Alloy powder, alloy paste, and semiconductor device

Abstract

Provided is an alloy powder that is compatible with environmental regulations, and is capable of forming a bonding layer that works at high temperatures and exhibits superior bonding reliability. An alloy powder according to the present disclosure has an AgSi eutectic structure and is characterized in that: one particle is selected from an image obtained by photographing a particle cross section by SEM at a magnification rate of 2,000-50,000 times, the total outer peripheral length of the particle and the length of an outer peripheral part in which the eutectic structure is present, excluding a region where there is no eutectic structure at all in a region 0.2 μm from the outer periphery in the center direction of the particle, are measured; and a method for calculating the ratio with respect to the total outer peripheral length as the ratio of the AgSi structure on the particle surface is performed on any 10 adjacent particles, and the ratio of the AgSi eutectic structure is 10% or more in at least eight of the particles.

Description

Alloy powder, alloy paste, and semiconductor device

[0001] This disclosure relates to an alloy powder, an alloy paste, and a semiconductor device. This application claims priority from Japanese Patent Application No. 2023-146495, filed on September 8, 2023, the contents of which are incorporated herein by reference.

[0002] Semiconductors used in power devices are required to have high efficiency, low loss, and high-frequency switching, and the use of wide-gap semiconductors such as SiC and GaN semiconductors is expanding. The operating temperatures of such semiconductors can exceed 200°C, so the bonding materials used for bonding must maintain high bonding reliability even when the semiconductors operate in high-temperature ranges or in harsh temperature cycle environments.

[0003] Furthermore, solder has traditionally been used as a high-temperature resistant joining material, but due to increasingly strict environmental regulations and safety concerns, lead-free materials have become necessary. Examples of such lead-free solder substitute materials include those described in Patent Documents 1 to 3.

[0004] JP 2003-311469 A JP 2020-069517 A JP 2019-56158 A

[0005] However, the lead-free solder of Patent Document 1 has a low melting point, and in particular, there is a problem in that Sn in the solder that has not been converted into a metal compound melts at about 230°C.

[0006] Furthermore, the lead-free solder of Patent Document 2 uses bismuth (Bi) to achieve a high melting point, and although it is possible to achieve a high melting point, there is a problem in that cracks propagate when heated repeatedly, which causes problems with connection reliability.

[0007] Furthermore, the silver (Ag) paste of Patent Document 3 does not melt in an operating environment of about 250°C, but repeated heating causes coarsening of the metal structure and aggregation of voids, resulting in problems with bonding reliability.

[0008] The present disclosure is intended to solve the above-mentioned problems, and its purpose is to provide an alloy powder that complies with environmental regulations, operates at high temperatures, and can form a bonding layer with excellent bonding reliability. Means to solve the problem

[0009] As a result of earnest efforts to solve the above problems, the present inventors have found that an alloy powder having an AgSi eutectic structure in which the AgSi eutectic structure is present on the surface at a specific ratio can comply with environmental regulations, operate at high temperatures, and have excellent bonding reliability.

[0010] That is, the present disclosure provides an alloy powder having an AgSi eutectic structure, in which one particle is selected from an image of the particle cross section photographed with an SEM at a magnification of 2000 to 50000 times, the total perimeter length and the length of the outer perimeter where the eutectic structure is present, excluding a region where the eutectic structure is completely absent in a region extending from the perimeter to a depth of 0.2 μm toward the center of the particle, are measured, and the proportion of the AgSi structure on the particle surface is calculated based on the proportion of the total perimeter length. This method is carried out for any 10 adjacent particles, and at least 8 of the particles have a proportion of the AgSi eutectic structure of 10% or more.

[0011] The presence of the AgSi eutectic structure and its proportion of 10% or more allows the silver (Ag) in the AgSi eutectic structure present on the surface to recrystallize due to heating during sinter bonding, and the silver (Ag) can seep out from the alloy powder surface, thereby firmly bonding to the adherend while reducing the linear expansion coefficient of the alloy powder itself, resulting in excellent bonding reliability.In addition, since silver (Ag) and silicon (Si) are used as raw materials, the alloy also complies with environmental regulations.

[0012] The alloy powder preferably has an average particle size (median diameter) of 0.1 to 100 μm.

[0013] Preferably, the silver (Ag) content is 15 to 97.6 mass % and the silicon (Si) content is 2.4 to 85 mass % relative to the total amount of the alloy powder. By having the silver (Ag) and silicon (Si) contents within the above ranges, it becomes easy to localize the AgSi eutectic structure at a sufficient rate on the surface of the alloy powder while suppressing the linear expansion coefficient.

[0014] The present disclosure also provides an alloy paste containing the alloy powder.

[0015] The alloy paste preferably further contains an organic substance.

[0016] The alloy paste preferably further contains silver (Ag) powder, and the content of the silver (Ag) powder is preferably 5 to 2000 parts by mass per 100 parts by mass of the alloy powder.

[0017] The present disclosure also provides a semiconductor device using the alloy paste.

[0018] The alloy powder of the present disclosure can provide a bonding layer that complies with environmental regulations, operates at high temperatures, and has excellent bonding reliability. Therefore, a semiconductor device using an alloy paste containing the alloy powder of the present disclosure can operate at high temperatures and has excellent bonding reliability, while complying with environmental regulations.

[0019] 1 is a cross-sectional view of an alloy powder according to the present disclosure, and FIG. 2 is a cross-sectional view of an example of an embodiment of a semiconductor device according to the present disclosure.

[0020] [Alloy Powder] The alloy powder according to one embodiment of the present disclosure has an AgSi eutectic structure, and is obtained by selecting one particle from an image of the particle cross section taken with an SEM at a magnification of 2,000 to 50,000 times, measuring the total perimeter and the length of the outer perimeter where the eutectic structure is present, excluding the region where the eutectic structure is completely absent in a region extending from the perimeter to a depth of 0.2 μm toward the center of the particle, and calculating the ratio of the AgSi structure to the total perimeter as the proportion of the AgSi structure on the particle surface. This method is performed on any 10 adjacent particles, and at least 8 of the particles have a proportion of the AgSi eutectic structure of 10% or more. Only one type of alloy powder may be used, or two or more types may be used in combination.

[0021] 1 and 2 are enlarged SEM images of the cross section of a particle of the alloy powder. The black areas in the images are regions made of silicon (Si), and the white areas are regions made of an AgSi eutectic structure in which silicon (Si) is dispersed in Ag.

[0022] In this disclosure, the term "eutectic structure" refers to a structure unique to eutectic alloys, in which two crystalline phases simultaneously crystallize from the liquid phase at a specific temperature, forming a very fine metal structure. The eutectic structure is formed at a constant composition ratio, and if the composition ratio is different, one crystal will crystallize first and generally grow coarsely. When the composition of the eutectic structure deviates from the ideal, the crystals that crystallize first and grow during cooling from the liquidus temperature to the eutectic temperature are called primary crystals. For example, in an AgSi alloy, if the Si content is in excess of the ideal eutectic structure, Si will crystallize as primary crystals, grow, and only when the AgSi composition in the remaining liquid phase reaches the ideal composition will a fine eutectic structure begin to form. In alloy powders having an AgSi eutectic structure with an excess of Si compared to the eutectic composition ratio, 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 approximately 100 nm or less. Furthermore, when an AgSi alloy contains more Ag than the ideal eutectic structure, Ag crystallizes as primary crystals, grows, and when the AgSi composition in the remaining liquid phase reaches the ideal composition, a fine eutectic structure begins to form. The size of the primary crystals varies depending on the particle size, but crystals with a difference of several to 10 times or more are observed within a single particle, and the larger of these can be identified as primary crystals.

[0023] The method for producing the alloy powder having the above-mentioned eutectic structure is not particularly limited, but it can be produced, for example, by a method in which a mixture of silver (Ag) and silicon (Si) heated until it becomes liquid is pulverized by a gas atomization method or a water atomization method.

[0024] The proportion of the AgSi eutectic structure on the particle surface of the alloy powder measured by the above-mentioned method is preferably 15% or more, more preferably 20% or more. When the proportion of the AgSi eutectic structure on the particle surface is 10% or more, silver (Ag) recrystallizes during sinter bonding and seeps out from the alloy powder surface, thereby enabling sufficient bonding strength to be exerted.

[0025] The linear expansion coefficient of the alloy powder measured with a thermomechanical analyzer (model name "TMA-60", manufactured by Shimadzu Corporation) is preferably 17 or less, more preferably 13 or less, and even more preferably 11 or less. When the linear expansion coefficient is within the above range, it becomes easier to exhibit connection reliability.

[0026] Preferably, the alloy powder particles are bonded together by a portion of the contact surface through recrystallized Ag, and more preferably by the entire surface through recrystallized Ag. Bonding by a portion of the crystallized Ag can provide excellent bonding reliability.

[0027] The silver (Ag) content of the alloy powder is preferably 15 to 97.6 mass%, more preferably 20 to 90 mass%, and even more preferably 30 to 80 mass%. By having a silver (Ag) content of 15 mass% or more, the proportion of eutectic structure on the surface of the alloy powder can be made sufficient. Furthermore, by having a silver (Ag) content of 97.6 mass% or less, the linear expansion coefficient can be made sufficiently low, and manufacturing costs can be kept low while maintaining bonding reliability.

[0028] The silicon (Si) content of the alloy powder is preferably 2.4 to 85 mass%, more preferably 10 to 80 mass%, and even more preferably 20 to 70 mass%. By ensuring that the silicon (Si) content in the alloy powder is 2.4 mass% or more, the linear expansion coefficient is kept sufficiently low, ensuring bonding reliability while facilitating low manufacturing costs. Furthermore, by ensuring that the silicon (Si) content is 85 mass% or less, the proportion of eutectic structures on the alloy powder surface can be made sufficient.

[0029] Furthermore, the alloy powder may contain other components in addition to silver (Ag) and silicon (Si), but from the viewpoint of complying with environmental regulations, being operable at high temperatures, and exhibiting connection reliability, it is preferable that the alloy powder does not contain any components in addition to silver (Ag) and silicon (Si).

[0030] The total content of silver (Ag) and silicon (Si) in the alloy powder is preferably 90 mass % or more, more preferably 95 mass % or more, and even more preferably 100 mass % based on the total amount of the alloy powder.

[0031] The average particle size (median diameter) of the 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. An average particle size of 0.1 μm or more makes it easy to handle, and an average particle size of 100 μm or less ensures sufficient surface area of ​​the alloy powder, making it easy to bond in a short time. The average particle size (median diameter) can be measured by a laser diffraction / scattering method.

[0032] The shape of the alloy powder is not particularly limited, but examples thereof include spherical, flake (flat), polyhedral, etc. Alloy powders of the same shape may be used alone, or alloy powders of different shapes may be used in combination. Of these, spherical shapes are preferred.

[0033] Furthermore, one embodiment of the present disclosure includes an alloy powder-containing composition containing the above-described alloy powder. The alloy powder-containing composition is not particularly limited and can take various forms. For example, an alloy powder-containing composition called alloy ink can be prepared by dispersing the alloy powder in a suspension state in an appropriate organic solvent (dispersion medium). Alternatively, an alloy powder-containing composition called alloy paste can be prepared by dispersing the alloy powder in a kneaded state in an organic solvent. Among these, the alloy powder-containing composition is preferably an alloy paste.

[0034] [Alloy Paste] In addition to the alloy powder, the alloy paste preferably contains the following organic substance, metal particles other than the alloy powder, etc. The alloy powder contained in the alloy paste may be of one type, or two or more types may be used in combination.

[0035] The alloy paste preferably contains the organic material. The organic material may be used alone or in combination of two or more.

[0036] Examples of the organic substance include organic solvents, binder resins, and additives.

[0037] The organic solvent preferably contains at least organic solvent (a), organic solvent (b), and organic solvent (c). The organic solvents (a), (b), and (c) are different compounds and satisfy the following formulas (1) to (6). Only one type of organic solvent (a), organic solvent (b), and organic solvent (c) may be used, or two or more types may be used. 150°C≦Ta≦250°C (1) 150°C≦Tb≦250°C (2) 250°C≦Tc≦350°C (3) δa≧10.0 (4) δc≦9.0 (5) δc≦δb≦δa (6)

[0038] In the formula, Ta to Tc represent the boiling points of the organic solvents (a) to (c), respectively, and δa to δc represent the Hansen solubility parameters of the organic solvents (a) to (c), respectively. In this specification, the Hansen solubility parameter is sometimes referred to as the "SP value" and abbreviated as "δ."

[0039] The organic solvents (a) to (c) may be any solvents that dissolve uniformly and become liquid when mixed in the compounding ratio used in the above-mentioned bondable conductor paste, and each of them may be liquid or solid at room temperature.

[0040] The organic solvent (a) at least satisfies formula (1). That is, the boiling point Ta of the organic solvent (a) satisfies 150° C.≦Ta≦250° C., preferably 150° C.<Ta<250° C., more preferably 155° C.≦Ta≦220° C., and even more preferably 160° C.≦Ta≦200° C. By using an organic solvent (a) having a boiling point within the above range, the organic solvent is easily volatilized during sintering, and a sintered body can be easily formed.

[0041] 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). When the δa is 10.0 or more, the dispersibility of the alloy powder and the metal particles described below is excellent, and 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 may be 15.0 or less.

[0042] Examples of the organic solvent (a) include alcohol solvents, urea-based solvents, and aprotic polar solvents. Examples of the alcohol solvent include compounds having one or more hydroxy groups, and among these, tertiary alcohols and ether alcohols are preferred. The alcohol solvent may have two or more hydroxy groups. Examples of the ether alcohol include compounds having an ether bond and a hydroxy group, such as (poly)alkylene glycol monoalkyl ethers and alkoxy-substituted alcohols.

[0043] Specific examples of the organic solvent (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).

[0044] The organic solvent (b) at least satisfies formula (2). That is, the boiling point Tb of the organic solvent (b) satisfies 150°C ≦ Tb ≦ 250°C, preferably 150°C < Tb < 250°C, more preferably 180°C ≦ Tb ≦ 248°C, and even more preferably 200°C ≦ Tb ≦ 245°C. By using an organic solvent (b) having a boiling point within the above range, the organic solvent is easily volatilized during sintering, making it easy to form a sintered body. Furthermore, by using an organic solvent (b) having a boiling point of 250°C or less, it is possible to suppress the generation of voids during sintering.

[0045] 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 satisfying formula (6). When δb is within the above range, the compatibility of the organic solvent (a) and the organic solvent (c) is improved, they are less likely to separate, and the continuous ejection stability and storage stability tend to be more excellent.

[0046] Examples of the organic solvent (b) include alcohol solvents, ester solvents, ketone solvents, and amine-based solvents. Examples of the alcohol solvent include solvent compounds having one or more hydroxy groups, and among these, tertiary alcohols, ether alcohols, and ester alcohols are preferred. Ether alcohols are compounds having an ether bond and a hydroxy group, such as (poly)alkylene glycol monoalkyl ethers and alkoxy group-substituted alcohols. Ester alcohols are compounds having an ester bond and a hydroxy group, such as (poly)alkylene glycol monoalkyl ether monoesters. Examples of ester solvents include diacetates of diols such as (poly)alkylene glycols. Preferred ketone solvents are cyclic ketones. Preferred amine-based solvents are alkylamines.

[0047] The organic solvent (b) is selected on the premise that it satisfies the formula (6) in relation to the organic solvents (a) and (c). Specific examples of the organic solvent (b) include d-camphor (δ 10.4, boiling point 204°C), 1-heptanol (δ 10.0, boiling point 177°C), butyl carbitol (diethylene glycol monobutyl ether) (δ 10.2, boiling point 231°C), ethyl carbitol (diethylene glycol monoethyl ether) (δ 10.5, boiling point 196°C), tripropylene glycol monomethyl ether (δ 9.4, boiling point 243°C), α-terpineol (δ 9 .3, boiling point 220°C), dihydroterpineol (δ 9.0, boiling point 210°C), 1,3-butanediol diacetate (δ 9.2, boiling point 232°C), propylene glycol diacetate (δ 9.3, boiling point 190°C), butyl carbitol acetate (δ 9.0, boiling point 247°C), dipropylene glycol butyl ether (δ 9.2, boiling point 230°C), isophorone (δ 9.5, boiling point 213°C), 1-decanol (δ 9.6, boiling point 230°C), propylene glycol monobutyl ether (δ 9.0, boiling point 170°C), 1-nonanol (δ 9.8, boiling point 214°C), etc. may be used.

[0048] The boiling point Tb of the organic solvent (b) is preferably higher than the boiling point Ta of the organic solvent (a), i.e., 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 temperature difference is 2°C or more, the generation of voids during sintering can be further suppressed.

[0049] The organic solvent (c) at least satisfies formula (3). That is, the boiling point Tc of the organic solvent (c) satisfies 250°C ≦ Tc ≦ 350°C, preferably 250°C < Tc < 350°C, more preferably 250°C < Tc ≦ 320°C, and even more preferably 250°C < Tc ≦ 300°C. By using an organic solvent (c) having a boiling point within the above range, rapid evaporation of the organic solvents (a) and (b) during sintering can be suppressed, and the generation of voids can be suppressed.

[0050] The organic solvent (c) at least satisfies 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 δc 9.0 or less, it is possible to suppress the generation of voids during sintering. The δc of the organic solvent (c) is, for example, 6.0 or more, and may be 7.0 or more.

[0051] Examples of the organic solvent (c) include ether solvents, alkane solvents, and ester solvents. Examples of the ether solvent include (poly)alkylene glycol dialkyl ethers. Examples of the alkane solvent include alkanes having 14 or more carbon atoms (e.g., 14 to 20 carbon atoms). Examples of the ester solvent include esters of (poly)alkylene glycol alkyl ethers and fatty acids.

[0052] Specific examples of the organic solvent (c) include dibutyl carbitol (diethylene glycol dibutyl ether) (δ 8.3, boiling point 255°C), tetradecane (δ 7.9, boiling point 254°C), and hexadecane (δ 8.0, boiling point 287°C).

[0053] The boiling point Tc of the organic solvent (c) is preferably higher than the boiling point Tb of the organic solvent (b), i.e., 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 temperature difference is 2°C or more, the generation of voids during sintering can be further suppressed.

[0054] The boiling point Tc of the organic solvent (c) is preferably higher than the boiling point Ta of the organic solvent (a), i.e., 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 temperature difference is 30°C or more, the generation of voids during sintering can be further suppressed.

[0055] The SP value δa of organic solvent (a), the SP value δb of organic solvent (b), and the SP value δc of organic solvent (c) satisfy the relationship of the above formula (6) [δc≦δb≦δa]. In particular, it is preferable that δb is higher than δc, i.e., δc<δb is satisfied. It is also preferable that δa is higher than δb, i.e., δb<δa is satisfied.

[0056] 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 superior and the continuous ejection stability is superior. 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 ejection stability and storage stability are superior.

[0057] 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 superior and the continuous ejection stability is superior. 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 ejection stability and storage stability are superior.

[0058] 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, based on formulas (4) and (5). 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 less likely to separate from the organic solvent, resulting in better continuous discharge stability and storage stability.

[0059] The ratio of organic solvent (a) to the total amount of organic solvents (a), (b), and (c) (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 ratio is within the above range, the organic solvent is easily volatilized during sintering, a sintered body can be easily formed, and the dispersibility of the alloy powder and metal particles is superior.

[0060] The ratio of organic solvent (b) to the total amount of organic solvent (a), organic solvent (b), and organic solvent (c) (100% by mass) [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 ratio is within the above range, the compatibility of the organic solvents is excellent, and the continuous ejection stability and storage stability are further improved.

[0061] The proportion of organic solvent (c) relative to the total mass of organic solvents (a), (b), and (c) (100 mass%) [organic solvent (c) / {organic solvent (a) + organic solvent (b) + organic solvent (c)}] is preferably 5 to 70 mass%, more preferably 10 to 60 mass%, and even more preferably 15 to 50 mass%. When this proportion is within the above range, the generation of voids during sintering can be further suppressed.

[0062] The content of organic solvent (c) relative to 100 parts by mass of organic solvent (a) 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. When the content is within the above range, the blending amounts of organic solvent (a) and organic solvent (c) are well balanced, resulting in better void suppression during sintering and better dispersibility of the alloy powder and metal particles.

[0063] The content of organic solvent (b) relative to 100 parts by mass of the total amount of organic solvent (a) and organic solvent (c) 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 ejection stability and low-temperature storage property are further improved.

[0064] The organic solvent may contain other solvents (organic solvents) in addition to organic solvents (a), (b), and (c). The total content of organic solvents (a), (b), and (c) in the organic solvent is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, relative to 100% by mass of the total amount of the organic solvents. When the content is 50% by mass or more, the dispersibility of metal particles and the compatibility of each organic solvent are excellent, and continuous discharge stability, storage stability, and void formation suppression during sintering are excellent.

[0065] When the organic solvents (a), (b), and (c) are mixed in the blending ratio used for the above-mentioned bondable conductor paste, it is preferable that the organic solvents (a), (b), and (c) dissolve uniformly at room temperature and do not undergo phase separation. Furthermore, it is preferable that the organic solvents (a), (b), and (c) dissolve uniformly at room temperature and do not undergo phase separation in the above-mentioned bondable conductor paste. It is particularly preferable that no phase separation occurs at 22 to 28°C (preferably 10 to 30°C, more preferably 0 to 35°C).

[0066] Specific examples of the binder resin include vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, polyester resin, acrylic resin, and cellulose resin (eg, ethyl cellulose).

[0067] Examples of the additives include surface conditioners, viscosity adjusters, dispersants, and antifoaming agents.

[0068] The content of the organic substance in the alloy paste 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, per 100 parts by mass of the total of the alloy powder and metal particles other than the alloy powder.

[0069] The alloy paste preferably contains, in addition to the alloy powder, metal particles other than the alloy powder, and particularly preferably silver (Ag) particles, since they can be firmly bonded to the silver (Ag) contained in the AgSi eutectic structure in the alloy powder.

[0070] The average particle size (median diameter) of 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. When the average particle size is 0.1 μm or more, the metal particles are easy to handle. When the average particle size is 100 μm or less, bonding reliability is easily achieved.

[0071] The shape of the metal particles other than the alloy powder is not particularly limited, but examples thereof include spherical, flake (flat), polyhedral, etc. Metal particles of the same shape may be used alone, or metal particles of different shapes may be used in combination. Among these, spherical shapes are preferred for proper dispersion in the alloy paste.

[0072] 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, even more 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. When the content of the metal particles other than the alloy powder is 5 parts by mass or more, sufficient bonding with the alloy powder can be achieved during sinter bonding, and when the content is 2000 parts by mass or less, it is easy to reduce the linear expansion coefficient.

[0073] The alloy paste may also contain other components in addition to the above-mentioned components. Examples of the other components include a non-organic surfactant and a non-organic viscosity modifier. The content of the other components is preferably 5% by mass or less, and may be 3% by mass or less, based on the total amount of the organic material.

[0074] [Semiconductor Device] One embodiment of the present disclosure includes a semiconductor device in which the alloy powder-containing composition (preferably the alloy paste) is used as a bonding layer for bonding a substrate and an object to be bonded. In the semiconductor device, the object to be bonded is bonded to the substrate via a bonding layer that is a sintered body of the alloy powder-containing composition. Figure 3 is a cross-sectional view schematically showing this semiconductor device. 1 denotes the semiconductor device, 10 denotes the substrate, 20 denotes the bonding layer, and 30 denotes the object to be bonded.

[0075] Examples of the substrate include metal substrates such as copper substrates, ceramic substrates, metal-clad ceramic substrates, SiC substrates, gallium nitride substrates, glass epoxy substrates, BT resin substrates, glass substrates, and resin substrates. Since the alloy paste according to one embodiment of the present disclosure can be sintered at low temperatures, substrates that are sensitive to heat can also be used. As the substrate, ceramic substrates and metal-clad ceramic substrates are preferred, and copper-clad ceramic substrates and aluminum-clad ceramic substrates are more preferred.

[0076] Examples of the bonded object include electronic components and heat dissipation substrates. Examples of electronic components include semiconductor elements, LED elements, and other electronic elements (chips, dies), and examples of the semiconductor elements include power semiconductor elements. In addition, it is preferable that the bonding surface of the bonded object with the bonding layer is silver-plated. Examples of the material of the bonded object include Si (silicon), SiC (silicon carbide), GaN, diamond, and the like.

[0077] The semiconductor device can be manufactured by applying the alloy powder-containing composition to a substrate by a printing method (specifically, a dispenser printing method, a mask printing method, a screen printing method, an inkjet printing method, etc.), mounting an object to be bonded on the applied layer, and then sintering the resulting layer.

[0078] The sintering temperature is preferably, for example, 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, for example, 0.5 minutes to 2 hours, more preferably 10 minutes to 1 hour, and even more preferably 3 to 10 minutes.

[0079] 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.

[0080] The sintering process recrystallizes and exudes the silver (Ag) present in the AgSi eutectic structure of the alloy powder in the alloy powder-containing composition, thereby firmly bonding the silver (Ag) to the substrate and the workpiece. Furthermore, since the bonding layer contains the alloy powder with a low linear expansion coefficient, the strength of the bond can be increased while maintaining a low thermal expansion coefficient. This essentially improves the properties of the bonding layer, such as thermal fatigue resistance. Therefore, a semiconductor device using the alloy powder-containing composition as a bonding layer for bonding a substrate and a workpiece can comply with environmental regulations, operate at high temperatures, and have excellent bonding reliability.

[0081] Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. Furthermore, each configuration and their combination in each embodiment is merely an example, and additions, omissions, and other modifications of configurations are possible as appropriate within the scope of the gist of this disclosure. The present disclosure is not limited by the embodiments, but is limited only by the scope of the claims.

[0082] Hereinafter, one embodiment of the present disclosure will be described in more detail based on examples.

[0083] Example 1 Silver (Ag) bullion (purity 99.99%) and silicon (Si) bullion (purity 99.9999%) were mixed to a content of 95% by mass and melted by heating at 1450°C. The resulting solution was pulverized using a gas atomizer (product name "RQP-20K", manufactured by Makabe Giken Co., Ltd.) to obtain the alloy powder of Example 1. The gas atomized material was then classified using an ultrasonic vibration sieve (product name "TSK-DGS type", manufactured by Tokyo Screen Co., Ltd.) to obtain particles with an average particle size of 15.86 μm. The powder particle size was then adjusted using a high-speed rotor-type classifier (product name "Turbo Classifier TC-15", manufactured by Nisshin Engineering Inc.) to obtain an average particle size of 3.2 μm. The linear expansion coefficient of the alloy powder of Example 1 measured using a thermomechanical analyzer (device name "TMA-60", manufactured by Shimadzu Corporation) was 16.42. The actual measurement result was 14.1 ppm.

[0084] Examples 2 to 5 Alloy powders of Examples 2 to 5 were prepared in the same manner as in Example 1, except that the contents of silver (Ag) particles and silicon (Si) particles were changed to the amounts shown in Table 1. The average particle sizes and linear expansion coefficients of Examples 2 to 5 were as shown in Table 1.

[0085] Comparative Example 1 Instead of the above alloy powder, silver (Ag) particles (average particle size: 2.0 μm to 3.4 μm, linear expansion coefficient: 19.3 ppm / K) were used.

[0086] Comparative Example 2: Instead of the alloy powder, a mixed powder containing 80% by mass of silver (Ag) particles and 20% by mass of silicon (Si) particles was used. The average particle size of the mixed powder was Ag particles (2.0 μm to 3.4 μm) and Si particles (D50 = 10 μm). The linear expansion coefficient of the mixed powder in Comparative Example 2 was 16.73.

[0087] [Evaluation] The physical properties of the alloy powders, silver particles, and mixed powders of the above Examples and Comparative Examples were evaluated, and the results are shown in Table 1. In Table 1, "-" indicates that the properties have not been evaluated or cannot be evaluated.

[0088] (1) Proportion of eutectic structure on particle surface The alloy powder of the example was cured in an epoxy resin, and the particle cross section was polished to an extent that it could be observed. One particle was selected from an image of the particle cross section taken with an SEM at a magnification of 2000 to 50,000 times, and the total perimeter length and the length of the outer perimeter portion where the eutectic structure was present in the region from the perimeter to a depth of 0.2 μm toward the center of the particle were measured. This method was then carried out for 10 adjacent particles, and the proportion of the AgSi structure on the particle surface was calculated as the proportion of the AgSi eutectic structure on the particle surface. Note that the portion of the particle other than that determined to be primary crystals was evaluated as the eutectic structure.

[0089] (2) Recrystallization (Exudation) The alloy powders, silver particles, and mixed powders of the examples and comparative examples were heated at 300°C for 30, 60, or 90 minutes, and then photographed at 3000x magnification using an SEM. Particles with particle sizes of less than 3 μm, 3 to 7 μm, 7 to 12 μm, and over 12 μm were selected from the photographed images. Selected particles whose surfaces were recrystallized and silver (Ag) exuded by 0.1 μm or more were evaluated as ◎, those in which recrystallization (exudation) of silver (Ag) was confirmed as ○, and those in which no exudation (recrystallization) was confirmed as × were evaluated.

[0090] (3) Bonding strength between particles In the examples and comparative examples, the alloy powders, silver particles, and mixed powders were marked with a double circle when the entire contact surface between the particles was bonded by recrystallized Ag, a circle when only a portion of the particles was bonded, and an x ​​when no bonding was observed.

[0091]

[0092] The alloy powder of the example is composed of silver (Ag) and silicon (Si), so it complies with environmental regulations while maintaining a low coefficient of linear expansion. It was confirmed that silver (Ag) recrystallizes when heated to 300°C, and bonding occurs via the silver (Ag) seeping out of the alloy powder. On the other hand, it was confirmed that the coefficient of linear expansion is high when silver (Ag) powder is used alone (Comparative Example 1). Furthermore, while the linear expansion coefficient was reduced with the mixed powder of silver (Ag) and silicon (Si), bonding via the seeping out silver (Ag) was not observed, and bonding reliability was poor.

[0093] Variations of the present disclosure are described below. [Appendix 1] An alloy powder having an AgSi eutectic structure, wherein a particle is selected from an image of the particle cross section taken with an SEM at a magnification of 2,000 to 50,000 times, and the total perimeter and the length of the outer perimeter where the eutectic structure is present, excluding a region where the eutectic structure is completely absent in a region extending from the perimeter to a depth of 0.2 μm toward the center of the particle, are measured, and the ratio of the total perimeter to the total perimeter is calculated as the ratio of the AgSi structure on the particle surface. This method is performed on any 10 adjacent particles, and at least 8 of the particles have a ratio of the AgSi eutectic structure of 10% or more. [Appendix 2] The alloy powder according to Appendices 1, wherein the ratio of the AgSi eutectic structure is 15% or more, preferably 20% or more. [Appendix 3] The alloy powder according to Appendices 1 or 2, wherein the linear expansion coefficient measured with a thermomechanical analyzer is 17 or less. [Appendix 4] The alloy powder according to any one of Appendices 1 to 3, wherein the contact surfaces of the alloy powder particles are partially bonded together by recrystallized Ag. [Appendix 5] The alloy powder according to any one of Appendices 1 to 4, wherein the contact surfaces of the alloy powder particles are entirely bonded together by recrystallized Ag. [Appendix 6] The alloy powder according to any one of Appendices 1 to 5, wherein the average particle size (median diameter) is 0.1 to 100 μm. [Appendix 7] The alloy powder according to any one of Appendices 1 to 6, wherein the shape is spherical. [Appendix 8] The alloy powder according to any one of Appendices 1 to 7, wherein the content of silver (Ag) is 15 to 97.6 mass% and the content of silicon (Si) is 2.4 to 85 mass% relative to the total amount of the alloy powder. [Appendix 9] The alloy powder according to any one of Appendices 1 to 8, wherein the content is free of components other than silver (Ag) and silicon (Si). [Appendix 10] An alloy paste comprising the alloy powder according to any one of Appendices 1 to 9. [Appendix 11] The alloy paste according to Appendix 10, further comprising an organic substance. [Appendix 12] The alloy paste according to Appendix 11, wherein the organic substance is an organic solvent. [Appendix 13] The alloy paste according to any one of Appendices 10 to 12, further comprising metal particles other than the alloy powder, the content of the metal particles other than the alloy powder being 5 to 2000 parts by mass per 100 parts by mass of the alloy powder.[Appendix 14] The alloy paste according to any one of Appendices 10 to 13, wherein the content of the organic substance is 0.5 to 50 parts by mass per 100 parts by mass of the total of the alloy powder and metal particles other than the alloy powder. [Appendix 15] A semiconductor device using the alloy paste according to any one of Appendices 10 to 14 as a bonding layer for bonding a substrate and an object to be bonded.

[0094] 1 Semiconductor device 10 Substrate 20 Bonding layer 30 Object to be bonded

Claims

1. An alloy powder having an AgSi eutectic structure, wherein a particle is selected from an image of the particle cross section taken with an SEM at a magnification of 2000 to 50000 times, the total perimeter and the length of the outer perimeter where the eutectic structure is present, excluding the region where the eutectic structure is completely absent in the region from the perimeter to a depth of 0.2 μm toward the center of the particle, are measured, and the ratio of the total perimeter to the AgSi structure on the particle surface is calculated. This method is carried out for any 10 adjacent particles, and the ratio of the AgSi eutectic structure on the particle surface is 10% or more in at least 8 of the selected 10 particles.

2. The alloy powder according to claim 1, having an average particle size (median diameter) of 0.1 to 100 μm.

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

4. An alloy paste containing the alloy powder according to claim 1 or 2.

5. An alloy paste containing the alloy powder according to claim 3.

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

7. An alloy paste according to claim 4, further comprising metal particles other than said alloy powder, the content of said metal particles other than said alloy powder being 5 to 2000 parts by mass per 100 parts by mass of said alloy powder.

8. A semiconductor device using the alloy paste according to claim 4 as a bonding layer for bonding a substrate and an object to be bonded.

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