JP2021019038A - Semiconductor device - Google Patents

Abstract

To provide a semiconductor device capable of suppressing damage to a semiconductor element due to a sudden serge voltage.SOLUTION: The semiconductor device includes: a supporting member for semiconductor element mounting; a semiconductor element mounted on the supporting member for semiconductor element mounting through a first sintering metal layer; and a second sintering metal layer provided on the semiconductor element.SELECTED DRAWING: Figure 2

Description

The present invention relates to a semiconductor device.

In recent years, heat resistance (excellent in stability and reliability under high temperature and high humidity) has been required for semiconductor package materials. For example, in hybrid vehicles, electric vehicles, electric railways, and distributed power sources, power semiconductors are often used for inverters, but the power density is significantly improved and the packaging material is exposed to high temperatures. In particular, a steep surge voltage is generated during the transitional period during operation of the power semiconductor element, and the temperature of the heat generating portion of the semiconductor element rises sharply. When the surge voltage is sufficiently large, phenomena such as dielectric breakdown are observed, leading to failure of the semiconductor device, and when the surge voltage is small, the semiconductor device deteriorates due to thermal stress or the like.

In a conventional power semiconductor device, a snubber circuit is formed on a substrate together with a semiconductor element. As the snubber circuit, an RC snubber circuit configured by connecting a resistance element and a capacitor element in series is adopted. The RC snubber circuit absorbs high-frequency noise caused by the surge voltage (see, for example, Patent Documents 1 to 3). However, from the investigation of the semiconductor device that failed in the field, it is known that the deterioration considered to be caused by this surge voltage is a failure mode that cannot be ignored in practical use (Non-Patent Document 1). In particular, in the case of a wide bandgap semiconductor such as SiC or GaN, since high-speed operation is possible as compared with conventional Si, the influence of deterioration due to surge voltage becomes larger.

JP-A-2010-206106 JP-A-2010-205833 JP-A-2010-199206

JEITA EDR-4701C Semiconductor Device Handling Guide

An object of the present invention is to provide a semiconductor device capable of suppressing damage to a semiconductor element due to a steep surge voltage.

One aspect of the present invention is a support member for mounting a semiconductor element, a semiconductor element mounted on the support member for mounting the semiconductor element via a first sintered metal layer, and a second provided on the semiconductor element. Provided is a semiconductor device including a sintered metal layer. Since the second sintered metal layer is not arranged on the heat dissipation path, in the above semiconductor device, the temperature rise of the heat generating portion of the semiconductor element when a surge voltage is generated is suppressed without affecting the heat dissipation path of the semiconductor element. .. It can be said that such a semiconductor device has a structure having excellent reliability.

In one aspect, the second sintered metal layer may include a structure derived from flake-shaped metal particles oriented substantially parallel to the interface with the semiconductor element.

In one aspect, the metal content in the second sintered metal layer may be 65% by volume or more and 90% by volume or less based on the total volume of the second sintered metal layer.

In one aspect, the semiconductor device may further include a metal plate on the second sintered metal layer.

In one aspect, the metal wiring may be connected to the second sintered metal layer or the metal plate.

In one aspect, the thickness of the second sintered metal layer may be 100 μm or more and 500 μm or less.

In one aspect, the semiconductor device may be a wide bandgap semiconductor.

According to the present invention, it is possible to provide a semiconductor device capable of suppressing damage to a semiconductor element due to a steep surge voltage. According to the present invention, more specifically, even when a steep surge voltage is generated during a transitional period during operation of a power semiconductor device, the power semiconductor device does not affect the thermal resistance of the semiconductor device. It is possible to suppress the temperature rise of the heat generating portion of the above.

It is a cross-sectional SEM image of a sintered copper layer. It is a schematic cross-sectional view which shows an example of the semiconductor device of this embodiment. It is a schematic cross-sectional view which shows an example of the semiconductor device of this embodiment. It is a schematic cross-sectional view which shows an example of the semiconductor device of this embodiment. It is a schematic cross-sectional view which shows an example of the semiconductor device of this embodiment. It is a figure which shows the result of temperature evaluation.

Hereinafter, embodiments for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments.

Hereinafter, preferred embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted.

<Sintered metal layer>
Each of the first sintered metal layer and the second sintered metal layer is made of a sintered body. The material constituting the first sintered metal layer and the second sintered metal layer is a sinterable metal, and includes, for example, silver (Ag), copper (Cu) and the like. The sinterable metal is a metal capable of forming a sintered body when the metal particles are heated at a temperature lower than the melting point. The first sintered metal layer and the second sintered metal layer are sintered products of a metal paste in which sinterable metal particles such as silver and copper are dispersed. The first sintered metal layer and the second sintered metal layer may be formed from pastes having the same composition, or may be formed from pastes having different compositions. That is, both sintered metal layers may be the same or different. Hereinafter, the sintered metal layer (sintered copper layer) will be described by taking the case where the sinterable metal is copper as an example. In the following description, "copper" is referred to as another "metal" having sinterability. May be replaced with.

(Copper paste)
The copper paste used to form the sintered copper layer contains metal particles and a dispersion medium. The metal particles can include submicrocopper particles and flaky microcopper particles.

(Metal particles)
Examples of the metal particles include submicro copper particles, flake-shaped micro copper particles, copper particles other than these, and other metal particles.

(Sub-micro copper particles)
Examples of the sub-micro copper particles include copper particles having a particle size of 0.12 μm or more and 0.8 μm or less. For example, copper particles having a volume average particle size of 0.12 μm or more and 0.8 μm or less may be used. it can. When the volume average particle size of the sub-micro copper particles is 0.12 μm or more, the effects of suppressing the synthesis cost of the sub-micro copper particles, good dispersibility, and suppressing the amount of the surface treatment agent used can be easily obtained. When the volume average particle diameter of the sub-micro copper particles is 0.8 μm or less, the effect of excellent sinterability of the sub-micro copper particles can be easily obtained. From the viewpoint that the above effect can be obtained more easily, the volume average particle size of the sub-micro copper particles may be 0.15 μm or more and 0.8 μm or less, or 0.15 μm or more and 0.6 μm or less. It may be 0.2 μm or more and 0.5 μm or less, and may be 0.3 μm or more and 0.45 μm or less.

The volume average particle diameter means a 50% volume average particle diameter. When determining the volume average particle size of copper particles, the particle size distribution by the light scattering method is obtained by dispersing the copper particles as a raw material or dried copper particles obtained by removing volatile components from a copper paste in a dispersion medium using a dispersant. It can be obtained by a method of measuring with a measuring device (for example, Shimadzu nanoparticle size distribution measuring device (SALD-7500 nano, manufactured by Shimadzu Corporation)). When a light scattering method particle size distribution measuring device is used, hexane, toluene, α-terpineol or the like can be used as the dispersion medium.

The sub-micro copper particles can contain 10% by mass or more of copper particles having a particle size of 0.12 μm or more and 0.8 μm or less. From the viewpoint of the sinterability of the copper paste, the sub-micro copper particles can contain 20% by mass or more of copper particles having a particle size of 0.12 μm or more and 0.8 μm or less, and can contain 30% by mass or more, 90% by mass. It can contain 100% by mass or more, and can contain 100% by mass. When the content ratio of the copper particles having a particle size of 0.12 μm or more and 0.8 μm or less in the sub-micro copper particles is 10% by mass or more, the dispersibility of the copper particles is further improved, the viscosity is increased, and the paste concentration is decreased. It can be more suppressed.

The particle size of the copper particles can be calculated from, for example, an SEM (scanning electron microscope) image. The powder of copper particles is placed on a carbon tape for SEM with a spatula to prepare a sample for SEM. This SEM sample is observed with an SEM device at a magnification of 5000. A quadrangle circumscribing the copper particles of this SEM image is drawn by image processing software, and one side thereof is used as the particle size of the particles.

The content of the sub-micro copper particles may be 10% by mass or more and 90% by mass or less, 30% by mass or more and 90% by mass or less, and 35% by mass or more, based on the total mass of the metal particles. It may be 85% by mass or less, and may be 40% by mass or more and 80% by mass or less. When the content of the sub-micro copper particles is within the above range, it becomes easy to form a desired sintered copper layer.

The content of the sub-micro copper particles may be 20% by mass or more and 90% by mass or less based on the total of the mass of the sub-micro copper particles and the mass of the flake-shaped micro copper particles. When the content of the sub-micro copper particles is 20% by mass or more, the space between the flake-shaped micro copper particles can be sufficiently filled, and a desired sintered copper layer can be easily formed. When the content of the sub-micro copper particles is 90% by mass or less, the volume shrinkage when the copper paste is sintered can be sufficiently suppressed, so that a desired sintered copper layer can be easily formed. From the viewpoint that the above effect can be obtained more easily, the content of the sub-micro copper particles is 30% by mass or more and 85% by mass or less based on the total of the mass of the sub-micro copper particles and the mass of the flake-shaped micro copper particles. It may be 35% by mass or more and 85% by mass or less, and may be 40% by mass or more and 80% by mass or less.

The shape of the sub-micro copper particles is not particularly limited. Examples of the shape of the sub-micro copper particles include spherical, lumpy, needle-like, flake-like, substantially spherical, and aggregates thereof. From the viewpoint of dispersibility and filling property, the shape of the sub-microcopper particles may be spherical, substantially spherical, or flake-shaped, and from the viewpoint of flammability, dispersibility, mixing with flake-shaped microparticles, etc., the shape is spherical. Alternatively, it may be substantially spherical.

The sub-micro copper particles may have an aspect ratio of 5 or less, or 3 or less, from the viewpoint of dispersibility, packing property, and mixing property with flake-shaped micro particles. As used herein, the "aspect ratio" refers to the long side / thickness of the particles. The measurement of the long side and the thickness of the particle can be obtained from, for example, an SEM image of the particle.

The sub-micro copper particles may be treated with a specific surface treatment agent. Specific surface treatment agents include, for example, organic acids having 8 to 16 carbon atoms. Examples of organic acids having 8 to 16 carbon atoms include caprylic acid, methylheptanic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid, methyloctanoic acid, ethylheptanic acid, propylhexanoic acid, capric acid, methylnonanoic acid, and ethyl. Octanoic acid, propylheptanic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanic acid, lauric acid, methylundecanoic acid, ethyldecanoic acid, propylnonanoic acid, butyloctanoic acid, pentylheptanic acid, Tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyldodecanoic acid, propylundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid , Methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, ethyltetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecane Acids, heptylnonanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, nonylcyclohexanecarboxylic acid, etc. Saturated fatty acids; octeneic acid, nonenic acid, methylnonenic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitreic acid, sabienoic acid and other unsaturated fatty acids; Aromas such as acid, pyromellitic acid, o-phenoxybenzoic acid, methylbenzoic acid, ethyl benzoic acid, propyl benzoic acid, butyl benzoic acid, pentyl benzoic acid, hexyl benzoic acid, heptyl benzoic acid, octyl benzoic acid, nonyl benzoic acid, etc. Group carboxylic acids include. One type of organic acid may be used alone, or two or more types may be used in combination. By combining such an organic acid with the above-mentioned sub-micro copper particles, there is a tendency that both the dispersibility of the sub-micro copper particles and the desorption of the organic acid at the time of sintering can be achieved at the same time.

The treatment amount of the surface treatment agent may be an amount that adheres to the surface of the sub-micro copper particles in a single-layer to a triple-layer. The amounts are the number of molecular layers (n) attached to the surface of the sub-micro copper particles, the specific area surface (A _p ) (unit: m ² / g) of the sub-micro copper particles, and the molecular weight (M _s ) of the surface treatment agent. the unit g / mol), the minimum coverage area of the surface treatment agent _(S S) (unit ^{m 2} / piece) can be calculated from Avogadro's number ^{_{(N a) (6.02 × 10}} 23 cells). Specifically, the processing amount of the surface treatment agent, the process amount of the surface treatment agent _{(wt%) = {(n · A} p · M s) / (S S · N A + n · A p · M s)} It is calculated according to the formula of × 100%.

The specific surface area of the sub-micro copper particles can be calculated by measuring the dried sub-micro copper particles by the BET specific surface area measurement method. Minimum coverage of the surface treatment agent, if the surface treatment agent is a straight-chain saturated fatty acids, is 2.05 × ¹⁰ -19 ^m 2/1 molecule. For other surface treatment agents, for example, calculation from a molecular model or "Chemistry and Education" (Akihiro Ueda, Sumio Inafuku, Iwao Mori, 40 (2), 1992, p114-117). It can be measured by the method described. An example of a method for quantifying a surface treatment agent is shown. The surface treatment agent can be identified by a thermal desorption gas / gas chromatograph mass spectrometer of the dry powder obtained by removing the dispersion medium from the copper paste, whereby the carbon number and molecular weight of the surface treatment agent can be determined. The carbon content ratio of the surface treatment agent can be analyzed by carbon content analysis. Examples of the carbon content analysis method include a high-frequency induction heating furnace combustion / infrared absorption method. The amount of the surface treatment agent can be calculated from the carbon number, molecular weight and carbon content ratio of the identified surface treatment agent by the above formula.

The treated amount of the surface treatment agent may be 0.07% by mass or more and 2.1% by mass or less, 0.10% by mass or more and 1.6% by mass or less, and 0.2% by mass. It may be 1.1% by mass or less.

As the sub-micro copper particles, commercially available ones can be used. Examples of commercially available sub-micro copper particles include CH-0200 (manufactured by Mitsui Metal Mining Co., Ltd., volume average particle size 0.36 μm) and HT-14 (manufactured by Mitsui Metal Mining Co., Ltd., volume average particle size 0. 41 μm), CT-500 (manufactured by Mitsui Metal Mining Co., Ltd., volume average particle size 0.72 μm), Tn-Cu100 (manufactured by Taiyo Nisshi Co., Ltd., volume average particle size 0.12 μm).

(Flake-shaped micro copper particles)
Examples of the flake-shaped microcopper particles include copper particles having a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of 4 or more. For example, an average maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of 4 are included. The above copper particles can be used. When the average maximum diameter and aspect ratio of the flake-shaped microcopper particles are within the above ranges, the volume shrinkage when the copper paste is sintered can be sufficiently reduced, and a desired sintered copper layer can be easily formed. .. From the viewpoint that the above effect can be more easily obtained, the average maximum diameter of the flake-shaped microcopper particles may be 1 μm or more and 10 μm or less, or 3 μm or more and 10 μm or less. The maximum diameter and the average maximum diameter of the flake-shaped microcopper particles can be measured, for example, from the SEM image of the particles, and can be obtained as the major axis X and the average value Xav of the flake-shaped structure described later.

The flake-shaped micro copper particles can contain 50% by mass or more of copper particles having a maximum diameter of 1 μm or more and 20 μm or less. From the viewpoint of orientation in the sintered copper layer, reinforcing effect, and filling property of the bonding paste, the flake-shaped micro copper particles can contain 70% by mass or more of copper particles having a maximum diameter of 1 μm or more and 20 μm or less, and have a maximum diameter of 80 mass%. It can contain% or more, and can contain 100% by mass. From the viewpoint of suppressing bonding defects, the flake-shaped microcopper particles preferably do not contain particles having a size exceeding the bonding thickness, such as particles having a maximum diameter of more than 20 μm.

A method of calculating the major axis X of flake-shaped microcopper particles from an SEM image will be illustrated. The powder of flake-shaped microcopper particles is placed on a carbon tape for SEM with a spatula to prepare a sample for SEM. This SEM sample is observed with an SEM device at a magnification of 5000. A rectangle circumscribing the flake-shaped microcopper particles of the SEM image is drawn by image processing software, and the long side of the rectangle is defined as the major axis X of the particles. Using a plurality of SEM images, this measurement is performed on 50 or more flake-shaped microcopper particles, and the mean value Xav of the major axis is calculated.

The flake-shaped microcopper particles may have an aspect ratio of 4 or more, or 6 or more. When the aspect ratio is within the above range, the flake-shaped microcopper particles in the copper paste are oriented substantially parallel to the bonding surface, so that volume shrinkage when the copper paste is sintered can be suppressed, which is desired. It becomes easy to form the sintered copper layer of.

The content of the flake-shaped microcopper particles may be 1% by mass or more and 90% by mass or less, 10% by mass or more and 70% by mass or less, or 20% by mass, based on the total mass of the metal particles. It may be 50% by mass or less. When the content of the flake-shaped micro copper particles is within the above range, it becomes easy to form a desired sintered copper layer.

The total content of the sub-micro copper particles and the content of the flake-shaped micro copper particles may be 80% by mass or more based on the total mass of the metal particles. When the total content of the sub-micro copper particles and the content of the micro copper particles is within the above range, it becomes easy to form a desired sintered copper layer. From the viewpoint of further exerting the above effect, the total content of the sub-micro copper particles and the content of the flake-shaped micro-copper particles may be 90% by mass or more based on the total mass of the metal particles. It may be 100% by mass or more, or 100% by mass.

In the flake-shaped microcopper particles, the presence or absence of treatment with the surface treatment agent is not particularly limited. From the viewpoint of dispersion stability and oxidation resistance, the flake-shaped microcopper particles may be treated with a surface treatment agent. The surface treatment agent may be one that is removed at the time of joining. Examples of such surface treatment agents include aliphatic carboxylic acids such as palmitic acid, stearyl acid, arachidic acid, and oleic acid; aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, and o-phenoxybenzoic acid; and cetyl alcohols. , Fatty alcohols such as stearyl alcohol, isobornylcyclohexanol, tetraethyleneglycol; aromatic alcohols such as p-phenylphenol; alkylamines such as octylamine, dodecylamine, stearylamine; fats such as stearonitrile and decanitrile. Group nitriles; silane coupling agents such as alkylalkoxysilanes; polymer-treated materials such as polyethylene glycols, polyvinyl alcohols, polyvinylpyrrolidones, and silicone oligomers. As the surface treatment agent, one type may be used alone, or two or more types may be used in combination.

The treatment amount of the surface treatment agent may be an amount of one molecular layer or more on the particle surface. The treatment amount of such a surface treatment agent varies depending on the specific surface area of the flake-shaped microcopper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent. The treatment amount of the surface treatment agent is usually 0.001% by mass or more. The specific surface area of the flake-shaped microcopper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent can be calculated by the above-mentioned method.

When a copper paste is prepared only from the above-mentioned sub-micro copper particles, the volume shrinkage and sintering shrinkage due to drying of the dispersion medium are large, so that the copper paste is easily peeled off from the adherend surface at the time of sintering, and the semiconductor element or the like is joined. It is difficult to obtain sufficient die-share strength and connection reliability. By using the sub-micro copper particles and the flake-shaped micro copper particles in combination, the volume shrinkage when the copper paste is sintered is suppressed, and it becomes easy to form a desired sintered copper layer.

In the copper paste, the content of micro copper particles having a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of less than 2 contained in the metal particles has a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of 4 or more. Based on the total amount of flake-shaped microcopper particles, it is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less. By limiting the content of microcopper particles having an average maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of less than 2, the flake-shaped microcopper particles in the copper paste are oriented substantially parallel to the bonding surface. This facilitates the process, and the volume shrinkage when the copper paste is sintered can be suppressed more effectively. This facilitates the formation of the desired sintered copper layer. In terms of making it easier to obtain such an effect, the content of microcopper particles having an average maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of less than 2 is such that the maximum diameter is 1 μm or more and 20 μm or less, and the aspect ratio. It may be 20% by mass or less, or 10% by mass or less, based on the total amount of flake-shaped microcopper particles having a value of 4 or more.

As the flake-shaped microcopper particles, commercially available ones can be used. Commercially available flake-shaped microcopper particles include, for example, MA-C025 (manufactured by Mitsui Mining & Smelting Co., Ltd., average maximum diameter 4.1 μm), 3L3 (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., maximum volume diameter 7.3 μm). ), 1110F (Mitsui Mining & Smelting Co., Ltd., average maximum diameter 5.8 μm), 2L3 (Fukuda Metal Foil Powder Industry Co., Ltd., average maximum diameter 9 μm).

In the copper paste, the micro copper particles to be blended include flake-shaped micro copper particles having a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of 4 or more, and have a maximum diameter of 1 μm or more and 20 μm or less, and have an aspect ratio. Microcopper particles having a content of less than 2 are 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, based on the total amount of the flake-shaped microcopper particles. be able to. When commercially available flake-shaped microcopper particles are used, the maximum diameter is 1 μm or more and 20 μm or less, the flake-shaped microcopper particles having an aspect ratio of 4 or more are included, and the maximum diameter is 1 μm or more and 20 μm or less. The content of the microcopper particles having a ratio of less than 2 is 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, based on the total amount of the flake-shaped microcopper particles. You may.

(Other metal particles other than copper particles)
The metal particles may include the above-mentioned sub-micro copper particles and other metal particles other than the micro-copper particles, and may include, for example, particles such as nickel, silver, gold, palladium, and platinum. The volume average particle diameter of the other metal particles may be 0.01 μm or more and 10 μm or less, 0.01 μm or more and 5 μm or less, or 0.05 μm or more and 3 μm or less. When the metal particles contain these other metal particles, the content thereof may be less than 20% by mass based on the total mass of the metal particles from the viewpoint of obtaining sufficient bondability, and may be 10% by mass. It may be less than or equal to%. Other metal particles may not be included. The shapes of the other metal particles are not particularly limited.

Since the metal particles contain metal particles other than copper particles, a sintered copper layer in which a plurality of types of metals are solid-dissolved or dispersed can be obtained, so that the yield stress, fatigue strength, etc. of the sintered copper layer are mechanical. The characteristics are improved and the connection reliability is likely to be improved. Further, the sintered copper layer formed by adding a plurality of types of metal particles tends to improve the bonding strength and the connection reliability with respect to a specific adherend.

(Dispersion medium)
The dispersion medium is not particularly limited and may be volatile. Examples of the volatile dispersion medium include monovalent and polyvalent and polyvalent such as pentanol, hexanol, heptanol, octanol, decanol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, α-terpineol and isobornylcyclohexanol (MTPH). Valuable alcohols; ethylene glycol butyl ether, ethylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol isobutyl ether, diethylene glycol hexyl ether, triethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol. Butyl methyl ether, diethylene glycol isopropyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, propylene glycol propyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, di Ethers such as propylene glycol dimethyl ether, tripropylene glycol methyl ether, tripropylene glycol dimethyl ether; ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate (DPMA), lactic acid Ethers such as ethyl, butyl lactate, γ-butyrolactone, propylene carbonate; acid amides such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide; cyclohexanone, octane, nonane, decane, Examples thereof include aliphatic hydrocarbons such as undecane; aromatic hydrocarbons such as benzene, toluene and xylene; mercaptans having an alkyl group having 1 to 18 carbon atoms; and mercaptans having a cycloalkyl group having 5 to 7 carbon atoms. Examples of mercaptans having an alkyl group having 1 to 18 carbon atoms include ethyl mercaptan, n-propyl mercaptan, i-propyl mercaptan, n-butyl mercaptan, i-butyl mercaptan, t-butyl mercaptan, pentyl mercaptan, and hexyl mercaptan. And dodecyl mercaptan. Examples of mercaptans having a cycloalkyl group having 5 to 7 carbon atoms include cyclopentyl mercaptan, cyclohexyl mercaptan and cycloheptyl mercaptan.

The content of the dispersion medium may be 5 to 50 parts by mass, where 100 parts by mass is the total mass of the metal particles. When the content of the dispersion medium is within the above range, the copper paste can be adjusted to a more appropriate viscosity, and the sintering of copper particles is less likely to be hindered.

(Additive)
Wetting improvers such as nonionic surfactants and fluorine-based surfactants; defoaming agents such as silicone oil; ion trapping agents such as inorganic ion exchangers, etc. are appropriately added to the copper paste, if necessary. May be good.

(Preparation of copper paste)
The copper paste may be prepared by mixing the above-mentioned sub-micro copper particles, micro copper particles, other metal particles and any additive with a dispersion medium. After mixing each component, stirring treatment may be performed. The maximum particle size of the metal particles contained in the copper paste may be adjusted by a classification operation.

In the copper paste, sub-micro copper particles, a surface treatment agent, and a dispersion medium are mixed in advance, and dispersion treatment is performed to prepare a dispersion liquid of sub-micro copper particles, and further micro copper particles, other metal particles, and any addition The agents may be mixed and prepared. By performing such a procedure, the dispersibility of the sub-micro copper particles is improved, the mixing property with the micro copper particles is improved, and the performance of the copper paste is further improved. The agglomerates may be removed by performing a classification operation on the dispersion liquid of the sub-micro copper particles.

FIG. 1 is a cross-sectional SEM image of a sintered copper layer, which is a sintered product of the copper paste. The figure shows typical morphology derived from flaky microcopper particles. The sintered copper layer shown in FIG. 1 has a structure derived from flaky copper particles oriented substantially parallel to a laminated interface (for example, an interface with a support member for mounting a semiconductor element and an interface with a semiconductor element). Hereinafter, it includes a sintered copper 1 having a “flake-like structure”), a sintered copper 2 derived from other copper particles, and a pore 3.

In the sintered copper layer, the ratio of the copper element in the elements excluding the light element among the constituent elements may be 95% by mass or more, 97% by mass or more, or 98% by mass or more. It may be 100% by mass. When the ratio of copper elements in the sintered copper layer is within the above range, the formation of intermetallic compounds or the precipitation of dissimilar elements at the metal copper crystal grain boundaries can be suppressed, and the properties of metallic copper constituting the sintered copper layer can be suppressed. Is easy to become strong, and it is easy to obtain even better connection reliability.

Sintered copper having a flake-shaped structure can be formed by sintering a copper paste containing flake-shaped copper particles. The flake shape includes a flat plate shape such as a plate shape or a reptile shape. In the flake-like structure, the ratio of the major axis to the thickness may be 5 or more. The number average diameter of the major axis of the flake-shaped structure may be 2 μm or more, 3 μm or more, or 4 μm or more. With the flake-shaped structure having such a shape, the reinforcing effect of the sintered copper layer is improved, and the joint body between the member and the sintered copper layer is further excellent in joint strength and connection reliability.

The major axis and thickness of the flake-like structure can be obtained, for example, from the SEM image of the bonded body of the member and the sintered copper layer. The method of measuring the major axis and the thickness of the flake-like structure from the SEM image will be illustrated below. The conjugate is poured with epoxy cast resin so that the entire sample is filled and cured. Cut the cast sample near the cross section you want to observe, grind the cross section by polishing, and perform CP (cross section polisher) processing. The cross section of the sample is observed with an SEM device at a magnification of 5000. A cross-sectional image (for example, 5000 times) of the joint is acquired, and it is a dense continuous part, which is a linear, rectangular parallelepiped, or elliptical part, and is the longest of the straight lines contained in this part. The length of the major axis is 1 μm or more and the ratio of the major axis / thickness is 4 or more when the one with the major axis and the one with the longest length among the straight lines included in this part orthogonal to the major axis are defined as the thickness. Is regarded as a flake-shaped structure, and the major axis and the thickness of the flake-shaped structure can be measured by image processing software having a length measuring function. The average value thereof can be obtained by calculating the number average with 20 points or more randomly selected.

The copper content (volume ratio) in the sintered copper layer can be 65% by volume or more based on the volume of the sintered copper layer. When the copper content in the sintered copper layer is within the above range, it is possible to prevent the formation of large pores inside the sintered copper layer and the sparseness of the sintered copper connecting the flake-like structures. .. Therefore, if the copper content in the sintered copper layer is within the above range, sufficient thermal conductivity can be obtained, the bonding strength between the member and the sintered copper layer is improved, and the obtained bonded body has connection reliability. It will be excellent in sex. The copper content in the sintered copper layer may be 67% by volume or more, or 70% by volume or more, based on the volume of the sintered copper layer. The copper content in the sintered copper layer may be 90% by volume or less based on the volume of the sintered copper layer from the viewpoint of easiness of the manufacturing process.

When the composition of the material constituting the sintered copper layer is known, for example, the copper content in the sintered copper layer can be determined by the following procedure. First, the sintered copper layer is cut into a rectangular body, the length and width of the sintered copper layer are measured with a caliper or an external shape measuring device, and the thickness is measured with a film thickness meter to measure the volume of the sintered copper layer. To calculate. The apparent density M ₁ (g / cm ³ ) is obtained from the volume of the cut out sintered copper layer and the weight of the sintered copper layer measured by a precision balance. Using the obtained M ₁ and the copper density of 8.96 g / cm ³ , the copper content (volume%) in the sintered copper layer can be determined from the following formula.
Copper content (volume%) in the sintered copper layer = [(M ₁ ) /8.96] × 100

The bonding strength of the bonded body between the member and the sintered copper layer may be 10 MPa or more, 15 MPa or more, 20 MPa or more, or 30 MPa or more. The bond strength can be measured using a universal bond tester (4000 series, manufactured by DAGE) or the like.

<Semiconductor device 100>
FIG. 2 is a schematic cross-sectional view showing an example of the semiconductor device of the present embodiment. The semiconductor device 100 shown in FIG. 2 includes a semiconductor element mounting support member 6, a semiconductor element 5 mounted on the semiconductor element mounting support member 6 via a first sintered metal layer 4, and a semiconductor element 5. The second sintered metal layer 7 provided in the above is provided. The first sintered metal layer 4 can be said to be a bonding layer because it mainly bears the bonding between the semiconductor element 5 and the semiconductor element mounting support member 6, and the second sintered metal layer 7 mainly generates a surge voltage. It can be called a heat storage layer because it instantly stores the heat at the time.

Examples of the semiconductor element 5 include semiconductor elements such as IGBTs, diodes, Schottky barrier diodes, MOS-FETs, thyristors, logics, sensors, analog integrated circuits, LEDs, semiconductor lasers, and transmitters. In addition to Si, the semiconductor element 5 may be a wide bandgap semiconductor such as SiC or GaN. The support member 6 for mounting a semiconductor element includes a lead frame, a ceramic substrate with a metal plate attached (for example, DBC), a base material for mounting a semiconductor element such as an LED package, a block body such as a metal block, and a power supply member such as a terminal. Examples include a heat radiating plate and a water cooling plate.

As the first sintered metal layer 4 and the second sintered metal layer 7, the above-mentioned sintered metal layer can be used. Both the first sintered metal layer 4 and the second sintered metal layer 7 can include a structure derived from flake-shaped metal particles oriented substantially parallel to the laminated interface. In particular, the second sintered metal layer 7 can include a structure derived from flake-shaped metal particles oriented substantially parallel to the interface with the semiconductor element.

As described above, the metal content in these sintered metal layers can be 65% by volume or more based on the total volume of the sintered metal layers. The metal content in the sintered metal layer may be 67% by volume or more, or 70% by volume or more, based on the volume of the sintered metal layer. The metal content in the sintered metal layer may be 90% by volume or less based on the volume of the sintered metal layer.

The thickness of the first sintered metal layer 4 and the second sintered metal layer 7 can be 1 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 50 μm or more, 100 μm or more, and 3000 μm or less. , 1000 μm or less, 500 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, and the like. In particular, in the second sintered metal layer 7, by setting the thickness to 100 μm or more and 500 μm or less, the sintered bonding is performed while ensuring the heat capacity for suppressing the temperature rise of the heat generating portion of the semiconductor element 5 when a surge voltage is generated. The desired sintered metal layer can be formed without pressurizing.

The second sintered metal layer 7 may be formed on the entire main surface of the semiconductor element 5, or may be partially formed.

<Manufacturing method of semiconductor device 100>
The manufacturing method of the semiconductor device 100 is not particularly limited, and is manufactured by, for example, the following method.

(1) A member including the semiconductor element 5, the support member 6 for mounting the semiconductor element, and the first sintered metal layer 4 for joining the semiconductor element 5 and the support member 6 for mounting the semiconductor element 6 is prepared in advance. After that, a metal paste is provided on the surface of the semiconductor element 5 and sintered to form a second sintered metal layer 7.
(2) A metal paste is provided on a support member 6 for mounting a semiconductor element, a semiconductor element 5 is laminated on the metal paste, and a copper paste is further provided on the semiconductor element 5 to perform sintering. As a result, the semiconductor element 5 and the semiconductor element mounting support member 6 are joined by the first sintered metal layer 4, and the second sintered metal layer 7 is formed on the semiconductor element 5.
(3) A metal paste is provided on the surface of the semiconductor element 5 in advance and sintered to form a second sintered metal layer 7. After that, a metal paste is provided on the support member 6 for mounting the semiconductor element, and the semiconductor element 5 provided with the second sintered metal layer 7 in advance is laminated and sintered. When a Si chip or the like is used as the semiconductor element 5, the metal paste is provided on the surface of the Si chip or the like and then sintered, and the second sintered metal layer 7 is provided on the surface of the Si chip in advance. It is possible. Such a Si chip may be obtained by providing a second sintered metal layer 7 on the entire surface in the state of a wafer and dicing the second sintered metal layer 7 into individual pieces. Further, the Si chip may be obtained by partially providing a second sintered metal layer 7 in the state of a wafer and dicing the second sintered metal layer 7 into individual pieces.

The method of providing the metal paste on the support member for mounting the semiconductor element or the necessary portion of the semiconductor element may be any method as long as the metal paste can be deposited. Examples of such a method include screen printing, transfer printing, offset printing, jet printing method, dispenser, jet dispenser, needle dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, concave printing, and gravure. Examples include printing, stencil printing, soft lithograph, bar coating, applicator, particle deposition method, spray coater, spin coater, dip coater, electrodeposition coating and the like. The thickness of the metal paste is not particularly limited as long as a sintered metal layer having a desired thickness can be obtained. That is, the thickness of the metal paste can be 1 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 50 μm or more, 100 μm or more, and 3000 μm or less, 1000 μm or less, 500 μm or less, 300 μm or less, 250 μm. Hereinafter, it can be 200 μm or less, 150 μm or less, and the like. The thickness may be, for example, 1 μm or more and 1000 μm or less, 10 μm or more and 500 μm or less, 50 μm or more and 200 μm or less, 10 μm or more and 3000 μm or less, and 15 μm or more and 500 μm or less. It may be 20 μm or more and 300 μm or less, 5 μm or more and 500 μm or less, 10 μm or more and 250 μm or less, or 15 μm or more and 150 μm or less.

The support member for mounting the semiconductor element and the metal paste provided on the semiconductor element may be appropriately dried from the viewpoint of suppressing flow and generation of voids during sintering. The gas atmosphere at the time of drying may be in the atmosphere, in an oxygen-free atmosphere such as nitrogen or rare gas, or in a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying by leaving at room temperature, heating drying, or vacuum drying. For heat drying or vacuum drying, for example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic wave. A heating device, a heater heating device, a steam heating furnace, a hot plate pressing device, or the like can be used. The drying temperature and time may be appropriately adjusted according to the type and amount of the dispersion medium used. The drying temperature and time can be, for example, 1 minute or more and 120 minutes or less at 50 ° C. or higher and 180 ° C. or lower.

Examples of the method of arranging the semiconductor element on the metal paste include a chip mounter, a flip chip bonder, and a positioning jig made of carbon or ceramics. The above-mentioned drying step may be performed after the step of arranging the semiconductor element.

By heat-treating the metal paste, the metal paste is sintered. For heat treatment, for example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, etc. A heater heating device, a steam heating furnace, or the like can be used.

The gas atmosphere at the time of sintering may be an oxygen-free atmosphere from the viewpoint of suppressing oxidation of the sintered body, the semiconductor element, and the support member for mounting the semiconductor element. The gas atmosphere at the time of sintering may be a reducing atmosphere from the viewpoint of removing surface oxides of metal particles of the metal paste. The anaerobic atmosphere is realized by introducing an anaerobic gas such as nitrogen or a rare gas or reducing the pressure (under vacuum). Examples of the reducing atmosphere include an atmosphere of pure hydrogen gas, a mixed gas of hydrogen and nitrogen typified by forming gas, nitrogen containing formic acid gas, a mixed gas of hydrogen and rare gas, and a rare gas containing formic acid gas. ..

The maximum temperature reached during the heat treatment may be 250 ° C. or higher and 450 ° C. or lower, and 250 ° C. or higher and 400 ° C. from the viewpoint of reducing thermal damage to the semiconductor element and the support member for mounting the semiconductor device and improving the yield. It may be 250 ° C. or higher and 350 ° C. or lower. When the maximum temperature reached is 200 ° C. or higher, sintering tends to proceed sufficiently when the maximum temperature reached is 60 minutes or less.

The maximum temperature retention time may be 1 minute or more and 60 minutes or less, or 1 minute or more and less than 40 minutes, from the viewpoint of volatilizing all the dispersion medium and improving the yield. It may be more than 30 minutes.

The pressure at the time of sintering can be a condition in which the metal content (deposition ratio) in the sintered body is 65% by volume or more based on the sintered body. For example, by using the above metal paste (copper paste), a desired sintered metal layer can be formed without pressurizing during sintering. For example, at the time of forming the first metal layer, only the weight of the semiconductor element placed on the metal paste, or in addition to the weight of the semiconductor element, 0.01 MPa or less, more preferably 0.008 MPa or less, still more preferably 0. Sufficient bonding strength can be obtained under a pressure of .005 MPa or less. When the pressure received at the time of sintering is within the above range, voids can be reduced, joint strength and connection reliability can be further improved without impairing the yield because a special pressurizing device is not required. Examples of the method in which the metal paste receives a pressure of 0.01 MPa or less include a method of placing a weight on a semiconductor element and the like. When forming the second metal layer, for example, when the metal plate described later is not used, sintering may be performed with no load, and when a metal plate is used, a weight is placed on the metal plate and sintered. You can do it.

<Semiconductor device 110>
FIG. 3 is a schematic cross-sectional view showing an example of the semiconductor device of the present embodiment. The semiconductor device 110 shown in FIG. 3 includes a semiconductor element mounting support member 6, a semiconductor element 5 mounted on the semiconductor element mounting support member 6 via the first sintered metal layer 4, and the semiconductor element 5. A second sintered metal layer 7 provided on the second sintered metal layer and a metal plate 8 provided on the second sintered metal layer are provided. The configuration other than the metal plate 8 is the same as that of the semiconductor device 100.

As the material of the metal plate, a composite material having a three-layer structure of copper, aluminum, molybdenum, tungsten, copper-invar-copper and the like can be used. The thickness of the metal plate can be 1 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 50 μm or more, and 3000 μm or less, 2000 μm or less, 1500 μm or less, 1300 μm or less, 1200 μm or less, 1000 μm or less, etc. Can be.

The area of the main surface of the metal plate 8 may be the same as or different from the area of the main surface of the second sintered metal layer 7.

<Manufacturing method of semiconductor device 110>
The manufacturing method of the semiconductor device 110 is not particularly limited, and is manufactured by, for example, the following method.

(1) A member including the semiconductor element 5, the support member 6 for mounting the semiconductor element, and the first sintered metal layer 4 for joining the semiconductor element 5 and the support member 6 for mounting the semiconductor element 6 is prepared in advance. After that, a metal paste is provided on the surface of the semiconductor element 5, a metal plate 8 is laminated on the metal paste, and sintering is performed. As a result, the metal plate 8 is provided via the second sintered metal layer 7.
(2) A metal paste is provided on the support member 6 for mounting the semiconductor element, and the semiconductor element 5 is laminated on the metal paste. Further, a metal paste is provided on the semiconductor element 5, the metal plates 8 are laminated, and then sintering is performed. As a result, the semiconductor element 5 and the support member 6 for mounting the semiconductor element are joined by the first sintered metal layer 4, and the semiconductor element 5 and the metal plate 8 are joined by the second sintered metal layer 7.
(3) A metal paste is provided on the surface of the semiconductor element 5 in advance, a metal plate 8 is laminated on the metal plate 8 and then sintered, and a metal plate is placed on the surface of the semiconductor element 5 via a second sintered metal layer 7. 8 is provided. After that, a metal paste is provided on the support member 6 for mounting the semiconductor element, and the semiconductor element 5 provided with the metal plate 8 is laminated in advance via the second sintered metal layer 7 to perform sintering. When a Si chip or the like is used as the semiconductor element 5, a metal paste is provided on the surface of the Si chip or the like, the metal plates 8 are laminated, and then sintering is performed, and the second sintering is performed on the surface of the Si chip in advance. It is possible to provide the metal plate 8 via the metal layer 7. Such a Si chip may be obtained by providing a second sintered metal layer 7 and a metal plate 8 on the entire surface in the state of a wafer and dicing them into individual pieces.

<Semiconductor device 200>
FIG. 4 is a schematic cross-sectional view showing an example of the semiconductor device of the present embodiment. The semiconductor device 200 shown in FIG. 4 includes a lead frame 10, a semiconductor element 5 mounted on the lead frame 10 via a first sintered metal layer 4, and a second sintered on the semiconductor element 5. A metal layer 7 is provided. The upper part of the second sintered metal layer 7 and the outer lead 10b of the lead frame are connected by a metal wiring 11, and the heat radiating surface 10c of the lead frame and a part of the outer leads 10a and 10b of the lead frame are removed. The portion is sealed with an insulating sealing resin cured product 12. The semiconductor device 200 has one semiconductor element 5 on the lead frame 10, but may have two or more semiconductor elements 5. In this case, the plurality of semiconductor elements 5 can be joined to the metal wiring 11 by the second sintered metal layer 7, respectively. The metal wiring 11 may connect the upper portion of the semiconductor element 5 to the outer lead 10b of the lead frame.

The metal wiring 11 is formed by wire bonding, ribbon bonding, or the like. Metals such as Al and Cu are usually used as the material of the wire and the ribbon, but the material is not particularly limited as long as the wiring material can be formed without damaging the second sintered metal layer 7 and the semiconductor element 5.

The first sintered metal layer 4, the semiconductor element 5, the second sintered metal layer 7, the metal wiring 11, and the like are exposed so that the heat radiating surface 10c of the lead frame and a part of the outer leads 10a and 10b of the lead frame are exposed. It is sealed by the sealing resin cured product 12. The sealing resin cured product 12 may be, for example, a cured product of a thermosetting resin (sealing resin) containing an epoxy resin and an inorganic filler.

<Semiconductor device 210>
FIG. 5 is a schematic cross-sectional view showing an example of the semiconductor device of the present embodiment. The semiconductor device 210 further includes a metal plate 8 on the second sintered metal layer 7, and points that the upper portion of the metal plate 8 and the outer lead 10b of the lead frame are connected by a metal wiring 11. Except for this, it has the same configuration as the semiconductor device 200.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples.

<Manufacturing of semiconductor devices>
(Example 1)
(Step a: Preparation of sintered copper paste)
5.2 g of α-terpineol (manufactured by Wako Pure Chemical Industries, Ltd.) and 6.8 g of isobornylcyclohexanol (MTPH, manufactured by Nippon Terpen Chemical Co., Ltd.) as dispersion media, and CH-0200 (Mitsui Metals) as submicro copper particles. 52.8 g of copper particles having a particle size of 0.12 μm or more and 0.8 μm or less (95% by mass) manufactured by Mining Co., Ltd. was mixed in a plastic bottle, and this was mixed with an ultrasonic homogenizer (US-600, Nippon Seiki Co., Ltd.). A dispersion was obtained by treating at 19.6 kHz, 600 W for 1 minute. To this dispersion, 35.2 g of MA-C025 (manufactured by Mitsui Mining & Smelting Co., Ltd., content of copper particles having a maximum diameter of 1 μm or more and 20 μm or less, 100% by mass) was added as flake-shaped micro copper particles, and dried powder with a spatula. Stir until no more. The plastic bottle is tightly closed, and the copper paste for sintering is stirred at 2000 rpm for 2 minutes under reduced pressure and at 2000 rpm for 2 minutes using a rotating and revolving stirring device (Plantery Vacuum Mixer ARV-310, manufactured by Shinky Co., Ltd.). Got

(Step b: Sample preparation)
A metal mask having a 6 × 6 mm square opening is placed on a stainless plate having a thickness of 200 μm on the semiconductor element mounting surface of the lead frame (TO247), and stencil printing using a metal squeegee is performed for sintering obtained in step a. A copper paste was applied. Further, as described later, a SiC Schottky barrier diode chip (5 mm × 5 mm × thickness 400 μm: hereinafter, may be simply referred to as “SiC chip”) having an electroless nickel plating / electroless palladium plating film is prepared. Then, it was placed on the copper paste for sintering coated as described above with the surface opposite to the plating coating surface facing down. This was set in a tube furnace (manufactured by ABC Co., Ltd.), and argon gas was flowed at 1 L / min to replace the air with argon gas. After that, the first sintered copper layer and the SiC chip were laminated on the semiconductor element mounting surface of the lead frame by sintering treatment under the conditions of a temperature rise of 10 minutes and 350 ° C. for 10 minutes while flowing hydrogen gas at 300 mL / min. .. The thickness of the first sintered copper layer was 100 μm. Then, the argon gas was changed to 0.3 L / min and cooled, and the sample was taken out into the air at 50 ° C. or lower.

(Formation of electroless nickel plating film)
After immersing the SiC chip in SA-100 (manufactured by Hitachi Kasei Co., Ltd., trade name), which is a plating activity treatment liquid at a liquid temperature of 25 ° C., for 5 minutes, while irradiating ultrasonic waves with a resonance frequency of 28 kHz and an output of 100 W, 2 Washed for minutes. Subsequently, the SiC chip is immersed in NIPS-100 (trade name, manufactured by Hitachi Kasei Co., Ltd.), which is an electroless nickel plating solution having a liquid temperature of 85 ° C., for 25 minutes while irradiating ultrasonic waves having a resonance frequency of 28 kHz and an output of 100 W. After that, it was washed with water for 1 minute while irradiating ultrasonic waves having a resonance frequency of 28 kHz and an output of 100 W. The thickness of the formed electroless nickel plating film was 0.5 μm. The phosphorus concentration in the electroless nickel plating film was 7% by weight.

(Formation of electroless palladium plating film)
An electroless nickel-plated SiC chip is applied to a pallet (manufactured by Kojima Chemicals Co., Ltd., trade name), which is an electroless palladium plating solution with a liquid temperature of 55 ° C., while irradiating ultrasonic waves with a resonance frequency of 28 kHz and an output of 100 W. After immersing for 2 seconds, it was washed with water for 1 minute while irradiating ultrasonic waves having a resonance frequency of 28 kHz and an output of 100 W. The thickness of the electroless palladium plating film formed was 0.1 μm. The palladium concentration in the electroless palladium coating was approximately 100% by weight.

(Step c: Formation of sintered copper layer on SiC chip)
A metal mask having a 4 × 4 mm square opening was placed on a stainless steel plate having a thickness of 200 μm on the plating film surface of the SiC chip, and the copper paste for sintering obtained in step a was obtained by stencil printing using a metal squeegee. It was applied. This was set in a tube furnace (manufactured by ABC Co., Ltd.), and argon gas was flowed at 1 L / min to replace the air with argon gas. Then, the second sintered copper layer was formed on the SiC chip by sintering treatment under the conditions of a temperature rise of 10 minutes and 350 ° C. for 10 minutes while flowing hydrogen gas at 300 mL / min. The thickness of the second sintered copper layer was 100 μm. Then, the argon gas was changed to 0.3 L / min and cooled, and the sample was taken out into the air at 50 ° C. or lower. The copper content (volume ratio) in the second sintered copper layer was 90% by volume based on the volume of the sintered copper layer. The second sintered metal layer contained a structure derived from flake-shaped copper particles oriented substantially parallel to the interface with the SiC chip.

(Step d: Wire bonding)
The second sintered copper layer and the outer reed of the lead frame were connected by six Al wires having a diameter of 200 μm. The Al wire was connected by pressing the Al wire against the second sintered copper layer while applying ultrasonic waves with a wire bonder.

(Step e: Mold)
The heat-dissipating surface of the lead frame and the portion of the outer lead excluding a part were sealed with a solid sealing material (CEL, manufactured by Hitachi Kasei Co., Ltd.). Sealing was performed using a ton-las fur molding apparatus under the conditions of a mold temperature of 180 ° C., a molding pressure of 6.9 MPa, and a curing heating time of 90 seconds. Then, the sealed sample was heated in an oven at 200 ° C. for 6 hours to complete the curing of the sealing resin. Finally, the excess outer lead was cut to obtain a semiconductor device.

(Example 2)
A semiconductor device was produced in the same manner as in Example 1 except that a copper paste for sintering was used in which the amount of solvent was adjusted so that the copper content in the second sintered copper layer was 80% by volume. ..

(Example 3)
A semiconductor device was produced in the same manner as in Example 1 except that a copper paste for sintering was used in which the amount of solvent was adjusted so that the copper content in the second sintered copper layer was 70% by volume. ..

(Example 4)
The thickness of the stainless steel plate in step c was set to 1000 μm, the thickness of the second sintered copper layer was set to 500 μm, and the copper content in the second sintered copper layer was 90% by volume. A semiconductor device was produced in the same manner as in Example 1 except that a copper paste for sintering was used in which the amount of the solvent was adjusted.

(Example 5)
A semiconductor device was produced in the same manner as in Example 4 except that a copper paste for sintering was used in which the amount of solvent was adjusted so that the copper content in the second sintered copper layer was 80% by volume. ..

(Example 6)
A semiconductor device was produced in the same manner as in Example 4 except that a copper paste for sintering was used in which the amount of solvent was adjusted so that the copper content in the second sintered copper layer was 70% by volume. ..

(Example 7)
In step c, a copper plate (4 mm × 4 mm × thickness 500 μm) was laminated on the coated copper paste for sintering, and in step d, the copper plate and the outer lead of the lead frame were formed by six Al wires having a diameter of 200 μm. A semiconductor device was manufactured in the same manner as in Example 1 except that the devices were connected.

(Example 8)
A semiconductor device was produced in the same manner as in Example 7 except that a copper paste for sintering was used in which the amount of solvent was adjusted so that the copper content in the second sintered copper layer was 80% by volume. ..

(Example 9)
A semiconductor device was produced in the same manner as in Example 7 except that a copper paste for sintering was used in which the amount of solvent was adjusted so that the copper content in the second sintered copper layer was 70% by volume. ..

(Example 10)
A semiconductor device was produced in the same manner as in Example 7 except that the thickness of the stainless steel plate in step c was 1000 μm and the thickness of the second sintered copper layer was 500 μm.

(Example 11)
A semiconductor device was produced in the same manner as in Example 10 except that a copper paste for sintering was used in which the amount of solvent was adjusted so that the copper content in the second sintered copper layer was 80% by volume. ..

(Example 12)
A semiconductor device was produced in the same manner as in Example 10 except that a copper paste for sintering was used in which the amount of solvent was adjusted so that the copper content in the second sintered copper layer was 70% by volume. ..

(Comparative Example 1)
A solder sheet (95% by mass Pb-3.5% by mass Sn-1.5% by mass Ag, length 6 mm x width 6 mm x thickness 100 μm) was placed on the semiconductor element mounting surface of the lead frame (TO247). .. Then, the SiC chip was placed so that the cathode side of the SiC chip and the solder sheet were in contact with each other. This was installed on the heater in the formic acid reflow furnace, and the inside of the furnace was evacuated to 13 Pa. Next, nitrogen was introduced into the formic acid vessel, and while bubbling, nitrogen saturated with formic acid gas was introduced from the formic acid vessel into the furnace at 8 L / min. After the furnace pressure reached 80,000 Pa, the introduction of nitrogen saturated with formic acid gas was stopped, and the vacuum displacement was adjusted so that the furnace pressure was maintained at 80,000 Pa. The heater was heated from room temperature to 350 ° C. at 15 ° C./min. Exhaust was started at 230 ° C. in the temperature raising process, and vacuum exhausted to 13 Pa or less. After reaching 350 ° C., the temperature was maintained at 350 ° C., and 5 minutes after the holding, nitrogen was introduced into the furnace at 10 L / min. After the pressure in the furnace reached atmospheric pressure, the temperature of the heater was lowered from 350 ° C. to 50 ° C. at 20 ° C./min. Then, the sample was taken out from the furnace. Subsequently, the anode side of the SiC chip and the outer lead of the lead frame were connected by six Al wires having a diameter of 200 μm. After that, the semiconductor device was manufactured in the same manner as in Example 1.

(Comparative Example 2)
Semiconductors in the same manner as in Example 1 except that step c was not carried out and in step d, the anode side of the SiC chip and the outer lead of the lead frame were connected by six Al wires having a diameter of 200 μm. The device was made.

<Temperature evaluation of semiconductor devices>
A heat-dissipating sheet (manufactured by Shinetsu Chemical Industry Co., Ltd., TC-100TXS, thermal conductivity 5 Wm ^-1 K ^{-1) is} placed on a copper cooling block (length 100 mm x width 100 mm x thickness 20 mm) whose temperature is controlled by cooling water at 25 ° C. 60 mm in length × 40 mm in width × 100 μm in thickness), and the semiconductor devices of each Example and Comparative Example were placed on the heat-dissipating surface of the lead frame of the semiconductor device so as to be in contact with the heat-dissipating sheet. A glass epoxy plate (length 80 mm × width 20 mm × thickness 1 mm) was placed on the upper surface of the semiconductor device, and the semiconductor device was fixed by pressing from above to prepare an evaluation sample.

An experiment was conducted on this evaluation sample simulating the case where a steep surge voltage was generated. That is, a current of 30 A was applied from the outer lead on the anode side to the outer lead on the cathode side, and the energization was stopped after 1.1 seconds. Also, the minute current I _C and 10mA energization until after energization from the previous energization of I _ON, to measure the minute voltage V _j to be generated on both sides of the anode side outer lead and the cathode-side outer leads immediately 30A energized by an oscilloscope. Using the temperature dependence of V _j, to determine the maximum temperature from a minimum of V _j immediately after de-energization. It was measured 10 times, and the average value is shown in FIG.

As shown in the results of Examples 1 to 3, the temperature rise of the chip is further suppressed by increasing the density of the second sintered copper layer (increasing the copper content in the second sintered copper layer). I was able to do it. As shown in Examples 1 and 4, the temperature rise of the chip could be further suppressed by increasing the thickness of the second sintered copper layer. As shown in Examples 7 to 12, the temperature rise of the chip could be further suppressed by connecting the chip to the wire via the second sintered copper layer and the metal plate. On the other hand, as shown in the comparative example, when the second sintered copper layer was not provided between the chip and the wire, the temperature of the chip increased significantly. Such a large temperature rise may damage the chip.

1 ... Sintered copper having a flake-like structure, 2 ... Sintered copper derived from copper particles, 3 ... Pore, 4 ... First sintered metal layer, 5 ... Semiconductor element, 6 ... Support member for mounting semiconductor element, 7 ... Second sintered metal layer, 8 ... Metal plate, 10 ... Lead frame, 10a, 10b ... Outer lead of lead frame, 10c ... Heat dissipation surface of lead frame, 11 ... Metal wiring, 12 ... Sealed resin cured product, 100, 110, 200, 210 ... Semiconductor device.

Claims (7)

A support member for mounting a semiconductor element, a semiconductor element mounted on the support member for mounting the semiconductor element via a first sintered metal layer, and a second sintered metal layer provided on the semiconductor element. A semiconductor device to be equipped. The semiconductor device according to claim 1, wherein the second sintered metal layer includes a structure derived from flake-shaped metal particles oriented substantially parallel to an interface with the semiconductor element. The semiconductor device according to claim 1 or 2, wherein the metal content in the second sintered metal layer is 65% by volume or more and 90% by volume or less based on the total volume of the second sintered metal layer. The semiconductor device according to any one of claims 1 to 3, further comprising a metal plate on the second sintered metal layer. The semiconductor device according to any one of claims 1 to 4, wherein a metal wiring is connected to the second sintered metal layer or the metal plate. The semiconductor device according to any one of claims 1 to 5, wherein the thickness of the second sintered metal layer is 100 μm or more and 500 μm or less. The semiconductor device according to any one of claims 1 to 6, wherein the semiconductor element is a wide bandgap semiconductor.