JP7651822B2 - Metal paste for bonding, bonded body, semiconductor device, and method for manufacturing bonded body - Google Patents

Description

The present invention relates to a metal paste for bonding, a bonded body using the same, a semiconductor device, and a method for manufacturing the bonded body.

When manufacturing a semiconductor device, various bonding materials are used to form a bonding layer that bonds a semiconductor element to a lead frame or the like (supporting member). For example, high-lead solder has been used to form a bonding layer for bonding power semiconductors, LSIs, and the like that operate at temperatures up to about 150°C. In recent years, semiconductor elements have become higher capacity and more space-saving, and there is an increasing demand for semiconductors to operate at high temperatures of 175°C or higher. In order to ensure the operational stability of such semiconductor devices, the bonding layer needs to have connection reliability and high thermal conductivity. However, in the temperature range of 175°C or higher, the bonding layer of the high-lead solder that has been used conventionally has problems with connection reliability and has insufficient thermal conductivity (30 Wm ^- 1K ^-1 ), so alternative materials are needed.

As one of the alternative materials, a sintered silver layer formed by the sintering phenomenon of silver particles has been proposed (see Patent Document 1 below). It has been reported that the sintered silver layer has high thermal conductivity (>100 Wm ^-1 K ^-1 ) and high connection reliability against power cycles, and has attracted attention (see Non-Patent Document 1 below). However, in order to ensure connection reliability, a thermocompression process involving high pressure is essential to improve the density of the sintered silver layer, and there are problems such as damage to semiconductor element chips and a decrease in throughput of the thermocompression process. Another problem is that silver has a high material cost.

As another alternative material, a sintered copper layer using copper has been proposed. Copper has superior mechanical strength compared to silver, and high-temperature reliability can be achieved without increasing the density as much as in the case of a sintered silver layer, and material costs can also be kept low. As such a sintered copper layer, a sintered copper layer obtained by reducing and sintering copper oxide particles has been proposed (see Patent Document 2 and Non-Patent Document 2 below).

Patent No. 4247800 Patent No. 5006081

R. Khazaka, L. Mendizabal, D. Henry: J. ElecTron. Mater, 43(7), 2014, 2459-2466 T. Morita, Y. Yasuda: Materials Transactions, 56(6), 2015, 878-882

The above-mentioned sintered copper layer is obtained by utilizing the reduction reaction of copper oxide to copper in a hydrogen atmosphere, and the thermocompression process prevents a decrease in bonding strength caused by volume shrinkage during the reduction reaction. However, the thermocompression process, which involves high pressure, has the issues mentioned above, and the pressurization process in a hydrogen atmosphere requires dedicated equipment, which increases the product cost.

The present invention aims to provide a metal paste for bonding that can provide sufficient bonding strength even when bonding in a hydrogen-free atmosphere and at low pressure, a bonded body and semiconductor device that use the same, and a method for manufacturing the bonded body.

One aspect of the present invention provides a metal paste for joining that includes metal particles and a dispersion medium, in which the metal particles include sub-micro copper particles coated with an aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms and having a volume average particle size of 0.1 μm to 0.9 μm, and micro copper particles coated with an aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms or copper oxide and having a volume average particle size of 2 μm to 50 μm, the dispersion medium includes an alcohol-based compound having a hydroxyl group at the end and no ether bond in the molecular chain, and a polyether alcohol-based compound having a hydroxyl group at the end and an ether bond in the molecular chain, and the content of the micro copper particles is 0.5% by mass to 50% by mass based on the total mass of the sub-micro copper particles and the micro copper particles.

The above-mentioned metal bonding paste can provide sufficient bonding strength even when bonding components together in a hydrogen-free atmosphere at low pressure.

The inventors speculate as follows about the reason why such an effect is obtained.
(i) First, by containing the sub-micro copper particles and the micro copper particles in a specific ratio, it is possible to sufficiently suppress the volumetric shrinkage during sintering caused by the monocarboxylic acid or dispersing medium that coats the copper particles while maintaining sufficient sinterability, and it is believed that this makes it possible to ensure the strength of the sintered body and improve the bonding strength with the adherend surface even when low pressure is applied.
(ii) In addition, it is believed that the monocarboxylic acid that covers the submicro copper particles and the micro copper particles reacts with the alcohol-based compound and the polyether alcohol-based compound, and the elimination of the monocarboxylic acid proceeds at a relatively low temperature, and an active copper surface appears. When the surface of the microparticle is covered with copper oxide (when the surface of the microparticle is a copper oxide layer), it is believed that the copper oxide is reduced by the alcohol-based dispersion medium or the polyether alcohol-based dispersion medium, and an active copper surface appears. It is believed that the active copper surfaces that appear due to these actions come into contact with each other and are sintered, forming a strong copper sintered body even at low pressure.
(iii) Furthermore, it is believed that the alcohol-based compound and the polyether alcohol-based compound function as reducing agents for copper, so that sintering of copper particles proceeds sufficiently without the need for an active reducing atmosphere, making it possible to achieve strong bonding even with a relatively low pressure.

In addition, the above-mentioned metal paste for bonding contains a combination of the above-mentioned alcohol-based compound and the above-mentioned polyether alcohol-based compound as a dispersion medium, so that even large-area components can be bonded while suppressing the occurrence of voids, and a decrease in bonding strength and bonding reliability due to voids can be prevented.

In the above-mentioned bonding metal paste, the boiling point of the alcohol-based compound under atmospheric pressure may be 100°C or more and less than 250°C, and the boiling point of the polyether alcohol-based compound under atmospheric pressure may be 250°C or more and 400°C or less. In this case, it is easy to obtain sufficient bonding strength while suppressing the occurrence of voids even in large-area components. The reason for this effect is thought to be that the carboxylic acid that coats the copper particles reacts with the low-boiling alcohol-based compound, making it easier to obtain the effect of desorption at a relatively low temperature, and the high-boiling polyether alcohol-based compound exists in the paste up to a higher heating temperature, which reduces the oxidized layer of the copper particles, and the ether bond makes it easy to decompose and less likely to remain in the sintered body.

The above-mentioned metal paste for joining may have a total content of aliphatic or aromatic monocarboxylic acids having 1 to 20 carbon atoms contained in the metal paste for joining of 0.1% by mass or more and 10% by mass or less based on the total amount of the metal paste for joining.

The total content of the sub-micro copper particles and the micro copper particles may be 80 mass% or more based on the total amount of metal particles. In this case, the joining metal paste makes it easier to form a sintered body with excellent connection reliability and high thermal conductivity properties.

Another aspect of the present invention provides a joint comprising a first member, a second member, and a sintered body of the above-mentioned joining metal paste that joins the first member and the second member.

The above-mentioned bonded body can be a bonded body in which the components are bonded with sufficient bonding strength by being bonded with a sintered body of the above-mentioned bonding metal paste.

Another aspect of the present invention provides a semiconductor device comprising a first member, a second member, and a sintered body of the above-mentioned bonding metal paste that bonds the first member and the second member, and at least one of the first member and the second member is a semiconductor element.

The semiconductor device described above can have excellent connection reliability and high thermal conductivity properties due to the sintered body of the bonding metal paste, and can have excellent operational stability at high temperatures.

Another aspect of the present invention provides a method for manufacturing a bonded body, comprising the steps of preparing a laminate in which a first member, the bonding metal paste, and a second member are laminated in this order, and sintering the bonding metal paste in the laminate.

According to the above-mentioned manufacturing method of a bonded body, a bonded body can be obtained in which components are bonded with sufficient bonding strength. Furthermore, according to the above-mentioned manufacturing method of a bonded body, by using the above-mentioned bonding metal paste, even components with a large area can be bonded while suppressing the occurrence of voids, and a decrease in bonding strength and bonding reliability due to voids can be prevented.

In the manufacturing method of the bonded body, at least one of the first member and the second member may be a semiconductor element. In this case, the sintered body of the bonding metal paste that bonds the semiconductor element can have excellent connection reliability and high thermal conductivity properties, so that a semiconductor device with excellent operational stability at high temperatures can be obtained as the bonded body.

In the manufacturing method of the above-mentioned joint body, the step of preparing the laminate includes a first step of forming a coating film of a metal paste for joining in the joint region between the first member and the second member, and a second step of laminating the first member and the second member via the coating film, and the joint region has a coating film-formed region where the coating film is formed and a non-coating film-formed region where the coating film is not formed, and the non-coating film-formed region may be continuous to the end of the joint region.

The above method makes it easy to obtain sufficient bonding strength even when the bonding area of the components is large. This method is particularly suitable for the manufacture of a bonded body in which a substrate on which a high-heat-generating semiconductor device is mounted is bonded to a heat sink.

When the bonding area is large, it becomes difficult for the gas generated during sintering of the metal paste to escape. However, with the above method, the non-film-forming area allows the gas to efficiently escape outside the bonding area, suppressing the occurrence of voids and peeling caused by the gas generated during sintering.

The content of the polyether alcohol-based compound in the joining metal paste may be 0.5% by mass or more and 4.0% by mass or less based on the total amount of the joining metal paste. When the content of the polyether alcohol-based compound is in this range, the above-mentioned effects are easily obtained, and deformation of the copper sintered body is suppressed when the metal paste is sintered, making it easier to suppress the metal paste from flowing too much during pressure joining, resulting in the non-film-formed areas being filled up.

In the above method, the micro copper particles may be flake-shaped. In this case, even if the coating of the bonding metal paste is dried, the flake-shaped micro copper particles function as a reinforcing material, thereby preventing peeling and cracking due to shrinkage of the coating. Therefore, the fluidity of the coating is reduced by drying, making it easier to prevent the metal paste from flowing too much during pressure bonding, resulting in the non-coating area being filled in.

Furthermore, in the above method, the total area of the coating film-forming region may be 900 ^mm2 or more, the shortest distance of the joining metal paste in the coating film-forming region to the edge of the non-coating film-forming region or the joining region may be within 8 mm, and the minimum width in the non-coating film-forming region may be 100 μm or more.

Another aspect of the present invention provides a semiconductor device comprising a first member, a second member, and a copper sintered body that joins the first member and the second member, one of the first member and the second member being a mounting substrate and the other being a heat sink, and the copper sintered body being divided into a plurality of copper sintered bodies by areas where no copper sintered body is present, or including areas where no copper sintered body is present, the areas continuing to the outside of the copper sintered body.

The semiconductor device described above has sufficient bonding strength even when the bonding area of the components is large.

The present invention provides a metal paste for bonding that can provide sufficient bonding strength even when bonding in a hydrogen-free atmosphere and at low pressure, a bonded body and a semiconductor device that use the same, and a method for manufacturing the bonded body.

1 is a schematic cross-sectional view showing an example of a bonded body produced using the bonding metal paste of the present embodiment. 1A to 1C are diagrams showing examples of printing patterns of a bonding metal paste. 1A to 1C are diagrams showing examples of printing patterns of a bonding metal paste. 1 is a schematic cross-sectional view showing an example of a bonded body produced using the bonding metal paste of the present embodiment. 1 is a schematic cross-sectional view showing an example of a semiconductor device manufactured using the bonding metal paste of the present embodiment. 1 is a SAM image of a 10 mm×10 mm chip after bonding in Example 15. 13 is an electron microscope image of a cross section of the bonded portion after bonding in Example 15. 13 is an electron microscope image of a cross section of the bonded portion after bonding in Example 24. 1 is a SAM image of a chip having an area of 10 mm×10 mm after bonding in Comparative Example 2. 13 is an electron microscope image of a cross section of the bonded portion after bonding in Comparative Example 2. 13 is an electron microscope image of a cross section of a joint after joining in Comparative Example 3. FIG. 13 is a diagram for explaining a printing pattern of a bonding metal paste.

The following describes in detail the form for implementing the present invention (hereinafter, referred to as the "present embodiment"). The present invention is not limited to the following embodiment.

<Metal paste for bonding>
The bonding metal paste of the present embodiment contains metal particles and a dispersion medium, and the metal particles include sub-micro copper particles and micro copper particles.

(Metal Particles)
Examples of the metal particles according to this embodiment include submicro copper particles, micro copper particles, and other metal particles other than these copper particles.

(Submicron copper particles)
The sub-micro copper particles may be copper particles having sinterability in a temperature range of 250° C. to 380° C. The sub-micro copper particles include copper particles having a particle size of 0.1 μm to 0.9 μm, for example, copper particles having a volume average particle size of 0.1 μm to 0.9 μm. If the volume average particle size of the sub-micro copper particles is 0.1 μm or more, effects such as reduction in the synthesis cost of the sub-micro copper particles, good dispersibility, and reduction in the amount of organic protective agent used can be easily obtained. If the volume average particle size of the sub-micro copper particles is 0.9 μm or less, the effect of excellent sinterability of the sub-micro copper particles can be easily obtained. From the viewpoint of further achieving the above-mentioned effect, the volume average particle size of the sub-micro copper particles may be 0.1 μm or more and 0.8 μm or less, 0.12 μm or more and 0.8 μm or less, 0.15 μm or more and 0.8 μm or less, 0.15 μm or more and 0.6 μm or less, 0.2 μm or more and 0.5 μm or less, or 0.3 μm or more and 0.45 μm or less.

In this specification, the volume average particle size means the 50% volume average particle size. For example, when determining the volume average particle size of copper particles, the copper particles to be used as raw material or dried copper particles obtained by removing volatile components from a bonding metal paste are dispersed in a dispersion medium using a dispersant, and the resulting dispersion medium is measured using a light scattering particle size distribution measuring device (for example, a Shimadzu nanoparticle size distribution measuring device (SALD-7500 nano, manufactured by Shimadzu Corporation)). When using a light scattering particle size distribution measuring device, the dispersion medium can be hexane, toluene, α-terpineol, 4-methyl-1,3-dioxolan-2-one, water, etc.

If the particles are not spherical, the particle diameter can be determined as the maximum particle diameter using the following method. Here is an example of a method for calculating the long diameter of copper particles from an SEM image. Copper particle powder is placed on carbon tape for SEM with a spatula to create an SEM sample. This SEM sample is observed at 100 to 5000 times magnification using an SEM device. A rectangle circumscribing the copper particle in this SEM image is drawn using image processing software, and the long side of the rectangle is taken as the long diameter of the particle. The particle diameters of other metal particles can also be determined using the same method.

The content of the sub-micro copper particles is preferably 50% by mass or more and 99.5% by mass or less, based on the sum of the mass of the sub-micro copper particles and the mass of the micro copper particles. If the content of the sub-micro copper particles is 50% by mass or more, the spaces between the micro copper particles can be sufficiently filled, and it is easy to ensure the bonding strength of the bonded body manufactured by sintering the bonding metal paste, and when the bonding metal paste is used for bonding a semiconductor element, the semiconductor device tends to exhibit good die shear strength and connection reliability. If the content of the sub-micro copper particles is 99.5% by mass or less, the volume shrinkage when the bonding metal paste is sintered can be sufficiently suppressed, so that it is easy to ensure the bonding strength of the bonded body manufactured by sintering the bonding metal paste, and when the bonding metal paste is used for bonding a semiconductor element, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of making the above-mentioned effect easier to obtain, the content of the sub-micro copper particles may be 60% by mass or more, 70% by mass or more, 75% by mass or more, 95% by mass or less, 90% by mass or less, 85% by mass or less, 80% by mass or less, 60% by mass or more and 99.5% by mass or less, 60% by mass or more and 95% by mass or less, 60% by mass or more and 90% by mass or less, 70% by mass or more and 85% by mass or less, or 75% by mass or more and 80% by mass or less, based on the total mass of the sub-micro copper particles and the micro copper particles.

The shape of the sub-micro copper particles is not particularly limited. Examples of the shape of the sub-micro copper particles include spherical, clumpy, needle-like, flake-like, nearly spherical, and aggregates thereof. From the viewpoint of dispersibility and packing property, the shape of the sub-micro copper particles may be spherical, nearly spherical, or flake-like, and from the viewpoint of combustibility, dispersibility, mixability with flake-like microparticles, etc., the shape may be spherical or nearly spherical. In this specification, "flake-like" includes flat shapes such as plate-like and scale-like.

From the viewpoints of dispersibility, packing property, and mixability with flake-shaped microparticles, the aspect ratio of the sub-micro copper particles may be 5 or less, or may be 3 or less. In this specification, the "aspect ratio" refers to the long side (major axis)/thickness of the particle. The long side (major axis) and thickness of the particle can be measured, for example, from an SEM image of the particle.

The submicro copper particles are preferably treated with an organic protective agent of an aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms. In other words, the submicro copper particles are preferably coated with an aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms.

Examples of aliphatic or aromatic monocarboxylic acids having 1 to 20 carbon atoms include formic acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, caprylic acid, methylheptanoic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid, methyloctanoic acid, ethylheptanoic acid, propylhexanoic acid, capric acid, methylnonanoic acid, ethyloctanoic acid, propylheptanoic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanoic acid, lauric acid, methylundecanoic acid, ethyl Tyldecanoic acid, propylnonanoic acid, butyloctanoic acid, pentylheptanoic acid, tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyldodecanoic acid, propylundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid, methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, ethyl Saturated fatty acids such as tetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, heptadecanoic acid, octadecanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, and nonylcyclohexanecarboxylic acid; octenoic acid, nonenoic acid, Examples of such unsaturated fatty acids include methylnonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, sabienoic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, and linolenic acid; and aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, o-phenoxybenzoic acid, methylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, butylbenzoic acid, pentylbenzoic acid, hexylbenzoic acid, heptylbenzoic acid, octylbenzoic acid, and nonylbenzoic acid.

Among these, by combining an aliphatic or aromatic monocarboxylic acid having 2 to 18 carbon atoms with the submicro copper particles, it tends to be possible to achieve both the dispersibility of the submicro copper particles and the release of the organic acid during sintering. Examples of such aliphatic or aromatic monocarboxylic acids include formic acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, dodecanoic acid (lauric acid), tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, and arachidic acid.

The organic protective agent may be used alone or in combination of two or more.

The amount of the organic protective agent to be treated may be an amount that adheres to the surface of the sub-micro copper particles in a single molecular layer to a triple molecular layer. This amount can be calculated from the number of molecular layers (n) attached to the surface of the sub-micro copper particles, the specific surface area (A _p ) (unit: m ² /g) of the sub-micro copper particles, the molecular weight (M _s ) (unit: g/mol) of the organic protective agent, the minimum coverage area (S _S ) (unit: m ² /piece) of the organic protective agent, and the Avogadro's number (N _A ) (6.02×10 ²³ pieces). Specifically, the amount of the organic protective agent to be treated is calculated according to the formula: Organic protective agent treatment amount (mass %)={(n·A _p ·M _s )/(S _S ·N _A +n·A _p ·M _s )}×100.

The specific surface area of the sub-micro copper particles can be calculated by measuring the dried sub-micro copper particles by the BET specific surface area measurement method. The minimum coverage area of the organic protective agent is 2.05×10 ⁻¹⁹ m ² /1 molecule when the organic protective agent is a linear saturated fatty acid. In the case of other organic protective agents, the area can be measured, for example, by calculation from a molecular model or by the method described in "Chemistry and Education" (Katsuhiro Ueda, Sumio Inafuku, Iwao Mori, 40 (2), 1992, pp. 114-117). An example of a method for quantifying the organic protective agent is shown below. The organic protective agent can be identified by a thermal desorption gas/gas chromatograph mass spectrometer of the dried powder obtained by removing the dispersion medium from the bonding metal paste, and the carbon number and molecular weight of the organic protective agent can be determined. The carbon content of the organic protective agent can be analyzed by carbon content analysis. Examples of carbon content analysis methods include high-frequency induction heating furnace combustion/infrared absorption method. The amount of the organic protective agent can be calculated from the carbon number, molecular weight and carbon content of the identified organic protective agent using the above formula.

The amount of the organic protective agent to be treated may be 0.1% by mass or more and 10% by mass or less, 0.5% by mass or more and 5% by mass or less, or 1% by mass or more and 3% by mass or less. From the viewpoint of low-temperature sintering, the amount of the organic protective agent to be treated may be 0.07% by mass or more and 2.1% by mass or less, 0.10% by mass or more and 1.6% by mass or less, or 0.2% by mass or more and 1.1% by mass or less.

As a method for experimentally measuring the amount of organic protective agent treated (amount attached), TG-DTA (Thermogrammetry-Differential Thermal Analysis) measurement can be used. By measuring copper particles treated with an organic protective agent in an oxygen-free atmosphere using TG-DTA, weight loss due to desorption of the organic protective agent can be observed. The temperature at which this weight loss begins is the starting temperature of desorption of the organic protective agent. The temperature at which the weight loss stops is the temperature at which desorption of the organic protective agent is completed, and the weight lost from the initial value is the amount of organic protective agent treated.

For example, TG-DTA measurements of sub-micro copper particles ("CH-0200" manufactured by Mitsui Mining & Smelting Co., Ltd.) (organic protective agent: dodecanoic acid) in a nitrogen atmosphere showed that dodecanoic acid was desorbed in two stages, at temperatures between 140°C and 195°C and between 240°C and 320°C. The desorption start temperature of the organic protective agent (dodecanoic acid) from these copper particles is 140°C, and the amount of dodecanoic acid to be treated is required to be approximately 2.5% by mass.

In this embodiment, it is desirable that the temperature at which the detachment of the carboxylic acid compound from the submicro copper particles begins is in the range of 140°C or higher and 380°C or lower.

Commercially available sub-micro copper particles can be used for the present embodiment. Examples of commercially available sub-micro particles include CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.36 μm), HT-14 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.41 μm), CT-500 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.72 μm), and Tn-Cu100 (manufactured by Taiyo Nissan Co., Ltd., volume average particle size 0.12 μm).

The above sub-micro copper particles have good sinterability, which can reduce issues such as high synthesis costs, poor dispersibility, and reduced volume shrinkage after sintering that are common in bonding materials that mainly use copper nanoparticles.

(Micro copper particles)
The micro copper particles include copper particles having a particle size of 2.0 μm or more and 50 μm or less, and for example, copper particles having a volume average particle size of 2.0 μm or more and 50 μm or less can be used. If the volume average particle size of the micro copper particles is within the above range, the volume shrinkage when the bonding metal paste is sintered can be sufficiently reduced, and it is easy to ensure the bonding strength of the bonded body manufactured by sintering the bonding metal paste, and when the bonding metal paste is used for bonding a semiconductor element, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of making it easier to obtain the above effect, the volume average particle size of the micro copper particles may be 2 μm or more, 3 μm or more, 4 μm or more, or 5 μm or more, and the upper limit may be 20 μm or less, or 10 μm or less.

The content of the micro copper particles may be 0.5% by mass or more and 50% by mass or less, 1% by mass or more and 50% by mass or less, 5% by mass or more and 40% by mass or less, or 10% by mass or more and 30% by mass or less, based on the total mass of the sub-micro copper particles and the micro copper particles. If the content of the micro copper particles is within the above range, it becomes easy to ensure the bonding strength of the bonded body produced by sintering the bonding metal paste, and when the bonding metal paste is used to bond semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability.

The total content of the sub-micro copper particles and the micro copper particles can be 80% by mass or more based on the total mass of the metal particles. If the total content of the sub-micro copper particles and the micro copper particles is within the above range, the volume shrinkage when the joining metal paste is sintered can be sufficiently reduced, and it is easy to ensure the joining strength of the joining body produced by sintering the joining metal paste. Furthermore, the sintered body of the joining metal paste can have high thermal conductivity characteristics. When the joining metal paste is used to join semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of further achieving the above effect, the total content of the sub-micro copper particles and the micro copper particles may be 90% by mass or more, 95% by mass or more, or 100% by mass based on the total mass of the metal particles. In addition, from the viewpoint of the sinterability of the copper particles, the total content of the sub-micro copper particles and the micro copper particles may be 99.99% by mass or less, or 99.0% by mass or less based on the total mass of the metal particles.

The shape of the micro copper particles is not particularly limited. Examples of the shape of the micro copper particles include spherical, clumpy, needle-like, flake-like, nearly spherical, and aggregates thereof. The shape of the micro copper particles is preferably flake-like. By using flake-like micro copper particles, the micro copper particles in the bonding metal paste are oriented nearly parallel to the bonding surface, thereby suppressing volumetric shrinkage when the bonding metal paste is sintered, and it becomes easy to ensure the bonding strength of the bonded body manufactured by sintering the bonding metal paste. In addition, it is possible to suppress the occurrence of peeling and cracks when the bonding metal paste is dried, and it becomes easy to reduce defects in the bonded body manufactured, ensure the bonding strength, and improve the bonding reliability. When the bonding metal paste is used to bond semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of making it easier to obtain the above-mentioned effect, the flake-like micro copper particles may have an aspect ratio of 4 or more, or 6 or more.

As the flake-shaped micro copper particles, copper particles having a particle size of 4.0 μm or more and 50 μm or less can be used, for example, copper particles having a volume average particle size of 4.0 μm or more and 50 μm or less can be used. If the volume average particle size of the flake-shaped micro copper particles is within the above range, the above-mentioned effects are easily obtained. From the viewpoint of further achieving the above-mentioned effects, the volume average particle size of the micro copper particles may be 4 μm or more and 45 μm or less, 6 μm or more and 40 μm or less, 4 μm or more and 40 μm or less, or 4 μm or more and 10 μm or less.

The content of the flake-shaped micro copper particles is preferably 5% by mass or more and 25% by mass or less, more preferably 7% by mass or more and 23% by mass or less, and even more preferably 10% by mass or more and 20% by mass or less, based on the total mass of the metal particles. If the content of the flake-shaped micro copper particles is equal to or more than the lower limit, peeling and cracking are suppressed when the joining metal paste is dried, making it easier to form a joint with fewer defects, and if it is equal to or less than the upper limit, large voids of several μm or more are less likely to occur in the copper sintered body, making it easier to obtain a joint with good adhesion to the member. When the joining metal paste is used to join semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability.

The micro copper particles are preferably treated with an organic protective agent of an aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms, i.e., coated with an aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms, or coated with a copper oxide layer. From the viewpoint of dispersion stability and oxidation resistance, it is preferable that the micro copper particles are treated with an organic protective agent. The organic protective agent may be one described above. The organic protective agent may be one that is removed during bonding. Examples of such organic protective agents include aliphatic carboxylic acids such as dodecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, arachidic acid, linoleic acid, linolenic acid, and oleic acid; aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, and o-phenoxybenzoic acid; aliphatic alcohols such as cetyl alcohol, stearyl alcohol, isobornylcyclohexanol, and tetraethylene glycol; aromatic alcohols such as p-phenylphenol; alkylamines such as octylamine, dodecylamine, and stearylamine; aliphatic nitriles such as stearonitrile and decanitrile; silane coupling agents such as alkylalkoxysilanes; and polymer treatment materials such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and silicone oligomers.

The organic protective agent may be used alone or in combination of two or more.

The amount of organic protective agent to be treated may be an amount of one molecular layer or more on the particle surface. The amount of such organic protective agent to be treated varies depending on the specific surface area of the micro copper particles, the molecular weight of the organic protective agent, and the minimum coverage area of the organic protective agent. The amount of organic protective agent to be treated is usually 0.001 mass% or more relative to the mass of the particles. The specific surface area of the micro copper particles, the molecular weight of the organic protective agent, and the minimum coverage area of the organic protective agent can be calculated by the method described above.

The method for experimentally measuring the amount of organic protective agent used is similar to that described above.

In the case of micro copper particles ("MA-C025KFD" manufactured by Mitsui Mining & Smelting Co., Ltd.) (lubricant-free, no organic protective agent treatment), the organic protective agent that is detached is not attached, and the surface is covered with a small amount of copper oxide layer, so no weight loss is observed in TG-DTA measurements in a nitrogen atmosphere. On the contrary, a slight weight increase is observed, which is due to further oxidation of the micro copper particles caused by the small amount of oxygen present in the atmosphere of the measurement device.

TG-DTA measurements of micro copper particles 3L3N (organic protective agent: stearic acid) in a nitrogen atmosphere showed a weight loss at 185°C to 345°C, indicating that the organic protective agent was desorbed at 185°C to 345°C. The desorption start temperature of the organic protective agent (stearic acid) from these copper particles is 185°C, and the amount of organic protective agent treated (adhered amount) is expected to be approximately 3.2 mass%.

It is desirable that the aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms that coats the micro copper particles has a desorption initiation temperature in the range of 180°C or higher and 380°C or lower.

The micro copper particles according to this embodiment can be commercially available. Examples of commercially available micro particles include MA-C025KFD (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 7.5 μm), 3L3N (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 8.0 μm), 1110F (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 3.8 μm), HWQ3.0 μm (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 3.0 μm), 4L3 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 3.0 μm), 2L3 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 9.9 μm), E3 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 37.5 μm), C3 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 37.3 μm), and MS-800 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 40.4 μm).

However, when the bonding metal paste is prepared from only submicro copper particles as copper particles, the volume shrinkage and sintering shrinkage accompanying drying of the dispersion medium are large, so that when the bonding metal paste is dried and sintered, the paste layer cracks or peels off from the adherend surface, making it difficult to obtain sufficient die shear strength and connection reliability in bonding semiconductor elements and the like. On the other hand, when the bonding metal paste is prepared from only micro copper particles as copper particles, the sintering temperature tends to be high, and a pressure sintering process at a temperature of 400 ° C or more and a pressure of 10 MPa or more is required. In addition, the flexibility of the particle deposition layer after drying decreases, and the adhesion between the bonding metal paste and the adherend surface decreases, causing peeling and voids to occur at the interface between the adherend surface and the copper sintered body. In this embodiment, by using submicro copper particles and micro copper particles in combination, it is possible to suppress both the volume shrinkage when the bonding metal paste is sintered and the deformation of the particle deposition layer during thermocompression bonding, and it becomes easy for the bonded body to have sufficient low defectivity, bonding strength, and connection reliability. When the bonding metal paste is used to bond semiconductor elements, it becomes easier to obtain the effect that the semiconductor device exhibits good die shear strength and connection reliability.

The bonding metal paste of this embodiment may contain copper nanoparticles as copper particles other than the submicro copper particles and the micro copper particles. The copper nanoparticles may have a volume average particle size of 0.001 μm or more and 0.09 μm or less, 0.01 μm or more and 0.09 μm or less, or 0.03 μm or more and 0.09 μm or less. When the bonding metal paste contains copper nanoparticles, the content is preferably less than 30 mass% and more preferably 20 mass% or less based on the total mass of the metal particles in order to avoid thickening of the bonding metal paste and increasing volume shrinkage during sintering. Copper nanoparticles may not be included. The shape of the copper nanoparticles is not particularly limited. When the bonding metal paste contains copper nanoparticles, the effect of lowering the sintering temperature is obtained. In addition, by mixing copper nanoparticles so as to fill the gaps between the particles, the density of the copper sintered body after sintering can be increased, and the effect of improving the die shear strength and the connection reliability can be obtained.

(Other metal particles, semi-metal particles)
The bonding metal paste of this embodiment may contain metal particles (also referred to as second metal particles) containing a metal element other than copper as the metal particles. The bonding metal paste of this embodiment may also contain metalloid particles containing a metalloid element. The particles containing a metal element or a metalloid element other than copper may be metal particles or metalloid particles containing at least one element selected from Mg, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ag, Zn, Ga, Ge, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Cd, In, Sn, Sb, Ta, W, Re, Os, Ir, Pt, Au, and Bi. The composition of the other metal particles may be a single metal, or an alloy (solid solution, intermetallic compound, heterogeneous mixture) or metal compound (metal oxide, metal nitride, etc.) containing two or more metals.

By adding the second metal particles, the metal elements derived from the second metal particles are dissolved or dispersed in the sintered copper, improving mechanical properties such as yield stress and fatigue strength, thereby further increasing the bonding strength and connection reliability. When metal particles other than copper particles are included, a sintered body in which multiple metals are dissolved or dispersed can be obtained, improving migration resistance and making it easier to improve connection reliability at high temperatures. In addition, by including second metal particles in the bonding metal paste, the sintered body of the metal paste can have high bonding strength to an adherend having an adhesion surface such as Au and Ag. When the second metal particles are blended for such a purpose, the metal species of the second metal particles is preferably zinc, gold, tin, indium, silver, vanadium, aluminum, or antimony, and it is more preferable that the second metal particles are flaky zinc particles.

The particle shape of the second metal particles and semi-metal particles is not particularly limited, but examples include spherical, clumpy, needle-like, flake-like, roughly spherical, and aggregates thereof. From the viewpoint of dispersibility and packing ability, the shape of the second metal particles and semi-metal particles may be spherical, roughly spherical, or flake-like, and from the viewpoints of combustibility, dispersibility, mixability with other copper particles, etc., the shape may be spherical or roughly spherical.

The volume average particle size of the second metal particles and semi-metal particles is preferably 0.01 μm or more and 50 μm or less, more preferably 0.02 μm or more and 20 μm or less, and even more preferably 0.03 μm or more and 5 μm or less. If the volume average particle size of the second metal particles and semi-metal particles is within the above range, the sintering of the copper particles is less likely to be hindered.

While there is no particular limitation on whether the second metal particles are treated with an organic protective agent, from the viewpoint of dispersion stability and oxidation resistance, the second metal particles may be treated with an organic protective agent. The organic protective agent may be one that is removed during bonding. As a specific organic protective agent for the second metal particles, the above-mentioned organic protective agents used for sub-micro copper particles or micro copper particles can be used.

Commercially available second metal particles can be used. Examples of commercially available second metal particles include silver particles AgC239 (50% volume average particle size 10 μm, Fukuda Metal Foil Co., Ltd.), zinc particles (50% volume average particle size 5 μm, Alfa Aeser), iron powder (50% volume average particle size 45 μm, Wako Pure Chemical Industries, Ltd.), cobalt powder Cobalt Powder S-160 (50% volume average particle size 3.0 μm, Freeport Cobalt Co.), and nickel particles (50% volume average particle size 1.5 μm, METAL FOIL & POWDERS MFG CO.).

The content of the second metal particles and semi-metal particles is preferably 0.001% by mass or more and 10% by mass or less, more preferably 0.01% by mass or more and 5% by mass or less, and even more preferably 0.1% by mass or more and 2% by mass or less, based on the total mass of the metal particles and semi-metal particles contained in the metal paste. If the content of the second metal particles and semi-metal particles is within the above range, it is unlikely to affect the sinterability of the joining metal paste.

(Dispersion medium)
The joining metal paste of this embodiment contains, as a dispersion medium, an alcohol-based compound having hydroxyl groups at the terminals and no ether bonds in the molecular chain (hereinafter also referred to as an "alcohol-based dispersion medium"), and a polyether alcohol-based compound having hydroxyl groups at the terminals and an ether bond in the molecular chain (hereinafter also referred to as a "polyether alcohol-based dispersion medium").

(Alcohol-based dispersion medium)
Examples of alcohol-based dispersion media include monohydric and polyhydric alcohols such as dihydroterpineol, terpineol, pentanol, hexanol, heptanol, octanol, decanol, dodecanol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, α-terpineol, and isobornylcyclohexanol (MTPH).

The boiling point of the alcohol-based dispersion medium is preferably 100°C or higher and lower than 250°C, more preferably 120°C or higher and 230°C or lower, and even more preferably 150°C or higher and 210°C or lower. In this specification, the boiling point refers to the boiling point under atmospheric pressure (1 atm).

It is desirable that the desorption temperature of the alcohol-based dispersion medium is lower than or equal to that of the organic protective agent of the copper particles. When there are multiple types of organic protective agents, it is preferable to use an alcohol-based dispersion medium having a desorption temperature lower than the desorption temperature of the organic protective agent that desorbs at the lowest temperature. Specifically, the desorption start temperature of the alcohol-based dispersion medium is preferably 20°C or higher and 150°C or lower, more preferably 30°C or higher and 100°C or lower, and even more preferably 40°C or higher and 80°C or lower. In this specification, the desorption temperature means the temperature at which desorption starts under atmospheric pressure (1 atm).

TG-DTA (Thermogrammetry-Differential Thermal Analysis) can be used as a method for experimentally measuring the desorption temperature of the dispersing medium. By measuring the dispersing medium with TG-DTA in an oxygen-free atmosphere, the weight loss due to desorption of the dispersing medium can be observed. The temperature at which the weight loss begins is the starting temperature of desorption of the dispersing medium. The temperature at which the weight loss stops is the temperature at which desorption of the dispersing medium is completed.

For example, in a TG-DTA measurement of dihydroterpineol in a nitrogen atmosphere, a weight loss is observed between 70°C and 165°C, indicating that dihydroterpineol is desorbed between 70°C and 165°C, and the desorption start temperature of dihydroterpineol is determined to be 70°C.

The content of the alcohol-based dispersion medium is preferably 0.1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less, based on the total mass of the joining metal paste.

(Polyether alcohol dispersion medium)
Examples of polyether alcohol-based dispersion media include ethylene glycol butyl ether, ethylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol isobutyl ether, diethylene glycol hexyl ether, triethylene glycol methyl ether, propylene glycol propyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, tripropylene glycol methyl ether, diethylene glycol, tetraethylene glycol, polyethylene glycol, triethylene glycol, pentaethylene glycol, hexaethylene glycol, glycerin, and diglycerin.

The boiling point of the polyether alcohol dispersion medium is preferably 250°C or higher and 400°C or lower, more preferably 250°C or higher and 380°C or lower, and even more preferably 250°C or higher and 350°C or lower.

The desorption temperature of the polyether alcohol-based dispersion medium is preferably equal to or higher than that of the organic protective agent for the copper particles, and is preferably 400°C or lower. Specifically, the desorption start temperature of the polyether alcohol-based dispersion medium is preferably 90°C or higher and 400°C or lower, more preferably 150°C or higher and 380°C or lower, and even more preferably 200°C or higher and 350°C or lower.

For example, TG-DTA measurement of tetraethylene glycol in a nitrogen atmosphere shows a weight loss at 155°C to 265°C, which indicates that tetraethylene glycol is desorbed at 155°C to 265°C, and the desorption start temperature of tetraethylene glycol is required to be 155°C. Also, TG-DTA measurement of polyethylene glycol 300 (PEG300) in a nitrogen atmosphere shows a weight loss at 160°C to 360°C or less, which indicates that PEG300 is desorbed at 160°C to 360°C, and the desorption start temperature of PEG300 is required to be 160°C.

The bonding metal paste preferably contains a polyether alcohol-based dispersion medium having a desorption temperature that is different from the desorption temperature of the organic protective agent of the copper particles by 0°C or more and 100°C or less. Furthermore, the difference between the desorption temperature of the polyether alcohol-based dispersion medium and the desorption temperature of the organic protective agent of the copper particles is preferably 0°C or more and 100°C or less. When there are multiple types of polyether alcohol-based dispersion mediums and multiple types of organic protective agents, it is preferable that the difference between the desorption temperature of the polyether alcohol-based dispersion medium that desorbs at the highest temperature and the desorption temperature of the organic protective agent that desorbs at the lowest temperature is 0°C or more and 100°C or less.

The content of the polyether alcohol-based dispersion medium is preferably 0.1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less, based on the total mass of the metal paste for joining. In addition, the content of the polyether alcohol-based dispersion medium in the metal paste for joining may be 0.5% by mass or more and 4.0% by mass or less, based on the total mass of the metal paste, from the viewpoint of achieving both removal of the oxide film and suppression of deformation of the sintered body.

In addition, in the bonding metal paste of this embodiment, the content ratio of the alcohol-based dispersion medium and the polyether alcohol-based dispersion medium is preferably 10% by mass or more and 90% by mass or less, more preferably 30% by mass or more and 70% by mass or less, and even more preferably 40% by mass or more and 60% by mass or less, based on the total content of the alcohol-based dispersion medium and the polyether alcohol-based dispersion medium.

Furthermore, the total content of the alcohol-based dispersion medium and the polyether alcohol-based dispersion medium in the bonding metal paste of this embodiment is preferably 1% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 20% by mass or less, and even more preferably 7% by mass or more and 15% by mass or less, based on the total mass of the bonding metal paste.

The metal paste for bonding of this embodiment preferably does not contain a dispersion medium whose weight loss rate at 500°C is 95% or less when measured by TG-DTA in a nitrogen atmosphere.

For example, in a TG-DTA measurement of phloroglucinol in a nitrogen atmosphere, weight loss was observed from 200°C, and it was confirmed that the desorption starting temperature of phloroglucinol was 200°C, but it was not completely desorbed even at 500°C (weight loss rate 68%). In addition, in a TG-DTA measurement of D-glucose in a nitrogen atmosphere, weight loss was observed from 210°C, and it was confirmed that the desorption starting temperature of D-glucose was 210°C, but it was not completely desorbed even at 500°C (weight loss rate 85%). It is preferable that the metal paste for bonding of this embodiment does not contain such a dispersion medium.

The bonding metal paste of this embodiment may contain a dispersion medium other than the above-mentioned alcohol-based dispersion medium and polyether alcohol-based dispersion medium, as long as the effect of the present invention is not impaired. Examples of the dispersion medium include ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl methyl ether, diethylene glycol isopropyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, dipropylene glycol dimethyl ether, and tripropylene glycol dimethyl ether, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, and diethylene glycol ethyl ether. Examples of the mercaptans having an alkyl group of 1 to 18 carbon atoms include esters such as ethyl mercaptan, n-propyl mercaptan, i-propyl mercaptan, n-butyl mercaptan, i-butyl mercaptan, t-butyl mercaptan, pentyl mercaptan, hexyl mercaptan, and dodecyl mercaptan. Examples of mercaptans having a cycloalkyl group with 5 to 7 carbon atoms include cyclopentyl mercaptan, cyclohexyl mercaptan, and cycloheptyl mercaptan.

It is preferable that the polyether alcohol-based dispersion medium does not contain metal ionic sites such as alkali metal ions, alkaline earth metal ions, boron ions, and aluminum ions. Such a solvent is easy to flow at 200 to 300°C, is less likely to cause the salting-out effect that reduces the dispersibility of the metal paste, and is less likely to leave metal ions after decomposition, making it easier to remove the oxide film without reducing the properties of the joining metal paste after sintering.

Examples of the polyether alcohol dispersion medium as described above include polyester and polyethylene glycol. As the polyethylene glycol, polyethylene glycol 300 and polyethylene glycol 400 can be used.

In the joining metal paste of this embodiment, the content of the polyether alcohol-based dispersion medium remaining when the paste is heated from 25°C to 200°C is preferably 1 mass% or more based on the mass of the metal paste when heated to 200°C. In addition, in the joining metal paste of this embodiment, the content of the polyether alcohol-based dispersion medium remaining when the paste is heated from 25°C to 300°C is preferably 11.7 mass% or less, and more preferably 8.0 mass% or less, based on the mass of the metal paste when heated to 300°C. In this case, the spaces between the particles are filled with the polyether alcohol-based dispersion medium, which prevents the gas generated by reduction or volatilization from being difficult to escape, making it easier to suppress the occurrence of voids and peeling.

In addition, in the joining metal paste of this embodiment, the content of the dispersion medium (including polyether alcohol-based dispersion medium) remaining when the paste is heated from 25 ° C to 300 ° C is preferably 11.7 mass % or less, and more preferably 8.0 mass % or less, based on the mass of the metal paste when heated to 300 ° C. In the thermocompression bonding process, if the dispersion medium containing the polyether alcohol-based dispersion medium is contained in a larger amount than the pore volume between the particles, the plasticity of the metal paste tends to become too large and bleeding out tends to occur easily during compression bonding. Furthermore, if there is a lot of gas generation due to evaporation and decomposition of the dispersion medium during sintering, voids and peeling tend to occur easily. From the viewpoint of suppressing these tendencies, it is preferable to set the content of the dispersion medium (including polyether alcohol-based dispersion medium) remaining at 300 ° C to an amount that does not fill the pore volume between the particles. The void volume between particles varies depending on the particle composition, but is thought to be a maximum of about 48% by volume for a cubic arrangement of spheres of the same size (Reference: Powder Industry Series, Vol. 7, Operation and Simulation of Powder Beds, Chapter 1, Particle Packing State, Pages 1-4, 2009). In this case, the content of the dispersion medium (including polyether alcohol-based dispersion medium) that fills the void volume is 11.7% by mass.

The type of polyether alcohol-based dispersion medium contained in the metal paste can be confirmed, for example, by analyzing the high-temperature desorbed gas using gas chromatography-mass spectrometry and TOF-SIMS. As another analytical method, the supernatant obtained by separating the particle components by centrifugation may be identified using conventional organic analysis, for example, FT-IR, NMR, liquid chromatography, or a combination of these. The ratio of polyether alcohol-based dispersion medium in the dispersion medium can be quantified using liquid chromatography, NMR, etc.

One aspect of the bonding metal paste of this embodiment includes, as metal particles, sub-micro copper particles having a volume average particle size of 0.1 μm or more and 0.8 μm or less, and flake-shaped micro copper particles having a volume average particle size of 2.0 μm or more and 50 μm or less, and as a dispersion medium, a polyether alcohol-based dispersion medium, the content of which may be 2 mass% or more based on the total mass of the bonding metal paste.

(Additives)
The bonding metal paste may further contain additives such as dispersants, surface protective agents, thickeners, and thixotropy imparting agents as necessary. When the bonding metal paste contains additives, the content of the additives that are nonvolatile or nondecomposable at temperatures of 200° C. or less is preferably 20% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less. If the content of the additives is within the above range, it is easy to suppress the decrease in the sinterability of the bonding metal paste.

In the joining metal paste of this embodiment, the total content of aliphatic or aromatic monocarboxylic acids having 1 to 20 carbon atoms contained in the joining metal paste is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 5% by mass or less, and even more preferably 1% by mass or more and 3% by mass or less, based on the total amount of the joining metal paste.

The joining metal paste of this embodiment has sufficient flexibility during joining, so even if the joining metal paste between two components is thermocompressed at a temperature of 250°C or higher and lower than 350°C, the copper particles (e.g., micro copper particles and submicro copper particles) sinter to form a metallic bond, and the two components can be joined with a die shear strength of 10 MPa or higher and a thermal conductivity of 100 W/(m·K) or higher.

(Preparation of metal paste for bonding)
The bonding metal paste can be prepared by mixing the above-mentioned submicro copper particles, micro copper particles, other metal particles, and any additives in a dispersion medium. After mixing the components, a stirring process may be performed. The bonding metal paste may be adjusted in maximum particle size by classification. In this case, the maximum particle size of the dispersion can be 20 μm or less, or 10 μm or less.

The bonding metal paste may be prepared by mixing sub-micro copper particles, an organic protective agent, and a dispersion medium in advance, carrying out a dispersion process to prepare a dispersion of sub-micro copper particles, and then mixing micro copper particles, other metal particles, and any additives. By following such a procedure, the dispersibility of the sub-micro copper particles is improved, and the mixability with the micro copper particles is improved, further improving the performance of the bonding copper paste. In addition, agglomerates may be removed from the dispersion of the sub-micro copper particles by a classification operation. The sub-micro copper particles and the organic protective agent may be sub-micro copper particles treated with an organic protective agent.

The stirring process can be carried out using a stirrer. Examples of stirrers include a rotation-revolution type stirrer, a mortar mixer, a twin-screw kneader, a three-roll mill, a planetary mixer, and a thin-layer shear disperser.

The classification operation can be carried out, for example, by filtration, natural sedimentation, or centrifugation. Examples of filters for filtration include metal mesh, metal filters, and nylon mesh.

Examples of dispersion treatments include thin layer shear dispersers, bead mills, ultrasonic homogenizers, high shear mixers, narrow gap three-roll mills, wet ultra-fine particle machines, supersonic jet mills, and ultra-high pressure homogenizers.

When molding, the copper paste for bonding may be adjusted to a viscosity suitable for each printing/coating method. The viscosity of the copper paste for bonding may be, for example, a Casson viscosity at 25°C of 0.05 Pa·s or more and 2.0 Pa·s or less, or 0.06 Pa·s or more and 1.0 Pa·s or less.

The joining metal paste of this embodiment can provide sufficient joining strength even when joining components in a hydrogen-free atmosphere and at low pressure.

The inventors speculate as follows about the reason why such an effect is obtained.
(i) First, by containing the sub-micro copper particles and the micro copper particles in a specific ratio, it is possible to sufficiently suppress the volumetric shrinkage during sintering caused by the monocarboxylic acid or dispersing medium that coats the copper particles while maintaining sufficient sinterability, and it is believed that this makes it possible to ensure the strength of the sintered body and improve the bonding strength with the adherend surface even when low pressure is applied.
(ii) In addition, it is believed that the monocarboxylic acid that covers the submicro copper particles and the micro copper particles reacts with the alcohol-based compound and the polyether alcohol-based compound, and the elimination of the monocarboxylic acid proceeds at a relatively low temperature, and an active copper surface appears. When the surface of the microparticle is covered with copper oxide (when the surface of the microparticle is a copper oxide layer), it is believed that the copper oxide is reduced by the alcohol-based dispersion medium or the polyether alcohol-based dispersion medium, and an active copper surface appears. It is believed that the active copper surfaces that appear due to these actions come into contact with each other and are sintered, forming a strong copper sintered body even at low pressure.
(iii) Furthermore, it is believed that the alcohol-based compound and the polyether alcohol-based compound function as reducing agents for copper, so that sintering of copper particles proceeds sufficiently without the need for an active reducing atmosphere, making it possible to achieve strong bonding even with a relatively low pressure.

In addition, according to the metal paste for joining of this embodiment, the above-mentioned alcohol-based compound and the above-mentioned polyether alcohol-based compound are combined as a dispersion medium, so that even large-area components can be joined while suppressing the occurrence of voids, and a decrease in joining strength and joining reliability due to voids can be prevented.

<Sintered body and its manufacturing method>
The sintered body of the present embodiment is a sintered body of the bonding metal paste of the present embodiment, and can bond members together.

The manufacturing method of the sintered body of this embodiment includes a step of sintering the bonding metal paste of this embodiment. For example, the step includes applying the bonding metal paste to a member or the like and then sintering the paste. The application method may be any method that can deposit the bonding metal paste. Examples of such methods include inkjet printing, super inkjet printing, screen printing, transfer printing, offset printing, jet printing, dispenser, jet dispenser, needle dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, bar coat, applicator, particle deposition method, spray coater, spin coater, dip coater, electrochemical coating, etc. The thickness of the bonding metal paste may be 1 μm or more, 5 μm or more, 10 μm or more, or 20 μm or more. The thickness of the joining metal paste may be 3000 μm or less, 1000 μm or less, 500 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, or 150 μm or less.

The applied bonding metal paste may be dried as appropriate to prevent flow and void generation during sintering. The gas atmosphere during drying may be air, an oxygen-free atmosphere such as nitrogen or a rare gas, or a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying by leaving at room temperature, drying by heating, or drying under reduced pressure.

For example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, a hot plate press device, etc. can be used for drying by heating or drying under reduced pressure. The drying temperature and time may be appropriately adjusted according to the type and amount of the dispersion medium used. The drying temperature and time are preferably 50°C or higher and 150°C or lower in the air or in an oxygen-free atmosphere.

Sintering can be performed by applying pressure and heat to the copper paste for bonding. For example, a heating device equipped with a compression mechanism, a press, etc. can be used for the pressure and heat treatment. In addition, even if a heating device without a compression mechanism, such as a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, etc., is used, pressure sintering bonding can be performed by applying pressure to a laminate in which the metal paste for bonding is sandwiched between members using a jig or weight, and then heating the laminate using these devices in this state.

The gas atmosphere during sintering may be an oxygen-free atmosphere from the viewpoint of suppressing oxidation of the sintered body and the members to be joined. The gas atmosphere during sintering may be a reducing atmosphere from the viewpoint of removing surface oxides of the copper particles of the joining metal paste. Examples of the oxygen-free atmosphere include the introduction of an oxygen-free gas such as nitrogen or a rare gas, or a vacuum. Examples of the reducing atmosphere include a pure hydrogen gas, a mixed gas of hydrogen and nitrogen such as forming gas, nitrogen containing formic acid gas, a mixed gas of hydrogen and a rare gas, and a rare gas containing formic acid gas.

In this embodiment, even when bonding is performed in an atmosphere that does not contain hydrogen and at low pressure, the components can be bonded with sufficient bonding strength. Examples of atmospheres that do not contain hydrogen include nitrogen, rare gas, heat-resistant organic gas, water vapor, a mixture of these gases, or a vacuum. Examples of low pressure conditions include 2 MPa or less, and may be 0.1 MPa or more and 2 MPa or less, or 0.3 MPa or more and 2 MPa or less.

The maximum temperature reached during the heat treatment may be 200°C or more and 450°C or less, 250°C or more and 400°C or less, 250°C or more and 350°C or less, or 250°C or more and 300°C or less, from the viewpoint of reducing thermal damage to the members being joined and improving the yield.

The time for which the maximum temperature is held may be from 1 minute to 60 minutes, from 1 minute to less than 40 minutes, or from 1 minute to less than 30 minutes, from the viewpoint of volatilizing all of the dispersion medium and improving the yield. In particular, when the maximum temperature is 250°C or higher, sintering tends to proceed sufficiently with a holding time of 60 minutes or less.

<Joint body and semiconductor device>
Hereinafter, preferred embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

Figure 1 is a schematic cross-sectional view showing an example of a bonded body manufactured using the bonding metal paste of this embodiment. The bonded body 100 of this embodiment includes a first member 1 having a first base 1a and a first metal layer 1b, a second member 3 having a second base 3a and a second metal layer 3b, and a sintered body 2 that bonds the first member and the second member.

Examples of the first member 1 and the second member 3 include semiconductor elements such as IGBTs, diodes, Schottky barrier diodes, MOS-FETs, thyristors, logic, sensors, analog integrated circuits, LEDs, semiconductor lasers, and oscillators, lead frames, ceramic substrates with metal plates attached (e.g., DBC), substrates for mounting semiconductor elements such as LED packages, power supply members such as copper ribbons, metal blocks, and terminals, heat sinks, and water-cooled plates.

The first member 1 and the second member 3 may have a first metal layer 1b and a second metal layer 3b that form a metal bond with the sintered body 2 of the bonding copper paste on the surface in contact with the sintered body 2 of the bonding metal paste. Examples of metals constituting the first metal layer 1b and the second metal layer 3b include copper, nickel, silver, gold, palladium, platinum, lead, tin, cobalt, etc. These metals may be used alone or in combination of two or more. The first metal layer 1b and the second metal layer 3b may also be an alloy containing the above metals. In addition to the above metals, examples of metals used in the alloy include zinc, manganese, aluminum, beryllium, titanium, chromium, iron, molybdenum, etc. Examples of members having the first metal layer 1b and the second metal layer 3b include members having various metal platings, wires, chips having metal platings, heat spreaders, ceramic substrates to which metal plates are attached, lead frames having various metal platings or lead frames made of various metals, copper plates, and copper foils.

From the viewpoint of sufficiently bonding the first member and the second member, the die shear strength of the bonded body may be 10 MPa or more, 15 MPa or more, 20 MPa or more, or 30 MPa or more. The die shear strength can be measured using a universal bond tester (4000 series, manufactured by DAGE Corporation) or the like.

The thermal conductivity of the sintered body may be 100 W/(m·K) or more, 120 W/(m·K) or more, or 150 W/(m·K) or more, from the viewpoint of heat dissipation and connection reliability at high temperatures. The thermal conductivity can be calculated from the thermal diffusivity, specific heat capacity, and density of the sintered body of the joining metal paste.

Next, we will explain the method for manufacturing a bonded body using the bonding metal paste of this embodiment.

The method for manufacturing a bonded body using the bonding metal paste of this embodiment includes a step of preparing a laminate in which a first member, the bonding metal paste, and a second member are laminated in this order, and a sintering step of sintering the bonding metal paste in the laminate.

The laminate can be prepared, for example, by applying the bonding metal paste of this embodiment to the necessary portion of the second member described above, and then placing the first member described above on the bonding metal paste. In this case, a laminate can be prepared in which the first member, the bonding metal paste, and the second member are laminated in this order on the side in which the weight of the first member acts, and the bonding metal paste of this laminate can be sintered under the weight of the first member alone, or under the weight of the first member and a predetermined pressure (for example, 0.3 MPa or more, preferably 1 MPa or more and 2 MPa or less) as necessary. The direction in which the weight of the first member acts can also be referred to as the direction in which gravity acts.

The method for applying the bonding metal paste of this embodiment to the necessary portion of the second member may be any method that allows the bonding copper paste to be deposited. As such a method, the above-mentioned application method may be used. The thickness of the bonding metal paste may also be within the above-mentioned range.

The joining metal paste applied to the second member may be dried as appropriate to prevent flow and the generation of voids during sintering. The drying conditions may be the same as those used in the drying method for the sintered body described above.

Methods for placing the first component on the bonding metal paste include, for example, a chip mounter, a flip chip bonder, and a carbon or ceramic positioning jig.

In this embodiment, the step of preparing the laminate includes a first step of forming a coating film of a bonding metal paste in the bonding region between the first member and the second member, and a second step of laminating the first member and the second member via the coating film, and the bonding region has a coating film-formed region where the coating film is formed and a non-coating film-formed region where the coating film is not formed, and the non-coating film-formed region may be continuous to the end of the bonding region. The non-coating film-formed region may be provided between the coating film-formed regions. The bonding region is also referred to as a region where the first member and the second member are bonded by a sintered body of the coating film of the bonding metal paste when viewed in plan.

The above method makes it easy to obtain sufficient bonding strength even when the bonding area of the components is large. This method is particularly suitable for manufacturing a bonded body in which a substrate on which a high-heat-generating semiconductor device is mounted is bonded to a heat sink.

When the bonding area is large, it becomes difficult for the gas generated during sintering of the metal paste to escape. However, with the above method, the non-film-forming area allows the gas to efficiently escape outside the bonding area, suppressing the occurrence of voids and peeling caused by the gas generated during sintering.

The coating film of the bonding metal paste formed in the first step may have a predetermined printing pattern. Figures 2 and 3 are diagrams showing examples of the printing pattern of the bonding metal paste. The printing pattern shown in (a) of Figure 2 is a pattern in which a line-shaped coating non-forming region 12 having a predetermined width is provided between the coating film forming regions 10. A plurality of the line-shaped coating non-forming regions 12 may be provided. The printing pattern shown in (a) of Figure 2 is a pattern in which the line-shaped coating non-forming regions 12 are provided so as to intersect with each other. The coating film forming region 10 may have any shape, and may be a strip shape (e.g., (a) of Figure 2), a square shape (e.g., (b) of Figure 2), a hexagonal shape (e.g., (c) of Figure 2), or a circle (e.g., (a) and (b) of Figure 3). The printing pattern may also have a coating non-forming region with one end closed and the other end leading to the end of the bonding region.

It is preferable that the coating film-forming region 10 is provided so that the shortest distance to the edge of the non-coating film-forming region 12 or the joining region is within 8 mm. For example, in the printing patterns shown in (a) to (c) of Figure 2 and (a) to (b) of Figure 3, the coating film-forming region 10 can be provided so that the width (W2)/2 does not exceed 8 mm.

The non-coating region 12 may have any shape, such as a line shape (e.g., FIG. 2(a)), a lattice shape (e.g., FIG. 2(b) and FIG. 3(a)), or a honeycomb shape (e.g., FIG. 2(c) and FIG. 3(b)). The non-coating region 12 may have a constant width (e.g., FIG. 2(a) to (c)) or different widths (e.g., FIG. 3(a) to (b)) as long as the width is set so that the non-coating region 12 is not filled with the joining metal paste during thermocompression bonding. The non-coating region 12 may have a straight, curved, or wavy shape.

The width W1 of the non-coating region 12 depends on the thickness of the coating, but for example, when the coating thickness is 50 to 500 μm, it may be 100 μm or more, or may be 200 μm or more. When the non-coating region 12 has different widths, the width of the narrowest part may be in the above range. When one end of the non-coating region 12 is closed, the smallest width of the path from the closed part to the end of the joining region may be in the above range.

From the viewpoint of making it easier to ensure bonding strength or thermal conductivity, the area ratio of the non-coated area in the bonding area (in other words, the ratio of the area of the non-coated area to the total area of the coated area and the non-coated area) is preferably 60% or less, more preferably 40% or less, and even more preferably 30% or less.

Furthermore, in the above method, the total area of the coating film-forming region may be 900 ^mm2 or more, the shortest distance of the joining metal paste in the coating film-forming region to the edge of the non-coating film-forming region or the joining region may be within 8 mm, and the minimum width in the non-coating film-forming region may be 100 μm or more.

The above-mentioned printing pattern can be formed using the above-mentioned application method, but it is also possible to uniformly apply the joining metal paste to the second member, dry it, and then remove a part of the joining metal paste coating to form a non-coating region between the coating regions. Methods for removing a part of the joining metal paste coating include a cutting method using a blade or scraper, and a method of pressing a die having a protrusion corresponding to the non-coating region. After removing a part of the joining metal paste coating, shavings may be removed using an air blower or the like.

The content of the polyether alcohol-based compound in the joining metal paste may be 0.5% by mass or more and 4.0% by mass or less based on the total amount of the joining metal paste. When the content of the polyether alcohol-based compound is in this range, the above-mentioned effects are easily obtained, and deformation of the copper sintered body is suppressed when the metal paste is sintered, making it easier to suppress the metal paste from flowing too much during pressure joining, resulting in the non-film-formed areas being filled up.

In the above method, the micro copper particles may be flake-shaped. In this case, even if the coating of the bonding metal paste is dried, the flake-shaped micro copper particles function as a reinforcing material, thereby preventing peeling and cracking due to shrinkage of the coating. Therefore, the fluidity of the coating is reduced by drying, making it easier to prevent the metal paste from flowing too much during pressure bonding, resulting in the non-coating area being filled in.

Furthermore, in the above method, the total area of the coating film-forming region may be 900 ^mm2 or more, the shortest distance of the joining metal paste in the coating film-forming region to the edge of the non-coating film-forming region or the joining region may be within 8 mm, and the minimum width in the non-coating film-forming region may be 100 μm or more.

In the sintering process, the laminate is heat-treated to sinter the joining metal paste. The sintering conditions can be the same as those used in the sintering method for the sintered body described above.

By using the bonding metal paste of this embodiment, a laminate can be pressurized, heated, and sintered to obtain a bonded body with sufficient bonding strength. For example, a bonded body with sufficient bonding strength can be obtained by heating the laminate while applying a pressure of 0.3 MPa or more, or 1 MPa or more, and preferably 2 MPa or less to the laminate. If the pressure applied during sintering is within the above range, this can be achieved using a jig equipped with a weight or pressure mechanism, and since no special pressure device is required, it is possible to reduce voids and further improve die shear strength and connection reliability without compromising yield.

In the above-mentioned bonded body, at least one of the first member and the second member may be a semiconductor element. Examples of the semiconductor element include a power module consisting of a diode, a rectifier, a thyristor, a MOS gate driver, a power switch, a power MOSFET, an IGBT, a Schottky diode, a fast recovery diode, etc., a transmitter, an amplifier, an LED module, etc. In such a case, the above-mentioned bonded body becomes a semiconductor device. The obtained semiconductor device can have sufficient die shear strength and connection reliability.

Figure 4 is a schematic cross-sectional view showing an example of a bonded body manufactured by carrying out the above-mentioned first and second steps. The bonded body 110 shown in Figure 4 includes a first member 1 having a first base 1a and a first metal layer 1b, a second member 3 having a second base 3a and a second metal layer 3b, and a sintered body 2' that bonds the first member and the second member, and the copper sintered body 2' is divided into a plurality of copper sintered bodies by areas where no copper sintered body is present, or the copper sintered body 2' includes an area where no copper sintered body is present, and the area is continuous to the outside of the copper sintered body. Other than the sintered body 2', the bonded body 110 can have the same configuration as the bonded body 100 in Figure 1.

The above-mentioned bonded body may be a semiconductor device in which one of the first member and the second member is a mounting substrate and the other is a heat sink.

Figure 5 is a schematic cross-sectional view showing an example of a semiconductor device manufactured using the bonding metal paste of this embodiment. The semiconductor device 200 shown in Figure 5 is composed of a semiconductor element 4 having a metal layer 4b and a base 4a connected to a lead frame 5 having a metal layer 5b and a base 5a via a sintered body 2 of the bonding copper paste of this embodiment, and a mold resin 6 that molds them. The semiconductor element 4 is connected to a lead frame 8 having a metal layer 8b and a base 8a via a wire 7.

Semiconductor devices manufactured using the bonding copper paste of this embodiment include, for example, power modules consisting of diodes, rectifiers, thyristors, MOS gate drivers, power switches, power MOSFETs, IGBTs, Schottky diodes, fast recovery diodes, etc., transmitters, amplifiers, high-brightness LED modules, semiconductor laser modules, logic, sensors, etc.

The semiconductor device can be manufactured in the same manner as the manufacturing method of the bonded body described above. That is, the manufacturing method of the semiconductor device may include a step of preparing a laminate in which a semiconductor element is used for at least one of the first member and the second member, the first member, the bonding metal paste, and the second member are laminated in this order, and heating the laminate in a state in which a pressure of 1 MPa or more, preferably 2 MPa or less, is applied to the laminate, thereby sintering the bonding metal paste. Such a step may include, for example, a step of providing a bonding metal paste on a lead frame 8, placing a semiconductor element 4, and heating the laminate under pressure. The semiconductor device obtained can have sufficient die shear strength and connection reliability even when bonding is performed at a relatively low pressure. The semiconductor device of this embodiment has sufficient bonding strength and is provided with a copper sintered body having a high thermal conductivity and melting point, and therefore has sufficient die shear strength, excellent connection reliability, and excellent power cycle resistance.

The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples.

The characteristics of each example and comparative example were measured using the following methods.

(1) Desorption temperature of the dispersion medium and the organic protective agent (measured by TG-DTA (Thermogrammetry-Differential Thermal Analysis))
10 mg of copper particles coated with a dispersion medium or an organic protective agent was placed on an Al sample pan for TG-DTA measurement, and this was set in the sample holder of a TG-DTA measurement device (SII Nano Technology Co., Ltd., EXSTAR6000 TG/DTA6300). While flowing nitrogen at a flow rate of about 400 mL/min, the sample was heated from room temperature (25 ° C) to about 500 ° C at a heating rate of 10 ° C/min, and the weight change and thermal behavior at that time were measured. The temperature at which the weight change started was the temperature at which desorption began, and the temperature at which the weight loss stopped was the temperature at which desorption was completed. In addition, for copper particles coated with an organic protective agent, the weight loss amount was taken as the amount of the organic protective agent treated (the amount attached to the copper particles).

(2) Die shear strength of 3 mm chip Metal paste was applied by stencil printing using a metal squeegee on a nickel-plated copper plate (19 mm x 25 mm x 3 mm) with a metal mask having nine 3 mm x 3 mm square openings on a 100 μm thick stainless steel plate. A silicon chip (area 3 mm x 3 mm, thickness 400 μm, having a nickel-plated layer as an adhesion surface with the metal paste) was placed on the applied metal paste and lightly pressed with tweezers to obtain a laminate. The laminate was heated at 90 ° C. for 30 minutes in air on a hot plate (manufactured by AS ONE Corporation, EC HOTPLATE EC-1200N). The laminate was set in a bonding device (manufactured by Ayumi Kogyo Co., Ltd.), and after reducing the pressure to 13 Pa to remove the air, the laminate was pressurized and heated to bond at the specified temperature, pressure, and time shown in Tables 1 to 6 while flowing nitrogen gas to an atmospheric pressure of 80 kPa, and a bonded body in which the copper plate and the silicon chip were bonded with a copper sintered body was obtained. The bonded body was cooled with nitrogen gas, and when it reached 50° C. or lower, it was taken out into the air.

The adhesive strength of the resulting bonded bodies was evaluated by die shear strength. Using a universal bond tester (4000 series, manufactured by DAGE) equipped with a 1 kN load cell, the silicon chip was pressed horizontally at a measurement speed of 500 μm/s and a measurement height of 100 μm to measure the die shear strength of the bonded bodies. The average value of the measurements for five bonded bodies was taken as the die shear strength.

(3) Die shear strength of 10 mm chip The metal paste was applied by stencil printing using a metal squeegee on a nickel-plated copper plate (19 mm x 25 mm x 3 mm) with a metal mask having one 10 mm x 10 mm square opening on a 100 μm thick stainless steel plate. A silicon chip (area 10 mm x 10 mm, thickness 400 μm, having a nickel-plated layer as the adhesion surface with the metal paste) was placed on the applied metal paste and lightly pressed with tweezers to obtain a laminate. The laminate was heated at 90 ° C. for 30 minutes in air on a hot plate (manufactured by AS ONE Corporation, EC HOTPLATE EC-1200N). The laminate was placed in a bonding device (manufactured by Ayumi Industries Co., Ltd.), and the pressure was reduced to 13 Pa to remove the air. Then, while flowing nitrogen gas to an atmospheric pressure of 80 kPa, the laminate was pressurized and heated to bond under the bonding conditions (temperature, pressure, and time) shown in Tables 1 to 6, to obtain a bonded body in which the copper plate and the silicon chip were bonded with a copper sintered body. This bonded body was cooled with nitrogen gas, and when it became 50°C or less, it was taken out into the air.

The adhesive strength of the resulting bonded bodies was evaluated by die shear strength. Using a universal bond tester (4000 series, manufactured by DAGE) equipped with a 1 kN load cell, the silicon chip was pressed horizontally at a measurement speed of 500 μm/s and a measurement height of 100 μm to measure the die shear strength of the bonded bodies. The average value of the measurements for five bonded bodies was taken as the die shear strength.

In the above die shear strength measurement, if the chip itself is destroyed, this is shown in the table as "chip destruction."

(4) Bonding area of sintered copper to chip The bonded bodies prepared in the above "(2) Die shear strength of 3 mm chip" and the bonded bodies prepared in the above "(3) Die shear strength of 10 mm chip" were analyzed for the bonding interface between the chip and the sintered copper using a probe with a frequency of 110 kHz in an ultrasonic flaw detector (Insight Insight-300), and an ultrasonic flaw detection image (SAM image) was obtained. The bonding area of the sintered copper to the chip was calculated from the ratio of the black area (area where the copper sintered body is bonded to the chip) and the white area (area where the copper sintered body is not bonded to the chip) to the chip area in the obtained SAM image.

(5) Joint cross section of sintered copper The joint made in the above "(3) Die shear strength of 10 mm chip" was fixed in a cup with a sample clip (Samplklip I, manufactured by Buehler), and epoxy casting resin (Epomount, manufactured by Refine Tech) was poured around until the entire joint was buried, and the joint was left to stand in a vacuum desiccator and depressurized for 1 minute to degas. After that, the joint was left to stand at room temperature for 10 hours to harden the epoxy casting resin, and a sample was prepared. The sample was cut near the silicon chip using a Refine Saw Excel (manufactured by Refine Tech). The joint was polished to the center with a polishing device (Refine Polisher HV, manufactured by Refine Tech) equipped with water-resistant abrasive paper (Carbomac Paper, manufactured by Refine Tech) to reveal a cross section. This cross section was subjected to cross-section polishing with Ar ions (Hitachi High-Technologies IM4000). The joint cross section of the copper sintered body was observed using a scanning electron microscope (Schottky FE-SEM SU5000, manufactured by Hitachi High-Technologies Corporation).

[Preparation of metal paste for bonding-1]
Metallic bonding pastes were prepared according to the formulations in Tables 1 to 6.

Example 1
As a dispersion medium, 9 parts by mass of dihydroterpineol (manufactured by Nippon Terpene Chemical Co., Ltd.), 0.5 parts by mass of tetraethylene glycol (manufactured by Fujifilm Wako Pure Chemical Co., Ltd.), and 1.5 parts by mass of polyethylene glycol 200 (PEG200) (manufactured by Fujifilm Wako Pure Chemical Co., Ltd.) were mixed. 10 parts by mass of 3L3N (manufactured by Fukuda Metal Foil and Powder Co., Ltd., product name, 50% volume average particle size 8.0 μm) as micro copper particles, and 91 parts by mass of CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, 50% volume average particle size 0.36 μm) as sub-micro copper particles were weighed and added, and mixed for 5 minutes in an automatic mortar. After transferring the mixture to a poly bottle, it was subjected to a Thinky Corporation stirrer (Awatori Rentaro ARE-310) at 2000 rpm for 2 minutes under reduced pressure to obtain a metal paste for bonding. Using this metal paste, a bonded body was produced under the bonding conditions (temperature, pressure, and time) shown in Table 1, and various measurements and analyses were carried out. The evaluation results are shown in Table 1.

(Examples 2 and 3)
A metal paste was obtained in the same manner as in Example 1, except that the blending amounts of tetraethylene glycol and PEG 200 were changed to the ratios shown in the table. Using this metal paste, a bonded body was produced under the bonding conditions (temperature, pressure, and time) shown in Table 1, and various measurements and analyses were performed. The evaluation results are shown in Table 1.

(Examples 4 to 6)
A metal paste was obtained in the same manner as in Example 1, except that polyethylene glycol 300 (PEG300) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of PEG200, and the blending amounts of tetraethylene glycol and PEG300 were set to the ratios shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 1, and various measurements and analyses were performed. The evaluation results are shown in Table 1.

(Examples 7 to 9)
A metal paste was obtained in the same manner as in Example 1, except that polyethylene glycol 400 (PEG400) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of PEG200, and the blending amounts of tetraethylene glycol and PEG400 were set to the ratios shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 2, and various measurements and analyses were performed. The evaluation results are shown in Table 2.

(Examples 10 to 12)
A metal paste was obtained in the same manner as in Example 1, except that diethylene glycol and PEG 300 were used instead of tetraethylene glycol and PEG 200, and the blending amounts of these were set to the ratios shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 2, and various measurements and analyses were performed. The evaluation results are shown in Table 2.

(Examples 13 to 18)
A metal paste was obtained in the same manner as in Example 1, except that MA-C025KFD (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, lubricant-free product, 50% volume average particle size 5 μm) was used as the micro copper particles and the blending amount was set to the ratio shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 3, and various measurements and analyses were performed. The evaluation results are shown in Table 3.

(Examples 19 to 30)
A metal paste was obtained in the same manner as in Example 15. Using this metal paste, a bonded body was produced under the bonding conditions (temperature, pressure, and time) shown in Tables 4 and 5, and various measurements and analyses were performed. The evaluation results are shown in Tables 4 and 5.

(Comparative Examples 1 and 2)
A metal paste was obtained in the same manner as in Example 1, except that micro copper particles were not blended, and the dispersion medium and submicro copper particles were blended as shown in the table. Using this metal paste, a bonded body was produced under the bonding conditions (temperature, pressure, and time) shown in Table 6, and various measurements and analyses were performed. The evaluation results are shown in Table 6.

(Comparative Examples 3 to 5)
A metal paste was obtained in the same manner as in Example 1, except that the amounts of CH-0200 submicro copper particles and 3L3 micro copper particles were mixed in the ratios shown in the table. Using this metal paste, a bonded body was produced under the bonding conditions (temperature, pressure, and time) shown in Table 6, and various measurements and analyses were performed. The evaluation results are shown in Table 6.

(Comparative Example 6)
A metal paste was obtained in the same manner as in Example 1, except that tetradecanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of tetraethylene glycol and PEG 200, and the blending amounts were set to the ratios shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 7, and various measurements and analyses were performed. The evaluation results are shown in Table 7.

(Comparative Example 7)
A metal paste was obtained in the same manner as in Example 1, except that tetradecane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of tetraethylene glycol and PEG 200, and the blending amounts were set to the ratios shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 7, and various measurements and analyses were performed. The evaluation results are shown in Table 7.

(Comparative Example 8)
A metal paste was obtained in the same manner as in Example 1, except that tetradecanol and tetradecane were used instead of dihydroterpineol, tetraethylene glycol, and PEG 200, and the blending amounts of these were set to the ratios shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 7, and various measurements and analyses were performed. The evaluation results are shown in Table 7.

(Comparative Example 9)
A metal paste was obtained in the same manner as in Example 1, except that tetradecane and PEG 300 were used instead of dihydroterpineol, tetraethylene glycol, and PEG 200, and the blending amounts of these were set to the ratios shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 7, and various measurements and analyses were performed. The evaluation results are shown in Table 7.

(Comparative Example 10)
A metal paste was obtained in the same manner as in Example 1, except that tetradecane and tributyrin (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were used instead of dihydroterpineol, tetraethylene glycol, and PEG 200, and the blending amounts of these were set to the ratios shown in the table. A bonded body was produced using this metal paste under the bonding conditions (temperature, pressure, and time) shown in Table 7, and various measurements and analyses were performed. The evaluation results are shown in Table 7.

The desorption starting temperatures of the dispersion media used in the examples and comparative examples were as follows.
Dihydroterpineol: 70°C
Tetraethylene glycol: 155°C
Diethylene glycol: 105°C
PEG200: 140℃
PEG300: 160℃
PEG400: 175℃

Figure 6 is an ultrasonic inspection image (SAM image) of a 10 mm x 10 mm chip after bonding in Example 15. In the SAM image, the entire chip is a black area, which indicates that the chip and the copper sintered body are bonded without voids. Figure 7 is an SEM image of the bonded cross section after bonding in Example 15. The substrate is bonded without voids by the copper sintered body. Similarly, Figure 8 is an SEM image of the bonded cross section after bonding in Example 24. The substrate is bonded without voids by the copper sintered body. On the other hand, Figure 9 is a SAM image of a 10 mm x 10 mm chip after bonding in Comparative Example 2. In the SAM image, the white area of the chip indicates that there are voids and peeling between the chip and the copper sintered body. Figure 10 is an SEM image of the bonded cross section after bonding in Comparative Example 2. It can be seen that a large peeling has occurred at the interface between the copper sintered body and the chip, and that the chip is not bonded to the chip. Similarly, Figure 11 is an SEM image of the bonded cross section after bonding in Comparative Example 3. It can be seen that there are large voids and cracks in the copper sintered body, and that the copper sintered body has peeled off from the chip and substrate.

[Preparation of metal paste for bonding-2]
(Example B-1)
7.2 parts by mass of dihydroterpineol (manufactured by Nippon Terpene Chemical Co., Ltd.) as a dispersion medium and 83.6 parts by mass of CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, laser scattering method 50% volume average particle size 0.36 μm) as submicron copper particles were mixed and stirred for 30 minutes at a rotation speed of 300 rpm using a planetary mixer (manufactured by Primix Co., Ltd.). The resulting mixture was dispersed once using a dispersizer (manufactured by Shinto Kogyo Co., Ltd.) under conditions of a gap of 50 μm and a rotation speed of 12,000 rpm to obtain a dispersion liquid. To this dispersion, 2.4 parts by mass of tetraethylene glycol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a dispersion medium, 2.4 parts by mass of polyethylene glycol 300 (PEG300) (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a reducing oligomer solvent, and 4.4 parts by mass of 3L3N (manufactured by Fukuda Metal Foil and Powder Co., Ltd., product name, laser scattering method 50% volume average particle size 6.0 μm) as micro copper particles were added, and the mixture was stirred using a planetary mixer at a rotation speed of 300 rpm for 30 minutes (15 minutes at normal pressure and 15 minutes at reduced pressure) to obtain a metal paste for joining.

(Examples B-2 to B-11)
A metal paste was obtained in the same manner as in Example B-1, except that the composition was changed to that shown in Table 8 or 9.

The details of each component in the table are as follows:
2L3N: Product name, manufactured by Fukuda Metal Foil & Powder Co., Ltd., Laser scattering method 50% volume average particle size 10 μm
4L3N: Product name, manufactured by Fukuda Metal Foil & Powder Co., Ltd., Laser scattering method 50% volume average particle size 3 μm
C3: Product name, manufactured by Fukuda Metal Foil and Powder Co., Ltd., Laser scattering method 50% volume average particle size 37 μm

[Preparation of bonded samples]
The metal paste obtained above was stencil printed on a copper plate measuring 100 mm x 100 mm x 3 mm thick, using a 300 μm thick stainless steel mask having ² a mm x a mm square openings in a grid pattern at intervals of b mm, and a squeegee (see FIG. 12). The grid pattern was arranged so as to be centrosymmetric.

Next, the copper plate on which the metal paste was printed was heated for 10 minutes on a hot plate heated to 90° C. After that, a copper plate measuring 100 mm×100 mm×thickness 3 mm was placed on the metal paste, and thermocompression bonded using an atmospherically controlled thermocompression bonding device (RF-100B, manufactured by Ayumi Industries Co., Ltd.) in the following manner.
(1) Set the sample. (2) Reduce pressure to 3 Pa. (3) Introduce nitrogen to normal pressure, then flow at 8 L/min. (4) Pressurize the bonded sample at 1.225 kN (1 MPa). (5) Heat the hot plate of the thermocompression bonding device so that the temperature is raised to 300°C over 15 minutes and maintained at 300°C for 30 minutes. (6) Stop heating and forcibly cool the hot plate by blowing nitrogen. (7) Remove the bonded sample when the temperature of the hot plate falls below 50°C.

[Evaluation of bonded samples]
A chisel was hammered between the joined copper plates, and the case where the joint layer was destroyed and the copper plates separated was recorded as "Yes", and the case where the copper plates did not separate was recorded as "No".

1...first member, 1a...first base, 1b...first metal layer, 2, 2'...sintered body, 3...second member, 3a...second base, 3b...second metal layer, 4...semiconductor element, 4a...base of semiconductor element, 4b...metal layer of semiconductor element, 5...lead frame, 5a...base, 5b...metal layer, 6...mold resin, 7...wire, 8...lead frame, 8a...base, 8b...metal layer, 10...coating film-formed area, 12...non-coating film-formed area, 100...joint, 200...semiconductor device

Claims (12)

preparing a laminate in which a first member, a bonding metal paste, and a second member are laminated in this order;
a sintering step of sintering the bonding metal paste in the laminate in an atmosphere not containing hydrogen;
Equipped with
The bonding metal paste contains metal particles and a dispersion medium,
The metal particles include sub-micro copper particles coated with an aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms and having a volume average particle size of 0.1 μm to 0.9 μm, and micro copper particles coated with an aliphatic or aromatic monocarboxylic acid having 1 to 20 carbon atoms or copper oxide and having a volume average particle size of 2 μm to 50 μm,
the dispersion medium comprises an alcohol-based compound having a hydroxyl group at its terminal and no ether bond in its molecular chain, and a polyether alcohol-based compound having a hydroxyl group at its terminal and an ether bond in its molecular chain;
The content of the submicro copper particles is 75 mass% or more and 95 mass% or less based on the total mass of the submicro copper particles and the micro copper particles . The alcohol-based compound has a boiling point under atmospheric pressure of 100° C. or higher and lower than 250° C.,
2. The method for producing a joined body according to claim 1, wherein the polyether alcohol compound has a boiling point of 250° C. or higher and 400° C. or lower under atmospheric pressure. The method for producing a joint body according to claim 1 or 2, wherein the polyether alcohol compound is polyethylene glycol 300. The method for manufacturing a joint body according to any one of claims 1 to 3, wherein the total content of aliphatic or aromatic monocarboxylic acids having 1 to 20 carbon atoms contained in the joining metal paste is 0.1% by mass or more and 10% by mass or less based on the total amount of the joining metal paste. The method for producing a joint body according to any one of claims 1 to 4, wherein the total content of the sub-micro copper particles and the micro copper particles is 80 mass% or more based on the total amount of metal particles. The method for producing a bonded body according to any one of claims 1 to 5 , wherein at least one of the first member and the second member is a semiconductor element. The step of preparing the laminate includes a first step of forming a coating film of the bonding metal paste in a bonding region between the first member and the second member, and a second step of laminating the first member and the second member via the coating film,
The bonding region has a coating film-formed region where the coating film is formed and a coating film-free region where the coating film is not formed,
The method for producing a bonded body according to any one of claims 1 to 6 , wherein the non-coated region is continuous to an end of the bonded region. The method for producing a bonded body according to claim 7 , wherein the non-coated region has a line-like, lattice-like, or honeycomb-like shape. The total area of the coating film forming region is 900 ^mm2 or more,
The shortest distance of the bonding metal paste in the coating film-forming region to the edge of the non-coating film-forming region or the bonding region is within 8 mm,
The method for producing a joined body according to claim 7 or 8 , wherein the minimum width of the non-coated region is 100 µm or more. The method for producing a joint body according to any one of claims 1 to 9 , wherein the content of the polyether alcohol-based compound in the bonding metal paste is 0.5 mass% or more and 4.0 mass% or less based on the total amount of the bonding metal paste. The method for producing a joint body according to any one of claims 1 to 10 , wherein the micro copper particles are in a flake shape. The method for producing a joint body according to any one of claims 1 to 11 , wherein the alcohol-based compound includes dihydroterpineol.

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