TWI889941B - Silver-containing paste and joined body - Google Patents

Abstract

The silver-containing paste of the present invention allows the silicon surface of a silicon wafer to be bonded to a metal surface, and comprises silver-containing particles, a bifunctional or higher-functional resin, and a solvent. The content of the silver-containing particles (A) is 88% by mass or more and 98% by mass or less relative to 100% by mass of the silver-containing paste excluding the organic solvent (C).

Description

Silver-containing paste and joint

The present invention relates to a silver-containing paste and a joint.

To improve the heat dissipation of semiconductor devices, a technology for manufacturing semiconductor devices using a thermosetting resin composition containing metal particles is known. By incorporating metal particles, which have a higher thermal conductivity than the resin itself, into the thermosetting resin composition, the thermal conductivity of the cured product can be improved. As specific examples applicable to semiconductor devices, the following Patent Documents 1 and 2 disclose technologies for bonding/joining semiconductor elements to substrates (supporting members) using thermosetting resin compositions containing metal particles.

Patent Document 1 discloses a semiconductor-bonding thermosetting resin composition containing a (meth)acrylate compound with a specific structure, a free radical initiator, silver microparticles, silver powder, and a solvent, and a semiconductor device in which a semiconductor element and a substrate are bonded using this composition. The document describes the ability to improve connection reliability against temperature cycling after mounting (paragraph 0011).

Patent Document 2 discloses a resin paste composition containing an imide acrylate compound, a free radical initiator, a filler, and a liquid rubber component, and a semiconductor device in which a semiconductor element and a substrate are bonded using this composition. The document states that by reducing the stress of the resin paste composition, chip cracking and chip warping can be suppressed (paragraph 0003).

Patent Document 3 discloses a semiconductor device having a structure in which a semiconductor element and a supporting member for mounting the semiconductor element are bonded via a silver paste composition comprising silver particles satisfying specific physical properties, a solvent, and an additive. This document describes an example using dipropylene glycol methyl ether acetate and isoborneol as solvents. Prior Art Documents Patent Documents

[Patent Document 1] Japanese Patent Application Publication No. 2014-74132 [Patent Document 2] Japanese Patent Application Publication No. 2000-239616 [Patent Document 3] Japanese Patent Application Publication No. 2014-225350

[The problem that the invention aims to solve]

However, when the silver paste described in Patent Documents 1-3 is used to bond the silicon surface of a silicon wafer to a metal surface, there is room for improvement in heat dissipation. Technology is required to improve heat dissipation from the non-metal-coated surface of the silicon wafer. [Technical Solution]

The inventors discovered that when a silver-containing paste containing a specific amount of silver-containing particles, a bifunctional or higher-functional resin, and an organic solvent is used to bond the silicon surface of a silicon wafer to a metal surface, excellent heat dissipation is achieved, leading to the completion of the present invention. That is, the present invention can be as follows.

According to the present invention, a silver-containing paste for bonding the silicon surface of a silicon wafer to a metal surface can be provided, comprising: (A) silver-containing particles; (B) a resin having two or more functional groups; and (C) an organic solvent, wherein the content of the silver-containing particles (A) is 88% by mass or more and 98% by mass or less relative to 100% by mass of the silver-containing paste excluding the organic solvent (C).

According to the present invention, a high thermal conductivity material can be provided, which is obtained by sintering the aforementioned silver-containing paste.

According to the present invention, a bonded body can be provided, wherein the silicon surface of a silicon wafer and a metal surface are bonded together using the aforementioned hardened body containing silver paste, wherein the storage elastic modulus of the hardened body as measured by dynamic viscoelasticity (DMA) is 1,000 to 20,000 MPa.

According to the present invention, a semiconductor device can be provided, comprising: a substrate containing metal; a silicon wafer; and a bonding layer, which bonds the metal surface of the substrate to the silicon surface of the silicon wafer, wherein the bonding layer is formed by sintering the silver-containing paste. [Effects of the Invention]

The silver-containing paste of the present invention can improve heat dissipation when bonding the silicon surface of a silicon wafer to a metal surface.

The following describes the embodiments of the present invention using the drawings. In all drawings, the same components are denoted by the same reference numerals, and descriptions thereof are omitted as appropriate. Furthermore, unless otherwise specified, "to" means "above" to "below."

The silver-containing paste (paste-like resin composition) of this embodiment bonds the silicon surface of a silicon wafer to a metal surface and comprises (A) silver-containing particles, (B) a bifunctional or higher-functional resin, and (C) an organic solvent. The content of the silver-containing particles (A) relative to 100% by mass of the silver-containing paste excluding the organic solvent (C) is 88% by mass or more and 98% by mass or less, preferably 88% by mass or more and 96% by mass or less, more preferably 88% by mass or more and 93% by mass or less, further preferably 89% by mass or more and 93% by mass or less, and particularly preferably 91% by mass or more and 93% by mass or less. The silver-containing paste according to this embodiment can also improve heat dissipation when bonding the silicon surface of a silicon wafer to a metal surface.

In this embodiment, a silicon wafer has functional components such as transistors, resistors, and capacitors on one side. The silver-containing paste of this embodiment can bond the silicon surface of the other side of the wafer to the metal surface of a substrate, such as a lead frame, a metal layer on various substrates, a heat spreader, or a heat sink, thereby improving heat dissipation between them.

[Silver-Containing Particles (A)] Silver-containing particles (A) can undergo sintering through appropriate heat treatment, forming a particle-linked structure (sintered structure).

In particular, by including silver-containing particles in the silver-containing paste (especially silver particles with a relatively small particle size and a relatively large specific surface area), a sintered structure can be easily formed even during heat treatment at relatively low temperatures (around 180°C). The preferred particle size will be discussed later.

The shape of the silver-containing particles (A) is not particularly limited. Spherical shapes are preferred, but non-spherical shapes such as ellipsoids, flats, plates, flakes, needles, scales, agglomerates, and polyhedrons are also acceptable. The silver-containing particles (A) can include at least one of these shapes. In this embodiment, the silver-containing particles (A) preferably contain two or more types of silver-containing particles selected from spherical, scaly, agglomerated, and polyhedral shapes, and more preferably contain spherical silver-containing particles (A1) and at least one type of silver-containing particles (A2) selected from scaly, agglomerated, and polyhedral shapes. This further increases the contact rate between the silver-containing particles, facilitating network formation after sintering the silver-containing paste, further improving thermal and electrical conductivity. By including the silver-containing particles (A2) in the silver-containing particles (A), resin cracking in the molded article obtained from the silver-containing paste can be further suppressed, and the linear expansion coefficient can be further suppressed.

In this embodiment, "spherical" is not limited to a perfect sphere and also includes shapes with slight surface irregularities. The surface of the silver-containing particles (A) may be treated with a carboxylic acid, a saturated fatty acid having 4 to 30 carbon atoms, a monovalent unsaturated fatty acid having 4 to 30 carbon atoms, or a long-chain alkyl nitrile.

Silver-containing particles (A) may be (i) silver particles (silver powder) consisting essentially of silver alone, or (ii) particles consisting of silver and components other than silver. Furthermore, both (i) and (ii) may be used in combination as metal-containing particles.

In this embodiment, the silver-containing particles (A) particularly preferably comprise silver-coated resin particles, in which the surfaces of the resin particles are coated with silver. This allows for the production of a silver-containing paste that yields a cured product with improved thermal conductivity and storage modulus. The silver-containing particles (A) in this embodiment can comprise at least one selected from silver particles and silver-coated resin particles.

Silver-coated resin particles have silver on the surface and resin inside, so they are believed to have good thermal conductivity and are softer than particles made of silver alone. Therefore, using silver-coated resin particles is believed to facilitate the design of appropriate thermal conductivity and storage modulus.

Generally, increasing the amount of silver particles can be considered to improve thermal conductivity. However, due to the hardness of metal, excessive silver particles can lead to excessively high elastic modulus after sintering. By using silver-coated resin particles as some or all of the silver particles, it is possible to easily design a silver paste that produces a cured product with the desired thermal conductivity and storage elastic modulus.

In silver-coated resin particles, the silver layer only needs to cover at least a portion of the surface of the resin particle. Of course, the silver layer can also cover the entire surface of the resin particle.

Specifically, in silver-coated resin particles, the silver layer preferably covers at least 50% of the resin particle surface, more preferably at least 75%, and even more preferably at least 90%. It is particularly preferred that the silver layer covers substantially the entire surface of the resin particle. From another perspective, when the silver-coated resin particle is cut along a certain cross-section, it is preferred that the silver layer be visible throughout the entire circumference of the cross-section.

From another perspective, the mass ratio of resin/silver in the silver-coated resin particles is preferably 90/10 to 10/90, more preferably 80/20 to 20/80, and even more preferably 70/30 to 30/70.

Examples of the "resin" in the silver-coated resin particles include silicone resins, (meth)acrylic resins, phenolic resins, polystyrene resins, melamine resins, polyamide resins, and polytetrafluoroethylene resins. Of course, other resins are also acceptable. Furthermore, the resin may be a single type or a combination of two or more. From the perspectives of elasticity and heat resistance, silicone resins or (meth)acrylic resins are preferred.

The polysiloxane may be particles composed of an organopolysiloxane obtained by polymerizing an organochlorosilane such as methylchlorosilane, trimethyltrichlorosilane, or dimethyldichlorosilane. Alternatively, the polysiloxane may be a polysiloxane having a three-dimensionally cross-linked structure as its basic skeleton.

The (meth)acrylic resin may be a resin obtained by polymerizing a monomer containing a (meth)acrylic acid ester as a main component (50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more). Examples of (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-propyl (meth)acrylate, chloro-2-hydroxyethyl (meth)acrylate, diethylene glycol mono(meth)acrylate, methoxyethyl (meth)acrylate, glycidyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and isoborneol (meth)acrylate. The monomer component of the acrylic resin may contain a small amount of other monomers. Examples of such other monomer components include styrene monomers. Regarding silver-coated (meth)acrylate resins, reference can also be made to the description in Japanese Patent Application Laid-Open No. 2017-126463, etc.

Various functional groups can be introduced into silicone resins or (meth)acrylic resins. The functional groups that can be introduced are not particularly limited. Examples include epoxy, amino, methoxy, phenyl, carboxyl, hydroxyl, alkyl, vinyl, and hydroxyl groups.

The resin particles in the silver-coated resin particles can contain various additives, such as a low-stress modifier. Examples of such low-stress modifiers include butadiene styrene rubber, butadiene acrylonitrile rubber, polyurethane rubber, polyisoprene rubber, acrylic rubber, fluororubber, liquid organopolysiloxane, liquid polybutadiene, and other liquid synthetic rubbers. In particular, when the resin particles contain a silicone resin, the inclusion of a low-stress modifier can enhance the elastic properties of the silver-coated resin particles.

The shape of the resin particle portion of the silver-coated resin particle is not particularly limited. However, a combination of a spherical shape and an irregular shape other than a spherical shape, such as a flat shape, a plate shape, or a needle shape, is preferred.

The specific gravity of the silver-coated resin particles is not particularly limited, but the lower limit is preferably 2 or greater, more preferably 2.5 or greater, and even more preferably 3 or greater. The upper limit is preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less. An appropriate specific gravity is preferred from the perspectives of dispersibility of the silver-coated resin particles themselves, or uniformity when the silver-coated resin particles are used in combination with other silver-containing particles.

In this embodiment, when the silver-containing particles (A) include silver-coated resin particles, the ratio b/a (the volume fraction b of the silver-coated resin particles relative to the volume fraction a of the silver-containing particles (A)) is preferably less than 0.6, more preferably 0.5 or less, and even more preferably 0.4 or less. By appropriately adjusting this ratio, it is possible to further improve heat dissipation while suppressing a decrease in adhesion due to thermal cycling. The lower limit of the ratio b/a is not particularly limited, but is 0.05 or greater.

Furthermore, in this embodiment, when the silver-containing particles (A) include silver-coated resin particles, from the viewpoint of the aforementioned effects, the ratio d/c (the weight fraction d of the silver-coated resin particles to the weight fraction c of the silver-containing particles (A)) is preferably less than 0.25, more preferably 0.20 or less, and even more preferably 0.15 or less. The lower limit of the ratio d/c is not particularly limited, but is 0.01 or greater.

Incidentally, when the ratio of the silver-coated resin particles in the entire silver-containing particles (A) is not 100 mass %, the silver-containing particles other than the silver-coated resin particles are, for example, particles consisting essentially only of silver (silver particles).

The median particle size _D50 of the silver-containing particles (A) is preferably 0.001 to 1000 μm, more preferably 0.01 to 100 μm, and even more preferably 0.1 to 20 μm. By setting the _D50 value appropriately, it is easier to maintain a balance between thermal conductivity, sintering properties, and resistance to thermal cycling. Furthermore, setting the _D50 value appropriately can sometimes improve coating/joining workability. The particle size distribution of the silver-containing particles (horizontal axis: particle size, vertical axis: frequency) can be unimodal or multimodal.

The median particle size _D50 of particles consisting essentially of silver is preferably 0.8 μm or greater, more preferably 1.0 μm or greater, and even more preferably 1.2 μm or greater. This can further improve thermal conductivity.

Furthermore, the median particle size _D50 of particles consisting essentially of silver is preferably 7.0 μm or less, more preferably 5.0 μm or less, and even more preferably 4.0 μm or less. This can further improve sinterability and sintering uniformity.

The median particle size _D50 of the silver-containing particles (A) is preferably 0.5 μm or larger, more preferably 1.5 μm or larger, and even more preferably 2.0 μm or larger. This facilitates setting the storage elastic modulus E' to an appropriate value.

The median particle size _D50 of the silver-containing particles (A) is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. This facilitates sufficient improvement in thermal conductivity.

The median particle size _D50 of the silver-containing particles (A) can be determined, for example, by particle imaging using a flow particle imaging analyzer (FPIA (registered trademark)-3000) manufactured by Sysmex Corporation. More specifically, the particle size of the silver-containing particles (A) can be determined by wet-analyzing the volume-based median particle size using this analyzer.

The content of the silver-containing particles (A) relative to 100 mass% of the silver-containing paste excluding the organic solvent (C) described below is 70 mass% to 98 mass%, preferably 75 mass% to 96 mass%, and more preferably 80 mass% to 93 mass%. The silver-containing paste of this embodiment can improve heat dissipation even when bonding the silicon surface of a silicon wafer to a metal surface.

Among the silver-containing particles (A), particles consisting essentially of silver can be obtained from, for example, DOWA HIGHTECH CO., LTD., Fukuda Metal Foil & Powder Co., Ltd., etc. Furthermore, silver-coated resin particles can be obtained from, for example, Mitsubishi Materials Corporation, Sekisui Chemical Co., Ltd., Sanno Co., Ltd., etc.

[Bifunctional or Higher-Level Resin (B)] The silver-containing paste of this embodiment contains a bifunctional or higher-level resin (B). The inclusion of the bifunctional or higher-level resin (B) improves the adhesion between the cured silver-containing paste and the silicon surface of a silicon wafer, thereby improving heat dissipation when the silicon surface of a silicon wafer is bonded to a metal surface.

Bifunctional or higher-functional resins (B) typically contain groups that polymerize/crosslink through the action of active chemical species such as free radicals and/or a chemical structure that reacts with the curing agent D described below. Examples of bifunctional or higher-functional resins (B) include two or more epoxy groups, oxetanyl groups, groups containing ethylenic carbon-carbon double bonds, hydroxyl groups, isocyanate groups, and butylenediimide structures. Preferred examples of bifunctional or higher-functional resins (B) include bifunctional or higher-functional epoxy resins.

Examples of bifunctional or higher functional epoxy resins include biphenyl type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, stilbene type epoxy resins, hydroquinone type epoxy resins, and other bifunctional or crystalline epoxy resins; cresol novolac type epoxy resins, phenol novolac type epoxy resins, naphthol novolac type epoxy resins, and other novolac type epoxy resins; phenol aralkyl type epoxy resins containing a phenylene skeleton, and biphenylene type epoxy resins containing a biphenylene skeleton; Phenol aralkyl epoxy resins such as phenol aralkyl epoxy resins with a phenylene skeleton and naphthol aralkyl epoxy resins containing a phenylene skeleton; trifunctional epoxy resins such as trisphenol methane epoxy resins and alkyl-modified trisphenol methane epoxy resins; modified phenol-type epoxy resins such as dicyclopentadiene-modified phenol-type epoxy resins and terpene-modified phenol-type epoxy resins; and epoxy resins containing heterocyclic groups such as tris(II) nuclei. These epoxy resins may be used alone or in combination of two or more. As bifunctional or higher-functional epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, etc. are preferred.

Furthermore, in addition to containing a bifunctional or higher functional epoxy resin, it may also contain a monofunctional epoxy group-containing compound such as 4-tert-butylphenyl epoxypropyl ether, m-cresol epoxypropyl ether, p-cresol epoxypropyl ether, phenyl epoxypropyl ether, cresol epoxypropyl ether, etc.

The amount of the bifunctional or higher functional resin (B) in the silver-containing paste of this embodiment is preferably 1 mass % or more and 15 mass % or less, and more preferably 2 mass % or more and 10 mass % or less, relative to 100 mass % of the silver-containing paste excluding the organic solvent (C) described below.

[Organic Solvent (C)] The silver-containing paste of this embodiment contains an organic solvent (C). The organic solvent (C) can, for example, adjust the fluidity of the silver-containing paste and improve workability when forming an adhesive layer on a substrate.

Examples of the organic solvent (C) include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, methyl methoxybutanol, α-terpineol, β-terpineol, hexylene glycol, benzyl alcohol, 2-phenylethyl alcohol, isopalmityl alcohol, isostearyl alcohol, lauryl alcohol, ethylene glycol, propylene glycol, butylglycerol, and glycerol. Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, diacetone alcohol (4-hydroxy-4-methyl-2-pentanone), 2-octanone, isophorone (3,5,5-trimethyl-2-cyclohexene-1-one), and diisobutyl ketone (2,6-dimethyl-4-heptanone); Ethyl acetate, butyl acetate, diethyl phthalate, dibutyl phthalate, acetoxyethane, methyl butyrate, methyl hexanoate, methyl octanoate, methyl decanoate, methylcellol acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, 1,2-diacetoxyethane, tributyl phosphate, tricresyl phosphate, and tripentyl phosphate; Ethers such as tetrahydrofuran, dipropyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, ethoxyethyl ether, 1,2-bis(2-diethoxy)ethane, and 1,2-bis(2-methoxyethoxy)ethane; Ether esters such as 2-(2-butoxyethoxy)ethane acetate; Ether alcohols such as 2-(2-methoxyethoxy)ethanol; Hydrocarbons such as toluene, xylene, n-alkanes, isoalkanes, dodecylbenzene, turpentine, kerosene, and light oil; Nitriles such as acetonitrile and propionitrile; Amides such as acetamide and N,N-dimethylformamide; Polysilicone oils such as low molecular weight volatile silicone oils and volatile organic modified silicone oils. The organic solvent (C) may be a single organic solvent or a combination of two or more organic solvents.

The amount of the organic solvent (C) is not particularly limited. The amount can be appropriately adjusted based on the desired fluidity, etc. For example, the organic solvent (C) is used in an amount such that the non-volatile component concentration in the silver-containing paste is 50 to 90% by mass.

[Hardener (D)] The silver-containing paste of this embodiment may further contain a hardener (D).

Examples of the hardener (D) include those having a reactive group that reacts with the bifunctional or higher functional resin (B). Examples of the hardener (D) include a reactive group that reacts with functional groups such as an epoxy group, a cis-butylenediimide group, and a hydroxyl group contained in the bifunctional or higher functional resin (B).

The hardener (D) preferably comprises a phenolic hardener and/or an imidazole hardener. These hardeners are particularly preferred when the thermosetting component contains an epoxy group. The phenolic hardener may be a low molecular weight compound or a high molecular weight compound (i.e., a phenolic resin).

Examples of low molecular weight phenolic curing agents include bisphenol A, bisphenol F (dihydroxydiphenylmethane), and other bisphenol compounds (phenolic resins having a bisphenol F skeleton); and compounds having a biphenyl skeleton, such as 4,4'-bisphenol.

Specific examples of phenolic resins include novolac-type phenolic resins such as phenol novolac resins, cresol novolac resins, bisphenol novolac resins, and phenol-biphenyl novolac resins; polyfunctional phenolic resins such as polyvinylphenol and triphenylmethane-type phenolic resins; modified phenolic resins such as terpene-modified phenolic resins and dicyclopentadiene-modified phenolic resins; and phenol aralkyl-type phenolic resins such as phenol aralkyl resins having a phenylene and/or biphenylene skeleton and naphthol aralkyl resins having a phenylene and/or biphenylene skeleton. When using a hardener (D), one type may be used alone or two or more types may be used in combination.

When the silver-containing paste of this embodiment contains a hardener (D), the amount of the hardener (D) is preferably 20 parts by mass or more and 150 parts by mass or less, and more preferably 30 parts by mass or more and 80 parts by mass or less, based on 100 parts by mass of the bifunctional or higher-functional resin (B).

[(Meth)acrylate-Containing Compound (E)] The silver-containing paste of this embodiment may further contain a (meth)acrylate-containing compound (E). The (meth)acrylate-containing compound (E) can be used without particular limitation, as long as it has a (meth)acrylate group with two or more functional groups and a linear or branched oxyalkylene group with two or more repeating units, as long as it can exhibit the effects of the present invention.

In this embodiment, by using a silver-containing paste containing a (meth)acrylic acid group-containing compound (E) having this structure, the stress in the material obtained by sintering the silver-containing paste is relaxed, resulting in excellent toughness (high fracture energy and resistance to fracture). Therefore, it is believed that semiconductor devices in which a semiconductor element and a substrate are bonded using the silver-containing paste of this embodiment can suppress delamination of the bonded portion, exhibit good long-term conductivity, and have excellent long-term reliability.

From the viewpoint of the effects of the present invention, the number of repeating units of the oxyalkylene group can be 2 or more, preferably 4 or more, more preferably 4 to 30, and particularly preferably 8 to 30.

Examples of the oxyalkylene group include linear or branched oxyalkylene groups having 2 to 10 carbon atoms, preferably linear or branched oxyalkylene groups having 2 to 8 carbon atoms, and more preferably linear or branched oxyalkylene groups having 2 to 5 carbon atoms.

Examples of the (meth)acrylate group-containing compound (E) include diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol #200 di(meth)acrylate (n: 4), polyethylene glycol #400 di(meth)acrylate (n: 9), polyethylene glycol #600 di(meth)acrylate (n: 14), and polyethylene glycol #1000 di(meth)acrylate (n: 23).

From the viewpoint of the effects of the present invention, the (meth)acrylic acid group-containing compound (E) can be contained in an amount of preferably 0.1% by mass to 15% by mass, more preferably 0.5% by mass to 10% by mass, and even more preferably 1.0% by mass to 8% by mass, relative to 100% by mass of the silver-containing paste excluding the organic solvent (C) described below.

Furthermore, within the range not impairing the effects of the present invention, a monofunctional (meth)acrylic monomer having only one (meth)acrylic group in one molecule may be contained together with the (meth)acrylic group-containing compound (E).

In this embodiment, a bifunctional or higher functional resin (B) and a (meth)acryl-containing compound (D) are preferably used in combination. The ratio (mass ratio) when using these together is not particularly limited. For example, a bifunctional or higher functional resin (B)/(meth)acryl-containing compound (D) ratio of 95/5 to 50/50 is preferred, and 90/10 to 30/20 is even more preferred.

[Silane Coupling Agent (F)] The silver-containing paste of this embodiment can also contain a silane coupling agent (F). This can further improve adhesion.

Examples of the silane coupling agent (F) include known silane coupling agents. Specifically, examples include vinyl silanes such as vinyltrimethoxysilane and vinyltriethoxysilane; epoxy silanes such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane, and 3-glycidyloxypropyltriethoxysilane; and styrylsilanes such as p-styryltrimethoxysilane. Methacryl silanes such as 3-methacryloyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropylmethyldiethoxysilane, and 3-methacryloyloxypropyltriethoxysilane; Acrylic silanes such as 3-(trimethoxysilyl)propyl methacrylate and 3-acryloyloxypropyltrimethoxysilane; Aminosilanes such as N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylene)propylamine, and N-phenyl-γ-aminopropyltrimethoxysilane; Isocyanatotrisilanes; Alkylsilanes; Ureasilanes such as 3-ureidopropyltrialkoxysilane; Alkylsilanes such as 3-butylenepropylmethyldimethoxysilane and 3-butylenepropyltrimethoxysilane; Isocyanatosilanes such as 3-isocyanatopropyltriethoxysilane. When using a silane coupling agent (F), one type may be used alone, or two or more types may be used in combination.

When the silver-containing paste of this embodiment contains a silane coupling agent (F), the amount of the silane coupling agent (F) is preferably 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 0.5 parts by mass or more and 5 parts by mass or less, based on 100 parts by mass of the thermosetting component (the total amount of the bifunctional or higher-functional resin (B) and the hardener (D)).

(Free Radical Initiator) The silver-containing paste of this embodiment may contain a free radical initiator. The free radical initiator can, for example, sometimes suppress insufficient curing, allow the curing reaction to proceed sufficiently at relatively low temperatures (e.g., 180°C), or further improve adhesion. Examples of free radical initiators include peroxides and azo compounds.

Examples of peroxides include organic peroxides such as diacyl peroxides, dialkyl peroxides, and peroxyketal. More specifically, examples include ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; peroxyketal such as 1,1-di(tertiary butylperoxy)cyclohexane and 2,2-di(4,4-di(tertiary butylperoxy)cyclohexyl)propane; hydroperoxides such as p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, isopropylbenzene hydroperoxide, and tertiary butyl hydroperoxide; and di(2-tertiary butylperoxyisopropyl)benzene and diisopropylphenyl peroxide. Peroxide), 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexane, tertiary butyl isopropyl peroxide, di-tertiary hexyl peroxide, 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexyne-3, di-tertiary butyl peroxide, etc. Dialkyl peroxides such as dibenzoyl peroxide and di(4-methylbenzoyl) peroxide; Peroxydicarbonates such as di-n-propyl peroxydicarbonate and diisopropyl peroxydicarbonate; Peroxyesters such as 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tertiary hexyl peroxybenzoate, tertiary butyl peroxybenzoate, and tertiary butyl peroxy-2-ethylhexanoate.

Examples of azo compounds include 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2,2'-azobis(2,4-dimethylvaleronitrile). When using a free radical initiator, either a single species or a combination of two or more species may be used.

When the silver-containing paste of this embodiment contains a free radical initiator, the amount of the free radical initiator is preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 2 parts by mass or more and 10 parts by mass or less, based on 100 parts by mass of the thermosetting component (the total amount of the bifunctional or higher-functional resin (B) and the hardener (D)).

(Hardening Accelerator) The silver-containing paste of this embodiment may further contain a hardening accelerator. Typically, the hardening accelerator promotes the reaction between the bifunctional or higher-functional resin (B) and the hardener (D).

Specific examples of curing accelerators include: compounds containing phosphorus atoms, such as organic phosphines, tetrasubstituted phosphonium compounds, phosphobetaine compounds, adducts of phosphine compounds and quinone compounds, and adducts of phosphonium compounds and silane compounds; amidines and tertiary amines, such as dicyandiamide, 1,8-diazabicyclo[5.4.0]undecene-7, and benzyldimethylamine; and nitrogen-containing compounds, such as quaternary ammonium salts of the above-mentioned amidines or tertiary amines. When using a curing accelerator, one type may be used alone, or two or more types may be used in combination.

When the silver-containing paste of this embodiment contains a curing accelerator, the amount of the curing accelerator is preferably 0.1 parts by mass to 10 parts by mass, more preferably 0.5 parts by mass to 5 parts by mass, based on 100 parts by mass of the bifunctional or higher-functional resin (B).

(Plasticizer) The silver-containing paste of this embodiment can contain a plasticizer. This plasticizer facilitates designing a low storage modulus. Furthermore, it further reduces the decrease in adhesion due to thermal cycling.

Specific examples of plasticizers include polyester compounds, silicone oils, silicone rubbers, and other silicone compounds, polybutadiene compounds such as polybutadiene maleic anhydride adducts, and acrylonitrile-butadiene copolymers. When using plasticizers, a single type may be used, or two or more types may be used in combination.

When the silver-containing paste of this embodiment contains a plasticizer, the amount of the plasticizer is preferably 5 parts by mass or more and 50 parts by mass or less, and more preferably 10 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass of the thermosetting component (the total amount of the bifunctional or higher-functional resin (B) and the hardener (D)).

(Properties of the Composition) The silver-containing paste of this embodiment is preferably in a paste-like state at 20°C. That is, the silver-containing paste of this embodiment can be applied to substrates, etc., as a paste at 20°C. This allows the silver-containing paste of this embodiment to be preferably used as an adhesive for semiconductor devices, etc. Of course, depending on the applicable process, the silver-containing paste of this embodiment can also be in a relatively low-viscosity varnish-like state.

<High Thermal Conductivity Material> Sintering the silver-containing paste of this embodiment produces a highly thermally conductive material. By varying the shape of the highly thermally conductive material, it can be applied to various parts requiring heat dissipation in the automotive and electric motor fields.

For example, a bonded body can be provided in which the silicon surface of a silicon wafer is bonded to a metal surface using a cured body (a highly thermally conductive material) containing silver paste according to this embodiment. The storage modulus of the cured body as measured by dynamic viscoelasticity (DMA) can be 20 or less, preferably 15 or less, and even more preferably 10 or less. By ensuring that the storage modulus of the cured body falls within this range, product reliability can be improved.

<Semiconductor Devices> The silver-containing paste of this embodiment can be used to manufacture semiconductor devices. For example, by using the silver-containing paste of this embodiment as a bonding agent between a metal-containing substrate and a semiconductor element (silicon wafer), a semiconductor device can be manufactured.

The semiconductor device of this embodiment comprises, for example, a metal-containing substrate, a silicon wafer, and an adhesive layer for bonding the metal surface of the substrate to the silicon surface of the silicon wafer. The adhesive layer is formed by sintering the silver-containing paste through a heat treatment. The semiconductor device of this embodiment exhibits excellent heat dissipation and product reliability. The silicon wafer can be used for ICs, LSIs, power semiconductor devices (power semiconductors), and various other devices. The substrate can be used for lead frames, BGA substrates, mounting substrates, heat sinks, heat sinks, and the like. The metal surface of these substrates can be bonded to the silicon surface of the silicon wafer using the adhesive layer.

An example of a semiconductor device is described below with reference to the drawings. Figure 1 is a cross-sectional view of an example semiconductor device. Semiconductor device 100 includes a substrate 30 and a semiconductor element (silicon wafer) 20 mounted on substrate 30 via an adhesive layer 10 (die attach material) that is a heat-treated body containing silver paste.

The semiconductor element 20 and the substrate 30 are electrically connected, for example, via bonding wires 40. The semiconductor element 20 is sealed, for example, with a sealing resin 50.

The thickness of the bonding layer 10 is preferably 5 μm or greater, more preferably 10 μm or greater, and even more preferably 20 μm or greater. This improves the stress absorption capacity of the silver-containing paste and enhances its resistance to thermal cycling. The thickness of the bonding layer 10 is, for example, 100 μm or less, preferably 50 μm or less.

In Figure 1, substrate 30 is, for example, a lead frame. Here, semiconductor device 20 is mounted on die pad 32 or substrate 30 via bonding layer 10. Furthermore, semiconductor device 20 is electrically connected to outer leads 34 (substrate 30) via bonding wires 40, for example. Substrate 30, serving as a lead frame, is made of, for example, 42 alloy or a Cu frame.

The substrate 30 can also be an organic substrate or ceramic substrate coated with a metal film such as silver or gold. This improves the adhesion between the bonding layer 10 and the substrate 30. Examples of organic substrates include those made of epoxy resins, cyanate resins, and butylene imide resins.

Figure 2 is a cross-sectional view of an example of a semiconductor device 100 that differs from Figure 1 . In semiconductor device 100 shown in Figure 2 , substrate 30 is, for example, an interposer. Substrate 30, acting as an interposer, has a metal layer made of, for example, Au, Cu, or Ti on the surface on which semiconductor element 20 is mounted, and a plurality of solder balls 52 , for example, are formed on the opposite surface. Semiconductor device 100 is connected to another wiring board via solder balls 52 .

An example method for manufacturing a semiconductor device will be described. First, a silver-containing paste is applied to the metal layer of a substrate 30. Next, the semiconductor element 20 is positioned on top of the metal layer so that the silicon surface faces the substrate 30. In other words, the substrate 30, the silver-containing paste, and the semiconductor element 20 are layered in this order. The method for applying the silver-containing paste is not particularly limited. Specific examples include dispensing, printing, and inkjet methods.

Next, the silver-containing paste is thermally cured. Thermal curing is preferably performed by pre-curing and post-curing. By thermal curing, the silver-containing paste is made into a heat-treated body (hardened product). By thermal curing (heat treatment), the metal-containing particles in the silver-containing paste are agglomerated, forming a structure in which the interfaces between the plurality of metal-containing particles disappear in the bonding layer 10. In this way, the substrate 30 and the semiconductor element 20 are bonded via the bonding layer 10. Next, the semiconductor element 20 and the substrate 30 are electrically connected using bonding wires 40. Next, the semiconductor element 20 is sealed with a sealing resin 50. In this way, a semiconductor device can be manufactured.

While the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can be employed. Furthermore, the present invention is not limited to the embodiments described above, and modifications and improvements that achieve the objectives of the present invention are encompassed by the present invention. [Examples]

Hereinafter, the present invention will be described in more detail with reference to embodiments, but the present invention is not limited thereto.

<Preparation of Silver-Containing Paste> The raw materials were mixed according to the blending ratios shown in Table 1 to produce a varnish. The varnish, solvent, and silver-containing particles (including silver-coated resin particles) were then blended according to the blending ratios shown in Table 1 and kneaded at room temperature using a three-roll mill. This produced a silver-containing paste.

Table 1 shows the raw material components below. (Bifunctional or higher-functional resins) • Epoxy resin 1: Bisphenol F liquid epoxy resin (RE-303S, manufactured by Nippon Kayaku Co., Ltd.)

(Hardener) • Phenolic Hardener 1: Phenolic resin with a bisphenol F skeleton (solid at room temperature 25°C, manufactured by DIC Corporation, DIC-BPF)

(Methacrylic acid group-containing compound) • Acrylic monomer 1: Ethylene glycol dimethacrylate (LIGHT ESTER EG, manufactured by Kyoeisha Chemical Co., Ltd.)

(Hardening Accelerator) • Imidazole Hardener 1: 2-Phenyl-1H-imidazole-4,5-dimethanol (Shikoku Chemicals Corporation, 2PHZ-PW)

(Polymerization Initiator) • Free Radical Polymerization Initiator 1: Diisopropylphenyl Peroxide (Perkadox BC, manufactured by Kayaku Akzo Corporation)

(Silver-Containing Particles) • Silver-Containing Particle 1: HKD-13A, D ₅₀ : 6 μm, manufactured by Fukuda Metal Foil & Powder Co., Ltd. • Silver-Containing Particle 2: Ag-DSB-114, D ₅₀ : 0.7 μm, manufactured by DOWA HIGHTECH CO., LTD. • Silver-Containing Particle 3: Silver-Coated Polysilicone Resin Particles (manufactured by Mitsubishi Materials Corporation, heat-resistant/surface-treated 10 μm product, spherical, D ₅₀ : 10 μm, specific gravity: 2.3, silver weight ratio 50 wt%, resin weight ratio 50 wt%)

(Organic Solvent) •Organic Solvent 1: Butyl propylene glycol (BFTG)

<Measurement of Thermal Conductivity λ> The resulting silver-containing paste was applied to a Teflon plate and heated from 30°C to 200°C in a nitrogen atmosphere over 60 minutes, followed by heat treatment at 200°C for 120 minutes. This produced a heat-treated body containing silver paste with a thickness of 1 mm ("Teflon" is a registered trademark for fluororesin). The heat diffusion coefficient α in the thickness direction of the heat-treated body was then measured using the laser flash method at a temperature of 25°C. The specific heat (Cp) was also measured using differential scanning calorimetry (DSC). Furthermore, the density (ρ) was measured in accordance with JIS K 6911. Using these values, the thermal conductivity λ is calculated based on the following formula. Thermal conductivity λ [W/(m•K)] = α [m ² /sec] × Cp [J/kg•K] × ρ [g/cm ³ ]

<Measurement of Thermal Conductivity Between Two Silicon Wafers> As shown in Figure 3, the thermal conductivity between two silicon wafers was measured. First, the obtained silver-containing paste was applied to the surface of one silicon wafer, and the applied silver-containing paste was pressed against the other silicon wafer. Next, the temperature was raised from 30°C to 200°C in a nitrogen atmosphere over 60 minutes, followed by a heat treatment at 200°C for 120 minutes. This produced a 20μm-thick test sample containing the silver-containing paste between the two silicon wafers. The thermal diffusion coefficient α of the heat-treated body in the thickness direction was then measured using the laser flash method. The measurement temperature was 25°C.

(Storage Modulus) The heat-treated product of the paste-like polymeric composition was cut into approximately 0.1 mm x 10 mm x 4 mm strips for evaluation. The storage modulus (E') at 25°C was measured using DMA (dynamic viscoelasticity measurement, tensile mode) at a heating rate of 5°C/min and a frequency of 1 Hz.

[Table 1] Comparative example 1 Example 1 Example 2 Comparative example 2 Example 3 Example 4 varnish Resins with two or more functional groups (B) Epoxy resin 1 50.0 50.0 50.0 50.0 50.0 50.0 Hardener Phenolic hardener 1 20.0 20.0 20.0 20.0 20.0 20.0 Compounds containing (meth)acrylic acid groups Acrylic monomer 1 20.0 20.0 20.0 20.0 20.0 20.0 Hardening accelerator Hardening accelerator 1 1.0 1.0 1.0 1.0 1.0 1.0 Polymerization initiator Free radical polymerization initiator 1 3.5 3.5 3.5 3.5 3.5 3.5 Silver paste varnish - 13.0 11.0 9.0 14.0 11.9 7.0 Silver-containing particles (A) Silver-containing particles 1 64.0 66.0 78.0 - - - Silver particles 2 - - - 86.0 87.1 90.0 Silver-containing particles 3 (silver-coated resin particles) 21.0 21.0 11.0 - - - Organic solvent (C) Organic solvent 1 2.0 2.0 2.0 - 1.0 3.0 Volume fraction a of silver-containing particles (A) (*1) vol.% 60 65 64 43 48 62 Volume fraction b of silver-coated resin particles (*1) vol.% 36 38 25 0 0 0 Volume fraction of silver-coated resin particles (b)/volume fraction of silver-containing particles (A) (a) - 0.60 0.58 0.33 0 0 0 Weight fraction c of silver-containing particles (A) (*2) wt% 87 89 91 86 88 93 Weight fraction d of silver-coated resin particles (*2) wt% twenty one twenty one 11 0 0 0 Weight fraction d of silver-coated resin particles/weight fraction c of silver-containing particles (A) - 0.25 0.24 0.12 0 0 0 Thermal conductivity W/mK 20 40 50 10 twenty two 55 Chip-to-chip thermal conductivity (Bare Si-Bare Si) mm ² /s 2.7 7.8 11.0 5.2 7.0 10.6 Elastic modulus@RT MPa 6000 8000 12000 14000 16000 18000 (*1): Amount relative to 100% by volume of the silver paste excluding the organic solvent (C) (*2): Amount relative to 100% by mass of the silver paste excluding the organic solvent (C)

As shown in Table 1, the silver-containing paste described in the examples contains silver-containing particles, a bifunctional or higher-functional resin, and an organic solvent. The content of the silver-containing particles (A) is within a range of 88% to 98% by mass relative to 100% by mass of the silver-containing paste excluding the organic solvent. Consequently, the paste exhibits excellent thermal conductivity, and consequently, excellent thermal conductivity between two silicon wafers. This demonstrates that heat dissipation can be improved when bonding the silicon surface of a silicon wafer to a metal surface.

This application claims priority based on Japanese Tokugan Application No. 2020-195062 filed on November 25, 2020, and incorporates herein the entire contents disclosed therein.

100: Semiconductor device 10: Adhesive layer 20: Semiconductor element 30: Substrate 32: Die pad 34: Outer leads 40: Bonding wires 50: Sealing resin 52: Solder balls

[Figure 1] is a schematic cross-sectional view of an example semiconductor device. [Figure 2] is a schematic cross-sectional view of an example semiconductor device. [Figure 3] illustrates a method for measuring thermal conductivity between two silicon wafers in an embodiment.

10: Next layer

20: Semiconductor components

32(30): Chip pad (substrate)

34(30):External lead (substrate)

40:Joint line

50:Sealing resin

100: Semiconductor devices

Claims (12)

A silver-containing paste for bonding the silicon surface of a silicon wafer to a metal surface, the paste comprising: (A) silver-containing particles; (B) a resin having two or more functional groups; and (C) an organic solvent, wherein the content of the silver-containing particles (A) is 88% by mass or more and 98% by mass or less relative to 100% by mass of the silver-containing paste excluding the organic solvent (C). The silver-containing particles (A) contain silver-coated resin particles, and the ratio b/a (volume fraction b of the silver-coated resin particles to volume fraction a of the silver-containing particles (A)) is less than 0.6. The silver-containing paste of claim 1, wherein the content of the silver-containing particles (A) is 89 mass % or more and 98 mass % or less relative to 100 mass % of the silver-containing paste excluding the organic solvent (C). The silver-containing paste of claim 1, wherein the silver-containing particles (A) contain silver particles and silver-coated resin particles. The silver-containing paste of claim 1, wherein the silver-containing particles (A) contain silver-coated resin particles, and a ratio d/c of a weight fraction d of the silver-coated resin particles to a weight fraction c of the silver-containing particles (A) is less than 0.25. The silver-containing paste of claim 1, wherein the mass ratio of resin to silver in the silver-coated resin particles is 70/30 to 30/70. The silver-containing paste of claim 1, wherein the bifunctional or higher-functional resin (B) comprises a bifunctional or higher-functional epoxy resin. The silver paste of claim 1 further comprises a hardener (D). The silver-containing paste of claim 1, further comprising a compound (E) containing a (meth)acrylic acid group. The silver-containing paste of claim 1, further comprising a silane coupling agent (F). A high thermal conductivity material obtained by sintering the silver-containing paste according to any one of claims 1 to 9. A bonded body comprising a silicon surface of a silicon wafer and a metal surface bonded together using a hardened body containing silver paste according to any one of claims 1 to 9, wherein the hardened body has a storage modulus of 1,000 to 20,000 MPa as measured by dynamic viscoelasticity (DMA). A semiconductor device comprising: a substrate containing metal; a silicon wafer; and a bonding layer for bonding the metal surface of the substrate to the silicon surface of the silicon wafer, wherein the bonding layer is formed by sintering the silver-containing paste of any one of claims 1 to 9.