Conductive paste, sintered body, and semiconductor device

Abstract

Provided is a conductive paste in which voids, cracks, and the like are less likely to occur.　This conductive paste contains metal particles and a solvent. The metal particles contain first nanoparticles having an average particle diameter of 80-500 nm. When thermogravimetric analysis is performed in a nitrogen atmosphere at a temperature warming speed of 10°C / minute from 25°C or lower, items [1] and [2] are satisfied. [1] The residual weight ratio at 120°C is 98% or more [2] The weight reduction ratio Δ 120°C-160°C from 120°C to 160°C is 2.0-5.0%

Description

Conductive Paste, Sintered Body, and Semiconductor Device

[0001] The present invention relates to a conductive paste, a sintered body, and a semiconductor device.

[0002] When using a conductive paste for bonding when mounting a semiconductor chip on a substrate such as a copper substrate, especially when the bonding area is large, since the conductive paste is sandwiched between the chip and the substrate, there is concern about the generation of voids and cracks due to the volatilization of the solvent.

[0003] In Patent Document 1, as a method for suppressing void generation, a plurality of solvents that cause voids are mixed to shift the timing of boiling and decomposition of the solvent so that they are not vaporized at once, and when the firing temperature is 250 ° C, solvents having a boiling point in the range of 200 to 300 ° C have been studied for use.

[0004] Also, a submicron powder with a relatively large average primary particle diameter of metal particles calculated from a scanning electron microscope (SEM) of 600 nm has been used, and efforts have been made to reduce voids by making it easier for the volatilized solvent to escape.

[0005] In Patent Document 2, it is described that a silver paste containing a first solvent composed of diol as a solvent and a second solvent composed of a polar solvent having a lower surface tension than the first solvent, and the additive being triol, can prevent voids generated in the foam bite and the silver bonding layer even when the coating film is thickened.

[0006] In Patent Document 3, it is described that in a paste in which a diol is used as a solvent in a silver paste and a triol having one or more methyl groups is mixed as an additive, it is possible to prevent cracks from occurring in the pre-dried film and the bonding strength from decreasing even when the pre-dried film is thickened.

[0007] International Publication No. 2022 / 070294, Japanese Unexamined Patent Application Publication No. 2017-201057, Japanese Unexamined Patent Application Publication No. 2016-008332

[0008] An object of the present invention is to provide a conductive paste in which voids and cracks are less likely to occur.

[0009] To achieve the above objective, the conductive paste of the present disclosure comprises metal particles and a solvent, wherein the metal particles include first nanoparticles having an average particle diameter of 80 nm to 500 nm, and satisfies the following conditions [1] and [2] when thermogravimetric analysis is performed in a nitrogen atmosphere at a heating rate of 10°C / min from 25°C or below: [1] Weight retention rate at 120°C is 98% or more [2] Weight loss rate Δ120°C-160°C from 120°C to 160°C is 2.0% to 5.0%

[0010] According to the present invention, a conductive paste that is less prone to the occurrence of voids and cracks is provided.

[0011] This is a schematic diagram illustrating the thermogravimetric (TG) curve and the state of the conductive paste. This is a flow chart showing the bonding method. This is a graph showing the weight loss rate Δ80°C–160°C in the examples and comparative examples. This is a graph showing the weight loss rate Δ120°C–160°C in the examples and comparative examples. This is a diagram showing the results of void and crack evaluation in the examples and comparative examples.

[0012] The following describes embodiments of the present invention (hereinafter referred to as "this embodiment"). This embodiment relates to a conductive paste, a sintered body, and a semiconductor device.

[0013] [Definitions] In this specification, ○ to △ (for example, ○ parts by mass to △ parts by mass) means ○ or more and △ or less (○ parts by mass or more and △ parts by mass or less). Also, in this specification, the terms "includes" or "contains" mean including the specified components, but do not exclude the existence of other components. Also, in this specification, the expression "A and / or B" includes "A only," "B only," and "both A and B." Also, in this specification, "room temperature" means 25°C.

[0014] [Conductive Paste] The conductive paste of this embodiment comprises metal particles and a solvent, wherein the metal particles include first nanoparticles with an average particle diameter of 80 nm to 500 nm, and satisfies the following conditions [1] and [2] when thermogravimetric analysis is performed in a nitrogen atmosphere at a heating rate of 10°C / min from 25°C or below: [1] Weight retention rate at 120°C is 98% or more [2] Weight loss rate Δ120°C-160°C from 120°C to 160°C is 2.0% to 5.0%

[0015] <Metal Particles> The metal particles are not particularly limited as long as they can be used for joining components. The metal used in the metal particles is not particularly limited as long as it can be used for joining components. Both noble metals and base metals can be used as the metals forming the metal particles. Examples of noble metals include silver (Ag), gold (Au), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), and platinum (Pt). From the viewpoint of availability, it is preferable to use silver or gold. From the viewpoint of cost, silver is particularly preferable. Examples of base metals include copper, aluminum, iron, and nickel. The metal used in the metal particles may be a single metal or an alloy. The metal particles are preferably spherical.

[0016] (First Nanoparticles) The metal particles include first nanoparticles having an average particle diameter of 80 nm to 500 nm. Here, the average particle diameter of the metal particles in this specification is the average primary particle diameter. The average particle diameter of the metal particles can be calculated, for example, from the primary particle diameters of 100 or more arbitrary metal particles on an electron microscope image (SEM image or TEM image) observed at a predetermined magnification using a scanning electron microscope (SEM) or transmission electron microscope (TEM). This calculation of the average primary particle diameter of the metal particles can be performed, for example, using image analysis software.

[0017] The average particle size of the first nanoparticles may be 80 nm to 500 nm, preferably 100 nm to 500 nm, more preferably 150 nm to 500 nm, even more preferably 200 nm to 400 nm, and particularly preferably 250 nm to 400 nm.

[0018] The content of the first nanoparticles (including the protective agent if coated with a protective agent) in the conductive paste is preferably 60 parts by mass or more, more preferably 65 parts by mass or more, even more preferably 70 parts by mass or more, and particularly preferably 75 parts by mass or more, when the total amount of the conductive paste is 100 parts by mass.

[0019] (Second Nanoparticles) The metal particles preferably include second nanoparticles with an average particle diameter of less than 80 nm. The first and second nanoparticles may be formed from the same metal or from different metals. The average particle diameter of the second nanoparticles may be 5 nm or more and less than 80 nm, preferably 10 nm or more and less than 80 nm, more preferably 15 nm or more and less than 80 nm, and even more preferably 20 nm or more and less than 80 nm. The second nanoparticles preferably include particles with an average particle diameter of 5 nm to 50 nm, preferably 10 nm to 30 nm.

[0020] The content of the second nanoparticles (including the protective agent if coated with one) in the conductive paste is, in one embodiment, preferably 3 to 30 parts by mass, more preferably 3 to 25 parts by mass, even more preferably 3 to 20 parts by mass, particularly preferably 3 to 15 parts by mass, and most preferably 3 to 10 parts by mass, when the total amount of the conductive paste is 100 parts by mass. In another embodiment, it is preferably 5 to 30 parts by mass, more preferably 10 to 30 parts by mass, and even more preferably 15 to 30 parts by mass. In yet another embodiment, it is preferably 5 to 25 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 5 to 15 parts by mass. In one embodiment, it is preferable that the second nanoparticles contain 5 to 15 parts by mass of particles with an average particle diameter of 5 nm to 50 nm.

[0021] When the metal particles include first nanoparticles and second nanoparticles, the mass ratio of the second nanoparticles to the first nanoparticles (mass of the second nanoparticles / mass of the first nanoparticles) is preferably 0.25 or less, more preferably 0.20 or less. Furthermore, the content of the first nanoparticles and second nanoparticles in the conductive paste is preferably 80 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 87 parts by mass or more, and particularly preferably 90 parts by mass or more, when the total amount of the conductive paste is 100 parts by mass.

[0022] In one embodiment, it is preferable that the metal particles substantially do not contain particles with an average particle diameter of 1 μm or more. Here, "substantially does not contain particles with an average particle diameter of 1 μm or more" means that the content of particles with an average particle diameter of 1 μm or more in the conductive paste is 1 part by mass or less when the total amount of the conductive paste is 100 parts by mass.

[0023] <Protective Agent> The surface of the metal particles is preferably coated with a protective agent made of organic matter. Depending on the size of the metal particles, the protective agent may be a capping agent to suppress spontaneous sintering or a lubricant. From the viewpoint of sinterability, the content of the protective agent is preferably 0.1 to 2 parts by mass, more preferably 0.1 to 1.5 parts by mass, and even more preferably 0.1 to 1 part by mass, when the total amount of conductive paste is 100 parts by mass.

[0024] The capping agent is preferably a substance having a boiling point at least below the sintering temperature, and is preferably a substance with a boiling point of 200°C or lower. Examples of such substances include carboxylic acids, dicarboxylic acids, unsaturated fatty acids, or amines with 12 or fewer carbon atoms. Specifically, examples of capping agents include octanoic acid, heptanoic acid, hexanoic acid, pentanoic acid, butanoic acid, propanoic acid, oxalic acid, malonic acid, ethyl malonic acid, succinic acid, methyl succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sorbic acid, maleic acid, hexylamine, octylamine, and the like.

[0025] <Solvent> The solvent is preferably a solvent (solvent A) that is liquid at room temperature and has a boiling point higher than 250°C at 1 atmosphere (standard atmospheric pressure, 101.325 kPa). Solvent A is not particularly limited, but may include texanol (255-260°C), 1-dodecanol (260°C), 1-tetradecanol (>260°C), Tersolve MTPH (308°C (5%), 313°C (95%)) (manufactured by Nippon Terpene Chemical Co., Ltd.), dihydroterpinyloxyethanol (249°C (5%), 259°C (95%)) (manufactured by Nippon Terpene Chemical Co., Ltd.), Tersolve TOE-100 (268°C (5%), 282°C (95%)) (manufactured by Nippon Terpene Chemical Co., Ltd.), hexyl diglycol (258°C), 2-ethylhexyl diglycol (275°C) Solvents containing hydroxyl groups in the molecule are preferred, such as monoalcohols (-277°C), 2,4-diethyl-1,5-pentanediol (Kyowadiol PD-9) (257°C) (manufactured by KH Neochem Co., Ltd.), glycerin (290°C), 3-methylbutane-1,2,3-triol (isoprecentriol A (IPTL-A) (255.5°C) (manufactured by Nippon Terpene Chemical Co., Ltd.), 2-methylbutane-1,3,4-triol (isoprecentriol B (IPTL-B) (278-282°C) (manufactured by Nippon Terpene Chemical Co., Ltd.)), and polyols (the temperatures in parentheses above are boiling points).

[0026] The solvent may include a solvent (solvent B) with a boiling point lower than 250°C at 1 atmosphere, provided that the conductive paste satisfies the following conditions [1] and [2]. Examples of solvent B are not limited to terpineol (219°C), butyl carbitol (230°C), butyl carbitol acetate (247°C), decanol (233°C), and 2-ethyl-hexanediol (245°C) (the temperatures in parentheses above are boiling points).

[0027] The solvent preferably contains a solvent (for example, solvent A) with a boiling point higher than the firing temperature when the conductive paste is sintered. Specifically, the content of the solvent with a boiling point higher than the firing temperature in the conductive paste is preferably 2 parts by mass or more, preferably 3 parts by mass or more, more preferably 3.5 parts by mass or more, even more preferably 4 parts by mass or more, and particularly preferably 5 parts by mass or more, when the total amount of the conductive paste is 100 parts by mass. In one embodiment, the content of solvent A in the conductive paste is preferably 2 to 7 parts by mass, more preferably 3 to 6.5 parts by mass, even more preferably 4 to 6.5 parts by mass, and particularly preferably 4 to 6 parts by mass.

[0028] It is preferable that the solvent substantially does not contain a solvent (for example, solvent B) with a boiling point lower than the firing temperature when the conductive paste is sintered. Here, substantially free from a solvent with a boiling point lower than the firing temperature means that the content of a solvent with a boiling point lower than the firing temperature in the conductive paste is 6 parts by mass or less, preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, and particularly preferably 1 part by mass or less, when the total amount of the conductive paste is 100 parts by mass. In addition, in one embodiment, the content of solvent B in the conductive paste is less than the content of solvent A. The total of solvent A and solvent B is preferably 2 to 7 parts by mass, more preferably 3 to 6.5 parts by mass, even more preferably 4 to 6.5 parts by mass, and particularly preferably 4 to 6 parts by mass, when the total amount of the conductive paste is 100 parts by mass.

[0029] <Dispersant> The conductive paste of this embodiment may contain a dispersant such as an acid-based dispersant or a phosphate ester-based dispersant. The dispersant is not particularly limited, but carboxylic acids such as 2-butoxyethoxyacetic acid (BEA) (manufactured by Fujifilm Wako Co., Ltd.) and 2-ethoxyacetic acid (manufactured by Fujifilm Wako Co., Ltd.) are preferred.

[0030] The content of the dispersant in the conductive paste is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less, when the total amount of the conductive paste is 100 parts by mass.

[0031] <Other Additives> Known additives can be added to conductive paste within an appropriate range, provided they do not affect the sinterability or bonding strength of the conductive paste. Specifically, these include viscosity modifiers, organic binders (e.g., resin binders), inorganic binders, pH adjusters, buffers, defoamers, leveling agents, and volatilization inhibitors. The content of additives in the conductive paste is preferably 0.1 parts by mass or less when the total amount of conductive paste is 100 parts by mass.

[0032] <Method for Manufacturing Conductive Paste> The conductive paste of this embodiment can be manufactured by kneading metal particles, a solvent, and other optional components in a known manner. The kneading method is not particularly limited; for example, each component can be prepared individually and kneaded in any order using ultrasonic dispersion, a disperser, a three-roll mill, a ball mill, a bead mill, a twin-screw kneader, or a revolving agitator to manufacture a bonding metal paste.

[0033] [Characteristics of Conductive Paste] <Thermogravimetric Properties> The inventors focused on the fact that when conductive paste is sintered, the evaporation of the solvent and the melting of metal particles occur in parallel. It is presumed that when heated, the concentration of metal particles in the conductive paste increases as the solvent evaporates, and sintering progresses as neighboring metal particles come into contact with each other while maintaining fluidity (State 1 in Figure 1). If the evaporation of the solvent is too fast compared to the melting of the metal particles, the metal particles in the conductive paste lose fluidity before they melt, so sintering does not proceed properly, and voids and cracks occur (State 2 in Figure 1). Also, if the evaporation of the solvent is too slow, the solvent is present between the metal particles when they melt, and the metal particles cannot come into contact with each other, so sintering does not proceed properly, and voids and cracks occur (State 3 in Figure 1).

[0034] Therefore, the inventors focused on the TG (thermogravimetric) curve in differential thermal-thermogravimetric analysis (TG-DTA). Specifically, they found that by defining the increase in metal particle concentration due to solvent evaporation and the timing of metal particle melting within a certain temperature range, it is possible to provide a conductive paste that is less prone to voids and cracks.

[0035] From this perspective, it is preferable that the conductive paste of this embodiment satisfies the following conditions [1] and [2], and further satisfies [3], when thermogravimetric analysis is performed in a nitrogen atmosphere at a heating rate of 10°C / min from 25°C or below: [1] Weight retention rate at 120°C is 98% or more [2] Weight loss rate Δ120°C-160°C from 120°C to 160°C is 2.0% to 5.0% [3] Weight loss rate Δ80°C-160°C from 80°C to 160°C is 2.3% to 6.2% Note that the type and content of metal particles and solvent can be adjusted so that the conductive paste satisfies [1], [2], and [3].

[0036] [1] The weight retention rate at 120°C should be 98% or more, preferably 98.5% or more, more preferably 98.9% or more, even more preferably 99.0% or more, and particularly preferably 99.2% or more. Here, the weight retention rate is calculated with the value at 30°C as 100%. If the weight retention rate at 120°C is less than 98%, the solvent evaporates too quickly, causing the metal particles to lose fluidity before they melt, resulting in improper sintering and the formation of voids and cracks (State 2 in Figure 1).

[0037] Furthermore, [2] the weight loss rate Δ120°C-160°C from 120°C to 160°C should be between 2.0% and 5.0%, preferably between 2.2% and 5.0%, more preferably between 2.2% and 4.7%, even more preferably between 2.3% and 4.6%, and particularly preferably between 2.4% and 4.5%. If the weight loss rate Δ120°C-160°C is less than 2%, the solvent evaporates too slowly, so when the metal particles melt, the solvent is present between the metal particles, preventing them from coming into contact with each other. As a result, sintering does not proceed properly, and voids and cracks occur (State 3 in Figure 1). If the weight loss rate Δ120°C-160°C is greater than 5%, the solvent evaporates too quickly, causing the metal particles to lose fluidity before they melt. As a result, sintering does not proceed properly, and voids and cracks occur (State 2 in Figure 1).

[0038] Furthermore, [3] the weight loss rate Δ80°C-160°C from 80°C to 160°C is preferably 2.3% to 6.2%, more preferably 2.4% to 6.0%, even more preferably 2.5% to 5.9%, and particularly preferably 2.8% to 5.9%. If the weight loss rate Δ80°C-160°C is less than 2.3%, the solvent evaporates too slowly, so when the metal particles melt, the solvent is present between the metal particles, preventing them from coming into contact with each other. As a result, sintering does not proceed properly, and voids and cracks occur (State 3 in Figure 1). If the weight loss rate Δ80°C-160°C is greater than 6.2%, the solvent evaporates too quickly, causing the metal particles to lose fluidity before they melt. As a result, sintering does not proceed properly, and voids and cracks occur (State 2 in Figure 1).

[0039] By satisfying conditions [1] and [2] above, the evaporation of the solvent is allowed to proceed slowly, thereby controlling the generation of voids. Furthermore, the inclusion of first nanoparticles with an average particle size of 80 nm to 500 nm in the metal particles maintains sinterability. Therefore, the conductive paste of this embodiment has the advantage of being less prone to the generation of voids and cracks.

[0040] <Viscosity> The viscosity of the conductive paste in this embodiment is not particularly limited and can be adjusted as appropriate depending on the printing method, such as dispensing by dispenser, screen printing, metal mask printing, or inkjet printing. For example, the components can be selected and the mixing ratio adjusted as appropriate so that the viscosity of the conductive paste at 25°C is in the range of 0.05 Pa·s to 200 Pa·s. In this specification, unless otherwise specified, viscosity is expressed as the value measured in accordance with the Japanese Industrial Standard JIS K6833. Specifically, it can be determined by measuring with an E-type viscometer at a rotation speed of 5 rpm. There are no particular restrictions on the equipment, rotor, or measurement range used.

[0041] From the viewpoint of improving coatability, the viscosity of the conductive paste at 25°C is preferably 0.05 Pa·s to 200 Pa·s, more preferably 10 Pa·s to 200 Pa·s, more preferably 20 Pa·s to 150 Pa·s, and even more preferably 30 Pa·s to 130 Pa·s.

[0042] <Shear Strength> The conductive paste of this embodiment, as a joined body by the method described in the examples, has a shear strength (joining strength) measured by the method described in the examples of 20 MPa or more, preferably 30 MPa or more, more preferably 50 MPa or more, and even more preferably 60 MPa or more.

[0043] [Joining Method] The joining method of this embodiment is a method of joining two joined members using the conductive paste of this embodiment. By this method, a uniform joining layer can be formed up to the end, the joining strength is high, and a joined body in which the generation of voids and cracks in the joining layer is suppressed can be obtained. The joining method of this embodiment has a coating film forming step S1, a placing step S2, and a firing step S3, and a pre-drying step or the like may be further performed (FIG. 2). Hereinafter, each step will be described.

[0044] [Coating Film Forming Step S1] In the coating film forming step S1, the conductive paste of this embodiment is applied to the first joined member by a printing method such as coating by a dispenser, screen printing, metal mask printing, inkjet printing, etc. to form a coating film. The viscosity of the paste or ink can be appropriately adjusted according to the selected printing method. Examples of the first joined member include a substrate. Examples of the substrate include a metal substrate such as a copper substrate, an alloy substrate of copper and some metal (for example, W (tungsten) or Mo (molybdenum)), a ceramic substrate in which a copper plate is sandwiched between SiN (silicon nitride) or AlN (aluminum nitride), etc., and further a plastic substrate such as a PET (polyethylene terephthalate) substrate, and in some cases, a printed wiring board, etc. Further, a laminated substrate in which these are laminated may also be used. The portion where the conductive paste is applied to the first joined member may be plated with metal. From the viewpoint of the joining compatibility with the metal component in the coating film, the type of metal in the metal plating of the first joined member is preferably the same as the constituent metal of the metal particles in the conductive paste.

[0045] [Placement Step S2] In placement step S2, the second member to be joined is placed on the coating film formed on the first member to be joined. Examples of the second member to be joined include semiconductor elements such as Si chips and SiC chips, and substrates similar to those mentioned as examples of the first member to be joined. Alternatively, paste may not be applied to the substrate, and the Si chip, SiC chip, or IC chip may be prepared by applying paste to the back surface. The area of ​​the second member to be joined that comes into contact with the coating film (the joining surface) may be plated with metal. From the viewpoint of bonding compatibility with the metal components in the coating film, it is preferable that the type of metal used in the metal plating of the second member to be joined is the same as the constituent metal of the metal particles in the conductive paste. When placing the members to be joined on the coating film, it is advisable to apply external pressure between the two members to be joined in a direction that compresses the coating film, in addition to the weight of the objects to be joined. However, it is important that the pressure is not so high that the chips or substrates are damaged by the external pressure. Furthermore, the joining method of this embodiment can be suitably applied to joining large-area semiconductor elements. In particular, the area of ​​the bonding surface of the semiconductor device (the surface that comes into contact with the coating film or the metal bonding layer that will be formed from it; the coating film is usually formed to cover the entire bottom surface of the semiconductor device) is 9 mm². ２ This is preferable when the area of ​​the surface to be joined is 25 mm². ２ It is more preferable when the area of ​​the surfaces to be joined is 36 to 400 mm². ２ This is preferable when the area of ​​the surfaces to be joined is 100 to 400 mm². ２ This is particularly preferable in the following cases.

[0046] [Firing Process S3] In the firing process S3, after performing the placement process S2 and, if necessary, the preliminary drying process, the temperature of the coating film sandwiched between the two joined members is raised from room temperature to a firing temperature of 150 to 300 °C in one step or multiple steps at a heating rate of 1.5 °C / min to 10 °C / min, and held at that firing temperature for a time of 1 minute or more and less than 3 hours, preferably 1 minute or more and less than 2 hours, to form a metal bonding layer from the coating film of the conductive paste. This metal bonding layer is excellent in bonding strength and the generation of voids and cracks is suppressed. Therefore, by sintering, the two joined members can be firmly joined with high reliability. The heating rate when heating to the firing temperature in the firing process S3 is preferably 2 °C / min to 6 °C / min, more preferably 2.5 °C / min to 4 °C / min, from the viewpoint of forming a joined body having a high bonding strength and a metal bonding layer with few voids. Also, with such a heating rate, the preliminary drying process can be combined with the heating to the firing temperature.

[0047] The firing temperature in the firing process S3 is preferably 150 to 250 °C, more preferably 180 to 250 °C, and even more preferably 200 to 250 °C, from the viewpoints of the bonding strength and cost of the formed metal bonding layer. The holding time at the firing temperature is preferably 1 to 120 minutes, more preferably 1 to 90 minutes, from the viewpoints of the bonding strength and cost of the formed metal bonding layer. Also, when heating to the firing temperature and holding at that firing temperature, there is no need to apply a pressure in the direction of compressing the coating film between the joined members, but for the purpose of forming a denser sintered film, a pressure of 5 MPa or less may be applied. Also, the firing process S3 may be carried out in an air atmosphere or in an inert atmosphere such as a nitrogen atmosphere, but particularly when a metal that is easily oxidized as a component of the substrate or metal particles is included as a constituent component (for example, assuming that copper or a copper alloy is the metal of the substrate or is used as the metal particles), it is preferably carried out in an inert atmosphere from the viewpoint of preventing oxidation, and further, from the viewpoint of cost, it is more preferable to carry out the firing process in a nitrogen atmosphere.

[0048] [Applications] The conductive paste of this embodiment can form a uniform bonding layer to the edges, resulting in a bonded body with high bonding strength and suppressed occurrence of voids and cracks in the bonding layer. Therefore, it is suitable for bonding applications to join two members to be joined.

[0049] [Sintered Body and Semiconductor Device] The conductive paste of this embodiment is suitable for bonding applications in semiconductor devices because the occurrence of voids and cracks is suppressed when a bonding layer is formed as a sintered body. The conductive paste of this embodiment can also be used for bonding applications in power semiconductors.

[0050] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, parts and % refer to parts by mass and mass%, respectively, unless otherwise specified.

[0051] [Preparation of Conductive Paste] Each component in Tables 1 to 3 was weighed and mixed using a hybrid mixer to prepare the conductive pastes for the examples and comparative examples. In Tables 1 to 3, the amount of each component is expressed in parts by mass (unit: g). The components used in the examples and comparative examples are as follows.

[0052] <Metal Particles> As metal particles, silver nanoparticles A, B, and C were used, with average primary particle diameters of 20 nm, 100 nm, and 300 nm, respectively, as measured by scanning electron microscopy. ・Silver nanoparticle A: 20 nm, 2.46% organic matter ・Silver nanoparticle B: 100 nm, 0.53% organic matter ・Silver nanoparticle C: 300 nm, 0.41% organic matter In Example 1, 92.4% by mass of metal particles were used, of which 0.55% by mass was organic matter. <Liquid Components> (Solvent A: Boiling point > 250°C) ・1-Dodecanol: Boiling point 260°C ・IPTL-B: Boiling point 278°C (Solvent B: Boiling point < 250°C) ・Terpineol: Boiling point 219°C ・Butylcarbitol: Boiling point 230°C ・Butylcarbitol acetate: Boiling point 247°C ・Decanol: Boiling point 233°C (Dispersant) ・2-Butoxyethoxyacetic acid: Boiling point 240°C

[0053] [Fluidity] The fluidity of the conductive paste was evaluated according to the following criteria: ○: Fluid △: Slightly fluid ×: Not fluid

[0054] [Viscosity Measurement] The viscosity of the conductive paste was measured using an E-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd., model "TVE type", 3° × R9.7 cone). The value was read 1 minute after the start of measurement at 25°C with a rotor speed of 5 rpm, within 1 hour of preparation.

[0055] [Thermogravimetric Analysis and Differential Thermal Analysis Measurement] Using a simultaneous differential thermal and thermogravimetric analysis device (TG-DTA STA 2500 Regulus, manufactured by Netch Japan Co., Ltd.), the TG-DTA curve of the conductive paste was measured by heating it from 25°C to 300°C in a nitrogen atmosphere at a heating rate of 10°C / min.

[0056] [Preparation of samples for evaluation of voids, cracks, and shear strength] Conductive paste was applied to a 25.4 mm × 25.4 mm (1 mm thick) copper substrate using a polyimide perforation plate (opening diameter 1.1 mm, thickness 125 μm). A 1 mm × 1 mm (0.25 mm thick) Si element with a square bottom surface (bonded surface) was placed on the coating of each bonding material formed on the copper substrate, adjusted with a feeler gauge to a height of 50 μm from the substrate surface, and a force of 0.06 MPa was applied for approximately 10 seconds. Subsequently, the temperature was increased from 25°C to 250°C at a rate of 3°C / min in a nitrogen atmosphere, and the substrate was fired at 250°C for 60 minutes to form a bonding layer and obtain a bonded body.

[0057] [Evaluation of Shear Strength of Joint] The shear strength of the joint was measured using a 4000Plus (manufactured by DAGE). Specifically, the joint consists of a copper substrate, a silver bonding layer formed on the copper substrate, and a Si element formed on the bonding layer. A shear tool was set to 200 μm / second and applied force horizontally to the copper substrate from the side of the Si element. The shear strength of the joint was determined by dividing the force at which fracture occurred by the area of ​​the bottom surface of the Si element. The above test was performed with the lower end of the shear tool touching the copper substrate at a height of 25 μm.

[0058] [Void and Crack Evaluation] The joint between the Si element, bonding layer, and copper substrate of each bond was observed by imaging with an X-ray inspection device (Cheetah EVO, Comet Exlon). The following criteria were used for evaluation: ○: No voids or cracks were observed. ×: Voids and / or cracks were observed.

[0059]

[0060]

[0061]

[0062]

[0063] [Results] The results are shown in Tables 1 to 4 and Figures 3 to 5. Examples 1 to 4 satisfied the following three conditions: [1] a weight retention rate of 98% or more at 120°C, [2] a weight loss rate Δ120°C–160°C from 120°C to 160°C of 2.0% to 5.0%, and [3] a weight loss rate Δ80°C–160°C from 80°C to 160°C of 2.3% to 6.2% (Table 4, Figures 3 and 4; Examples 3 and 4 are the same as Examples 1 and 2). No voids or cracks occurred in Examples 1 to 4 (Figure 5), and they showed sufficient shear strength and good bonding properties (Table 1). In addition, the conductive pastes of Examples 1 to 4 had low viscosity (Table 1).

[0064] Example 5 contained only dodecanol as the solvent, but it satisfied all three conditions [1], [2], and [3] (Table 4, Figures 3 and 4). In Example 5, no voids or cracks were observed (Figure 5), and it showed sufficient shear strength and good bonding properties (Table 1). In addition, the conductive paste of Example 5 had low viscosity (Table 2).

[0065] Example 6 contained only decanol with a boiling point of 233°C as the solvent, but it satisfied all three conditions [1], [2], and [3] (Table 4, Figures 3 and 4). In Example 6, no voids or cracks were observed (Figure 5), and it showed sufficient shear strength and good bonding properties (Table 1). In addition, the conductive paste of Example 6 had low viscosity (Table 2).

[0066] Example 7 contained decanol with a boiling point of 233°C and IPTL-B with a boiling point of 278°C as solvents, and satisfied the three conditions [1], [2], and [3] (Table 4, Figures 3 and 4). In Example 6, no voids or cracks were observed (Figure 5), and it showed sufficient shear strength and good bonding properties (Table 1). In addition, the conductive paste of Example 7 had low viscosity (Table 2).

[0067] Comparative Examples 1-3 did not satisfy conditions [1] and [3] (Table 4, Figures 3 and 4; Comparative Examples 2 and 3 were similar to Comparative Example 1). Voids and cracks were present in Comparative Examples 1-3 (Figure 5), and fluidity was poor. Comparative Examples 4 and 5 did not satisfy conditions [2] and [3] (Table 4, Figures 3 and 4). Voids and cracks were present in Comparative Example 4 (Figure 5), and viscosity could not be measured. Voids and cracks were present in Comparative Example 5 (Figure 5). The presence or absence of a dispersant did not affect the above results.

[0068] Although the present invention has been described above with reference to embodiments and examples, the present invention is not limited to the above embodiments and examples. Various modifications to the configuration and details of the present invention can be understood by those skilled in the art within the scope of the present invention.

[0069] The patents, patent applications, and documents cited herein are incorporated herein by reference in the same manner as their contents are specifically described herein.

[0070] <Notes> Some or all of the above embodiments and examples may be described as follows, but are not limited to the following. <Conductive Paste> (Note 1) A conductive paste comprising metal particles and a solvent, wherein the metal particles include first nanoparticles with an average particle diameter of 80 nm to 500 nm, and satisfies the following [1] and [2] when thermogravimetric analysis is performed in a nitrogen atmosphere from 25°C or below at a heating rate of 10°C / min: [1] Weight retention rate at 120°C is 98% or more [2] Weight loss rate Δ120°C-160°C from 120°C to 160°C is 2.0% to 5.0% (Note 2) The conductive paste according to Note 1, which satisfies the following [3] when thermogravimetric analysis is performed in a nitrogen atmosphere from 25°C or below at a heating rate of 10°C / min. [3] Weight loss rate Δ80°C-160°C is 2.3% to 6.2% from 80°C to 160°C. (Note 3) The conductive paste according to Note 2, wherein the metal particles include second nanoparticles having an average particle diameter of less than 80 nm. (Note 4) The conductive paste according to Note 3, wherein the mass ratio of the second nanoparticles to the first nanoparticles is 0.25 or less. (Note 5) The conductive paste according to any one of Notes 1 to 4, wherein the metal particles substantially do not contain particles with an average particle diameter of 1 μm or more. (Note 6) The conductive paste according to any one of Notes 1 to 5, which is fired at a firing temperature of 150 to 250°C. (Note 7) The conductive paste according to Note 6, wherein the solvent includes a solvent with a boiling point higher than the firing temperature. (Note 8) The conductive paste according to Note 6 or 7, wherein the solvent substantially does not contain a solvent with a boiling point lower than the firing temperature. (Note 9) A conductive paste described in any of Notes 1 to 8, for bonding purposes. (Note 10) A conductive paste described in any of Notes 1 to 8, used in power semiconductors. (Note 11) A sintered body of a conductive paste described in any of Notes 1 to 10. (Note 12) A semiconductor device comprising the sintered body described in Note 11.

[0071] The conductive paste of the present invention is particularly useful for bonding applications in semiconductor devices because it is less prone to the formation of voids and cracks.

Claims

1. A conductive paste comprising metal particles and a solvent, wherein the metal particles include first nanoparticles with an average particle diameter of 80 nm to 500 nm, and satisfies the following conditions [1] and [2] when thermogravimetric analysis is performed in a nitrogen atmosphere at a heating rate of 10°C / min starting from 25°C or below: [1] Weight retention rate at 120°C is 98% or more [2] Weight loss rate Δ120°C-160°C from 120°C to 160°C is 2.0% to 5.0% 2. A conductive paste according to claim 1, which satisfies the following [3] when thermogravimetric analysis is performed in a nitrogen atmosphere from 25°C or below at a heating rate of 10°C / min: [3] Weight loss rate Δ80°C-160°C from 80°C to 160°C is 2.3% to 6.2% 3. The conductive paste according to claim 2, wherein the metal particles include second nanoparticles having an average particle diameter of less than 80 nm.

4. The conductive paste according to claim 3, wherein the mass ratio of the second nanoparticles to the first nanoparticles is 0.25 or less.

5. The conductive paste according to any one of claims 1 to 4, wherein the metal particles substantially do not contain particles with an average particle diameter of 1 μm or more.

6. A conductive paste according to any one of claims 1 to 5, which is fired at a firing temperature of 150 to 250°C.

7. The conductive paste according to claim 6, wherein the solvent includes a solvent with a boiling point higher than the firing temperature.

8. The conductive paste according to claim 6 or 7, wherein the solvent substantially does not contain a solvent with a boiling point lower than the firing temperature.

9. A conductive paste according to any one of claims 1 to 8, for bonding purposes.

10. A conductive paste used in power semiconductors, according to any one of claims 1 to 8.

11. A sintered body of a conductive paste according to any one of claims 1 to 10.

12. A semiconductor device comprising the sintered body described in claim 11.

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