JP5982954B2 - Power module and method for manufacturing power module - Google Patents

Description

  The present invention relates to a power module including a power module substrate having a circuit layer disposed on one surface of an insulating layer, and a semiconductor element mounted on the circuit layer, and a method for manufacturing the power module. It is.

Among various semiconductor elements, a power element for high power control used for controlling an electric vehicle or an electric vehicle has a large amount of heat generation. Therefore, as a substrate on which the power element is mounted, for example, AlN (aluminum nitride) 2. Description of the Related Art Conventionally, a power module substrate in which a metal plate having excellent conductivity is bonded as a circuit layer on a ceramic substrate made of, for example, has been widely used.
In such a power module substrate, a semiconductor element as a power element is mounted on the circuit layer via a solder material. In addition, as this kind of power module substrate, a metal plate with excellent thermal conductivity is joined to the lower surface of the ceramic substrate, and a cooler is joined via the metal plate to dissipate heat. Is known.

As the metal constituting the circuit layer, aluminum or an aluminum alloy, or copper or a copper alloy is used.
Here, since the aluminum oxide film is formed on the surface of the circuit layer made of aluminum, it cannot be satisfactorily bonded to the solder material. Further, in the circuit layer made of copper, there is a problem that the molten solder material reacts with the copper and the components of the solder material enter the inside of the circuit layer to deteriorate the conductivity of the circuit layer.

Therefore, conventionally, as disclosed in, for example, Patent Document 1, a Ni plating film is formed on the surface of a circuit layer by electroless plating or the like, and a solder material is disposed on the Ni plating film to provide a semiconductor element. It was joined.
However, as described in Patent Document 1, in the power module substrate in which the Ni plating film is formed on the surface of the circuit layer, the surface of the Ni plating film deteriorates due to oxidation or the like in the process until the semiconductor element is joined, There is a possibility that the reliability of bonding with a semiconductor element bonded via a solder material may be reduced.

Therefore, a technique for joining a semiconductor element and a circuit layer without using a solder material has been proposed.
For example, Patent Document 2 proposes a technique for joining semiconductor elements using Ag nanopaste.
Patent Documents 3 and 4 propose techniques for joining semiconductor elements using an oxide paste containing metal oxide particles and a reducing agent made of an organic substance.

JP 2004-172378 A JP 2006-202938 A JP 2008-208442 A JP 2009-267374 A

By the way, when joining a semiconductor element and a circuit layer, Au layer is formed in the junction surface of a semiconductor element. When semiconductor elements are bonded using Ag nanopaste as disclosed in Patent Document 2, Ag and Au layer of Ag nanopaste are interdiffused.
Here, as disclosed in Patent Document 2, when a semiconductor element is bonded using an Ag nano paste without using a solder material, a bonding layer made of the Ag nano paste is formed thinner than the solder material. For this reason, the stress at the time of thermal cycle load tends to act on the semiconductor element, and the semiconductor element itself may be damaged.
In addition, as disclosed in Patent Documents 3 and 4, when a semiconductor element is bonded using a metal oxide and a reducing agent, the fired layer of the oxide paste is still formed thinly. The stress at the time of the cycle load tends to act on the semiconductor element, and the performance of the power module may be deteriorated. In addition, it takes time for the mutual diffusion of the Ag and Au layers, resulting in a problem that the bonding time becomes long.

  In particular, recently, power modules have been reduced in size and thickness, and the usage environment has become severe, and the amount of heat generated from electronic components tends to increase. For this reason, when the power module is used, the stress acting on the bonding interface between the circuit layer and the semiconductor element tends to increase, and the bonding reliability between the circuit layer and the semiconductor element is improved compared to the conventional case. In addition, joining in a short time is required.

  The present invention has been made in view of the above-described circumstances, and can reliably bond a semiconductor element to one surface of a circuit layer even in a short time, and is excellent in thermal cycle and power cycle reliability. Another object is to provide a power module and a method for manufacturing the power module.

In order to solve such problems and achieve the above object, a power module of the present invention is mounted on a power module substrate having a circuit layer disposed on one surface of an insulating layer, and on the circuit layer. A first fired layer made of a fired body of a glass-containing Ag paste containing a glass component is formed on one surface of the circuit layer. On the fired layer, a second fired layer made of a fired body of Ag reduced in silver oxide is formed, and a metal Ag layer and an Au layer are formed between the second fired layer and the semiconductor element. The Au layer is formed on the bonding surface of the semiconductor element, the metal Ag layer is formed between the Au layer and the second fired layer, and the Au layer and the metal Ag layer are interdiffused. It is characterized by that.

According to the power module having this configuration, the first fired layer made of the fired body of the glass-containing Ag paste containing the glass component is formed on one surface of the circuit layer. The formed oxide film can be removed, and the bonding strength between the first fired layer and the circuit layer can be ensured.
Moreover, since the 2nd baking layer which consists of a baking body of Ag by which silver oxide was reduced is formed on this 1st baking layer, a semiconductor element is joined when forming this 2nd baking layer. Is possible. Here, when silver oxide is reduced, fine Ag particles are generated, so that the fired body constituting the second fired layer can have a dense structure.
Furthermore, since the first fired layer and the second fired layer are laminated, the thickness of the bonding layer interposed between the circuit layer and the semiconductor element can be ensured. Therefore, it can suppress that the stress at the time of a heat cycle load acts on a semiconductor element, and can prevent damage to semiconductor element itself.

Since the metal Ag layer is formed between the second fired layer and the semiconductor element, the metal Ag layer and the second fired layer are joined by sintering of Ag, and the semiconductor element and The circuit layer can be firmly bonded in a short time.
That is, in the case where the second fired layer made of a fired body of Ag reduced in silver oxide and the Au layer formed on the bonding surface of the semiconductor element are directly joined, mutual diffusion between the Au layer and the second fired layer is achieved. May become insufficient. Here, by forming the metal Ag layer between the second fired layer and the semiconductor element, the second fired layer and the metal Ag layer can be firmly bonded in a short time by sintering. .

Here, it is preferable that the thickness of the metal Ag layer is 15 nm or more and 2.5 μm or less.
In this case, since the metal Ag layer is formed with a thickness of 15 nm or more, the second fired layer and the semiconductor element can be reliably bonded. On the other hand, since the thickness is 2.5 μm or less, the amount of silver in the metal Ag layer can be suppressed, and the metal Ag layer can be formed relatively inexpensively.

The first fired layer includes a glass layer formed on one surface of the circuit layer, and an Ag layer laminated on the glass layer. Glass particles are dispersed in the Ag layer. Preferably it is.
In this case, the oxide film formed on the surface of the circuit layer can be removed by reacting with the glass layer, and the circuit layer and the semiconductor element can be reliably bonded.

The second fired layer is preferably a fired body of silver oxide paste containing silver oxide and a reducing agent.
In this case, when the silver oxide paste is fired, the silver oxide is surely reduced by the reducing agent to produce fine Ag particles, and the second fired layer can be formed of a dense fired body. Further, since the reducing agent is decomposed when the silver oxide is reduced, it is difficult to remain in the second fired layer, and the conductivity in the second fired layer can be ensured. Further, since firing can be performed under a relatively low temperature condition such as 300 ° C., the junction temperature of the semiconductor element can be kept low, and the thermal load on the semiconductor element can be reduced.

Here, the silver oxide paste may contain Ag particles in addition to the silver oxide and the reducing agent.
In this case, the reduced Ag particles obtained by reducing the silver oxide and the Ag particles contained in the silver oxide paste are sintered, and the second fired layer can be composed of a denser fired body. . In this case, the average particle size of the Ag particles is desirably 20 nm or more and 800 nm or less.

A method for manufacturing a power module of the present invention includes a power module substrate having a circuit layer disposed on one surface of an insulating layer, and a semiconductor element mounted on the circuit layer. A step of forming a first fired layer by applying a glass-containing Ag paste containing a glass component on one surface of the circuit layer and heat-treating the same, on the first fired layer; A step of applying a silver oxide paste containing silver oxide and a reducing agent, a step of forming an Au layer on the bonding surface of the semiconductor element, and a step of forming a metal Ag film on the surface of the Au layer. A step of laminating a semiconductor element formed with a metal Ag film on the silver oxide paste, and heating the semiconductor element and the power module substrate in a laminated state; Two fired layers are formed Comprising forming a Rutotomoni metal Ag layer, and is characterized in that bonding the circuit layer and the semiconductor element.

According to the method for manufacturing a power module having this configuration, the step of forming the first fired layer by applying a glass-containing Ag paste containing a glass component to one surface of the circuit layer and heat-treating it. Since it is provided, the oxide film formed on the surface of the circuit layer can be removed, and the circuit layer and the first fired layer can be reliably bonded.
A step of forming a metal Ag film on the bonding surface of the semiconductor element; a step of applying a silver oxide paste containing silver oxide and a reducing agent on the first fired layer; and a step of applying the applied silver oxide paste. A step of laminating a semiconductor element thereon, and a step of heating the semiconductor element and the power module substrate in a laminated state to form a second fired layer on the first fired layer. Thus, the second fired layer is formed by firing the silver oxide paste, and a metal Ag layer is formed between the second fired layer and the semiconductor element. Therefore, the metal Ag layer and the second fired layer are joined by sintering of Ag, and the semiconductor element and the circuit layer can be firmly joined in a short time.

Here, it is preferable that the thickness of the metal Ag layer is 15 nm or more and 2.5 μm or less.
In this case, since the metal Ag layer is formed with a thickness of 15 nm or more, the second fired layer and the semiconductor element can be reliably bonded. On the other hand, since the thickness is 2.5 μm or less, the amount of silver in the metal Ag layer can be suppressed, and the metal Ag layer can be formed relatively inexpensively.

Moreover, it is preferable that the said silver oxide paste contains Ag particle | grains in addition to the said silver oxide and the said reducing agent.
In this case, the Ag particles are interposed between the silver oxide powders, and the reduced Ag particles obtained by reducing the silver oxide and the Ag particles contained in the silver oxide paste are sintered, and the second fired layer Can be made into a denser structure. Moreover, the pressurization pressure of the semiconductor element at the time of joining can be set low.

    ADVANTAGE OF THE INVENTION According to this invention, the semiconductor element can be reliably joined to one side of a circuit layer for a short time, and the manufacturing method of a power module and power module excellent in thermal cycle and power cycle reliability are provided. it can

It is a schematic explanatory drawing of the power module which is embodiment of this invention. FIG. 2 is an enlarged explanatory view of a bonding interface between a circuit layer and a semiconductor element of the power module shown in FIG. 1. FIG. 3 is an enlarged explanatory diagram of a circuit layer surface in FIG. 2. It is a flowchart which shows the manufacturing method of glass containing Ag paste. It is a flowchart which shows the manufacturing method of a silver oxide paste. It is a flowchart which shows the manufacturing method of the power module of FIG. It is a cross-sectional observation photograph of the junction interface of the circuit layer and semiconductor element of the power module of Example 8. It is the observation photograph which expanded the cross section of the junction interface of the circuit layer of a power module of Example 8, and a semiconductor element. It is a cross-sectional observation photograph of the junction interface of the circuit layer of a power module of comparative example 1, and a semiconductor element. It is the observation photograph which expanded the cross section of the junction interface of the circuit layer of the power module of the comparative example 1, and a semiconductor element.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a power module 1 according to an 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 element 3 bonded to one surface of the circuit layer 12 (upper surface in FIG. 1), and the other of the power module substrate 10. And a cooler 40 disposed on the side.

The power module substrate 10 includes a ceramic substrate 11 constituting an insulating layer, a circuit layer 12 disposed on one surface of the ceramic substrate 11, and a metal layer 13 disposed on the other surface of the ceramic substrate 11. And.
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.

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

  The metal layer 13 is formed by bonding a metal plate to the other surface of the ceramic substrate 11. In the present embodiment, the metal layer 13 is formed by joining an aluminum plate 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. Has been.

  The cooler 40 is for cooling the power module substrate 10 described above. The top plate portion 41 joined to the power module substrate 10 and the top plate portion 41 are suspended downward. The heat radiation fin 42 and the flow path 43 for distribute | circulating a cooling medium (for example, cooling water) are provided. The cooler 40 (top plate portion 41) is preferably made of a material having good thermal conductivity, and is made of A6063 (aluminum alloy) in the present embodiment.

  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 41 of the cooler 40 and the metal layer 13. Yes.

In the power module 1 shown in FIG. 1, the first fired layer 31 and the second fired layer 36 are formed between the circuit layer 12 and the semiconductor element 3. Here, the first fired layer 31 is laminated on one surface of the circuit layer 12, the second fired layer 36 is laminated on the first fired layer 31, and the semiconductor element 3 is placed on the second fired layer 36. Are stacked. Further, a metal Ag layer 38 and an Au layer 39 are formed between the second fired layer 36 and the semiconductor element 3.
As shown in FIG. 1, the first fired layer 31 and the second fired layer 36 are not formed on the entire surface of the circuit layer 12, and are selectively formed only on the portion where the semiconductor element 3 is disposed. Is formed.

Here, the 1st baking layer 31 is made into the baking body of the glass containing Ag paste containing a glass component so that it may mention later. As shown in FIGS. 2 and 3, the first fired layer 31 includes a glass layer 32 formed on the circuit layer 12 side, and an Ag layer 33 formed on the glass layer 32.
In the glass layer 32, fine conductive particles 34 having a particle diameter of about several nanometers are dispersed. The conductive particles 34 are crystalline particles containing at least one of Ag or Al. In addition, the electroconductive particle 34 in the glass layer 32 is observed by using a transmission electron microscope (TEM), for example.
In addition, fine glass particles 35 having a particle size of about several nanometers are dispersed inside the Ag layer 33.

  In addition, the electrical resistance value P in the thickness direction of the first fired layer 31 is set to 0.5Ω or less. Here, in the present embodiment, the electrical resistance value P in the thickness direction of the first fired layer 31 is an electrical resistance value between the upper surface of the first fired layer 31 and the upper surface of the circuit layer 12. This is because the electrical resistance of 4N aluminum constituting the circuit layer 12 is very small compared to the electrical resistance in the thickness direction of the first fired layer 31. In the measurement of the electrical resistance, the upper center point of the first fired layer 31 and the distance from the upper surface center point of the first fired layer 31 to the end of the first fired layer 31 are the same. The electrical resistance between the point on the circuit layer 12 that is distant from the end of the first fired layer 31 is measured.

In the present embodiment, since the circuit layer 12 is made of aluminum having a purity of 99.99%, an aluminum oxide film naturally generated in the atmosphere is formed on the surface of the circuit layer 12. Here, in the portion where the first fired layer 31 is formed, the aluminum oxide film is removed, and the first fired layer 31 is formed directly on the circuit layer 12. That is, the aluminum constituting the circuit layer 12 and the glass layer 32 are directly bonded.
In the present embodiment, the thickness tg of the glass layer 32 is 0.01 μm ≦ tg ≦ 5 μm, the thickness ta of the Ag layer 33 is 1 μm ≦ ta ≦ 100 μm, and the total thickness t1 of the first fired layer 31 is 1.01 μm. It is comprised so that it may become <= t1 <= 105micrometer.

  The second fired layer 36 formed on the first fired layer 31, that is, the Ag layer 33, is an Ag fired body obtained by reducing silver oxide. In the present embodiment, as will be described later. And a sintered body of silver oxide paste containing silver oxide and a reducing agent. Here, particles precipitated by reducing silver oxide (reduced Ag particles) are very fine, for example, having a particle diameter of 10 nm to 1 μm, so that the second fired layer 36 made of a dense Ag fired body is formed. Will be.

In the second fired layer 36, the glass particles observed in the Ag layer 33 of the first fired layer 31 are not present or very few. It is possible to distinguish between the Ag layer 33 of the first fired layer 31 and the second fired layer 36 based on the density of the glass particles.
In the present embodiment, the thickness t2 of the second fired layer 36 is 5 μm ≦ t2 ≦ 50 μm.

  In addition, a metal Ag layer 38 and an Au layer 39 are formed between the semiconductor element 3 and the second fired layer 36. That is, the Au layer 39 is formed on the bonding surface of the semiconductor element 3, and the metal Ag layer 38 is formed between the Au layer 39 and the second fired layer 36. The metal Ag layer 38 and the Au layer 39 are joined by mutual diffusion.

  Here, the metal Ag layer 38 preferably has a thickness of 15 nm to 2.5 μm. Examples of the method for forming the metal Ag layer include a spin coating method, a plating method, and a sputtering method in which an Ag fine particle dispersion containing Ag fine particles is applied to the surface of the Au layer 39. In the case of a spin coating method in which an Ag fine particle dispersion containing Ag fine particles is applied to the surface of the Au layer 39, it is desirable to use Ag fine particles having a particle diameter of 20 nm or more and 200 nm or less. Ag fine particles Since the metal Ag layer 38 has fewer pores than the second fired layer 36 made of a fired body of silver oxide paste, it can be distinguished from the second fired layer 36.

Next, the glass containing Ag paste which comprises the 1st baking layer 31 is demonstrated.
This glass-containing Ag paste contains Ag powder, glass powder, resin, solvent, and dispersant, and the content of the powder component composed of Ag powder and glass powder is the glass-containing Ag paste. The total content is 60% by mass or more and 90% by mass or less, and the remainder is a resin, a solvent, and a dispersant. In addition, in this embodiment, content of the powder component which consists of Ag powder and glass powder is 85 mass% of the whole glass containing Ag paste.
Further, the viscosity of the glass-containing Ag paste is adjusted to 10 Pa · s or more and 500 Pa · s or less, more preferably 50 Pa · s or more and 300 Pa · s or less.

The Ag powder has a particle size of 0.05 μm or more and 1.0 μm or less. In this embodiment, an Ag powder having an average particle size of 0.8 μm was used.
The glass powder contains Bi ₂ O ₃ , ZnO, and B ₂ O ₃ as main components, and has a glass transition temperature of 300 ° C. or higher and 450 ° C. or lower, a softening temperature of 600 ° C. or lower, and a crystallization temperature of 450 ° C. It is above ℃. The weight ratio A / G between the weight A of the Ag powder and the weight G of the glass powder is adjusted within the range of 80/20 to 99/1. In this embodiment, A / G = 80/5 It was.

A solvent having a boiling point of 200 ° C. or higher is suitable. In this embodiment, diethylene glycol dibutyl ether is used.
The resin is used to adjust the viscosity of the glass-containing Ag paste, and those that decompose at 500 ° C. or higher are suitable. In this embodiment, ethyl cellulose is used.
In this embodiment, a dicarboxylic acid-based dispersant is added. In addition, you may comprise a glass containing Ag paste, without adding a dispersing agent.

Here, in this embodiment, lead-free glass powder was used. The glass composition of the lead-free glass powder in this embodiment is
Bi ₂ O ₃ : 68 mass% or more and 93 mass% or less,
ZnO: 1% by mass or more and 20% by mass or less,
B ₂ O ₃ : 1% by mass or more and 11% by mass or less,
SiO ₂ : 5% by mass or less,
Al ₂ O ₃ : 5% by mass or less,
Fe ₂ O ₃ : 5% by mass or less,
CuO: 5 mass% or less,
CeO ₂ : 5% by mass or less,
ZrO ₂ : 5% by mass or less,
Alkali metal oxide: 2% by mass or less,
Alkaline earth metal oxide: 7% by mass or less,
It is said that.

That is, in this embodiment, Bi ₂ O ₃ , ZnO, B ₂ O ₃ is included, and this includes SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CuO, CeO ₂ , ZrO ₂ , Li ₂ O, Na Alkali metal oxides such as ₂ O and K ₂ O, and alkaline earth metal oxides such as MgO, CaO, BaO and SrO are appropriately added as necessary.

Such glass powder is manufactured as follows. The above-mentioned various oxides, carbonates or ammonium salts are used as raw materials. This raw material is charged into a platinum crucible, an alumina crucible, a quartz crucible or the like and melted in a melting furnace. Although there is no restriction | limiting in particular in melting conditions, It is preferable to set it as the range of 900 degreeC or more and 1300 degrees C or less and 30 minutes or more and 120 minutes or less so that all the raw materials may be mixed uniformly by a liquid phase.
The obtained melt is dropped on carbon, steel, copper plate, twin rolls, water, etc., and rapidly cooled to produce a uniform glass lump.
The glass lump is pulverized with a ball mill, a jet mill or the like, and coarse particles are classified to obtain a lead-free glass powder. Here, in this embodiment, the center particle diameter d50 of the lead-free glass powder is set in the range of 0.1 μm or more and 5.0 μm or less.

Next, the manufacturing method of glass containing Ag paste is demonstrated with reference to the flowchart shown in FIG.
First, the above-described Ag powder and lead-free glass powder are mixed to produce a mixed powder (mixed powder forming step S01). Moreover, a solvent and resin are mixed and an organic mixture is produced | generated (organic substance mixing process S02).
Then, the mixed powder, the organic mixture, and the dispersant are premixed by a mixer (preliminary mixing step S03).
Next, the preliminary mixture is mixed while kneading using a roll mill (kneading step S04).
And the obtained kneading is filtered with a paste filter (filtration process S05).
In this way, the above-mentioned glass-containing Ag paste is produced.

Next, the silver oxide paste which comprises the 2nd baking layer 36 is demonstrated.
This silver oxide paste contains a silver oxide powder, a reducing agent, a resin, and a solvent. In this embodiment, in addition to these, an organic metal compound powder is contained.
The content of the silver oxide powder is 60% by mass or more and 80% by mass or less of the entire silver oxide paste, and the content of the reducing agent is 5% by mass or more and 15% by mass or less of the entire silver oxide paste. The content is 0% by mass or more and 10% by mass or less of the entire silver oxide paste, and the remainder is a solvent.
The silver oxide paste has a viscosity adjusted to 10 Pa · s to 100 Pa · s, more preferably 30 Pa · s to 80 Pa · s.

  Silver oxide powder having a particle size of 0.1 μm or more and 40 μm or less was used. Such silver oxide powder is available as a commercial product.

The reducing agent is an organic substance having reducibility, and for example, alcohol and organic acid can be used.
If it is an alcohol, for example, methanol, ethanol, propanol, butyl alcohol, pentyl alcohol, hexyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, dodecyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, etc. The primary alcohol can be used. In addition to these, a dihydric alcohol, a trihydric alcohol, a polyhydric alcohol, or a compound having an alcohol group may be used as the reducing agent.
If it is an organic acid, for example, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, Saturated fatty acids such as octadecanoic acid and nonanedecanoic acid can be used. In addition to these, unsaturated fatty acids may be used.

  The organometallic compound has an action of promoting the reduction reaction of silver oxide by an organic acid generated by thermal decomposition. Examples of the organometallic compound having such an action include carboxylic acid metal salts such as formic acid Ag, acetic acid Ag, propionic acid Ag, benzoic acid Ag, and oxalic acid Ag.

From the viewpoint of ensuring the storage stability and printability of the silver oxide paste, it is preferable to use a solvent having a high boiling point (150 ° C. to 300 ° C.).
Specifically, α-terpineol, 2-ethylhexyl acetate, 3-methylbutyl acetate, or the like can be used.

Next, the manufacturing method of the above-mentioned silver oxide paste is demonstrated with reference to the flowchart shown in FIG.
First, the above-mentioned silver oxide powder, reducing agent (solid), and organometallic compound powder are mixed to produce a solid component mixture (solid component mixing step S11).
Next, a solvent is added to the solid component mixture and stirred (stirring step S12).
Then, the agitated material is mixed while kneading using a roll mill (for example, a three-roll mill) (kneading step S13).
In this way, the aforementioned silver oxide paste is produced. In addition, it is preferable to preserve | save the obtained silver oxide paste at low temperature (for example, 5-15 degreeC) with a refrigerator.

Next, a case where the metal Ag layer is formed by a spin coating method will be described. In this method, an Ag fine particle dispersion containing Ag fine particles is used.
This metal Ag dispersion liquid contains Ag fine particles having a particle size of 20 nm or more and 200 nm or less, and a solvent having a boiling point of 50 ° C. or more and 200 ° C. or less.
Here, the content of Ag fine particles is set to 60% by mass to 95% by mass, and the content of the solvent having a boiling point of 50 ° C. to 200 ° C. is set to 5% by mass to 40% by mass.

  The solvent may be a combination of solvents having different boiling points. Specific examples of the solvent include alcohols such as methanol, ethanol, isopropyl alcohol, diacetone alcohol, 2-butoxyethanol, methylmethoxybutanol, and ethylene glycol, acetone, methyl ethyl ketone, ethyl acetate, pentyl acetate, isobutyl acetate, and cyclohexanone. , 2-ethoxyethyl acetate, methoxyacetic acid and the like.

Next, the manufacturing method of the power module 1 which is this embodiment is demonstrated with reference to the flowchart shown in FIG.
First, an aluminum plate to be the circuit layer 12 and an aluminum plate to be the metal layer 13 are prepared, and these aluminum plates are laminated on one surface and the other surface of the ceramic substrate 11 through brazing materials, respectively, and pressed. -The said aluminum plate and the ceramic substrate 11 are joined by cooling after a heating (circuit layer joining process S21). The brazing temperature is set to 640 ° C to 650 ° C.

  Next, the cooler 40 is joined to the other surface side of the metal layer 13 via a brazing material (cooler joining step S22). Note that the brazing temperature of the cooler 40 is set to 590 ° C to 610 ° C.

And a glass containing Ag paste is apply | coated to the surface of the circuit layer 12 (glass containing Ag paste application | coating process S23).
In addition, when apply | coating a glass containing Ag paste, various means, such as a screen printing method, an offset printing method, and a photosensitive process, are employable. In the present embodiment, the glass-containing Ag paste is formed on the portion of the circuit layer 12 where the semiconductor element 3 is mounted by screen printing.

Next, after drying in a state where the glass-containing Ag paste is applied to the surface of the circuit layer 12, the glass-containing Ag paste is baked by being placed in a heating furnace (first baking step S24). In addition, the firing temperature at this time is set to 350-645 degreeC.
By this first firing step S <b> 24, the first fired layer 31 including the glass layer 32 and the Ag layer 33 is formed on one surface of the circuit layer 12. At this time, the aluminum oxide film naturally generated on the surface of the circuit layer 12 is melted and removed by the glass layer 32, and the glass layer 32 is formed directly on the circuit layer 12.

In addition, fine conductive particles 34 having a particle size of about several nanometers are dispersed inside the glass layer 32. The conductive particles 34 are crystalline particles containing at least one of Ag or Al, and are presumed to have precipitated in the glass layer 32 during firing.
Further, fine glass particles 35 having a particle size of about several nanometers are dispersed inside the Ag layer 33. The glass particles 35 are presumed to be agglomerated residual glass components in the course of the sintering of the Ag particles.

On the other hand, an Au layer 39 is formed on the bonding surface of the semiconductor element 3 (Au layer forming step S31).
And the above-mentioned Ag fine particle dispersion is apply | coated to the surface of Au layer 39 with a spin coater, and a metal Ag film | membrane is formed (metal Ag film | membrane formation process S32).
Here, as a method for applying the Ag fine particle dispersion, spray coating method, dispenser coating method, spin coating method, knife coating method, slit coating method, ink jet coating method, screen printing method, offset printing method, die coating method, etc. Is mentioned. In addition, the Ag layer 39 may be formed by plating or sputtering.
Further, the coating thickness of the metal Ag film is preferably in the range of 15 nm to 2.5 μm. More preferably, it is 20 nm or more and 2 μm or less.

Next, a silver oxide paste is applied to the surface of the first fired layer 31 (silver oxide paste application step S25).
In addition, when apply | coating a silver oxide paste, various means, such as a screen printing method, an offset printing method, and a photosensitive process, are employable. In this embodiment, the silver oxide paste was printed by the screen printing method.

Next, after the silver oxide paste is applied and dried (for example, stored at room temperature in an air atmosphere for 24 hours), the semiconductor element 3 on which the Au layer 39 and the metal Ag film are formed is laminated on the silver oxide paste. (Semiconductor element stacking step S26).
Then, the semiconductor element 3 and the power module substrate 10 are stacked in a heating furnace, and the silver oxide paste is fired (second firing step S27). At this time, the load is set to 0 to 10 MPa, and the firing temperature is set to 150 to 400 ° C.
Desirably, the semiconductor element 3 and the power module substrate 10 can be bonded more reliably by heating them while being pressed in the stacking direction. In this case, the applied pressure is desirably 0.5 to 10 MPa.

  In this way, the second fired layer 36 is formed on the first fired layer 31, the metal Ag layer 38 is formed, and the semiconductor element 3 and the circuit layer 12 are joined. Thereby, the power module 1 which is this embodiment is manufactured.

  In the power module 1 according to the present embodiment configured as described above, a first fired layer 31 made of a fired body of a glass-containing Ag paste containing a glass component is formed on one surface of the circuit layer 12. Therefore, the oxide film formed on the surface of the circuit layer 12 by the glass component can be removed, and the bonding strength between the first fired layer 31 and the circuit layer 12 can be ensured.

In addition, since the second fired layer 36 made of a fired body of Ag with reduced silver oxide is formed on the first fired layer 31, the semiconductor element 3 is formed when the second fired layer 36 is formed. Can be joined. Here, when silver oxide is reduced, fine reduced Ag particles are generated, so that the fired body constituting the second fired layer 36 can have a dense structure.
Further, since the first fired layer 31 and the second fired layer 36 are laminated, the thickness of the bonding layer interposed between the circuit layer 12 and the semiconductor element 3 can be ensured. Therefore, it can suppress that the stress at the time of a heat cycle load acts on the semiconductor element 3, and damage to the semiconductor element 3 itself can be prevented.

And since the metal Ag layer 38 is formed between the 2nd baking layer 36 and the semiconductor element 3, the metal Ag layer 38 and the 2nd baking layer 36 will be joined by sintering of Ag. The semiconductor element 3 and the circuit layer 12 can be firmly bonded.
In the present embodiment, the metal Ag layer has a thickness of 15 nm to 2.5 μm. In this case, since the metal Ag layer is formed with a thickness of 15 nm or more, the second fired layer and the semiconductor element can be reliably bonded. On the other hand, since the thickness is 2.5 μm or less, the amount of silver in the metal Ag layer can be suppressed, and the metal Ag layer can be formed relatively inexpensively.

  The first fired layer 31 includes a glass layer 32 formed on one surface of the circuit layer 12 and an Ag layer 33 laminated on the glass layer 32. The Ag layer 33 includes: Since the glass particles are dispersed, the oxide film formed on the surface of the circuit layer 12 can be removed by reacting with the glass layer 32, and the circuit layer 12 and the semiconductor element 3 can be reliably bonded. it can.

  Further, since the second fired layer 36 is a fired body of a silver oxide paste containing silver oxide and a reducing agent, a structure in which fine Ag particles (reduced Ag particles) generated by reduction of silver oxide are fired. Thus, the second fired layer can be composed of a dense fired body. Further, since the reducing agent is decomposed when the silver oxide is reduced, it is difficult to remain in the second fired layer 36 and the conductivity in the second fired layer 36 can be ensured. Furthermore, since firing can be performed under a relatively low temperature condition such as 300 ° C., the junction temperature of the semiconductor element 3 can be kept low, and the thermal load on the semiconductor element 3 can be reduced.

Further, in the present embodiment, since the fine conductive particles 34 having a particle size of about several nanometers are dispersed inside the glass layer 32, conductivity can be ensured even in the glass layer 32. Specifically, in this embodiment, the electrical resistance value P in the thickness direction of the first fired layer 31 including the glass layer 32 is set to 0.5Ω or less.
Accordingly, it is possible to reliably conduct electricity between the semiconductor element 3 and the circuit layer 12 via the first fired layer 31 and the second fired layer 36, and the highly reliable power module 1 can be configured. it can.

In this embodiment, since the ceramic substrate 11 made of AlN (aluminum nitride) having excellent insulation and strength is used as the insulating layer, the reliability of the power module substrate 10 can be improved. Further, the circuit layer 12 can be easily formed by brazing an aluminum plate on the ceramic substrate 11.
Furthermore, in the present embodiment, the cooler 40 is disposed on the other side (lower side in FIG. 1) of the ceramic substrate 11 via the metal layer 13 and the buffer layer 15. It can prevent that the power module 1 becomes high temperature.

  Moreover, according to the manufacturing method of the power module 1 which is this embodiment, the glass-containing Ag paste containing a glass component is apply | coated to one surface of the circuit layer 12, and the 1st baking layer 31 is heat-processed. Since the oxide film formed on the surface of the circuit layer 12 can be removed, the circuit layer 12, the first fired layer 31, and the glass layer-containing Ag paste applying step S 23 and the first firing step S 24 are provided. Can be reliably joined.

  Further, a step of forming the Au layer 39 on the bonding surface of the semiconductor element 3 (Au layer forming step S31), a step of forming a metal Ag film on the surface of the Au layer 39 (metal Ag film forming step S32), 1 A step of applying a silver oxide paste containing silver oxide and a reducing agent on the fired layer 31 (silver oxide paste application step S25), and a step of laminating the semiconductor element 3 on the applied silver oxide paste ( Semiconductor element stacking step S26) and a step of heating the semiconductor element 3 and the power module substrate 10 in a stacked state to form the second fired layer 36 on the first fired layer 31 (second fired step S27). ), The second fired layer 36 is formed by firing the silver oxide paste, and the metal Ag layer 38 is formed between the second fired layer 36 and the semiconductor element 3. . Therefore, the metal Ag layer 38 and the second fired layer 36 are bonded by sintering of Ag, and the semiconductor element 3 and the circuit layer 12 can be bonded firmly.

  In the present embodiment, in the metal Ag film forming step S32, the metal Ag film is formed by applying an Ag fine particle dispersion containing Ag fine particles having a particle diameter of 20 nm or more and 200 nm or less. The fine Ag particles produced by reduction of silver (reduced Ag particles) have the same particle size as the Ag fine particles constituting the metal Ag film, and the metal Ag layer 38 and the silver oxide paste are reduced. 2 The fired layer 36 can be firmly bonded.

  Further, since the firing temperature in the second firing step S27 for forming the second fired layer 36 is set to 400 ° C. or less, the thermal load on the semiconductor element 3 at the time of bonding can be reduced. Further, since the firing temperature in the second firing step S27 is 150 ° C. or higher, the reducing agent and the like contained in the silver oxide paste can be removed, and the conductivity and strength in the second fired layer 36 are ensured. Can do.

  In addition, since the firing temperature in the first firing step S24 for forming the first fired layer 31 is 350 ° C. or higher, the first fired layer 31 can be reliably formed by firing the glass-containing Ag paste. Moreover, since the firing temperature in the first firing step S24 is 645 ° C. or lower, the deterioration of the circuit layer 12 and the ceramic substrate 11 can be prevented.

Moreover, in this embodiment, since the organometallic compound is added to the silver oxide paste, the reduction reaction of silver oxide is promoted by the organic acid generated by thermal decomposition of the organometallic compound. become.
Furthermore, since the reducing agent mixed with the silver oxide paste is a solid that is solid at room temperature, it is possible to prevent the reduction reaction from proceeding before firing.

  Further, since the viscosity of the silver oxide paste is adjusted to 10 Pa · s or more and 100 Pa · s or less, more preferably 30 Pa · s or more and 80 Pa · s or less, the oxidation for applying the silver oxide paste on the first fired layer 31 is performed. In the silver paste application step S25, a screen printing method or the like can be applied, and the second fired layer 36 can be selectively formed only on the portion where the semiconductor element 3 is disposed. Therefore, the amount of silver oxide paste used can be reduced, and the manufacturing cost of the power module 1 can be greatly reduced.

  Moreover, in this embodiment, since the glass containing Ag paste which comprises the 1st baking layer 31 contains Ag powder and glass powder, since the softening temperature of glass powder is set to 600 degrees C or less, The glass-containing Ag paste can be fired at a relatively low temperature. Specifically, the firing temperature in the first firing step S24 for forming the first fired layer 31 can be set to 350 ° C. or higher and 645 ° C. or lower. Therefore, it is possible to prevent problems such as deterioration of the circuit layer 12 and reduction in bonding strength between the circuit layer 12 and the ceramic substrate 11 due to the firing of the glass-containing Ag paste, and a high-quality power module 1 is produced. It becomes possible to do.

  Furthermore, since the viscosity of the glass-containing Ag paste is adjusted to 10 Pa · s or more and 500 Pa · s or less, more preferably 50 Pa · s or more and 300 Pa · s or less, the glass-containing Ag paste is applied to the surface of the circuit layer 12. In the Ag paste application step S23, a screen printing method or the like can be applied, and the first fired layer 31 can be selectively formed only on the portion where the semiconductor element 3 is disposed. Therefore, it becomes possible to reduce the usage-amount of glass containing Ag paste, and can reduce the manufacturing cost of this power module 1 significantly.

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, although 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%, it is not limited to this, and is composed of other aluminum or aluminum alloy. It may be. Further, the metal plate constituting the circuit layer and the metal layer may be made of pure copper or a copper alloy.

Moreover, although it demonstrated as what joins an aluminum plate and a ceramic substrate by brazing, it is not limited to this, Even if it applies a transient liquid phase bonding method (Transient Liquid Phase Bonding), a casting method, etc. Good.
Furthermore, when the metal plate constituting the circuit layer and the metal layer is made of copper or a copper alloy, when joining the metal plate made of copper or copper alloy to the ceramic substrate, the direct joining method (DBC method), the activity A metal method, a casting method, or the like can be applied.

Moreover, about the raw material of a glass containing Ag paste, and a compounding quantity, it is not limited to what was described in embodiment. For example, although it demonstrated as using lead-free glass powder, the glass containing lead may be sufficient.
Furthermore, the raw material and blending amount of the silver oxide paste are not limited to those described in the embodiment. For example, it may not contain an organometallic compound.
Further, the thickness of the glass layer 32 and the Ag layer 33 in the first fired layer 31 and the thickness of the second fired layer 36 are not limited to the present embodiment.

Further, it is described that uses a ceramic substrate made of AlN as an insulating layer, is not limited thereto, it may be used a ceramic substrate made of Si ₃ N ₄ or Al ₂ O _3, or the like, insulating The insulating layer may be made of resin.

  In addition, it has been described that the first fired layer is formed on the circuit layer after the aluminum plate to be the circuit layer is bonded to the ceramic substrate and the cooler is bonded. However, the present invention is not limited to this. The first fired layer may be formed before the plate is bonded to the ceramic substrate or before the cooler is bonded.

Moreover, although it 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 the cooler and the metal layer, this buffer layer is provided. It does not have to be.
Furthermore, although demonstrated as what comprised the top-plate part of the cooler with aluminum, you may be comprised with the composite material containing aluminum alloy or aluminum, etc., and may be comprised with another material. Furthermore, although it demonstrated as a cooler having the radiation fin and the flow path of a cooling medium, there is no limitation in particular in the structure of a cooler.

In addition to the silver oxide powder and the reducing agent, the silver oxide paste may contain fine Ag particles having a particle size of 20 nm to 800 nm. When the fine Ag particles are interposed between the silver oxide powders, the Ag obtained by reducing the silver oxide and the fine Ag particles are sintered, and the second fired layer has a more dense structure. Can do. Thereby, it becomes possible to set the pressurization pressure of the semiconductor element at the time of joining low.
Furthermore, the fine Ag particles may contain an organic substance. In this case, it is possible to improve the sinterability at a low temperature by using heat when the organic substance is decomposed.

  Moreover, it is good also as a structure by which the metal Ag particle | grains exceeding a particle size of 0.8 micrometer and 20 micrometers or less were disperse | distributed to the 2nd baking layer which consists of a baking body of a silver oxide paste. In this case, generation of large pores in the second fired layer can be suppressed.

  In the present embodiment, the metal Ag film is described as being formed by applying an Ag fine particle dispersion containing Ag fine particles having a particle diameter of 20 nm or more and 200 nm or less. However, the present invention is not limited to this. The Ag film may be formed by a plating method or a sputtering method. In addition, when forming a metal Ag film | membrane by the plating method, it is preferable that the film thickness shall be 0.5 micrometer or more and 2.5 micrometers or less. Moreover, when forming a metal Ag film | membrane by sputtering method, it is preferable that the film thickness shall be 15 nm or more and 30 nm or less.

  Below, the result of the confirmation experiment performed in order to confirm the effect of this invention is demonstrated.

(Example)
As an example, the power module 1 described in the above embodiment was prepared. That is, the first fired layer 31 made of a fired body of glass-containing Ag paste is formed on the circuit layer 12 made of an aluminum plate having a purity of 99.99% or more, and the Au layer 39 is formed on the bonding surface of the semiconductor element 3. Then, a metal Ag film was formed on the surface of the Au layer 39. Then, a second fired layer 36 made of a fired body of silver oxide paste was formed on the first fired layer 31 to join the semiconductor element 3.

The ceramic substrate 11 is made of AlN and has a size of 27 mm × 17 mm and a thickness of 0.6 mm.
The circuit layer 12 and the metal layer 13 are made of 4N aluminum, and have a size of 25 mm × 15 mm and a thickness of 0.6 mm.
The semiconductor element 3 was an IGBT element having a size of 13 mm × 10 mm and a thickness of 0.25 mm.

At this time, as the glass powder of the glass-containing Ag paste, a lead-free glass powder containing 90.6% by mass of Bi ₂ O ₃ , 2.6% by mass of ZnO and 6.8% by mass of B ₂ O ₃ was used. . Further, ethyl cellulose was used as the resin, and diethylene glycol dibutyl ether was used as the solvent. Furthermore, a dicarboxylic acid-based dispersant was added.

  The silver oxide paste is a commercially available silver oxide powder (manufactured by Wako Pure Chemical Industries, Ltd.), myristyl alcohol as a reducing agent, and 2,2,4-trimethyl-1,3-pentanediol mono (2-methylproparate) as a solvent. Noate), and silver oxide powder; 80% by mass, reducing agent (myristyl alcohol); 10% by mass, solvent (2,2,4-trimethyl-1,3-pentanediol mono (2-methylpropaline) Nooate)); the silver oxide paste mixed in the ratio of the remainder.

In addition, in the glass containing Ag paste application | coating process S23 which apply | coats a glass containing Ag paste on the surface of the circuit layer 12, the application | coating thickness of the glass containing Ag paste was 10 micrometers. In the first firing step S24, the firing temperature was 575 ° C. and the firing time was 10 minutes.
In addition, in the silver oxide paste application step S25 in which the silver oxide paste is applied on the first fired layer 31, the coating thickness of the silver oxide paste was set to 50 μm. In the second firing step S27, the firing temperature was set to 300 ° C., and the joining time was set to the time shown in Table 1.

And the conditions of metal Ag film formation process S32 were changed.
In Example 1-12, a metal Ag film was formed by spin coating. The spin coating has a thickness described in Table 1 by dropping an Ag fine particle dispersion liquid in which Ag fine particles having a particle diameter of 20 nm are dispersed in an ethylene glycol solvent by dropping the Ag fine particle dispersion liquid a plurality of times using a spin coater. A metal Ag film was formed.
In Examples 13-19, a metal Ag film having the thickness shown in Table 1 was formed by a plating method. Silver plating formed the metal Ag film | membrane which has the thickness of Table 1 by the electrolytic plating method using the silver cyanide plating bath.

In Examples 20-22, a metal Ag film having the thickness shown in Table 1 was formed by sputtering. A metal Ag film having a thickness shown in Table 1 was formed using an RF magnetron sputtering apparatus using a silver target having a purity of 99.9% by mass.

(Comparative example)
As Comparative Example 1-4, a power module was manufactured under the same conditions as in the example except that the metal Ag layer was not formed on the back surface of the element.

(SEM observation)
First, in the power module of Example 8, the result of SEM observation of the bonding interface between the circuit layer and the semiconductor element is shown in FIGS. In this case, a metal Ag layer 38 is observed between the second fired layer 36 and the Au layer 39. As shown in FIGS. 7 and 8, there are large pores in the second fired layer 36 made of a fired body of silver oxide paste, and the first fired layer 31, the second fired layer 36, and the second fired layer 36 are secondly fired. It is possible to distinguish between the fired layer 36 and the metal Ag layer 38.
Next, in the power module of Comparative Example 1 in which the metal Ag film was not formed, the result of SEM observation of the bonding interface between the circuit layer and the semiconductor element is shown in FIGS. In this case, the metal Ag layer 38 is not recognized between the second fired layer 36 and the Au layer 39.

(Evaluation)
Next, a thermal cycle test and a power cycle test were carried out using the power modules of the examples, conventional examples, and comparative examples, and the initial joining rate, the rate of increase in thermal resistance after the thermal cycle test, and the power cycle test. Later, the rate of increase in thermal resistance was evaluated.
The joining rate was evaluated using an ultrasonic flaw detector and calculated from the following equation. Here, the initial bonding area is an area to be bonded before bonding, that is, a semiconductor element area. In the ultrasonic flaw detection image, peeling is indicated by a white portion in the joint, and thus the area of the white portion was taken as the peeling area.
Bonding rate = (initial bonding area-peeling area) / initial bonding area

  The thermal resistance was measured as follows. The IGBT element was heated with a power of 100 W, and the temperature of the IGBT element was measured using a thermocouple. Further, the temperature of the cooling medium (ethylene glycol: water = 9: 1) flowing through the heat sink was measured. And the value which divided the temperature difference of the IGBT element and the temperature of a cooling medium by electric power was made into thermal resistance.

The thermal cycle test is performed by applying a thermal cycle of −40 ° C. ← → 110 ° C. to the test piece. In this example, this thermal cycle was performed 3000 times.
In the power cycle test, the IGBT element was repeatedly subjected to an energization time of 2 seconds and a cooling time of 8 seconds under an energization condition of 15 V and 150 A, and the temperature of the IGBT element was changed in the range of 30 ° C to 130 ° C. In this example, this power cycle was performed 200,000 times.
After this thermal cycle test, the rate of increase in thermal resistance was measured. Further, after the power cycle test, the rate of increase in thermal resistance was measured.
The evaluation results are shown in Table 1.

In Examples 1 to 12 in which the metal Ag layer was formed by the spin coating method, good results were obtained in the bonding rate, the thermal cycle test, and the power cycle test. In Examples 13 to 17 formed by plating, good results were obtained in the joining rate, thermal cycle test, and power cycle test. In Examples 18 and 19, although the joining rate was slightly lower, it was in a practically acceptable range. Furthermore, in Examples 20 to 22 formed by the sputtering method, good results were obtained in the joining rate, the thermal cycle test, and the power cycle test.
On the other hand, in Comparative Examples 1 to 4 in which the metal Ag layer was not formed, since the bonding was performed in a short time, the bonding property was insufficient, and in the thermal cycle test and the power cycle test, the results were inferior to the examples. .

1 Power Module 3 Semiconductor Element 10 Power Module Substrate 11 Ceramic Substrate 12 Circuit Layer 31 First Firing Layer 32 Glass Layer 33 Ag Layer 34 Conductive Particles 35 Glass Particles 36 Second Firing Layer 38 Metal Ag Layer 39 Au Layer

Claims (8)

A power module comprising: a power module substrate having a circuit layer disposed on one surface of an insulating layer; and a semiconductor element mounted on the circuit layer,
A first fired layer made of a fired body of a glass-containing Ag paste containing a glass component is formed on one surface of the circuit layer,
On this 1st baking layer, the 2nd baking layer which consists of a baking body of Ag by which silver oxide was reduced is formed,
A metal Ag layer and an Au layer are formed between the second fired layer and the semiconductor element, the Au layer is formed on the bonding surface of the semiconductor element, and the Au layer, the second fired layer, The power module is characterized in that the metal Ag layer is formed therebetween, and the Au layer and the metal Ag layer are interdiffused .   The power module according to claim 1, wherein a thickness of the metal Ag layer is 15 nm or more and 2.5 μm or less. The first fired layer includes a glass layer formed on one surface of the circuit layer, and an Ag layer laminated on the glass layer,
The power module according to claim 1, wherein glass particles are dispersed in the Ag layer.   The power module according to any one of claims 1 to 3, wherein the second fired layer is a fired body of a silver oxide paste containing silver oxide and a reducing agent.   The power module according to claim 4, wherein the silver oxide paste contains Ag particles in addition to the silver oxide and the reducing agent. A power module manufacturing method comprising: a power module substrate having a circuit layer disposed on one surface of an insulating layer; and a semiconductor element mounted on the circuit layer,
Applying a glass-containing Ag paste containing a glass component to one surface of the circuit layer and heat-treating it, thereby forming a first fired layer;
Applying a silver oxide paste containing silver oxide and a reducing agent on the first fired layer;
Forming an Au layer on the bonding surface of the semiconductor element;
Forming a metal Ag film on the surface of the Au layer ;
Laminating a semiconductor element on which a metal Ag film is formed on the applied silver oxide paste;
Heating the semiconductor element and the power module substrate in a stacked state to form a second fired layer on the first fired layer and forming a metal Ag layer,
A method of manufacturing a power module, comprising bonding the semiconductor element and the circuit layer.   7. The method of manufacturing a power module according to claim 6, wherein, in the step of forming the metal Ag film on the bonding surface of the semiconductor element, the metal Ag film having a thickness of 15 nm to 2.5 μm is formed. .   The method for manufacturing a power module according to claim 6 or 7, wherein the silver oxide paste contains Ag particles in addition to the silver oxide and the reducing agent.