Alloy powder, alloy paste, and semiconductor device

Abstract

This invention provides an alloy powder capable of forming a bonding layer that meets environmental limitations, operates at high temperatures, and exhibits excellent bonding reliability. The alloy powder of this invention has an AgSi eutectic structure, and when selecting one particle from an image obtained by photographing a particle profile using SEM at a magnification of 2000 to 50000x, and performing the following method on any of its ten adjacent particles, the proportion of the aforementioned AgSi eutectic structure in at least eight of them is 10% or more. The method includes: measuring the total outer perimeter of the particle, and the length of the outer perimeter containing the eutectic structure in a region of 0.2 μm from the outer perimeter towards the center of the particle, excluding regions completely devoid of eutectic structure, and calculating the proportion relative to the total outer perimeter as the proportion of the aforementioned AgSi structure on the particle surface.

Description

Technical Field

[0001] This invention relates to alloy powders, alloy pastes, and semiconductor devices. Furthermore, this application claims priority to Japanese Patent Application No. 2023-146495, filed on September 8, 2023, the contents of which are incorporated herein by reference. Background Technology

[0002] Semiconductors used in power devices require high efficiency, low loss, and high-frequency switching, leading to the expanding use of wide-bandgap semiconductors such as SiC and GaN. For these semiconductors, operating temperatures sometimes exceed 200°C, and the bonding materials used for bonding need to maintain high bonding reliability even when operating in the high-temperature range of the semiconductor and under harsh temperature cycling conditions.

[0003] Furthermore, while solder has been used as a high-temperature resistant bonding material in the past, lead-free materials have become necessary due to increasingly stringent environmental restrictions and safety considerations. Examples of lead-free materials that can serve as alternatives to solder include those described in Patent Documents 1-3.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2003-311469

[0007] Patent Document 2: Japanese Patent Application Publication No. 2020-069517

[0008] Patent Document 3: Japanese Patent Application Publication No. 2019-56158 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] However, the lead-free solder in Patent Document 1 has the problem of a low melting point, especially the unmetallized Sn in the solder will melt at around 230°C.

[0011] In addition, regarding the lead-free solder in Patent Document 2, bismuth (Bi) is used to achieve a high melting point. Although a high melting point can be achieved, there is a problem of crack propagation due to repeated heating, which leads to problems with the reliability of the connection.

[0012] In addition, regarding the silver (Ag) paste in Patent Document 3, it will not melt in an environment of about 250°C, but repeated heating will cause the metal structure to coarsen and the voids to agglomerate, resulting in problems with the reliability of the bonding.

[0013] The present invention aims to solve the above-mentioned problems and its purpose is to provide an alloy powder that can form a bonding layer that meets environmental restrictions, operates at high temperatures, and has excellent bonding reliability.

[0014] Problem Solving Methods

[0015] In order to solve the above problems, the inventors conducted in-depth research and found that if the alloy powder has an AgSi eutectic structure and the AgSi eutectic structure exists on the surface in a specific proportion, it meets environmental limitations, works at high temperatures, and has excellent bonding reliability.

[0016] That is, the present invention provides an alloy powder having an AgSi eutectic structure, wherein, for the alloy powder, one particle is selected from an image obtained by taking a cross-section of the particle using SEM at a magnification of 2000 to 50000x, and the following method is performed on any 10 adjacent particles, wherein the proportion of the AgSi eutectic structure in at least 8 of them is 10% or more, the method comprising: measuring the total outer perimeter of the particle, and the length of the outer perimeter containing the eutectic structure in a region extending from the outer perimeter to a depth of 0.2 μm in the direction from the outer perimeter toward the center of the particle, excluding the region where the eutectic structure is completely absent, and calculating the proportion of the AgSi structure on the particle surface as the proportion of the total outer perimeter.

[0017] By ensuring the presence of the aforementioned AgSi eutectic structure at a proportion of 10% or more, the silver (Ag) within the AgSi eutectic structure present on the surface can recrystallize and leach from the alloy powder surface through heating during sintering. This allows for strong bonding with the substrate and reduces the coefficient of linear expansion of the alloy powder itself, resulting in excellent bonding reliability. Furthermore, since silver (Ag) and silicon (Si) are used as raw materials, this method also complies with environmental restrictions.

[0018] Preferably, the average particle size (median particle size) of the above alloy powder is 0.1~100μm.

[0019] Preferably, relative to the total amount of the alloy powder, the silver (Ag) content is 15-97.6% by mass and the silicon (Si) content is 2.4-85% by mass. By keeping the silver (Ag) and silicon (Si) contents within the above ranges, it is easy to suppress the coefficient of linear expansion and to ensure that the AgSi eutectic structure exists locally on the surface of the alloy powder in a sufficient proportion.

[0020] In addition, the present invention provides an alloy paste comprising the above-mentioned alloy powder.

[0021] Preferably, the alloy paste further contains organic matter.

[0022] Preferably, the alloy paste further comprises silver (Ag) powder, and the content of silver (Ag) powder is 5 to 2000 parts by mass relative to 100 parts by mass of the alloy powder.

[0023] In addition, the present invention provides a semiconductor device using the above-described alloy paste.

[0024] The effects of the invention

[0025] The alloy powder according to the present invention can provide a bonding layer that meets environmental limitations, operates at high temperatures, and exhibits excellent bonding reliability. Therefore, semiconductor devices using alloy pastes containing the alloy powder of the present invention can meet environmental limitations, operate at high temperatures, and exhibit excellent bonding reliability. Attached Figure Description

[0026] Figure 1 This is a SEM image of a cross-section of the alloy powder of the present invention.

[0027] Figure 2 This is a SEM image of a cross-section of the alloy powder of the present invention.

[0028] Figure 3 This is a cross-sectional view schematically illustrating an example of an embodiment of the semiconductor device of the present invention.

[0029] Symbol Explanation

[0030] 1. Semiconductor device

[0031] 10 substrate

[0032] 20 Bonding Layer

[0033] 30. The object to be joined Detailed Implementation

[0034] [Alloy Powder]

[0035] As one embodiment of the present invention, the alloy powder has an AgSi eutectic structure, and when selecting one particle from an image obtained by taking a particle profile using SEM at a magnification of 2000 to 50000x and performing the following method on any 10 adjacent particles, the proportion of the AgSi eutectic structure in at least 8 of them is 10% or more. The method includes: measuring the total outer perimeter of the particle and the length of the outer perimeter containing the eutectic structure in a region extending from the outer perimeter to a depth of 0.2 μm in the direction from the outer perimeter to the center of the particle, excluding regions where the eutectic structure is completely absent, and calculating the proportion of the AgSi structure on the particle surface as the proportion relative to the total outer perimeter.

[0036] Figure 1 and Figure 2This is a magnified SEM image of the cross-section of the aforementioned alloy powder particles. The black areas in the image are regions composed of silicon (Si), and the white areas are regions composed of AgSi eutectic structures formed by silicon (Si) dispersed in Ag.

[0037] It should be noted that, in this invention, the eutectic structure refers to the unique structure of eutectic alloys, which is formed by the crystallization of two crystals in the liquid phase at a specific temperature, resulting in a very fine metallic structure. In this case, the eutectic structure is formed with a specific composition ratio. If the composition ratio deviates, one type of crystal crystallizes first and usually grows coarsely. In cases where the composition deviates from the ideal eutectic structure, the crystal that crystallizes first and grows during the cooling period from the liquidus temperature to the eutectic temperature is called the primary crystal.

[0038] For example, in AgSi alloys, when Si is present in excess compared to the ideal eutectic composition, Si crystallizes and precipitates as primary crystals. A fine eutectic structure only begins to form when the growth of these primary Si crystals brings the AgSi composition in the residual liquid phase to the ideal level. In alloy powders with an AgSi eutectic structure and an excess of Si compared to such a eutectic composition, primary Si crystals of several μm in size are dispersed within the particles, and in the AgSi eutectic structure, Si is finely dispersed in Ag at a level of less than 100 nm. Furthermore, in AgSi alloys, when Ag is present in excess compared to the ideal eutectic composition, Ag crystallizes and precipitates as primary crystals. A fine eutectic structure only begins to form when the growth of these primary Ag crystals brings the AgSi composition in the residual liquid phase to the ideal level. The size of the primary crystals varies depending on the particle size; crystals with differences of several times to more than ten times can be observed within a single particle. The larger crystals are identified as primary crystals.

[0039] There are no particular limitations on the method for producing alloy powder having the above-mentioned eutectic structure. For example, it can be produced by micronizing a mixture of silver (Ag) and silicon (Si) heated to liquid state using a gas atomization method or a water atomization method.

[0040] Furthermore, the proportion of AgSi eutectic structure on the particle surface of the alloy powder, as measured by the above method, is preferably 15% or more, more preferably 20% or more. By making the proportion of AgSi eutectic structure on the particle surface 10% or more, silver (Ag) can recrystallize during sintering and seep out from the surface of the alloy powder, thereby fully utilizing the bonding strength.

[0041] The coefficient of linear expansion of the aforementioned alloy powder, as measured using a thermomechanical analysis apparatus (TMA-60, manufactured by Shimadzu Corporation), is preferably 17 or less, more preferably 13 or less, and even more preferably 11 or less. By keeping the coefficient of linear expansion within the above range, it is easier to achieve reliable connection.

[0042] Preferably, at the contact surfaces of the alloy powders, a portion is bonded by recrystallized Ag, and more preferably, the entire surface is bonded by recrystallized Ag. By bonding a portion of the powders through crystallized Ag, excellent bonding reliability can be achieved.

[0043] Furthermore, the silver (Ag) content of the aforementioned alloy powder is preferably 15 to 97.6% by mass, more preferably 20 to 90% by mass, and even more preferably 30 to 80% by mass. By making the silver (Ag) content 15% by mass or more, the proportion of eutectic structure on the surface of the alloy powder can be sufficiently increased. In addition, by making it 97.6% by mass or less, the coefficient of linear expansion can be sufficiently low, thereby ensuring bonding reliability and keeping manufacturing costs at a low level.

[0044] The silicon (Si) content of the aforementioned alloy powder is preferably 2.4 to 85% by mass, more preferably 10 to 80% by mass, and even more preferably 20 to 70% by mass. By ensuring that the silicon (Si) content in the alloy powder is 2.4% by mass or more, it is easy to maintain a sufficiently low coefficient of linear expansion, thereby achieving reliable bonding and keeping manufacturing costs low. Furthermore, by setting it to 85% by mass or less, the proportion of eutectic structure on the surface of the alloy powder can be sufficiently increased.

[0045] In addition, the alloy powder may contain other components besides silver (Ag) and silicon (Si), but from the viewpoint of complying with environmental restrictions and being able to work at high temperatures and perform reliable connection, it is preferable not to contain components other than silver (Ag) and silicon (Si).

[0046] The total amount of silver (Ag) and silicon (Si) content in the alloy powder is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass, relative to the total amount of the alloy powder.

[0047] The average particle size (median particle size) of the aforementioned alloy powder is preferably 0.1 to 100 μm, more preferably 0.5 to 50 μm, even more preferably 0.7 to 10 μm, and particularly preferably 1.0 to 3 μm. By making the average particle size 0.1 μm or more, processing becomes easier; by making it 100 μm or less, the surface area of ​​the alloy powder becomes sufficient, facilitating bonding in a short time. It should be noted that the aforementioned average particle size (median particle size) can be determined by laser diffraction / scattering.

[0048] Furthermore, the shape of the alloy powder is not particularly limited; examples include spherical, flake-shaped (flat), and polyhedral shapes. Alloy powders of the same shape can be used alone, or alloy powders of different shapes can be used in combination. Among these, spherical shapes are preferred.

[0049] Furthermore, as one embodiment of the present invention, a composition containing the aforementioned alloy powder can be provided. The composition containing the aforementioned alloy powder is not particularly limited and can take various forms. For example, an alloy powder composition, referred to as alloy ink, can be prepared by dispersing the alloy powder in a suspended state in a suitable organic solvent (dispersion medium). Alternatively, an alloy powder composition, referred to as alloy paste, can be prepared by dispersing the aforementioned alloy powder in a mixed state in an organic solvent. Preferably, the alloy powder composition is an alloy paste.

[0050] [Alloy Paste]

[0051] The alloy paste preferably contains, in addition to the alloy powder, the following organic matter and metal particles other than the alloy powder. It should be noted that the alloy powder included in the alloy paste may be a single type or a combination of two or more types.

[0052] The alloy paste preferably contains the aforementioned organic compound. Furthermore, one type of organic compound may be used, or two or more may be used in combination.

[0053] Examples of such organic substances include organic solvents, adhesive resins, and additives.

[0054] The aforementioned organic solvent preferably comprises at least organic solvent (a), organic solvent (b), and organic solvent (c). Organic solvent (a), organic solvent (b), and organic solvent (c) are different compounds and satisfy the following formulas (1) to (6). Only one of organic solvent (a), organic solvent (b), and organic solvent (c) may be used, or more than two may be used.

[0055] 150℃≤Ta≤250℃(1)

[0056] 150℃≤Tb≤250℃(2)

[0057] 250℃≤Tc≤350℃(3)

[0058] δa≥10.0(4)

[0059] δc≤9.0(5)

[0060] δc≤δb≤δa(6)

[0061] In the formula, Ta~Tc represent the boiling points of organic solvents (a)~(c), respectively, and δa~δc represent the Hansen solubility parameters of organic solvents (a)~(c), respectively. It should be noted that in this specification, the Hansen solubility parameter is referred to as the "SP value", and sometimes expressed as "δ".

[0062] It should be noted that the organic solvents (a) to (c) are any solvents that can be uniformly dissolved into a liquid state when mixed in the proportions used in the above-mentioned bonding conductor paste. Each of them can be liquid or solid at room temperature.

[0063] The organic solvent (a) at least satisfies formula (1). That is, the boiling point Ta of the organic solvent (a) satisfies 150℃≤Ta≤250℃, preferably 150℃<Ta<250℃, more preferably 155℃≤Ta≤220℃, and even more preferably 160℃≤Ta≤200℃. By using an organic solvent (a) with a boiling point within the above range, the organic solvent readily volatilizes during sintering, making it easy to form a sintered body.

[0064] The organic solvent (a) at least satisfies formula (4) [δa ≥ 10.0]. The SP value δa of the organic solvent (a) is 10.0 or more, preferably 10.3 or more, and more preferably 10.4 or more, within the range satisfying formula (6). By making the above-mentioned δa 10.0 or more, the dispersibility of the above-mentioned alloy powder and the following metal particles is excellent, and the separation of the alloy powder and metal particles from the organic solvent is less likely to occur. The δa of the organic solvent (a) is, for example, 16.0 or less, and can be 15.0 or less.

[0065] Examples of organic solvents (a) include alcohol solvents, urea solvents, and aprotic polar solvents. Among the aforementioned alcohol solvents, compounds having one or more hydroxyl groups are examples, with tertiary alcohols and ether alcohols being preferred. The aforementioned alcohol solvents may also have two or more hydroxyl groups. Ether alcohols are compounds having both an ether bond and a hydroxyl group, and examples include (poly)alkylene glycol monoalkyl ethers and alkoxy-substituted alcohols.

[0066] Examples of organic solvents (a) include: pinacol (δ 10.7, boiling point 172 °C), tetramethylurea (δ 10.6, boiling point 177 °C), 3-methoxybutanol (δ 10.6, boiling point 161 °C), 1-methylcyclohexanol (δ 10.4, boiling point 155 °C), and methyl carbitol (diethylene glycol monomethyl ether) (δ 10.7, boiling point 193 °C).

[0067] The organic solvent (b) at least satisfies formula (2). That is, the boiling point Tb of the organic solvent (b) satisfies 150℃≤Tb≤250℃, preferably 150℃<Tb<250℃, more preferably 180℃≤Tb≤248℃, and even more preferably 200℃≤Tb≤245℃. By using an organic solvent (b) with a boiling point within the above range, the organic solvent readily volatilizes during sintering, making it easy to form a sintered body. In addition, by using an organic solvent (b) with a boiling point below 250℃, the generation of voids during sintering can be suppressed.

[0068] The organic solvent (b) at least satisfies formula (6). The SP value δb of the organic solvent (b) is preferably 8.0 to 12.0, more preferably 8.5 to 11.0, and even more preferably 9.0 to 10.5 within the range of formula (6). When δb is within the above range, the compatibility of organic solvent (a) and organic solvent (c) is improved, they are not easy to separate, and they tend to have better continuous discharge stability and storage stability.

[0069] Examples of organic solvents (b) include alcohol solvents, ester solvents, ketone solvents, and amine solvents. Among the aforementioned alcohol solvents, solvent compounds having one or more hydroxyl groups are examples, with tertiary alcohols, ether alcohols, and ester alcohols being preferred. Ether alcohols are compounds having both an ether bond and a hydroxyl group, and examples include (poly)alkylene glycol monoalkyl ethers and alkoxy-substituted alcohols. Ester alcohols are compounds having both an ester bond and a hydroxyl group, and examples include (poly)alkylene glycol monoalkyl ether monoesters. Examples of ester solvents include diacetates of (poly)alkylene glycols and other diols. Cyclic ketone solvents are preferred. Alkylamine solvents are preferred.

[0070] As an organic solvent (b), it can be selected based on the premise that it satisfies equation (6) in relation to organic solvents (a) and (c). Specifically, it can be used for example: d-Camphor (δ10.4, boiling point 204℃), 1-Heptanol (δ10.0, boiling point 177℃), butylcarbitol (diethylene glycol monobutyl ether) (δ10.2, boiling point 231℃), ethylcarbitol (diethylene glycol monoethyl ether) (δ10.5, boiling point 196℃), tripropylene glycol monomethyl ether (δ9.4, boiling point 243℃), α-terpineol (δ9.3... The following are listed: dihydroterpineol (δ 9.0, boiling point 210℃), 1,3-butanediol diacetate (δ 9.2, boiling point 232℃), propylene glycol diacetate (δ 9.3, boiling point 190℃), butyl carbitol acetate (δ 9.0, boiling point 247℃), dipropylene glycol butyl ether (δ 9.2, boiling point 230℃), isophorone (δ 9.5, boiling point 213℃), 1-decyl alcohol (δ 9.6, boiling point 230℃), propylene glycol monobutyl ether (δ 9.0, boiling point 170℃), 1-nonanol (δ 9.8, boiling point 214℃), etc.

[0071] The boiling point Tb of the organic solvent (b) is preferably higher than the boiling point Ta of the organic solvent (a), that is, preferably Tb > Ta. The temperature difference between Tb and Ta [Tb-Ta] is preferably 2°C or more, more preferably 5°C or more, and even more preferably 10°C or more. When the above temperature difference is 2°C or more, the generation of voids during sintering can be further suppressed.

[0072] The organic solvent (c) at least satisfies equation (3). That is, the boiling point Tc of the organic solvent (c) satisfies 250℃≤Tc≤350℃, preferably 250℃<Tc<350℃, more preferably 250℃<Tc≤320℃, and even more preferably 250℃<Tc≤300℃. By using an organic solvent (c) with a boiling point within the above range, the rapid volatilization of organic solvent (a) and organic solvent (b) during sintering can be suppressed, thereby suppressing the formation of voids.

[0073] The organic solvent (c) must at least satisfy formula (5) [δc ≤ 9.0]. The SP value δc of the organic solvent (c) is 9.0 or less, preferably 8.7 or less, and more preferably 8.5 or less. By making the above-mentioned δc 9.0 or less, the generation of voids during sintering can be suppressed. The δc of the organic solvent (c) is, for example, 6.0 or more, and can be 7.0 or more.

[0074] Examples of organic solvents (c) include ether solvents, alkane solvents, and ester solvents. Examples of ether solvents include (poly)alkylene glycol dialkyl ethers. Examples of alkane solvents are alkanes with 14 or more carbon atoms (e.g., 14 to 20 carbon atoms). Examples of ester solvents are esters of (poly)alkylene glycol alkyl ethers and fatty acids.

[0075] Examples of organic solvents (c) include: dibutylcarbitol (diethylene glycol dibutyl ether) (δ8.3, boiling point 255℃), tetradecane (δ7.9, boiling point 254℃), hexadecane (δ8.0, boiling point 287℃), etc.

[0076] The boiling point Tc of the organic solvent (c) is preferably higher than the boiling point Tb of the organic solvent (b), that is, preferably Tc > Tb. The temperature difference between Tc and Tb [Tc-Tb] is preferably 2°C or more, more preferably 6°C or more, and even more preferably 10°C or more. When the above temperature difference is 2°C or more, the generation of voids during sintering can be further suppressed.

[0077] The boiling point Tc of the organic solvent (c) is preferably higher than the boiling point Ta of the organic solvent (a), that is, preferably Tc > Ta. The temperature difference between Tc and Ta [Tc-Ta] is preferably 30°C or more, more preferably 50°C or more, and even more preferably 60°C or more. When the above temperature difference is 30°C or more, the generation of voids during sintering can be further suppressed.

[0078] The SP values ​​δa, δb, and δc of organic solvent (a), organic solvent (b), and organic solvent (c) satisfy the relationship [δc ≤ δb ≤ δa] of the above equation (6). Preferably, δb is higher than δc, i.e., preferably δc < δb. Furthermore, preferably, δa is higher than δb, i.e., preferably δb < δa.

[0079] The difference between δb and δc [δb-δc] is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.5 or more. When the difference is 0.1 or more, the dispersibility of the metal particles is better, and the continuous discharge stability is better. The difference is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.3 or less. When the difference is 2.0 or less, the alloy powder and metal particles are less likely to separate from the organic solvent, and the continuous discharge stability and storage stability are better.

[0080] The difference between δa and δb [δa-δb] is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.5 or more. When the difference is 0.1 or more, the dispersibility of the metal particles is better, and the continuous discharge stability is better. The difference is preferably 2.5 or less, more preferably 2.0 or less, and even more preferably 1.8 or less. When the difference is 2.5 or less, the alloy powder and metal particles are less likely to separate from the organic solvent, and the continuous discharge stability and storage stability are better.

[0081] Based on equations (4) and (5), the difference between δa and δc [δa-δc] is 1.0 or more, preferably 1.5 or more, and more preferably 2.0 or more. When the difference is 1.0 or more, the generation of voids during sintering can be further suppressed. The difference is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less. When the difference is 5.0 or less, the alloy powder and metal particles are not easily separated from the organic solvent, resulting in better continuous discharge stability and storage stability.

[0082] The ratio of organic solvent (a) to the total amount of organic solvent (a), organic solvent (b), and organic solvent (c) in 100% by mass [organic solvent (a) / {organic solvent (a) + organic solvent (b) + organic solvent (c)}] is preferably 5 to 70% by mass, more preferably 10 to 60% by mass, and even more preferably 15 to 50% by mass. When the above ratio is within the above range, the organic solvent is easy to volatilize during sintering, which can easily form a sintered body, and the dispersibility of alloy powder and metal particles is better.

[0083] The ratio of organic solvent (b) to the total amount of organic solvent (a), organic solvent (b) and organic solvent (c) in a 100% mass percentage [organic solvent (b) / {organic solvent (a) + organic solvent (b) + organic solvent (c)}] is preferably 5 to 70% by mass, more preferably 10 to 60% by mass, and even more preferably 15 to 50% by mass. When the above ratios are within the above ranges, the compatibility of each organic solvent is excellent, and the continuous discharge stability and storage stability are even better.

[0084] The ratio of organic solvent (c) to the total amount of organic solvent (a), organic solvent (b), and organic solvent (c) in 100% by mass [organic solvent (c) / {organic solvent (a) + organic solvent (b) + organic solvent (c)}] is preferably 5 to 70% by mass, more preferably 10 to 60% by mass, and even more preferably 15 to 50% by mass. When the above ratio is within the above range, the generation of voids during sintering can be further suppressed.

[0085] The content of organic solvent (c) is preferably 20 to 400 parts by mass, more preferably 30 to 300 parts by mass, and even more preferably 50 to 200 parts by mass, relative to 100 parts by mass of organic solvent (a). When the content is within the above range, the balance between the amount of organic solvent (a) and organic solvent (c) is good, and the void suppression during sintering and the dispersion of alloy powder and metal particles are better.

[0086] Relative to the combined mass of organic solvent (a) and organic solvent (c) of 100 parts by mass, the content of organic solvent (b) is preferably 10 to 200 parts by mass, more preferably 20 to 150 parts by mass, and even more preferably 40 to 100 parts by mass. When the content is within the above range, the compatibility between organic solvent (a) and organic solvent (c) is further improved, and the continuous discharge stability and low-temperature storage performance are superior.

[0087] The aforementioned organic solvents may also include other solvents (organic solvents) besides organic solvent (a), organic solvent (b), and organic solvent (c). The total content of organic solvents (a), (b), and (c) relative to 100% by mass is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more. When the content is 50% by mass or more, the dispersibility of the metal particles and the compatibility of each organic solvent are superior, as are the continuous discharge stability, storage stability, and void formation suppression during sintering.

[0088] When organic solvents (a), (b), and (c) are mixed in the proportions used in the bonding conductor paste described above, they preferably dissolve uniformly at room temperature without phase separation. Furthermore, in the bonding conductor paste described above, organic solvents (a), (b), and (c) preferably dissolve uniformly at room temperature without phase separation. Particularly, it is preferable that phase separation does not occur at 22–28°C (preferably 10–30°C, more preferably 0–35°C).

[0089] Examples of such adhesive resins include: vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, polyester resin, acrylic resin, and cellulose resin (e.g., ethyl cellulose).

[0090] Examples of such additives include surface conditioners, viscosity modifiers, dispersants, and defoamers.

[0091] In the above alloy paste, relative to the total of 100 parts by mass of the above alloy powder and metal particles other than the above alloy powder, the content of organic matter is preferably 0.5 to 50 parts by mass, more preferably 0.7 to 30 parts by mass, and even more preferably 1 to 12 parts by mass.

[0092] Furthermore, the aforementioned alloy paste preferably contains metal particles other than the aforementioned alloy powder. Among these, silver (Ag) particles are preferred because they can strongly bond with the silver (Ag) contained in the AgSi eutectic structure of the aforementioned alloy powder.

[0093] The average particle size (median particle size) of the metal particles other than the alloy powder is preferably 0.1 to 100 μm, more preferably 0.3 to 50 μm, and even more preferably 0.5 to 10 μm. By making the average particle size 0.1 μm or more, the processing of the metal particles becomes easier. By making it 100 μm or less, bonding reliability is easily achieved.

[0094] The shape of the metal particles other than alloy powder is not particularly limited. Examples include spherical, sheet-like (flat), and polyhedral shapes. Metal particles of the same shape can be used alone, or metal particles of different shapes can be used in combination. Among these, spherical shapes are preferred for ideal dispersion in the alloy paste.

[0095] The content of the metal particles other than the alloy powder is preferably 5 to 2000 parts by mass, more preferably 10 to 1000 parts by mass, further preferably 20 to 500 parts by mass, and particularly preferably 40 to 400 parts by mass, relative to 100 parts by mass of the alloy powder. By making the content of the metal particles other than the alloy powder 5 parts by mass or more, they can be fully bonded to the alloy powder during sintering, and by making it 2000 parts by mass or less, the coefficient of linear expansion is easily reduced.

[0096] In addition, the alloy paste may also contain other components besides those mentioned above. Examples of such other components include surfactants other than organic compounds and viscosity modifiers other than organic compounds. The content of these other components is preferably 5% by mass or less, and may also be 3% by mass or less, relative to the total amount of the organic compound.

[0097] [Semiconductor Devices]

[0098] As one embodiment of the present invention, a semiconductor device using the above-described alloy powder-containing composition (preferably the above-described alloy paste) as a bonding layer for bonding a substrate to a workpiece can be cited. In the above-described semiconductor device, the workpiece is bonded to the substrate via a bonding layer that is a sintered body of the above-described alloy powder-containing composition. Figure 3 This is a schematic cross-sectional view of the semiconductor device. 1 is the semiconductor device, 10 is the substrate, 20 is the bonding layer, and 30 is the substrate to be bonded.

[0099] Examples of substrates include: metal substrates such as copper substrates, ceramic substrates, metal-ceramic substrates, SiC substrates, gallium nitride substrates, glass epoxy substrates, BT resin substrates, glass substrates, and resin substrates. As one embodiment of the present invention, the alloy paste can be sintered at low temperatures, therefore substrates with low heat resistance can also be used. Ceramic substrates and metal-ceramic substrates are preferred as the aforementioned substrates, and copper-ceramic substrates and aluminum-ceramic substrates are more preferred.

[0100] Examples of the objects to be joined include electronic components and heat sinks. Examples of electronic components include semiconductor elements, LED elements, and other electronic components (chips, dies). Specifically, examples of semiconductor elements include power semiconductor elements. Furthermore, it is preferable that the bonding surface between the object to be joined and the bonding layer is silver-plated. Examples of materials for the objects to be joined include Si (silicon), SiC (silicon carbide), GaN, and diamond.

[0101] The aforementioned semiconductor device can be manufactured by coating the alloy powder-containing composition onto a substrate using a printing method (specifically, distributor printing, mask printing, screen printing, inkjet printing, etc.), mounting the substrate on the coating layer, and then sintering it.

[0102] The sintering temperature is preferably 150°C to 300°C, more preferably 160°C to 280°C, even more preferably 200°C to 270°C, and particularly preferably 230°C to 260°C. The sintering time is preferably 0.5 minutes to 2 hours, more preferably 10 minutes to 1 hour, and even more preferably 3 to 10 minutes.

[0103] The thickness of the bonding layer formed by the above method is preferably 3 μm to 500 μm, more preferably 10 to 300 μm, and even more preferably 40 to 150 μm.

[0104] Through the aforementioned sintering process, the silver (Ag) present in the AgSi eutectic structure of the alloy powder in the aforementioned alloy powder composition recrystallizes and leaches out, thereby enabling a strong bond between the silver (Ag) and the substrate and the substrate. Furthermore, since the bonding layer contains the alloy powder with a low coefficient of linear expansion, the strength of the bond is improved, and the coefficient of thermal expansion is kept low. Therefore, the thermal fatigue resistance and other properties of the bonding layer are substantially improved. Thus, for semiconductor devices using the aforementioned alloy powder composition as a bonding layer for bonding a substrate and a substrate, environmental limitations can be met, and operation at high temperatures is possible with excellent bonding reliability.

[0105] The various methods disclosed in this specification can also be combined with any other features disclosed in this specification. Furthermore, the various configurations and combinations thereof in each embodiment are examples, and appropriate additions, omissions, and other modifications can be made without departing from the spirit of the invention. The invention is not limited to the embodiments, but only to the scope of the claims.

[0106] Example

[0107] Hereinafter, an embodiment of the present invention will be described in more detail based on an example.

[0108] Example 1

[0109] The mixture was prepared by mixing silver (Ag) ingots (99.99% purity) at 95% by mass and silicon (Si) ingots (99.9999% purity) at 5% by mass, and then heated to 1450°C to melt the mixture. The resulting solution was pulverized using a gas atomizing device (trade name "RQP-20K", manufactured by Makabe Giken Co., Ltd.) to obtain the alloy powder of Example 1. Furthermore, the powder atomized by the gas atomizing device was classified using an ultrasonic vibrating sieve (trade name "TSK-DGS type", manufactured by TOKYO-SCREEN Co., Ltd.) to obtain particles with an average particle size of 15.86 μm. Further, the powder particle size was adjusted using a high-speed rotor classifier (trade name "Turbo Classifier TC-15", manufactured by Nisshin Engineering Co., Ltd.) to achieve an average particle size of 3.2 μm. It should be noted that the coefficient of linear expansion of the alloy powder in Example 1, measured using a thermomechanical analysis apparatus (TMA-60, manufactured by Shimadzu Corporation), was 16.42. The actual measured result was 14.1 ppm.

[0110] Examples 2-5

[0111] The contents of silver (Ag) particles and silicon (Si) particles were changed to the amounts recorded in Table 1. Otherwise, the alloy powders of Examples 2-5 were prepared in the same manner as in Example 1. It should be noted that the average particle size and coefficient of linear expansion of Examples 2-5 are shown in Table 1.

[0112] Comparative Example 1

[0113] Instead of the aforementioned alloy powder, silver (Ag) particles (average particle size 2.0 μm~3.4 μm, coefficient of linear expansion: 19.3 ppm / K) were used.

[0114] Comparative Example 2

[0115] Instead of the aforementioned alloy powder, a mixed powder containing 80% by mass silver (Ag) particles and 20% by mass silicon (Si) particles was used. Regarding the average particle size of the mixed powder, Ag particles (2.0 μm to 3.4 μm) and Si particles (D50 = 10 μm) were used. Furthermore, the coefficient of linear expansion of the mixed powder in Comparative Example 2 was 16.73.

[0116] [evaluate]

[0117] The physical properties of the alloy powder, silver particles, and mixed powder of the above embodiments and comparative examples were evaluated, and the results are recorded in Table 1. It should be noted that "-" in Table 1 indicates that no evaluation or evaluation was possible.

[0118] (1) The proportion of eutectic structure on the particle surface

[0119] The alloy powder of the example was cured in epoxy resin, and the particle profile was ground to a level that could be observed. From images of the particle profile obtained by SEM at magnification of 2000 to 50000x, one particle was selected, and its total outer perimeter and the length of the outer perimeter containing eutectic structure in a region extending 0.2 μm from the outer perimeter towards the center of the particle were measured. The ratio of this ratio to the total outer perimeter was calculated as the proportion of AgSi structure on the particle surface. This method was performed on any 10 adjacent particles, and the proportion of AgSi eutectic structure in the 8th particle was recorded. It should be noted that the portion of the particle other than the primary crystal portion was evaluated as eutectic structure.

[0120] (2) Recrystallization (exudation)

[0121] The alloy powder, silver particles, and mixed powder of the examples and comparative examples were heated at 300°C for 30 minutes, 60 minutes, or 90 minutes, and then imaged using SEM at 3000x magnification. Particles with diameters of less than 3 μm, 3–7 μm, 7–12 μm, and greater than 12 μm were selected from the captured images. Among the selected particles, those with surface recrystallization and silver (Ag) exudation of 0.1 μm or more were evaluated as ◎, those with confirmed silver (Ag) recrystallization (exudation) were evaluated as ○, and those without confirmed exudation (recrystallization) were evaluated as ×.

[0122] (3) The bonding strength between particles

[0123] In the examples and comparative examples, the contact surfaces of the alloy powder, silver particles, and mixed powders are evaluated as follows: the entire surface is bonded together by recrystallized Ag. The case where a portion of the powder is bonded is evaluated as ○. The case where no powder is bonded is evaluated as ×.

[0124]

[0125] It was confirmed that the alloy powder of the embodiment, being composed of silver (Ag) and silicon (Si), complies with environmental limitations, and the coefficient of linear expansion is suppressed to a low level. Upon heating to 300°C, silver (Ag) recrystallizes, and the alloy powder bonds through the exudated silver (Ag). On the other hand, it was confirmed that in the case of silver (Ag) powder alone, the coefficient of linear expansion becomes high (Comparative Example 1). Furthermore, in the mixed powder of silver (Ag) and silicon (Si), a reduction in the coefficient of linear expansion was achieved, but bonding based on the exudated silver (Ag) was not confirmed, resulting in poor bonding reliability.

[0126] The following describes variations of the present invention.

[0127] [Postscript 1]

[0128] An alloy powder having an AgSi eutectic structure, wherein, for the alloy powder, one particle is selected from an image obtained by taking a cross-section of the particle using SEM at a magnification of 2000 to 50000x, and the following method is performed on any 10 adjacent particles, wherein the proportion of the AgSi eutectic structure in at least 8 of them is 10% or more, the method comprising: measuring the total outer perimeter of the particle and the length of the outer perimeter containing the eutectic structure in a region extending from the outer perimeter to a depth of 0.2 μm in the direction from the outer perimeter toward the center of the particle, excluding regions where the eutectic structure is completely absent, and calculating the proportion of the AgSi structure on the particle surface as the proportion of the total outer perimeter.

[0129] [Postscript 2]

[0130] According to the alloy powder described in Appendix 1, the proportion of the above-mentioned AgSi eutectic structure is 15% or more, preferably 20% or more.

[0131] [Postscript 3]

[0132] According to Appendix 1 or 2, the alloy powder has a coefficient of linear expansion of 17 or less, as determined by a thermomechanical analysis apparatus.

[0133] [Postscript 4]

[0134] According to any one of Appendix 1 to 3, in the alloy powder, a portion of the contact surfaces of the alloy powders are bonded by recrystallized Ag.

[0135] [Postscript 5]

[0136] According to any one of Appendix 1 to 4, the alloy powder is bonded to each other at the contact surfaces of the alloy powders by recrystallized Ag.

[0137] [Postscript 6]

[0138] The alloy powder according to any one of Appendices 1 to 5 has an average particle size (median particle size) of 0.1 to 100 μm.

[0139] [Postscript 7]

[0140] The alloy powder according to any one of Appendices 1 to 6 is spherical in shape.

[0141] [Postscript 8]

[0142] According to any one of the appendices 1 to 7, the alloy powder contains, relative to the total amount of the alloy powder, 15 to 97.6% by mass of silver (Ag) and 2.4 to 85% by mass of silicon (Si).

[0143] [Postscript 9]

[0144] The alloy powder according to any one of Appendices 1 to 8 does not contain any components other than silver (Ag) and silicon (Si).

[0145] [Postscript 10]

[0146] An alloy paste comprising any one of the alloy powders described in Appendix 1 to 9.

[0147] [Postscript 11]

[0148] The alloy paste described in Appendix 10 further contains organic matter.

[0149] [Postscript 12]

[0150] According to the alloy paste described in Appendix 11, the aforementioned organic matter is an organic solvent.

[0151] [Postscript 13]

[0152] The alloy paste according to any one of Appendices 10 to 12 further comprises metal particles other than the alloy powder, wherein the content of metal particles other than the alloy powder is 5 to 2000 parts by mass relative to 100 parts by mass of the alloy powder.

[0153] [Postscript 14]

[0154] According to any one of Appendix 10 to 13, the content of the organic matter is 0.5 to 50 parts by mass relative to a total of 100 parts by mass of the alloy powder and metal particles other than the alloy powder.

[0155] [Postscript 15]

[0156] A semiconductor device that uses the alloy paste described in any one of Appendices 10 to 14 as a bonding layer for bonding a substrate to an object.

Claims

1. An alloy powder having an AgSi eutectic structure, For the alloy powder, one particle is selected from an image obtained by photographing a particle profile using SEM at a magnification of 2000 to 50000x. The following method is then applied to any 10 adjacent particles, wherein at least 8 of these particles contain at least 10% AgSi eutectic structure. The method includes: The total outer perimeter of the particle and the length of the outer perimeter containing eutectic structure in the region extending 0.2 μm from the outer perimeter toward the center of the particle, excluding the region where no eutectic structure exists, are measured. The ratio of this length to the total outer perimeter is then calculated as the proportion of the AgSi structure on the particle surface.

2. The alloy powder according to claim 1, wherein the average particle size (median particle size) is 0.1~100μm.

3. The alloy powder according to claim 1 or 2, wherein, The content of silver (Ag) is 15 to 97.6% by mass and the content of silicon (Si) is 2.4 to 85% by mass relative to the total amount of the alloy powder.

4. An alloy paste comprising the alloy powder of claim 1 or 2.

5. An alloy paste comprising the alloy powder of claim 3.

6. The alloy paste according to claim 4, further comprising organic matter.

7. The alloy paste according to claim 4, further comprising metal particles other than the alloy powder. The content of metal particles other than the alloy powder is 5 to 2000 parts by mass relative to 100 parts by mass of the alloy powder.

8. A semiconductor device that uses the alloy paste of claim 4 as a bonding layer for bonding a substrate to a substrate.

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