellent insulating properties and heat radiation, and in the present embodiment, the ceramic substrate <NUM> is made of aluminum nitride (AlN). The thickness of the ceramic substrate <NUM> is set to be in a range of, for example, <NUM> or more and <NUM> or less, and in the present embodiment, the thickness is set to <NUM>.

As shown in <FIG>, the circuit layer <NUM> is formed by bonding the copper sheet <NUM> made of copper or a copper alloy to one surface (upper surface in <FIG>) of the ceramic substrate <NUM>.

In the present embodiment, the circuit layer <NUM> is formed by bonding the copper sheet <NUM> made of a rolled plate of oxygen-free copper to the ceramic substrate <NUM>.

The thickness of the copper sheet <NUM> serving as the circuit layer <NUM> is set to be in a range of <NUM> or more and <NUM> or less, and in the present embodiment, the thickness is set to <NUM>.

As shown in <FIG>, the metal layer <NUM> is formed by bonding the copper sheet <NUM> made of copper or a copper alloy to the other surface (lower surface in <FIG>) of the ceramic substrate <NUM>.

In the present embodiment, the metal layer <NUM> is formed by bonding the copper sheet <NUM> made of a rolled plate of oxygen-free copper to the ceramic substrate <NUM>.

The thickness of the copper sheet <NUM> serving as the metal layer <NUM> is set to be in a range of <NUM> or more and <NUM> or less, and in the present embodiment, the thickness is set to <NUM>.

At the bonded interface between the ceramic substrate <NUM> and the circuit layer <NUM> (metal layer <NUM>), as shown in <FIG>, an active metal compound layer <NUM> containing an active metal compound that is a compound of one or more active metals selected from Ti, Zr, Nb, and Hf is formed.

The active metal compound layer <NUM> is formed by reacting an active metal contained in a bonding material with the ceramic substrate <NUM>.

In the present embodiment, Ti is used as the active metal and the ceramic substrate <NUM> is made of aluminum nitride, so that the active metal compound layer <NUM> becomes a titanium nitride (TiN) layer.

The observation results of the active metal compound layer <NUM> are shown in <FIG>. As shown in <FIG>, Al and Cu are present in the interior of the active metal compound layer <NUM>. In the present embodiment, Ag contained in the bonding material is also present.

As shown in <FIG>, Al, Cu, and Ag are present in aggregated state at the grain boundary of the active metal compound (TiN in the present embodiment).

As a result of line analysis of the vicinity of the grain boundary of the active metal compound (TiN in the present embodiment), it is confirmed that the concentration of Al, Cu, and Ag is increased in the grain boundary portion as shown in <FIG>.

In the present embodiment, as shown in <FIG>, it is preferable that the maximum particle size of the active metal compound particles in the active metal compound layer <NUM> is <NUM> or less. That is, it is preferable that the active metal compound layer <NUM> has a large number of grain boundary regions (metal phases). In <FIG>, TiN particles are present, and the maximum particle size of the TiN particles is <NUM> or less. The maximum particle size of the active metal compound particles in the active metal compound layer <NUM> is more preferably <NUM> or less, and still more preferably <NUM> or less. The lower limit may be, for example, <NUM> or more. It is difficult to make the particle size less than <NUM> in production.

In the insulating circuit substrate <NUM> according to the present embodiment, it is preferable that the maximum indentation hardness in a region from <NUM> to <NUM> from the bonded interface between the circuit layer <NUM> (metal layer <NUM>) and the ceramic substrate <NUM> to the circuit layer <NUM> (metal layer <NUM>) side is in a range of <NUM> mgf/µm<NUM> or more and <NUM> mgf/µm<NUM> or less.

The maximum indentation hardness is more preferably <NUM> mgf/µm<NUM> or more, and still more preferably <NUM> mgf/µm<NUM> or more. On the other hand, the maximum indentation hardness is more preferably <NUM> mgf/µm<NUM> or less, and still more preferably <NUM> mgf/µm<NUM> or less.

Hereinafter, a method for producing the insulating circuit substrate <NUM> according to the present embodiment will be described with reference to <FIG> and <FIG>.

First, the ceramic substrate <NUM> made of aluminum nitride (AlN) is prepared, and as shown in <FIG>, an Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM> is disposed as a bonding material between the copper sheet <NUM> serving as the circuit layer <NUM> and the ceramic substrate <NUM>, and between the copper sheet <NUM> serving as the metal layer <NUM> and the ceramic substrate <NUM>.

As the Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM>, for example, it is preferable to use a composition containing Cu in an amount of <NUM> mass% or more and <NUM> mass% or less, and Ti as an active metal in an amount of <NUM> mass% or more and <NUM> mass% or less, with a balance being Ag and inevitable impurities. The thickness of the Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM> is preferably in a range of <NUM> or more and <NUM> or less.

Next, in a state where the ceramic substrate <NUM> and the copper sheets <NUM> and <NUM> are pressed in a lamination direction, the ceramic substrate <NUM> and the copper sheets <NUM> and <NUM> are loaded into a heating furnace in a vacuum or in argon atmosphere, and are heated and held.

A holding temperature in the low temperature holding step S02 is set to be in a temperature range of a eutectic point temperature of Cu and Al or more and lower than a eutectic point temperature of Ag and Cu. In the low temperature holding step S02, a temperature integration value at the above-described holding temperature is in a range of <NUM>·h or higher and <NUM>·h or lower.

A pressing load in the low temperature holding step S02 is preferably in a range of <NUM> MPa or more and <NUM> MPa or less.

Next, the copper sheets <NUM> and <NUM> and the ceramic substrate <NUM> are heated in a heating furnace in a vacuum atmosphere in a state of being pressed, to melt the Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM>.

A heating temperature in the heating step S03 is in a range of the eutectic point temperature of Ag and Cu or more and <NUM> or less. By suppressing the heating temperature low, it is possible to suppress the maximum particle size of the active metal compound particles in the active metal compound layer <NUM> small. The heating temperature is preferably <NUM> or lower, more preferably <NUM> or lower, and still more preferably <NUM> or lower.

In the heating step S03, a temperature integration value at the above-described heating temperature is in a range of <NUM>·h or higher and <NUM>-h or lower. Preferably, the temperature integral value may be in a range of <NUM>·h or higher and <NUM>-h or lower.

A pressing load in the heating step S03 is in a range of <NUM> MPa or more and <NUM> MPa or less.

Then, after the heating step S03, the molten Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM> is solidified by cooling.

A cooling rate in the cooling step S04 is not particularly limited, and is preferably in a range of <NUM>/min or higher and <NUM>/min or lower.

In the above-described low temperature holding step S02, since the temperature is held at a temperature of the eutectic point temperature of Cu and Al or more, Cu in the copper sheets <NUM> and <NUM> and the Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM>, and Al produced by the reaction of the ceramic substrate <NUM> made of AlN with Ti are subjected to a eutectic reaction, to generate a eutectic liquid phase, as shown in <FIG>. In this eutectic liquid phase, Ti in the Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM> reacts with N (nitrogen) in the ceramic substrate <NUM> to generate TiN. As a result, the active metal compound layer <NUM> made of TiN is formed in such a manner that the surface of the ceramic substrate <NUM> is eroded in the order of (a) of <FIG>, (b) of <FIG>, and (c) of <FIG>.

As shown in <FIG>, in the active metal compound layer <NUM>, a eutectic liquid phase is present at the grain boundary of the active metal compound (TiN in the present embodiment), and Al on the ceramic substrate <NUM> side and Ag, Cu, and Ti of the Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM> diffuse into each other by using the eutectic liquid phase as a diffusion path, to promote the interfacial reaction of the ceramic substrate <NUM>.

As a result, Al, Cu, and Ag are present in aggregated state at the grain boundary of the active metal compound (TiN in the present embodiment).

As described above, the ceramic substrate <NUM> and the copper sheets <NUM> and <NUM> are bonded to each other by the laminating step S01, the low temperature holding step S02, the heating step S03, and the cooling step S04; and thereby, the insulating circuit substrate <NUM> according to the present embodiment is produced.

Next, the heat sink <NUM> is bonded to the other surface side of the metal layer <NUM> of the insulating circuit substrate <NUM>.

The insulating circuit substrate <NUM> and the heat sink <NUM> are laminated with a solder material interposed therebetween and are loaded into a heating furnace such that the insulating circuit substrate <NUM> and the heat sink <NUM> are solder-bonded to each other with the solder layer <NUM> interposed therebetween.

Next, the semiconductor element <NUM> is bonded to one surface of the circuit layer <NUM> of the insulating circuit substrate <NUM> by soldering.

The power module <NUM> shown in <FIG> is produced by the above-described steps.

According to the insulating circuit substrate <NUM> (copper/ceramic bonded body) of the present embodiment having the above-described configuration, in the active metal compound layer <NUM> formed at the bonded interface between the circuit layer <NUM> (metal layer <NUM>) and the ceramic substrate <NUM>, Al and Cu are present at the grain boundary of the active metal compound (TiN), so that the active metal (Ti) contained in the Ag-Ti-based brazing material (Ag-Cu-Ti-based brazing material) <NUM> which is a bonding material sufficiently reacts with the ceramic substrate <NUM>, and the ceramic substrate <NUM> and the circuit layer <NUM> (metal layer <NUM>) are firmly bonded to each other.

In the low temperature holding step S02, since the active metal (Ti) is sufficiently diffused to the ceramic substrate <NUM> side via a liquid phase (Al-Cu eutectic liquid phase) formed by the reaction, the ceramic substrate <NUM> and the circuit layer <NUM> (metal layer <NUM>) can be firmly bonded to each other. Accordingly, reliability of a thermal cycle can be improved.

In the insulating circuit substrate <NUM> according to the present embodiment, since Ag is present at the grain boundary of the active metal compound in the active metal compound layer <NUM>, an Al-Ag-Cu eutectic liquid phase having a lower eutectic temperature than the Al-Cu eutectic is present during the reaction, so that the energy of the system can be lowered and the reaction can be further promoted.

When the maximum particle size of the active metal compound particles in the active metal compound layer <NUM> is <NUM> or less, a proportion of the grain boundary region (metal phase) having a relatively low hardness in the active metal compound layer <NUM> increases, and the impact resistance of the active metal compound layer <NUM> is improved. Thereby, the generation of cracks in the active metal compound layer <NUM> can be suppressed. Therefore, even when ultrasonic waves are applied to the insulating circuit substrate <NUM> (copper/ceramic bonded body) for ultrasonic bonding of a terminal material or the like to the circuit layer <NUM> (metal layer <NUM>), the peeling of the circuit layer <NUM> (metal layer <NUM>) from the ceramic substrate <NUM> and the generation of cracks in the ceramic substrate <NUM> can be suppressed.

In the insulating circuit substrate <NUM> according to the present embodiment, when the maximum indentation hardness in a region from <NUM> to <NUM> from the bonded interface between the circuit layer <NUM> (metal layer <NUM>) and the ceramic substrate <NUM> to the circuit layer <NUM> (metal layer <NUM>) side is set to <NUM> mgf/µm<NUM> or more, the copper at or in the vicinity of the bonded interface is sufficiently melted to generate a liquid phase, and the ceramic substrate <NUM> and the circuit layer <NUM> (metal layer <NUM>) are more firmly bonded to each other.

On the other hand, when the maximum indentation hardness is suppressed to <NUM> mgf/µm<NUM> or less, the vicinity of the bonded interface is not harder than necessary, and the generation of cracks during loading of the thermal cycle can be suppressed.

Hereinafter, results of confirmation experiments performed to confirm the effects of the present invention will be described.

First, a ceramic substrate (<NUM> × <NUM> × <NUM>) made of the materials shown in Table <NUM> was prepared.

A copper sheet (<NUM> × <NUM> × thickness of <NUM>) made of oxygen-free copper was bonded to both surfaces of the ceramic substrate under the conditions shown in Table <NUM> by using an Ag-Cu-based brazing material containing the active metal (composition: <NUM> mass% of Cu, and <NUM> mass% of active metal, with the balance being Ag and inevitable impurities, thickness: <NUM>) shown in Table <NUM>, to obtain an insulating circuit substrate (copper/ceramic bonded body). A degree of vacuum of a vacuum furnace at the time of bonding was set to <NUM> × <NUM>-<NUM> Pa.

For the obtained insulating circuit substrate (copper/ceramic bonded body), the presence or absence of Al, Cu, and Ag at a grain boundary in an active metal compound layer, the maximum indentation hardness in the vicinity of a bonded interface, and the reliability of the thermal cycle were evaluated as follows.

(Presence or Absence of Al and Cu at Grain Boundary in Active Metal Compound Layer).

Elemental mapping of the grain boundary in the active metal compound layer was acquired at an acceleration voltage of <NUM> kV and at a magnification of <NUM> to <NUM> by using a transmission electron microscope (Titan ChemiSTEM manufactured by FEI Company), and when a region in which Al and Cu coexisted was present, determination was made that Al and Cu were "present" at the grain boundary.

Line analysis was performed on the grain boundary in the active metal compound layer across the grain boundary at an acceleration voltage of <NUM> kV and at a magnification of <NUM> to <NUM> by using a transmission electron microscope (Titan ChemiSTEM manufactured by FEI Company).

In a case where the ceramic substrate was AlN, when a total value of Cu, Ag, Al, N, and active metal elements was <NUM> atomic% and the concentration of Ag was <NUM> atomic% or more, determination was made that Ag was "present" at the grain boundary.

In a case where the ceramic substrate was Al<NUM>O<NUM>, when a total value of Cu, Ag, Al, O, and active metal elements was <NUM> atomic% and the concentration of Ag was <NUM> atomic% or more, determination was made that Ag was "present" at the grain boundary.

The maximum indentation hardness was measured in a region from <NUM> to <NUM> from the bonded interface between the copper sheet and the ceramic substrate to the copper sheet side by using an indentation hardness tester (ENT-1100a manufactured by Elionix Inc. As shown in <FIG>, the measurement was performed at intervals of <NUM>, and the measurement was performed at <NUM> points.

After the sample was passed through the following atmosphere, the bonded interface between the copper sheet and the ceramic substrate was inspected by SAT inspection, and the presence or absence of ceramic breaking was determined.

The number of cycles in which breaking occurred was evaluated. A case where breaking was confirmed in less than <NUM> times of cycle was evaluated as "C", a case where breaking was confirmed in <NUM> times or more and less than <NUM> times of cycle was evaluated as "B", and a case where breaking was not confirmed even in <NUM> times or more of cycle was evaluated as "A".

In Comparative Example <NUM> in which a temperature integration value in the low temperature holding step was <NUM> h, Al and Cu were not confirmed at the grain boundary of the active metal compound layer, and the reliability of the thermal cycle was "C".

In Comparative Example <NUM> in which a temperature integration value in the low temperature holding step was <NUM>·h, Al and Cu were not confirmed at the grain boundary of the active metal compound layer, and the reliability of the thermal cycle was "C".

In Comparative Example <NUM> in which a temperature integration value in the heating step was <NUM>-h, the copper sheet and the ceramic substrate could not be sufficiently bonded to each other. Therefore, other evaluations were discontinued.

On the other hand, in Invention Examples <NUM> to <NUM> in which Al and Cu were confirmed at the grain boundary of the active metal compound layer, the reliability of the thermal cycle was "B" or "A" regardless of the material of the ceramic substrate and the active metal element.

In particular, Invention Examples <NUM> to <NUM> in which the maximum indentation hardness in a region from <NUM> to <NUM> from the bonded interface between the copper sheet and the ceramic substrate to the copper sheet side was in a range of <NUM> mgf/µm<NUM> or more and <NUM> mgf/µm<NUM> or less, the reliability of the thermal cycle was "A", and the reliability of the thermal cycle was particularly excellent.

Under the conditions shown in Table <NUM>, the copper sheet and the ceramic substrate were bonded to each other by the same procedure as in Example <NUM> described above to obtain an insulating circuit substrate (copper/ceramic bonded body).

For the obtained insulating circuit substrate (copper/ceramic bonded body), the presence or absence of Al, Cu, and Ag at a grain boundary in an active metal compound layer and the maximum indentation hardness in the vicinity of a bonded interface were evaluated by the same procedure as in Example <NUM>.

The maximum particle size of the active metal compound particles in the active metal compound layer and ultrasonic welding property were evaluated as follows.

The active metal compound layer was observed at a magnification of <NUM> by using a transmission electron microscope (Titan ChemiSTEM manufactured by FEI Company), to obtain a HAADF image.

By image analysis of the HAADF image, the equivalent circle diameter of the active metal compound particles was calculated. From the results of image analysis in <NUM> fields of view, the maximum equivalent circle diameter of the observed active metal compound particles is shown in Table <NUM> as the maximum particle size.

A copper terminal (<NUM> × <NUM> × <NUM> in thickness) was ultrasonically bonded to the insulating circuit substrate by using an ultrasonic metal bonding machine (60C-<NUM> manufactured by Ultrasonic Engineering Co. ) under the conditions where a load was <NUM> N, a collapse amount was <NUM>, and a bonding area was <NUM> × <NUM>. <NUM> copper terminals were bonded at a time.

After bonding, the bonded interface between the copper sheet and the ceramic substrate was inspected by using an ultrasonic flaw detector (FineSAT200 manufactured by Hitachi Solutions, Ltd. A case where peeling of the copper sheet from the ceramic substrate or ceramic breaking was observed in <NUM> pieces or more out of <NUM> pieces was evaluated as "D", a case where peeling of the copper sheet from the ceramic substrate or ceramic breaking was observed in <NUM> pieces or more and <NUM> pieces or less out of <NUM> pieces was evaluated as "C", a case where peeling of the copper sheet from the ceramic substrate or ceramic breaking was observed in <NUM> piece or more and <NUM> pieces or less out of <NUM> pieces was evaluated as "B", and a case where peeling of the copper sheet from the ceramic substrate or ceramic breaking was not observed in all <NUM> pieces was evaluated as "A".

From the comparison among Invention Examples <NUM> to <NUM> in which the ceramic substrate was made of AlN and the active metal was Ti and among Invention Examples <NUM> to <NUM> in which the ceramic substrate was made of Al<NUM>O<NUM> and the active metal was Zr, it is confirmed that the maximum particle size of the active metal compound particles in the active metal compound layer was reduced; and thereby, the peeling of the copper sheet from the ceramic substrate and the generation of cracks in the ceramic substrate during ultrasonic bonding could be suppressed.

As a result of Examples described above, according to Invention Examples, it was confirmed that it is possible to provide a copper/ceramic bonded body and an insulating circuit substrate, which have a high bonding strength and particularly excellent reliability of a thermal cycle.

Claim 1:
A copper/ceramic bonded body comprising:
a copper member (<NUM>) made of copper or a copper alloy; and
a ceramic member (<NUM>) made of aluminum-containing ceramics, the copper member (<NUM>) and the ceramic member (<NUM>) being bonded to each other,
wherein, at a bonded interface between the copper member and the ceramic member, an active metal compound layer (<NUM>) containing an active metal compound that is a compound of one or more active metals selected from Ti, Zr, Nb, and Hf is formed on a ceramic member side,
in the active metal compound layer (<NUM>),
Al and Cu are present at a grain boundary of the active metal compound, and
a maximum indentation hardness in a region from <NUM> to <NUM> from the bonded interface between the copper member (<NUM>) and the ceramic member (<NUM>) to a copper member side is in a range of <NUM> mgf/µm<NUM> or more and <NUM> mgf/ µm<NUM> or less.