JP7492256B2 - Joint structure and manufacturing method thereof - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies ▲1▼ Date: February 4, 2020 Meeting name and location: Osaka University New Technology Briefing JST Tokyo Headquarters Annex 1F Hall (7-5-chome, Chiyoda-ku, Tokyo) Published by: Chen Chuan

The present invention relates to a bonded structure in which a substrate and a semiconductor element are bonded, and a method for manufacturing the same.

A bonded structure (hereinafter sometimes simply referred to as a "bonded structure") in which a substrate and a semiconductor element are bonded is known. In order to increase the bonding strength between the substrate and the semiconductor element (hereinafter sometimes simply referred to as the "bonding strength"), a bonded structure may be manufactured using a semiconductor element having a metal layer (hereinafter sometimes referred to as a "metallized layer") on the surface layer on the bonding surface side.

For example, Patent Document 1 describes a bonded structure (semiconductor device) in which a semiconductor element having a nickel layer as a metallization layer is used to bond a substrate and a semiconductor element.

JP 2010-73908 A

However, when manufacturing the joint structure described in Patent Document 1, it is necessary to provide a process for forming a metallized layer, making it difficult to reduce manufacturing costs.

The present invention was made in consideration of the above problems, and its purpose is to provide a joint structure and a manufacturing method thereof that can reduce manufacturing costs while ensuring high joint strength.

The bonded structure according to the present invention comprises a substrate, a semiconductor element, and a bonding layer that bonds the substrate and the semiconductor element. The semiconductor element does not have a metallized layer for bonding to the substrate. The bonding layer includes a porous silver sintered body and silver nanoparticles having a number-average primary particle diameter of 1 nm or more and 20 nm or less. At least a portion of the silver nanoparticles are present between the porous silver sintered body and the semiconductor element.

In one embodiment, the substrate is a semiconductor element separate from the semiconductor element.

The method for manufacturing a bonded structure according to the present invention is a method for manufacturing a bonded structure including a substrate, a semiconductor element, and a bonding layer that bonds the substrate and the semiconductor element. The method for manufacturing a bonded structure according to the present invention includes at least a bonding step of bonding the substrate and the semiconductor element using a silver paste. The semiconductor element does not have a metallized layer for bonding to the substrate. The silver paste includes silver particles having a residual strain of 5.0% or more as measured using an X-ray diffraction method, and a solvent.

In one embodiment, the 50% cumulative diameter of the silver particles on a volume basis is 100 nm or more and 50 μm or less.

In one embodiment, the content of the silver particles in the silver paste is 85% by mass or more and 95% by mass or less with respect to the total mass of the silver paste.

In one embodiment, the silver particles have a residual strain of 20.0% or less as measured using X-ray diffraction.

In one embodiment, the silver particles are flake silver particles.

In one embodiment, the bonding process includes a coating process of coating the silver paste onto the substrate, a laminate formation process of overlapping the substrate and the semiconductor element with the silver paste interposed therebetween to form a laminate, and a heating process of heating the laminate.

In one embodiment, the laminate is heated without applying pressure during the heating step.

In one embodiment, the laminate is heated at a temperature of 150°C or higher and 350°C or lower in the heating step.

The present invention provides a joint structure and a manufacturing method thereof that can reduce manufacturing costs and ensure high joint strength.

1 is a cross-sectional view showing an example of a joint structure according to a first embodiment of the present invention. 2 is a partial cross-sectional view showing an example of a joint portion of the joint structure according to the first embodiment of the present invention. FIG. 10A, 10B, and 10C are cross-sectional views illustrating steps in an example of a method for manufacturing a joint structure according to a second embodiment of the present invention. 1 is a scanning electron microscope photograph showing an example of flaky silver particles. 1 is a scanning electron microscope photograph showing an example of spherical silver particles. 1 is a transmission electron microscope photograph showing an example of flaky silver particles. 1 is a scanning electron microscope photograph showing a cross section of a joint of the joint structure of Example 1. 8 is a scanning electron microscope photograph showing an enlarged view of a joint between a semiconductor element and a porous silver sintered body in the cross section shown in FIG. 7. 1 is a transmission electron microscope photograph showing a cross section of a joint of the joint structure of Example 1. 1 is a scanning electron microscope photograph of a semiconductor element taken from the bonded portion side after measuring the shear strength of the bonded structure of Example 1.

The following describes preferred embodiments of the present invention. However, the present invention is not limited to the following embodiments, and can be implemented in various forms without departing from the spirit of the invention. Note that where explanations overlap, they may be omitted as appropriate.

First, the terms used in this specification will be explained. "Flake-shaped silver particles" are silver particles having a shape other than spherical, such as flat-shaped (more specifically, leaf-shaped, scale-shaped, etc.). Note that "spherical" includes both true spheres and spheres other than true spheres (more specifically, oblate spheres, etc.).

"Porous silver sintered body" refers to a porous sintered body obtained by sintering an aggregate of silver particles at a temperature lower than the melting point of the silver particles.

The "50% cumulative diameter on a volume basis" is a particle diameter at which the cumulative frequency from the small particle size side in the volume-based particle size distribution (volume particle size distribution) is 50%. Hereinafter, the 50% cumulative diameter on a volume basis may be referred to as the "volume median diameter (D ₅₀ )". Unless otherwise specified, the measured value of the volume median diameter (D ₅₀ ) of a particle (specifically, a powder of particles) is the median diameter measured using a zeta potential/particle size measurement system (ELSZ-1000ZS manufactured by Otsuka Electronics Co., Ltd.). Unless otherwise specified, the measured value of the number-average primary particle diameter of a particle is the number-average value of the cross-sectional circle equivalent diameter (the diameter of a circle having the same area as the cross-sectional area of a primary particle) of 100 primary particles measured using a transmission electron microscope (JEM-2100 manufactured by JEOL Ltd., accelerating voltage: 200 kV).

Unless otherwise specified, the "major component" of a material means the component that is present in the largest amount in that material by mass.

Hereinafter, the residual strain measured using the X-ray diffraction method may be referred to simply as "residual strain." In addition, in this specification, both the solvent and the dispersion medium are referred to as "solvent."

<First embodiment: joint structure>
Hereinafter, a joint structure according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a joint structure according to the first embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing an example of a joint portion of the joint structure according to the first embodiment of the present invention. Note that the drawings shown are mainly schematic views of each component for ease of understanding, and the size, number, shape, etc. of each illustrated component may differ from the actual ones for convenience of drawing creation.

The bonded structure 10 shown in FIG. 1 includes a substrate 11, a semiconductor element 12, and a bonding layer 13 that bonds the substrate 11 and the semiconductor element 12. The semiconductor element 12 does not have a metallized layer for bonding to the substrate 11. Therefore, when manufacturing the bonded structure 10, a process for forming a metallized layer on the semiconductor element 12 is not required, and the bonded structure 10 is a bonded structure that can reduce manufacturing costs.

As shown in FIG. 2, the bonding layer 13 includes a porous silver sintered body 14 and a plurality of silver nanoparticles 15. The number-average primary particle diameter of the silver nanoparticles 15 is 1 nm or more and 20 nm or less. In addition, at least a portion of the silver nanoparticles 15 is present between the porous silver sintered body 14 and the semiconductor element 12.

The reason why the bonded structure 10 can ensure high bonding strength is presumed to be as follows. Since the silver nanoparticles 15 have a relatively high surface free energy, they function as an adhesive between the porous silver sintered body 14 and the semiconductor element 12 to bond the porous silver sintered body 14 and the semiconductor element 12. This increases the bonding strength between the bonding layer 13 and the semiconductor element 12. Therefore, the bonded structure 10 can ensure high bonding strength.

In order to further reduce the manufacturing cost of the bonded structure 10, it is preferable that the substrate 11 does not have a metallized layer for bonding to the semiconductor element 12. In this case, it is preferable that some of the silver nanoparticles 15 are present between the porous silver sintered body 14 and the substrate 11. When some of the silver nanoparticles 15 are present between the porous silver sintered body 14 and the substrate 11, the bonding strength between the bonding layer 13 and the substrate 11 can be increased even if the substrate 11 does not have a metallized layer.

In order to ensure a higher bonding strength, the number average primary particle diameter of the silver nanoparticles 15 is preferably 1 nm or more and 10 nm or less, and more preferably 3 nm or more and 8 nm or less. The number average primary particle diameter of the silver nanoparticles 15 can be adjusted, for example, by changing the volume median diameter ( _D50 ) of the specific silver particles described later.

Examples of the semiconductor element 12 include a semiconductor element containing silicon as a main component (hereinafter sometimes referred to as a Si semiconductor element), a semiconductor element containing gallium nitride as a main component (hereinafter sometimes referred to as a GaN semiconductor element), a semiconductor element containing silicon carbide as a main component (hereinafter sometimes referred to as a SiC semiconductor element), a semiconductor element containing silicon nitride as a main component, and a semiconductor element containing aluminum nitride (aluminum nitride) as a main component. An oxide layer may be formed on the surface of the semiconductor element 12.

In order to ensure a higher bonding strength, the area of the semiconductor element 12 is preferably 0.1 mm ² or more and 1000 mm ² or less, and more preferably 1 mm ² or more and 100 mm ² or less.

To ensure higher bonding strength, the thickness of the semiconductor element 12 is preferably 0.1 mm or more and 100 mm or less, and more preferably 0.1 mm or more and 1 mm or less.

The material of the substrate 11 is not particularly limited. The area of the substrate 11 is also not particularly limited, as long as an area for bonding the semiconductor element 12 can be secured. The thickness of the substrate 11 is, for example, 0.1 mm or more and 1000 mm or less. Examples of the substrate 11 include a substrate (mounting substrate) for mounting the semiconductor element 12, a ceramic plate, a glass plate, and a flexible substrate.

Examples of mounting substrates that can be used as the substrate 11 include ceramic substrates with aluminum circuits (more specifically, DBA (registered trademark) substrates), ceramic substrates with copper circuits (more specifically, DBC substrates), and flexible substrates. When a flexible substrate is used as the mounting substrate, examples of flexible substrates for forming the flexible substrate include polyimide films, polyethylene terephthalate films, and polyethylene naphthalate films.

Examples of ceramic plates that can be used as the substrate 11 include aluminum nitride plates, alumina plates, and zirconia plates.

Flexible substrates that can be used as substrate 11 include, for example, the substrates exemplified as flexible substrates for forming the flexible substrate described above.

The substrate 11 may also be a semiconductor element (hereinafter, sometimes referred to as a second semiconductor element) different from the semiconductor element 12. When the substrate 11 is the second semiconductor element, the joint structure 10 has a so-called chip-on-chip structure. Therefore, when the substrate 11 is the second semiconductor element, it is possible to increase the density of the mounting structure (a structure on which electronic components are mounted) formed using the joint structure 10.

The second semiconductor element may be the same type of semiconductor element as the semiconductor element 12, or may be a different type of semiconductor element from the semiconductor element 12. Examples of the second semiconductor element include the semiconductor elements exemplified as the semiconductor element 12 described above. Furthermore, the dimensions of the second semiconductor element may be the same as or different from the dimensions of the semiconductor element 12.

The above describes the bonded structure according to the first embodiment of the present invention, but the bonded structure of the present invention is not limited to the above-mentioned first embodiment. For example, the bonded structure of the present invention may be a bonded structure in which three or more semiconductor elements are bonded via a bonding layer.

Second embodiment: manufacturing method of bonded structure
Hereinafter, a method for manufacturing a joint structure according to a second embodiment of the present invention will be described with reference to the drawings. The method for manufacturing a joint structure according to the second embodiment is, for example, a suitable method for manufacturing the joint structure according to the first embodiment described above. Hereinafter, description of contents that overlap with the first embodiment described above may be omitted. Note that the drawings referred to are mainly schematic illustrations of each component for ease of understanding, and the size, number, shape, etc. of each illustrated component may differ from the actual ones due to the convenience of drawing.

First, an overview of the method for manufacturing a bonded structure according to the second embodiment will be described with reference to FIGS. 3(a) to (c). FIGS. 3(a) to (c) are cross-sectional views showing an example of a method for manufacturing a bonded structure according to the second embodiment, one step at a time. The method for manufacturing a bonded structure according to the second embodiment includes a bonding step of bonding a substrate 11 (see FIG. 3(a)) and a semiconductor element 12 (see FIG. 3(b)) using silver paste. In the second embodiment, the bonding step includes a coating step, a laminate formation step, and a heating step. Note that in FIGS. 3(a) to (c), components that are the same as those shown in FIG. 1 are denoted by the same reference numerals as in FIG. 1.

In the coating process, as shown in FIG. 3(a), silver paste is coated onto the substrate 11 to form a coating film 20 made of silver paste. The silver paste to be coated onto the substrate 11 contains silver particles having a residual strain of 5.0% or more as measured using X-ray diffraction, and a solvent. The method for measuring the residual strain of the silver particles is the same as or similar to the method described in the examples below. Hereinafter, silver particles having a residual strain of 5.0% or more as measured using X-ray diffraction may be referred to as specific silver particles.

After the coating step and before the laminate formation step, a step of heating the coating film 20 may be performed to remove at least a portion of the solvent in the coating film 20.

In the laminate formation process, as shown in FIG. 3(b), the substrate 11 and the semiconductor element 12 are laminated together via a coating film 20 made of silver paste to form a laminate 40.

In the heating step, the laminate 40 obtained in the laminate formation step is heated. By heating the laminate 40, the specific silver particles in the coating film 20 (see FIG. 3(b)) are sintered together, forming a bonding layer 13 (see FIG. 3(c)) that bonds the substrate 11 and the semiconductor element 12. This results in the bonded structure 10 shown in FIG. 3(c).

Next, each step of the manufacturing method for the joint structure according to the second embodiment will be described in detail.

[Coating process]
The silver paste used in the coating step contains specific silver particles and a solvent. The volume median diameter ( _D50 ) of the specific silver particles is preferably 100 nm or more and 50 μm or less, more preferably 1.0 μm or more and 10.0 μm or less, and even more preferably 1.0 μm or more and 5.0 μm or less. When the volume median diameter ( _D50 ) of the specific silver particles is 100 nm or more, the residual strain of the specific silver particles can be easily adjusted to a range of 5.0% or more. In addition, when the volume median diameter ( _D50 ) of the specific silver particles is 50 μm or less, the bonding strength can be further increased.

When applying the silver paste to the substrate 11 by the printing method, in order to easily form the coating film 20 on the substrate 11, the content of the specific silver particles in the silver paste is preferably 85% by mass or more and 95% by mass or less, and more preferably 90% by mass or more and 95% by mass or less, relative to the total mass of the silver paste. The silver paste may contain silver particles other than the specific silver particles. However, in order to further increase the bonding strength, the content of the specific silver particles in the silver paste is preferably 50% by mass or more, more preferably 80% by mass or more, and particularly preferably 100% by mass, relative to the total mass of the silver particles in the silver paste.

To further increase the bonding strength, the residual strain of the specific silver particles is preferably 10.0% or more. Furthermore, to stably maintain the crystal structure of the specific silver particles in the silver paste, the residual strain of the specific silver particles is preferably 20.0% or less, and more preferably 15.0% or less.

In order to further increase the bonding strength, it is preferable that the residual strain of the specific silver particles is 10.0% or more and 15.0% or less and that the volume median diameter ( _D50 ) of the specific silver particles is 1.0 μm or more and 5.0 μm or less, and it is more preferable that the residual strain of the specific silver particles is 11.0% or more and 14.0% or less and that the volume median diameter ( _D50 ) of the specific silver particles is 2.0 μm or more and 4.0 μm or less.

The specific silver particles include, for example, flake-shaped silver particles. Flake-shaped silver particles having residual strain can be obtained, for example, by reducing a silver compound (more specifically, a silver salt, etc.) with a reducing agent to obtain spherical silver particles, which are then stirred in a stirring device (more specifically, a ball mill, etc.). The residual strain and volume median diameter ( _D50 ) of the flake-shaped silver particles can each be adjusted by, for example, changing the stirring conditions (more specifically, stirring speed, stirring time, etc.) when stirring with the stirring device.

Examples of the solvent contained in the silver paste include a solvent having an ether bond (hereinafter, sometimes referred to as an ether-based solvent) and alcohol. Examples of the ether-based solvent include ether and glycol ether. As the solvent contained in the silver paste, one type of solvent may be used alone, or two or more types of solvents may be used in combination.

When ether is used as a solvent for the silver paste, examples of ethers that can be used include diisopropyl ether, tetrahydrofuran, and 1,4-dioxane.

When glycol ether is used as the solvent for the silver paste, examples of glycol ethers that can be used include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, diethylene glycol monohexyl ether, and diethylene glycol mono 2-ethylhexyl ether.

When alcohol is used as a solvent for the silver paste, examples of alcohol that can be used include 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, 1-pentanol, 1-octanol, and 2-octanol.

The silver paste used in the coating process may further contain components (other components) other than the specific silver particles and the solvent. Examples of other components include a dispersant for increasing the dispersibility of the specific silver particles in the silver paste.

The method of applying the silver paste onto the substrate 11 is not particularly limited, but examples thereof include a printing method and a potting method. In order to easily form the coating film 20 on the substrate 11, a printing method (more specifically, a screen printing method, etc.) is preferred as a method of applying the silver paste onto the substrate 11.

[Laminate formation process]
The semiconductor element 12 used in the laminate formation step does not have a metallized layer for bonding to the substrate 11. In the method for manufacturing a bonded structure according to the second embodiment, the step of forming a metallized layer on the semiconductor element 12 is not required, and therefore, according to the method for manufacturing a bonded structure according to the second embodiment, it is possible to reduce manufacturing costs.

[Heating process]
Examples of the method for heating the laminate 40 in the heating step include a method for heating the laminate 40 with a hot plate and a method for heating the laminate 40 in a heating furnace.

The heating temperature when heating the laminate 40 is not particularly limited as long as it is a temperature at which the specific silver particles in the coating film 20 sinter together, and is, for example, 100°C or higher and 400°C or lower. In order to further increase the bonding strength, the heating temperature when heating the laminate 40 is preferably 150°C or higher and 350°C or lower. The heating rate until the heating temperature is reached is, for example, 10°C/min or higher and 20°C/min or lower. In order to further increase the bonding strength, the heating time when heating the laminate 40 (the time to maintain the heating temperature) is preferably 15 minutes or higher and 5 hours or lower, and more preferably 30 minutes or higher and 3 hours or lower.

The heating of the laminate 40 may be performed under atmospheric pressure or under reduced pressure. The heating of the laminate 40 may also be performed in air or in an inert gas (more specifically, argon gas, nitrogen gas, etc.) atmosphere.

In the heating step, the laminate 40 may be heated without applying pressure, or the laminate 40 may be heated while applying pressure to the laminate 40. In order to suppress damage to the semiconductor element 12, it is preferable to heat the laminate 40 without applying pressure in the heating step. In the second embodiment, the substrate 11 and the semiconductor element 12 are bonded using a silver paste containing specific silver particles, so that the bonding strength between the substrate 11 and the semiconductor element 12 can be increased without applying pressure to the laminate 40 in the heating step.

The thickness of the bonding layer 13 obtained by sintering the specific silver particles in the coating film 20 in the heating process is, for example, 1 μm or more and 100 μm or less. The thickness of the bonding layer 13 can be adjusted, for example, by changing the content of the specific silver particles in the silver paste used in the coating process.

Furthermore, the manufacturing method for the joint structure according to the second embodiment ensures high joint strength. The reason for this is presumed to be as follows.

In the second embodiment, the residual strain of the specific silver particles in the coating film 20 is relaxed during the heating process. When the residual strain of the specific silver particles is relaxed, minute silver nanoparticles 15 (see FIG. 2) are generated from dislocation sites (crystal defect sites) in the crystals of the specific silver particles.

The silver nanoparticles 15 generated from the dislocation sites of the specific silver particles will be described below with reference to FIG. 2. The number-average primary particle diameter of the silver nanoparticles 15 is, for example, 1 nm or more and 20 nm or less, preferably 1 nm or more and 10 nm or less, and more preferably 3 nm or more and 8 nm or less. At least a part of the silver nanoparticles 15 is present between the porous silver sintered body 14 and the semiconductor element 12. The generated silver nanoparticles 15 have a higher surface free energy than the specific silver particles, and therefore function as an adhesive between the porous silver sintered body 14 and the semiconductor element 12 to bond the porous silver sintered body 14 and the semiconductor element 12. This makes it possible to increase the bonding strength between the bonding layer 13 and the semiconductor element 12. Therefore, according to the manufacturing method of the bonded structure according to the second embodiment, a high bonding strength can be ensured.

The bonding layer 13 may contain, for example, silver oxide (not shown). Silver oxide is generated, for example, from dislocations in the crystals of the specific silver particles when the residual strain in the specific silver particles is relaxed.

Some of the silver nanoparticles 15 generated from the specific silver particles may be integrated with the porous silver sintered body 14 during the heating process.

To further increase the bonding strength, it is preferable that the region in which the silver nanoparticles 15 are present between the porous silver sintered body 14 and the semiconductor element 12 is a region in which only silver nanoparticles 15 are present, or a region in which only silver nanoparticles 15 and silver oxide (not shown) are present.

The manufacturing method for the joint structure according to the second embodiment has been described above, but the manufacturing method for the joint structure according to the present invention is not limited to the second embodiment described above.

For example, as described with reference to Figures 3(a) to (c), in the method for manufacturing a bonded structure according to the second embodiment, the bonding step includes a coating step, a laminate formation step, and a heating step, but in the method for manufacturing a bonded structure according to the present invention, the bonding step is not particularly limited as long as the semiconductor element and the substrate are bonded using the specific silver paste described above.

The manufacturing method of the bonded structure of the present invention may also include a process (other process) other than the bonding process. An example of the other process is a process of electrically connecting the semiconductor element and the substrate.

The following describes examples of the present invention, but the present invention is not limited to the scope of the examples. All scanning electron microscope (SEM) photographs were taken using an SEM ("SU8020" manufactured by Hitachi High-Technologies Corporation) at an acceleration voltage of 5 kV. All transmission electron microscope (TEM) photographs were taken using a TEM ("JEM-2100" manufactured by JEOL Ltd.) at an acceleration voltage of 200 kV.

The residual strain of silver particles (more specifically, either flaky silver particles FP or spherical silver particles SP, described below) was determined by obtaining the interplanar spacing of the crystal lattice of the silver particles (powder) using X-ray diffraction, and then calculating the obtained interplanar spacing of the crystal lattice. Details of the method for measuring the residual strain of silver particles are given below.

<Method for measuring residual strain in silver particles>
First, the X-ray diffraction spectrum of a silver particle powder (sample) was measured under the measurement conditions shown below using a curved IP X-ray diffractometer (RINT (registered trademark) RAPID II manufactured by Rigaku Corporation).
Characteristic X-rays: Cu-Kα rays (λ=1.5418 Å)
Tube voltage: 40 kV
Tube current: 30mA
Measurement range (2θ): 0° to 160° Scanning speed: 1°/sec

Next, based on the obtained X-ray diffraction spectrum, the interplanar spacings of the (111), (200), and (220) planes of the crystal lattice of the sample were calculated using integrated powder X-ray analysis software (PDXL Ver. 2.0, manufactured by Rigaku Corporation). Hereinafter, the interplanar spacing of the (111) plane obtained is referred to as d1, the interplanar spacing of the (200) plane obtained is referred to as d2, and the interplanar spacing of the (220) plane obtained is referred to as d3.

Next, the residual strain ε1 (unit: %) was calculated based on d1 and the interplanar spacing of the (111) plane of the silver crystal without residual strain (hereinafter referred to as d1 ₀ ) according to the following formula (1). The residual strain ε2 (unit: %) was calculated based on d2 and the interplanar spacing of the (200) plane of the silver crystal without residual strain (hereinafter referred to as d2 ₀ ) according to the following formula (2). The residual strain ε3 (unit: %) was calculated based on d3 and the interplanar spacing of the (220) plane of the silver crystal without residual strain (hereinafter referred to as d3 ₀ ) according to the following formula (3).
Residual strain ε1 = 100 × (d1 - d1 ₀ ) / d1 ₀ ... (1)
Residual strain ε2 = 100 × (d2 - d2 ₀ ) / d2 ₀ ... (2)
Residual strain ε3 = 100 × (d3 - d3 ₀ ) / d3 ₀ ... (3)

Then, the average value of residual strain ε1, residual strain ε2, and residual strain ε3 was calculated using the formula "(residual strain ε1 + residual strain ε2 + residual strain ε3)/3", and the obtained average value was taken as the residual strain of the sample (unit: %).

<Preparation of silver particles>
As the silver particles to be used in the silver paste described below, flake silver particles FP ("Silcoat (registered trademark) AgC-239" manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume median diameter (D ₅₀ ): 3.0 μm, residual strain: 12.5%) and spherical silver particles SP ("S211A-10" manufactured by Daiken Chemical Co., Ltd., volume median diameter (D ₅₀ ): 320 nm, residual strain: 0%) were prepared. FIG. 4 shows an SEM photograph of the flake silver particles FP. FIG. 5 shows an SEM photograph of the spherical silver particles SP. The volume median diameter (D ₅₀ ) and residual strain of the flake silver particles FP were both measured using a powder of flake silver particles FP obtained by removing the solvent from the silver paste used to prepare a joined structure SA-1 described below, and the same results were obtained. Similarly, the volume median diameter (D ₅₀ ) and residual strain of the spherical silver particles SP were both measured with the powder of spherical silver particles SP obtained by removing the solvent from the silver paste used to prepare the bonded structure SB-1 described below, and the same results were obtained.

Flake-shaped silver particles FP were also observed using a TEM. Figure 6 shows a TEM photograph of flake-shaped silver particles FP. As shown in Figure 6, the flake-shaped silver particles FP had dislocation sites (dislocation lines DL).

<Preparation of bonded structure>
Next, the manufacturing method of the bonded structure of Examples 1 to 5 and the bonded structure of Comparative Example 1 will be described. Hereinafter, the bonded structure of Example 1, the bonded structure of Example 2, the bonded structure of Example 3, the bonded structure of Example 4, the bonded structure of Example 5, and the bonded structure of Comparative Example 1 may be described as bonded structure SA-1, bonded structure SA-2, bonded structure SA-3, bonded structure SA-4, bonded structure SA-5, and bonded structure SB-1, respectively. Note that none of the semiconductor elements used in producing the bonded structures SA-1 to SA-5 and SB-1 had a metallized layer for bonding with the substrate. In addition, none of the substrates used in producing the bonded structures SA-1 to SA-5 and SB-1 had a metallized layer for bonding with the semiconductor element.

[Preparation of joint structure SA-1]
(Preparation of objects to be joined)
A Si semiconductor element (dimensions: 3 mm×3 mm×0.4 mm, hereinafter referred to as the "first Si semiconductor element") was prepared as the semiconductor element. A Si semiconductor element (dimensions: 5 mm×5 mm×0.4 mm, hereinafter referred to as the "second Si semiconductor element") was prepared as the substrate.

(Silver paste preparation process)
Flake silver particles FP and an ether-based solvent (CELTOL (registered trademark) IA, manufactured by Daicel Corporation) were mixed at a mass ratio (flake silver particles FP:ether-based solvent) of 12:1 to obtain a silver paste.

(Joining process)
A silver paste (the silver paste obtained by the above-mentioned preparation process) was applied by a screen printing method using a mask having a thickness of 100 μm to the main surface of the second Si semiconductor element on which the electrodes were not formed (application process). Next, the first Si semiconductor element was placed on the coating film made of the printed silver paste to obtain a laminate (laminar body formation process). When placing the first Si semiconductor element, the first Si semiconductor element was placed so that the main surface on which the electrodes of the first Si semiconductor element were not formed was in contact with the coating film. Next, the obtained laminate was heated by a hot plate (heating process). In the heating process, under atmospheric pressure, the heating part of the hot plate was heated from room temperature (temperature 25 ° C.) to the heating temperature of 250 ° C. at a heating rate of 15 ° C./min with the laminate placed on the heating part of the hot plate, and then the temperature of the heating part was maintained at 250 ° C. for 30 minutes. In addition, in the heating process, the laminate was heated without applying pressure. By the above-described manufacturing method, a joint structure SA-1 was obtained.

[Preparation of bonded structure SA-2]
A joined structure SA-2 was obtained in the same manner as the joined structure SA-1, except for the changes shown below.

(change point)
In the production of the bonded structure SA-2, a GaN semiconductor element (dimensions: 3 mm × 3 mm × 0.4 mm) was prepared as a semiconductor element instead of the first Si semiconductor element. In the production of the bonded structure SA-2, a GaN semiconductor element (dimensions: 5 mm × 5 mm × 0.4 mm) was prepared as a substrate instead of the second Si semiconductor element.

[Preparation of bonded structure SA-3]
A joined structure SA-3 was obtained in the same manner as the joined structure SA-1, except for the following changes.

(change point)
In the production of the bonded structure SA-3, a SiC semiconductor element (dimensions: 3 mm × 3 mm × 0.4 mm) was prepared as a semiconductor element instead of the first Si semiconductor element. In the production of the bonded structure SA-3, a SiC semiconductor element (dimensions: 5 mm × 5 mm × 0.4 mm) was prepared as a substrate instead of the second Si semiconductor element.

[Preparation of bonded structure SA-4]
A joined structure SA-4 was obtained in the same manner as the joined structure SA-1, except for the following changes.

(change point)
In producing the joint structure SA-4, a glass plate ("S1111" manufactured by Matsunami Glass Industry Co., Ltd., dimensions: 10 mm x 10 mm x 1.0 mm) was prepared as a substrate in place of the second Si semiconductor element.

[Preparation of bonded structure SA-5]
A joined structure SA-5 was obtained in the same manner as the joined structure SA-1, except for the following changes.

(change point)
In producing the joint structure SA-5, an aluminum nitride plate ("SH-30" manufactured by Tokuyama Corporation, dimensions: 50 mm x 50 mm x 0.6 mm) was prepared as a substrate in place of the second Si semiconductor element.

[Preparation of bonded structure SB-1]
Except for the changes shown below, the joined structure SB-1 was obtained in the same manner as in the production of the joined structure SA-1.

(change point)
In producing the bonded structure SB-1, an aluminum nitride plate ("SH-30" manufactured by Tokuyama Corporation, dimensions: 50 mm x 50 mm x 0.6 mm) was prepared as a substrate instead of the second Si semiconductor element. In producing the bonded structure SB-1, in the silver paste preparation step, a silver paste was prepared using spherical silver particles SP instead of flaky silver particles FP. More specifically, in producing the bonded structure SB-1, in the silver paste preparation step, the spherical silver particles SP and an ether-based solvent ("CELTOL (registered trademark) IA" manufactured by Daicel Corporation) were mixed at a mass ratio (spherical silver particles SP:ether-based solvent) of 12:1 to obtain a silver paste.

<Observation of the bonded structure by electron microscope>
[Observation by SEM]
The obtained bonded structure SA-1 was observed by SEM. FIG. 7 is an SEM photograph showing a cross section of the bonded portion of the bonded structure SA-1. As shown in FIG. 7, in the bonded structure SA-1, the first Si semiconductor element 50 and the second Si semiconductor element 60 were bonded via the bonding layer 13. In addition, as shown in FIG. 8, which is an SEM photograph of an enlarged bonded portion between the first Si semiconductor element 50 and the porous silver sintered body 14 in the cross section shown in FIG. 7, the bondability between the first Si semiconductor element 50 and the porous silver sintered body 14 was good.

[TEM Observation]
The obtained bonded structure SA-1 was observed by TEM. FIG. 9 is a TEM photograph showing a cross section of the bonded portion of the bonded structure SA-1. As shown in FIG. 9, in the bonded structure SA-1, some of the silver nanoparticles 15 were present between the porous silver sintered body 14 and the first Si semiconductor element 50. In addition, the number-average primary particle diameter of the silver nanoparticles 15 contained in the bonded structure SA-1 was 5 nm.

Although not shown, some silver nanoparticles were present between the porous silver sintered body and the semiconductor element in the bonded structures SA-2 to SA-5. The silver nanoparticles contained in the bonded structures SA-2 to SA-5 all had a number-average primary particle diameter of 5 nm. Meanwhile, the bonded structure SB-1 did not contain any silver nanoparticles with a number-average primary particle diameter of 1 nm or more and 20 nm or less.

<Measurement of shear strength of bonded structure>
[Measurement of shear strength of joined structure SA-1]
A shear tester (Nordson DAGE's "XD-7500") was used to measure the shear strength (shear strength between the first Si semiconductor element 50 and the second Si semiconductor element 60) of the bonded structure SA-1. In detail, the shear strength (shear stress when shear fracture occurs) was measured by applying a shear force to the first Si semiconductor element 50 and the second Si semiconductor element 60 using the shear tester. As a result, a shear strength of 46.0 MPa was obtained. Note that the higher the shear strength, the higher the bond strength of the bonded structure.

Figure 10 is an SEM photograph of the first Si semiconductor element 50 taken from the bonded portion side after measuring the shear strength of the bonded structure SA-1. As shown in Figure 10, the porous silver sintered body 14 remained on the surface of the first Si semiconductor element 50. In other words, in the bonded structure SA-1, even when a shear force was applied by the shear tester, a part of the porous silver sintered body 14 remained bonded to the first Si semiconductor element 50.

[Measurement of shear strength of joined structure SA-2]
The shear strength of the joint structure SA-2 was measured under the same conditions as those for the joint structure SA-1 described above, and the result was a shear strength of 45.8 MPa.

[Measurement of shear strength of joined structure SA-3]
The shear strength of the joint structure SA-3 was measured under the same conditions as those for the joint structure SA-1 described above, and the result was a shear strength of 53.5 MPa.

[Measurement of shear strength of joined structure SA-4]
The shear strength of the joint structure SA-4 was measured under the same conditions as those for the joint structure SA-1 described above, and the result was a shear strength of 29.0 MPa.

[Measurement of shear strength of joined structure SA-5]
The shear strength of the joint structure SA-5 was measured under the same conditions as those for the joint structure SA-1 described above, and the result was a shear strength of 29.8 MPa.

[Measurement of shear strength of joined structure SB-1]
The shear strength of the joint structure SB-1 was measured under the same conditions as those for the joint structure SA-1 described above, and the result was a shear strength of 0.4 MPa.

The results of measuring the shear strength of the joint structures SA-1 to SA-5 and SB-1 show that the present invention can provide joint structures that ensure high joint strength.

The joint structure according to the present invention can be used, for example, as a component of a mounting structure in which electronic components are mounted.

10: Bonded structure 11: Substrate 12: Semiconductor element 13: Bonding layer 14: Porous silver sintered body 15: Silver nanoparticles 40: Laminate

Claims (10)

A bonded structure including a substrate, a semiconductor element, and a bonding layer bonding the substrate and the semiconductor element,
The semiconductor element does not have a metallized layer for bonding to the substrate,
The bonding layer includes a porous silver sintered body and silver nanoparticles having a number average primary particle diameter of 1 nm or more and 20 nm or less,
A bonded structure, in which at least a portion of the silver nanoparticles are present between the porous silver sintered body and the semiconductor element. The bonded structure according to claim 1, wherein the substrate is a semiconductor element separate from the semiconductor element. A method for manufacturing a bonded structure including a substrate, a semiconductor element, and a bonding layer that bonds the substrate and the semiconductor element, comprising:
The method includes at least a bonding step of bonding the base material and the semiconductor element using a silver paste,
The semiconductor element does not have a metallized layer for bonding to the substrate,
The silver paste comprises silver particles having a residual strain of 5.0% or more as measured by X-ray diffraction, and a solvent. The method for manufacturing a bonded structure according to claim 3, wherein the 50% cumulative diameter of the silver particles on a volume basis is 100 nm or more and 50 μm or less. The method for manufacturing a joint structure according to claim 3 or 4, wherein the content of the silver particles in the silver paste is 85% by mass or more and 95% by mass or less with respect to the total mass of the silver paste. The method for manufacturing a bonded structure according to any one of claims 3 to 5, wherein the silver particles have a residual strain of 20.0% or less as measured using an X-ray diffraction method. The method for manufacturing a bonded structure according to any one of claims 3 to 6, wherein the silver particles are flake-shaped silver particles. The joining step includes:
a coating step of coating the silver paste on the base material;
a laminate forming step of forming a laminate by overlapping the base material and the semiconductor element via the silver paste;
The method for manufacturing a bonded structure according to any one of claims 3 to 7, further comprising a heating step of heating the laminate. The method for manufacturing a bonded structure according to claim 8, wherein the laminate is heated without applying pressure in the heating step. The method for manufacturing a bonded structure according to claim 8 or 9, wherein the laminate is heated at a temperature of 150°C or more and 350°C or less in the heating step.

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