Silver particles, silver particle composition, metal bonding composition, semiconductor element, and method for producing silver particles

Abstract

To provide silver particles, a silver particle composition, a metal bonding composition, a semiconductor element, and a method for producing silver particles, which enable improvement of bonding strength.SOLUTION: Silver particles have an average particle diameter of 1 to 12 μm, including silver microparticles and silver nanoparticles attached to surfaces of the silver microparticles, the average circularity of the silver particles being 0.40 to 0.79, and the total amount of organic substances relative to the total amount of the silver particles being 30 ppm or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to silver particles, a silver particle composition, a composition for metal bonding, a semiconductor element, and a method for producing silver particles. [Background technology]

[0002] In recent years, with the increasing efficiency and performance of semiconductor elements, products have been developed that generate more heat and operate at higher temperatures than before. Furthermore, there is a demand for improved practicality and heat dissipation at high temperatures for the bonding materials that join semiconductor elements. While traditionally used solder and silver paste are candidates for bonding materials, there is a strong demand for materials that are more suitable for high-temperature operation.

[0003] Patent Document 1 describes a method for producing a nanoparticle-based nanoparticle composite comprising microparticles made of metals and unavoidable impurities and having an average crystallite size in the range of 0.6 to 10 μm, and nanoparticles attached to the surface of the microparticles and having an average particle size of 3 to 100 nm, with a resolution of 1.2 to 2000 cm -1 According to Patent Document 1, composite particles can be obtained that can be sintered at low temperatures and can form a sintered body that exhibits large elongation.

[0004] In Patent Document 2, silver particles having a silver powder and a silver layer made of primary particles smaller than the silver powder have a tap density of 4.0 to 7.0 g / cm. 3 and the specific surface area determined by the BET method is 0.5 to 1.5 m 2 / g. According to Patent Document 2, a paste composition containing silver particles has low viscosity and excellent dispersibility, and a cured product of the paste composition has high thermal conductivity and little warping. Furthermore, semiconductor packages obtained using the paste composition are said to have excellent adhesiveness, with no chip peeling observed after a thermal cycle test. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-110013 [Patent Document 2] Japanese Patent Publication No. 2023-106423 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Documents 1 and 2, an organic protective compound is added from the viewpoint of particle stability, and there are concerns that decomposition products may be generated from the organic protective compound during the sintering process, contaminating the semiconductor material, affecting the sintering temperature, and reducing the bonding strength.

[0007] Therefore, an object of the present disclosure is to provide silver particles, a silver particle composition, a composition for metal bonding, a semiconductor device, and a method for producing silver particles that can suppress the generation of decomposition products from an organic protective compound and improve bonding strength, as well as silver particles, a silver particle composition, a composition for metal bonding, a semiconductor device, and a method for producing silver particles that can be sintered at low temperatures. [Means for solving the problem]

[0008] As a result of extensive investigations aimed at achieving the above-mentioned object, the present inventors have discovered silver particles, a silver particle composition, a composition for metal bonding, a semiconductor element, and a method for producing silver particles that are capable of improving bonding strength by reducing the amount of a protective agent such as an organic protective compound and controlling the surface shape of the silver particles, and have completed the present disclosure.

[0009] [1] Silver particles having an average particle size of 1 to 12 μm, silver microparticles and silver nanoparticles attached to the surfaces of the silver microparticles; the average circularity of the silver particles is 0.40 to 0.79, Silver particles, wherein the total amount of organic matter relative to the total amount of the silver particles is 30 ppm or less. [2] Silver particles according to [1], in which the sodium element present on the particle surface of the silver particles is 8.0 atom % or less. [3] The silver particles according to [1] or [2], wherein the average degree of envelopment of the silver particles is 0.75 to 0.97. [4] Silver particles according to any one of [1] to [3], wherein the standard deviation of the particle size distribution of the silver nanoparticles is 2 to 50 nm. [5] Silver particles according to any one of [2] to [4], wherein the sodium element present on the particle surface of the silver particles is 1.0 atom % or more. [6] Silver particles according to any one of [1] to [5], wherein the average particle size of the silver microparticles is 1 to 12 μm. [7] Silver particles according to any one of [1] to [6], wherein the average particle size of the silver nanoparticles is 15 to 80 nm. [8] A silver particle composition comprising the silver particles according to any one of [1] to [7] and an organic solvent. [9] A composition for metal bonding, comprising the silver particle composition according to [8].

[10] A semiconductor element manufactured using the metal bonding composition according to [9].

[11] A first step of mixing a solution containing a metal compound containing elemental silver and a solution containing a reducing agent using a micromixer to obtain a first solution; a second step of mixing the first solution with a second solution containing silver microparticles with an average particle diameter of 1 to 12 μm, and attaching the nanoparticles containing elemental silver to the surfaces of the silver microparticles.

[12] The method for producing silver particles according to

[11] , wherein the reducing agent is sodium borohydride. [Effects of the Invention]

[0010] It is possible to provide silver particles, a silver particle composition, a composition for metal bonding, a semiconductor element, and a method for manufacturing silver particles that can improve bonding strength.It is also possible to provide silver particles, a silver particle composition, a composition for metal bonding, a semiconductor element, and a method for manufacturing silver particles that can be sintered at low temperatures. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram (plan view) of silver particles. [Figure 2] FIG. 1 is a schematic diagram illustrating a method for producing silver particles. [Figure 3] 1 is an SEM image of silver particles of Example 1. [Figure 4] 1 is an SEM image of silver particles in Comparative Example 1. [Figure 5] 1 is an SEM image of silver particles of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes in detail the embodiments of the present disclosure. Note that the silver particles and the like described below are intended to embody the technical concept of the present disclosure, and unless otherwise specified, the present disclosure is not limited to the following.

[0013] <Silver particles> The silver particles of the present disclosure are capable of exhibiting electrical conductivity and thermal conductivity, for example, as shown in FIG. 3, and constitute a silver particle group as an aggregate of a large number of silver particles.

[0014] The average particle size, standard deviation, and coefficient of variation of silver particles are calculated as follows. Images of silver particles are taken using a scanning electron microscope (SEM) at 2,000 to 10,000 times magnification. Images measured using a transmission electron microscope (TEM) may be used instead of a scanning electron microscope (SEM). The diameter (equivalent circle diameter) of a perfect circle having the same area as the projected area (i.e., the area in the photograph) of the silver particles projected onto a plane (plan view) is considered to be the particle size of the silver particles (hereinafter sometimes simply referred to as particles). Such particle size measurements using SEM and TEM photographs are performed on multiple particles shown in the images, and the arithmetic mean value of the particle sizes of these particles is taken as the average particle size. Furthermore, the standard deviation is calculated using this average particle size and the measured values ​​of each particle size. Furthermore, the coefficient of variation is calculated by dividing the standard deviation of particle sizes by the average particle size (average particle size).

[0015] From the viewpoint of calculating the average particle size, standard deviation, and coefficient of variation more accurately, the particle size can be determined by using the measured values ​​of particle sizes of 50 or more particles.

[0016] <Average particle size> The average particle size of the silver particles calculated by the above method is 1 to 12 μm (1 μm or more and 12 μm or less). The lower limit is preferably 1.3 μm or more, and more preferably 1.5 μm or more. The upper limit is preferably 8.0 μm or less, and more preferably 5.0 μm or less. Within the above ranges, various evaluations of the bonded member can be performed while maintaining good handleability.

[0017] <Average circularity> The average circularity of the silver particles, as expressed by the following formula (1), is 0.40 to 0.79. Circularity = 4πS / L 2 ···(1) where π is the ratio of the circumference of a circle to its circumference (3.14), and S is the area of ​​the silver particle (μm 2 ), and L is the perimeter (μm) of the silver particle. These area and perimeter are determined by taking a photograph of an image magnified 2000 to 10000 times using a scanning electron microscope (SEM) and calculating the projected area of ​​the silver particle and the perimeter of the projected view (plan view). Images measured using a transmission electron microscope (TEM) may also be used instead of a scanning electron microscope (SEM). Measurement of particle diameters using such SEM and TEM photographs is performed on multiple particles shown in the image, and the area (μm) of these particles is calculated. 2 The circularity of each particle is calculated from the particle diameter and perimeter. The circularity of multiple particles in the image is calculated, and the arithmetic mean value of the circularities of these particles is taken as the average circularity.

[0018] To calculate the average circularity more accurately, it is determined by using the measured particle diameters of 50 or more particles. In FIG. 1, the length of the solid line L of a silver particle 1 in the plan view is the perimeter, and the area of ​​this silver particle 1 is S. The average circularity is preferably 0.50 to 0.78, more preferably 0.60 to 0.77, and even more preferably 0.70 to 0.76. Within these ranges, the bonding strength (hereinafter sometimes referred to as shear strength) can be improved. When the average circularity is within the above range, the number of contact points between the silver particles and the substrate or the like to be bonded increases, which is thought to be one of the reasons for the improved shear strength.

[0019] <Average envelope degree> The average degree of envelopment of silver particles, expressed by the following formula (2), is preferably 0.75 to 0.97. Envelopment degree=L1 / L ···(2) Here, L1 is the envelope perimeter, and L is the actual perimeter described above. The envelope perimeter is the length of a line surrounding a silver particle in a plan view of the silver particle, tangent to the convex portions of the silver particle (for example, the surface of silver nanoparticle 2 in FIG. 1). In FIG. 1, the length of the dashed-dotted line L1 tangent to the convex portions of silver particle 1 in the solid line is the envelope perimeter. The envelope perimeter can also be considered as a value calculated from a virtual rubber band wrapped around the outline of a silver particle. The average envelope degree is the average value of the envelope degrees of multiple silver particles (approximately 50 to 100 particles). The average envelope degree is preferably 0.80 to 0.97, more preferably 0.85 to 0.96, and even more preferably 0.90 to 0.96. The average envelope degree may be 0.92 or more, or 0.94 or more. Furthermore, the average envelope degree may be 0.95 or less. Within the above range, the shear strength can be improved. If the average degree of envelopment is within the above range, the number of contact points with the substrate or the like to be joined by the silver particles increases, which is thought to be one of the reasons for the improvement in shear strength.

[0020] The silver particles of the present disclosure are characterized by not containing a protective agent such as an organic protective compound, or by using a protective agent in an extremely small amount. The silver particles have a total organic content (the mass ratio of the total organic content to the entire silver particles) of 30 ppm or less relative to the total weight of the silver particles. The total organic content is determined using a thermal desorption gas-gas chromatography mass spectrometer (TDS-GC / MS) and refers to the total mass of substances other than metal elements (carbon, nitrogen, hydrogen, etc.). The total organic content may be 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, or 5 ppm or less. By adjusting the content within these ranges, it is possible to suppress the generation of decomposition gases from the silver particles during sintering. The total organic content relative to the total weight of the silver particles of the present disclosure can also be determined by elemental analysis. According to elemental analysis (detection limit 0.3% by mass), the carbon source, nitrogen source, and hydrogen source are each preferably 0.3% by mass or less relative to the total weight of the silver particles.

[0021] As shown in FIG. 1 , silver particles 1 of the present disclosure include silver microparticles 3 and a plurality of silver nanoparticles 2 attached to the surfaces of the silver microparticles 3. The silver particles 1 may also include elemental sodium 4 attached to the surface of at least one of the nanoparticles 2 and the microparticles 3 (the surface of the nanoparticles 2 in FIG. 1 ). The nanoparticles 2 and the elemental sodium 4 may be referred to as a coating layer that covers the surface of the silver microparticles 3. Note that the coating layer may also refer to cases where the nanoparticles 2 and the elemental sodium 4 do not completely cover the surface of the silver microparticles 3, but only partially. The average particle diameter of the silver microparticles 3 is on the order of micrometers, preferably 1 to 12 μm. The average particle diameter of the silver nanoparticles 2 is on the order of nanometers, and may be 15 nm to 80 nm (15 to 80 nm), 30 nm to 70 nm, 45 nm to 60 nm, or 50 nm to 58 nm. The standard deviation of the particle size distribution (particle diameter distribution) of the silver nanoparticles 2 is preferably 2 to 50 nm, more preferably 3 to 40 nm, and even more preferably 3 to 30 nm. The thickness of the coating layer is not particularly limited, but is preferably at least 1 nm from the viewpoint of the need for low-temperature sintering ability. The thickness of the coating layer may be several nanometers or several tens of nanometers. From the viewpoint of improving shear strength, the thickness of the coating layer may be 100 nm or less, several tens of nm or less, or even a dozen nm or less. The general shape of the silver particles of the present disclosure is not particularly limited, and may be spherical (circular in plan view), ellipsoidal, flat, or irregular.

[0022] The sodium element present on the silver particle surface can be expressed as the surface atomic concentration in the so-called near-surface region, which is approximately 20 nm deep from the silver particle surface, and is measured using X-ray photoelectron spectroscopy (XPS). The sodium element present on the silver particle surface is 8.0 atom% or less, 1.0 atom% to 8.0 atom%, 3.0 atom% to 7.5 atom%, 5.0 atom% to 7.0 atom%, or 6.0 atom% to 6.5 atom%. This range enables low-temperature sintering of the silver particles, and improves the bonding strength of the sintered body.

[0023] <Surface coverage> The surface coverage in the present disclosure refers to the percentage obtained by dividing the area of ​​silver nanoparticles by the area of ​​the entire silver particles. These areas may be calculated, for example, from a plan view obtained by photographing with a scanning electron microscope (SEM). The surface coverage may be 16 to 100, 30 to 90, 45 to 80, or 55 to 70. This range allows for low-temperature sintering of the silver particles, improving the bonding strength of the sintered body.

[0024] <Silver particle composition> The silver particle composition of the present disclosure contains silver particles and an organic solvent. The organic solvent is not particularly limited, as long as it can disperse silver particles. Examples of organic solvents include alkanes such as linear or branched alkanes having 5 to 10 carbon atoms and cyclohexane; linear or branched alkanols having 1 to 5 carbon atoms, cyclohexanol, alcohols such as 3-methoxy-3-methyl-1-butanol and 3-methoxy-1-butanol; 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-hexanediol, 1,6-hexanediol, 1,2-pentanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, and 3-methyl-1,5-pentanediol. Examples of suitable esters include diols such as hexanediol, 1,2-octanediol, 1,8-octanediol, and 2-ethyl-1,3-hexanediol; glycol ethers such as monoalkyl ethers of alkanediols or polyalkanediols, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and diethylene glycol monoethyl ether; ketones such as acetone, acetylacetone, and methyl ethyl ketone; and esters such as ethyl acetate, butyl acetate, ethyl butyrate, ethyl formate, and texanol.

[0025] <Method of manufacturing silver particles> The method for producing silver particles according to the embodiment includes at least the following steps 1 and 2. In this production method, silver particles can be produced in the following manner using a microreactor system equipped with a micromixer 12 and the like, as shown in FIG.

[0026] (1st step) A solution A containing a metal compound containing at least one kind of first metal element and a solution B containing a reducing agent are mixed in a micromixer 12 to obtain a first solution C. In this process, the solution A is sent to the micromixer 12 from a first supply unit 10 such as a syringe pump via a microtube. The solution B is sent to the micromixer 12 from a second supply unit 11 such as a syringe pump via a microtube. The solutions A and B join and mix inside the micromixer 12, and are sent to a container 13 as a first solution (mixed solution) C.

[0027] (2nd process) The first solution C is mixed with the second solution D containing silver microparticles with an average particle diameter of 1 to 12 μm. In this step, the first solution C produced in the first step is dropped into the container 13. In the container 13, the first solution C is dropped into the second solution D while stirring the second solution D using, for example, a stirring bar, thereby mixing the first solution C and the second solution D. This also allows nanoparticles containing a metal element (second metal) to adhere to the surface of the silver microparticles. This results in a solution containing silver particles (a silver particle-containing liquid). In the step of mixing the first solution C and the second solution D, the first solution C and the second solution D may be homogenized in the container 13. This may result in the silver particles being dispersed in the solvent in the silver particle-containing liquid. The silver particle-containing liquid may be subjected to a known method such as filtration or centrifugation to remove the solvent and extract the silver particles.

[0028] In all of Steps 1 and 2, a protective agent having the function of maintaining the dispersion state of the metal particles in the solvent may not be used, provided that the total amount of organic matter relative to the total amount of the silver particles is 30 ppm or less.

[0029] At least the first step is carried out in a microreactor system equipped with a micromixer. The second step may also be carried out using a micromixer (the first and second steps may be carried out in a microreactor system equipped with multiple micromixers). The second step may also be carried out in batches using a container or the like.

[0030] A step similar to step 1 (step 3) may be carried out one or more times between steps 1 and 2. In step 3, the same metal element as the first metal element or a third metal element different from the first metal element may be used.

[0031] Various process conditions (such as the amount of reagents, the concentration of reagents, the reaction temperature, the flow rate, the inner diameter of the micromixer, the shape of the micromixer, and the length of the reaction channel) used in producing silver particles are adjusted as appropriate. Conventional process conditions are described, for example, in International Publication No. 2018 / 181568.

[0032] The terms used in this embodiment will be explained below. The meanings of the terms apply not only to this embodiment but also to other embodiments and modifications.

[0033] <Metal compounds> The first metal compound used in the first step and the third metal compound used in the third step are metal compounds having at least one metal element selected from the group consisting of gold (Au), silver (Ag), copper (Cu), platinum (Pt), iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh), ruthenium (Ru), iron (Fe), cobalt (Co), nickel (Ni), chromium (Cr), zinc (Zn), and rhenium (Re) as a constituent element. Among these, the first metal compound contains at least silver (Ag) as a constituent element.

[0034] The silver compound is not particularly limited, and examples thereof include inorganic silver compounds such as silver iodide, silver bromide, silver chloride, silver sulfite, silver phosphate, silver oxide, silver chromate, silver dichromate, silver tungstate (I), silver chlorite, silver nitrate, silver bromate, and silver sulfate, and organic silver compounds such as silver thiocyanide and silver carbonate. The above-mentioned silver compounds may be used alone or in combination of two or more. Furthermore, the metal compound is not particularly limited as long as it contains the above-mentioned metal element as a constituent element. From the viewpoint of efficient production of metal particles, metal salts or metal complexes are preferred. Specifically, suitable metal salts include halides such as chlorides, bromides, and iodides, hydroxides, sulfides, sulfates, nitrates, carbonates, acetates, and complex oxides such as potassium complex oxides, ammonium complex oxides, and sodium complex oxides. Suitable metal complexes include ammine complexes, cyano complexes, halogeno complexes, and hydroxy complexes. Among these, halides, sulfates, and nitrates are preferably used because they are easily available industrially and have high solubility in water.

[0035] The solvent used in the solution containing each metal compound is not particularly limited as long as it does not inhibit the production of silver particles. From the viewpoint of improving the solubility of each metal compound and the stability of the metal compound in each solution, water, aliphatic alcohols, and ethers are preferred.

[0036] <Reducing agents and solutions containing them> The reducing agent is not particularly limited as long as it can reduce the metal compound to a zero-valent metal, and any known reducing agent can be used.

[0037] Examples of reducing agents include hydrazine compounds (e.g., hydrazine, hydrazine hydrochloride, hydrazine sulfate, hydrazine hydrate, and phenylhydrazine), boron hydride compounds (e.g., tetrabutylammonium borohydride (TBAB), tetraethylammonium borohydride (TEAB), sodium borohydride, potassium borohydride, lithium borohydride, sodium triethylborohydride, potassium triethylborohydride, lithium triethylborohydride, and sodium cyanoborohydride). Examples of reducing agents include ammonium, borane complexes (e.g., borane-tert-butylamine complex, borane-tetrahydrofuran complex), organic carboxylic acid compounds (citric acid, trisodium citrate dihydrate, oxalic acid, sodium oxalate, sodium acetate), triethylsilane, sodium sulfite, sodium bisulfite, sodium thiosulfate, sodium nitrite, sodium hyponitrite, phosphorous acid, sodium phosphite, hypophosphorous acid, sodium hypophosphite, aldehydes, alcohols, amines, and sugars. From the viewpoint of industrially suitable reduction of metal compounds, it is preferable to use at least one reducing agent selected from the group consisting of hydrazine compounds, boron hydride compounds, and organic carboxylic acid compounds. These reducing agents may be used alone or in combination of two or more.

[0038] Specifically, it is preferable to use at least one selected from the group consisting of hydrazine, sodium borohydride, potassium borohydride, and citric acid as the reducing agent, and it is more preferable to use sodium borohydride. The use of sodium borohydride as the reducing agent not only enables efficient reduction of the first metal compound to a zero-valent metal, but is also suitable for industrial processes due to its easy availability and ease of handling.

[0039] The solvent used in the solution containing the reducing agent is not particularly limited as long as it does not inhibit the production of silver particles. From the viewpoint of the solubility of the reducing agent, preferred solvents include water and aliphatic alcohols. Some of these reducing agents are too reactive with protic solvents such as water and alcohol, so aprotonic polar solvents (e.g., tetrahydrofuran, diglyme, N,N-dimethylformamide, dimethyl sulfoxide, etc.) may be used as the solvent. The use of such solvents can prevent the reducing agent from decomposing. Depending on the solubility and reactivity of the reducing agent, the aprotonic polar solvents described above may be used alone or in combination with water or alcohol to reduce the amount of solvent used, or the amount of water or alcohol and solvent used. In this case, the order in which the reducing agent and solvent, and water or alcohol are mixed is not particularly limited. For example, the reducing agent may be dissolved in the aprotonic polar solvent before the first step and then mixed with water or alcohol immediately before the reaction. Mixing may be performed using a microflow process using a micromixer (microreactor) or a batch process.

[0040] The amount of the reducing agent used is not particularly limited, and may be 100 mol % to 800 mol % or 150 mol % to 400 mol % relative to the molar amount of the metal compound to be reduced, so as to ensure sufficient progress of reduction.

[0041] <Silver microparticles> The second solution may contain at least silver microparticles having an average particle size of 1 μm or more. These silver microparticles may be fine particles containing at least zero-valent silver and having an average particle size in the range of 1 to 12 μm as measured by the above-mentioned method. The average particle size of these silver microparticles may be 10 μm or less, 5 μm or less, or 3 μm or less. The shape of the silver microparticles is not particularly limited, and spherical, ellipsoidal, flat particles with a large aspect ratio, irregular shapes, etc. may be used. Note that composite silver particles may also be used for the purpose of adjusting the ratio with the metal compound to fall within the range described below.

[0042] The amount of metal compound (first metal compound, third metal compound) used relative to the silver microparticles is not particularly limited. From the viewpoint of the need for low-temperature sintering ability, the content of silver after reduction relative to the total amount of silver particles is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more. By setting the amount of metal compound used within the above range, the surface of the silver microparticles can be sufficiently coated, and silver particles having low-temperature sintering ability can be produced. Furthermore, from the viewpoint of reducing agglomerates of the metal compound, the amount of metal compound used relative to the total amount of silver microparticles is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or more. In addition to silver, the silver microparticles may contain at least one metal element selected from the group consisting of gold (Au), copper (Cu), platinum (Pt), iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh), ruthenium (Ru), iron (Fe), cobalt (Co), nickel (Ni), chromium (Cr), zinc (Zn), and rhenium (Re).

[0043] <Dispersion solvent> The solvent used in the dispersion of silver microparticles is not particularly limited as long as it does not inhibit the production of the silver particle composition, and examples thereof include water, alcohols (e.g., methanol, ethanol, isopropyl alcohol, t-butyl alcohol, ethylene glycol, triethylene glycol, etc.), ketones (e.g., acetone, butanone, cyclohexanone), aliphatic hydrocarbons (e.g., n-pentane, n-hexane, n-heptane, cyclohexane, etc.), ethers (e.g., diethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, Examples of the solvent include benzene, toluene, xylene, halogenated aromatic hydrocarbons (e.g., chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, etc.), nitrated aromatic hydrocarbons (e.g., nitrobenzene, etc.), halogenated hydrocarbons (e.g., methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, etc.), and carboxylic acid esters (e.g., methyl formate, ethyl acetate, propyl acetate, butyl acetate, etc.). These solvents may be used alone or in combination.

[0044] Among these, water, aliphatic alcohols, and ethers are preferred in order to improve the dispersibility of silver microparticles.

[0045] Of the aliphatic alcohols, those having mono- to tri-hydroxyl groups are more preferred, and aliphatic alcohols having 1 to 4 carbon atoms are even more preferred. Specific examples include methanol, ethanol, ethylene glycol, glycerin, 2-methoxyethanol, and diethylene glycol.

[0046] The aliphatic ethers are preferably alkyl ethers having 1 to 8 carbon atoms, specifically diethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, diglyme, and the like.

[0047] Of the above solvents, water, methanol, ethanol, diglyme, ethylene glycol, diethyl ether, tetrahydrofuran, and methyl formate are preferred, and water, ethanol, and diglyme are more preferred.

[0048] In the above-described method for producing silver particles, sodium borohydride is used as the reducing agent in solution B, silver microparticles in second solution D have an average particle size in the range of 1 to 12 μm, and no protective agent for metal particles in the solvent is used. When this method is used, the resulting silver particles can have an average circularity in the range of 0.40 to 0.79, and a total organic content of 30 ppm or less relative to the total amount of silver particles. Furthermore, this production method can produce silver particles with an average envelopment index in the range of 0.75 to 0.97, a standard deviation in the particle size distribution of silver nanoparticles in the range of 2 to 50 nm, a sodium content of 1 atom% or more on the surface of the silver particles, and an average particle size of 15 to 80 nm. Silver particles with this configuration can also be obtained by homogenizing the mixture (merged) of first solution C and second solution D in container 13 in the second step of the above-described method for producing silver particles. This homogenization may be performed using a homomixer, colloid mill, homogenizer (rotating disk homogenizer, high-pressure homogenizer, ultrasonic homogenizer), etc. Among these, a homogenizer is preferred. The smaller the average particle size of the silver microparticles in the second solution D, the smaller the average circularity and average degree of envelopment can be.

[0049] <Metal bonding composition> The metal bonding composition of this embodiment contains a silver particle composition and is used to bond metal surfaces by firing. The metal bonding composition can be used in a metal bonding laminate containing a metal bonding material (a sintered body of the metal bonding composition) that bonds a first metal surface and a second metal surface. The metal bonding laminate is formed by bonding a first object to be bonded having a first metal surface and a second object to be bonded having a second metal surface using a metal bonding material made of a silver particle sintered layer obtained by sintering the metal bonding composition.

[0050] The types of the first and second objects to be bonded are not particularly limited, but are preferably members having heat resistance to an extent that they are not damaged by the temperature during heating and sintering of the metal bonding composition, and may be rigid or flexible. In addition, the shapes and thicknesses of the first and second objects to be bonded are not particularly limited and can be selected appropriately.

[0051] The metal bonded laminate can be used as a semiconductor element fabricated using a metal bonding composition. Here, the semiconductor element refers to, for example, a Si crystal or SiC crystal element on which a semiconductor circuit is formed. In the present disclosure, the semiconductor element also includes a laminate including the element and the metal bonded laminate. The type of semiconductor element is not particularly limited, but a suitable example is a power semiconductor element (power device). It is preferable that the first metal surface be part of a semiconductor chip, and the second metal surface be part of a substrate. Furthermore, from the viewpoint of obtaining high bonding strength, it is preferable that at least one of the first metal surface and the second metal surface be the surface of a base material or a plating layer composed of Cu, Ag, or Au.

[0052] The first and / or second bodies to be joined may be surface-treated to enhance adhesion to the silver particle sintered layer. Examples of the surface treatment include dry treatments such as corona treatment, plasma treatment, UV treatment, and electron beam treatment, and methods of providing a primer layer or a conductive paste-receiving layer on the bodies to be joined.

[0053] The method for producing the metal bonded laminate uses a metal bonding composition as a raw material and may include, for example, a step of applying the metal bonding composition to a first object to be bonded, a step of heating and drying the applied metal bonding composition (coating), a step of pressing a second object to be bonded against the heated and dried metal bonding composition, and a step of heating and sintering the metal bonding composition to form a silver particle sintered layer.

[0054] The use of the bonded metal laminate (semiconductor element) of this embodiment is not particularly limited, but when the bonded metal laminate is a power semiconductor element (power device), it can be used in electrical control equipment, etc. Electrical control equipment including the bonded metal laminate of the present disclosure is also one aspect of the present disclosure. Electrical control equipment is used for electrical control (such as power switching) in fields such as automotive, electric railway, industrial, consumer (home appliance), and electric power (power generation). [Example]

[0055] Next, the present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0056] [Production of silver particles] Example 1 (Preparation of reducing agent solution) 76 mg of the reducing agent NaBH4 (manufactured by Wako Pure Chemical Industries, Ltd.) was weighed out and diluted with pure water to a total volume of 25 mL (NaBH4 concentration: 80 mmol / L), thereby preparing a reducing agent solution (corresponding to solution B in Figure 2).

[0057] (Preparation of metal compound solution) 1704 mg of AgNO3 (Wako Pure Chemical Industries, Ltd.), a metal compound, was weighed out and diluted with pure water to a total volume of 200 mL (Ag concentration: 50 mmol / L), thereby preparing a metal compound solution (corresponding to solution A in Figure 2).

[0058] Approximately 20 mL of each of the obtained solutions (solutions B and A) was filled into a syringe, which was then set in a syringe pump manufactured by HARVARD (corresponding to the second supply unit 11 and the first supply unit 10 in FIG. 2, respectively).

[0059] (Preparation of silver microparticle slurry) 1237.6 mg of silver microparticles (Ag-HWQ-2.5 μm manufactured by Fukuda Metal Foil Powder Co., Ltd.) were weighed out and 40 ml of pure water was added to prepare a silver microparticle slurry (corresponding to solution D in FIG. 2).

[0060] (Production of Silver Particle Composition Using Microflow Process) The microreactor system shown in Figure 2 was fabricated as follows. One end of each of the two microtubes was connected to a syringe pump in each supply section. The other ends of the two microtubes were connected to two fluid inlets located at both ends of the micromixer 12.

[0061] The micromixer 12 and the receiving vessel 13 were connected by a microtube. The above-mentioned silver microparticle slurry was placed in the receiving vessel 13, and stirring was continued using a magnetic stirrer.

[0062] Using a syringe pump, the reducing agent solution and the metal compound solution were delivered at a constant flow rate. First, the reducing agent solution and the metal compound solution were mixed and reacted in a micromixer 12 to obtain a reaction liquid (first solution C in Figure 2). The reaction liquid discharged from the tip of the microtube was then stirred using a magnetic stirrer and homogenized using a homogenizer (Sonifier SFX, manufactured by Branson) and collected in a receiver 13. The silver microparticle slurry was then mixed with the reaction liquid to obtain a silver particle-containing liquid.

[0063] The residence time from when the reducing agent solution and the metal compound solution joined in the micromixer 12 until when the reaction solution and the silver microparticle slurry joined in the receiving vessel 13 was 0.3 seconds.

[0064] The solid content contained in the silver particle-containing liquid collected in the receiver vessel 13 was filtered and dried under reduced pressure at room temperature for 4 hours. In this way, the silver particles of Example 1 were produced.

[0065] <Comparative Example 1> The silver particles of Comparative Example 1 were produced in the same manner as in Example 1, except that the reaction liquid discharged from the tip of the microtube was collected in a receiving vessel 13 that was being stirred using a magnetic stirrer, and the reaction liquid was mixed with the silver microparticle slurry (the reaction liquid and the silver microparticle slurry were mixed without using a homogenizer).

[0066] <Comparative Example 2> Silver microparticles (Ag-HWQ-2.5 μm manufactured by Fukuda Metal Foil Powder Co., Ltd.) were used as the silver particles of Comparative Example 2. In this comparative example, the above-mentioned reducing agent was not used, and reaction in a microreactor and mixing / homogenization in the receiving vessel 13 were not performed.

[0067] [Evaluation test] The silver particles produced in the above Examples and Comparative Examples were subjected to the following evaluations. The results are shown in Table 1. In Table 1, if a homogenizer was used when mixing the reaction solution and the silver microparticle slurry, the item regarding the presence or absence of a homogenization step is indicated as "Yes," and if a homogenizer was not used, it is indicated as "No." In Table 1, values ​​marked with "-" indicate values ​​that were not measured or calculated.

[0068] (Measurement of the average particle size of silver particles) Silver particles were photographed at 5000x magnification using a JEOL Ltd. scanning electron microscope (model number: JSM-7000F) (see Figure 3, etc.). The photographs (plan view) of the silver particles obtained by the photographs were evaluated using image analysis software (ImageJ, WinROOF2023). The diameter (circle equivalent diameter) of a perfect circle having the same area as the projected area (i.e., the area in the photograph) of a single silver particle projected onto a plane (plan view) was considered to be the particle size of the silver particles (hereinafter sometimes simply referred to as particles). Such particle size measurements using SEM photographs were performed on multiple particles shown in the image, and the arithmetic mean value of the particle sizes of 50 or more particles was taken as the average particle size.

[0069] (Measurement of the concentration of sodium element present on the surface of silver particles) The concentration of sodium element present on the silver particle surface was measured using X-ray photoelectron spectroscopy (XPS). The measurement equipment was an ULVAC-PHI PHI Quantera II scanning X-ray photoelectron spectrometer, with an AlKα (monochrome: 25W) X-ray source at 1486.6 eV and an analysis area of ​​100 μm diameter. The horizontal axis of the spectrum obtained by the measurement was corrected by assuming the main peak of the C1s spectrum to be the hydrocarbon state (CH / CC: 284.6 eV (CH / CC: 284.6 eV)). The identification of each state was based on the handbook provided by ULVAC-PHI. The surface atomic concentration was calculated from the peak area using the sensitivity coefficient provided by ULVAC-PHI.

[0070] (Measurement of the average thickness of the coating layer) The average thickness of the coating layer of the silver particles was calculated from the difference in the average particle diameter calculated from the SEM images.

[0071] (Calculation of surface coverage) The surface coverage of silver particles was calculated as a percentage by dividing the area of ​​the silver nanoparticles by the area of ​​the entire silver particle. These areas were measured using image analysis software (ImageJ, WinROOF2023) from photographs (plan view) of the silver particles obtained by SEM.

[0072] (Calculation of the average particle size and standard deviation of silver nanoparticles) The average particle size and standard deviation of silver nanoparticles attached to silver microparticles were calculated from TEM images. Silver particles were photographed at 150,000x magnification using a JEOL field-emission transmission electron microscope (model: JEM-2100F). The photographs (plan view) of the silver particles obtained from the photographs were evaluated using image analysis software. The diameter (circle-equivalent diameter) of a perfect circle having the same area as the projected area (i.e., the area in the photograph) of a single silver particle projected onto a plane was considered to be the particle size of the silver particle (hereinafter simply referred to as particle). Such particle size measurements using TEM photographs were performed on multiple particles shown in the images, and the arithmetic mean value of the particle sizes of 50 or more particles was taken as the average particle size. The standard deviation of the resulting particle sizes was also calculated.

[0073] (Measurement of total organic matter) The total organic matter content was measured using a temperature-programmed desorption gas chromatography-mass spectrometry (TDS-GC / MS). First, 5–6 mg of sample was introduced into a GL Sciences silicon wafer analyzer (model SWA-256). The sample was heated to 400°C over 20 minutes and held at 400°C for 10 minutes. The gas was adsorbed into a Tenax tube at room temperature. After heating, the Tenax tube was heated to 270°C to desorb the adsorbed gas. The desorbed gas was then cold trapped at −130°C, heated to 280°C, and introduced into the GC / MS. The GC / MS used was an Agilent Technologies 5975C system and an Agilent Technologies CP-SIL5CB column. The column temperature was held at 40°C for 5 minutes, then increased to 280°C at 10°C / min and held at 280°C. He was used as the carrier gas, with a flow rate of 1.0 mL / min. Electron ionization (EI) was used as the ionization method, with an ion source temperature of 230°C and a mass measurement range of m / z 30-600. The peaks of each detected component were quantified using hexadecane as the standard in the resulting TIC (total ion current) chromatogram, and the sum was used to calculate the total organic matter. The peaks detected in a blank measurement (performed in the same manner without using a sample) were used as the procedural blank and were subtracted from the calculation of the total organic matter.

[0074] (Measurement of average circularity and average envelopment) A photograph of the surface of a silver particle taken with a scanning electron microscope (JEOL Ltd., JSM-7000F) at a magnification of 5000 times was used as a projection (plan view) of the silver particle. In this plan view, the silver particle was analyzed using image analysis software (ImageJ, WinROOF2023) within the field of view shown in Figure 3, i.e., within a range in which the entire outline of the silver particle could be captured, to measure the perimeter (L) and area (S) of the silver particle (see Figure 1). In addition, in the plan view of the silver particle, the envelope perimeter (L1), which is the length of a line surrounding the silver particle in contact with the convex portion of the silver particle, was measured. The circularity and envelopment ratio of the silver particle were calculated using these values ​​and the above-mentioned formulas (1) and (2). The average value of the circularities of 50 or more silver particles was taken as the average circularity, and the average value of the envelopment ratio was taken as the average envelopment ratio.

[0075] (Share strength) A silver particle composition (a silver particle composition containing silver particles and an organic solvent: a metal bonding composition. The organic solvents used were isoamyl alcohol, butyl butyrate, and 2-ethyl-1,3-hexanediol) was applied to a nickel / silver-plated copper plate (silver substrate, 39.2 mm long x 22 mm wide x 3 mm thick) using a dispenser or stamp. A titanium / nickel / gold-plated silicon chip (gold substrate, 2.5 mm long x 2.5 mm wide x 500 μm thick) was placed on the silver particle composition and gently pressed down with tweezers. The chip was then placed in a hot press and heated to 300°C under pressure (work pressure: 33.5 MPa) in air. The chip was then held at this temperature and pressure for 1 hour for sintering, resulting in a bonded assembly in which the copper plate and silicon chip were bonded with the silver particle composition (metal bonding composition). The assembly was then cooled to room temperature and removed from the hot press.

[0076] The adhesive strength of the bonded structure was evaluated by die shear strength (shear strength). Using a die bond tester (PTR-1101 manufactured by Rhesca Co., Ltd.) equipped with a 50 kgF load cell, the silicon chip was pressed horizontally at a constant speed to measure the die shear strength of the bonded structure.

[0077] [Table 1]

[0078] As shown in Table 1, the shear strength of Example 1 was 35 MPa or more, which was about 40 MPa higher than that of the comparative example. The shear strength of Comparative Examples 1 and 2 was poor. The shear strength of Comparative Example 1 was less than 30 MPa.

Claims

1. Silver particles having an average particle size of 1 to 12 μm, silver microparticles and silver nanoparticles attached to the surfaces of the silver microparticles; the average circularity of the silver particles is 0.40 to 0.79; Silver particles, wherein the total amount of organic matter relative to the total amount of the silver particles is 30 ppm or less.

2. 2. The silver particles according to claim 1, wherein the sodium element present on the particle surface of the silver particles is 8.0 atom % or less.

3. 3. The silver particles according to claim 1, wherein the average degree of envelopment of the silver particles is 0.75 to 0.

97.

4. 3. The silver particles according to claim 1, wherein the standard deviation of the particle size distribution of the silver nanoparticles is 2 to 50 nm.

5. 3. The silver particles according to claim 2, wherein the sodium element present on the surface of the silver particles is 1.0 atom % or more.

6. 3. The silver particles according to claim 1, wherein the average particle size of the silver microparticles is 1 to 12 μm.

7. 3. The silver particles according to claim 1, wherein the average particle size of the silver nanoparticles is 15 to 80 nm.

8. A silver particle composition comprising the silver particles according to claim 1 or 2 and an organic solvent.

9. A composition for metal bonding, comprising the silver particle composition of claim 8 .

10. A semiconductor element produced using the metal bonding composition according to claim 9.

11. a first step of mixing a solution containing a metal compound containing elemental silver and a solution containing a reducing agent in a micromixer to obtain a first solution; a second step of mixing the first solution with a second solution containing silver microparticles having an average particle diameter of 1 to 12 μm, and attaching the nanoparticles containing elemental silver to the surfaces of the silver microparticles.

12. The method for producing silver particles according to claim 11, wherein the reducing agent is sodium borohydride.

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