Silver oxide paste and method for manufacturing semiconductor device using same

Abstract

The purpose of the present invention is to provide a silver oxide paste capable of achieving an excellent bonding strength even from bonding at a low temperature and capable of yielding a bonding layer having a thickness exceeding 20 µm. The present invention provides a silver oxide paste containing: silver oxide particles that are in flake shapes and have an average thickness of 1-100 nm and D50 of 100-350 nm; and silver-containing particles having an aspect ratio of 6.0 or lower and D50 of 2.0 µm or smaller.

Description

Silver oxide paste and method for manufacturing semiconductor device using the silver oxide paste

[0001] The present disclosure relates to a silver oxide paste and a method for manufacturing a semiconductor device using the silver oxide paste.

[0002] Power semiconductor devices have traditionally been used for power control and motor control in automobiles, power transmission systems, railways, solar cells, home appliances, etc. Until now, Si-based semiconductor devices using Si have been mainstream, but with the demand for higher currents and voltages, power semiconductor devices using SiC, GaN, etc. are being considered.

[0003] The operating temperature of power semiconductor devices is expected to reach 200°C or higher, which is higher than the operating temperature of currently mainstream Si-based semiconductor devices. This poses a problem in that conventionally used bonding materials such as solder alloys and epoxy-based conductive adhesives cannot withstand such operating temperatures.

[0004] In recent years, the use of silver-based bonding materials such as silver and silver oxide has been considered as bonding materials that are durable at temperatures above 200°C, have low electrical resistance, and have excellent heat dissipation properties. Patent Document 1 discloses that silver oxide particles are used as a material for bonding a semiconductor element and a circuit layer in a power module, and that the bonding temperature to the semiconductor element can be kept low, thereby reducing the thermal load on the semiconductor element. Patent Document 1 also discloses silver oxide particles of 0.1 μm to 40 μm in size as the silver oxide particles, and in its examples, micron-sized silver oxide particles are tested. Typically, such fine silver oxide particles are obtained by precipitation from a silver salt solution and generally have a relatively isotropic shape, such as a spherical or approximately spherical shape.

[0005] JP 2014-96545 A

[0006] It has been found that the bonding materials made of spherical silver oxide particles discussed above may result in insufficient bonding strength, for example, at relatively low temperatures of around 250° C., and that improvements are necessary for practical use. The present inventors have focused on nanosizing silver oxide particles and have discovered a bonding material that can provide good bonding strength without cracking or peeling due to thermal shrinkage by making the silver oxide particles flaky, specifically, by using flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm, and have already filed patent applications (Japanese Patent Application Nos. 2023-067078, 2023-175174, and PCT / JP2024 / 014464).

[0007] According to information published on the website of Nippon Superior Co., Ltd. (https: / / www.anpl.jp / pdf / flyer_japanese_03.pdf) (June 3, 2024), it is recommended that the thickness of the bonding layer made of the bonding material exceed 20 μm. Furthermore, IEEE TRANSACTIONS ON COMPONENTS, PACKAGING AND MANUFACTURING TECHNOLOGY, VOL. 13, NO. 2, FEBRUARY 2023, describes the relationship between the thickness of the bonding layer and reliability, and discloses that a thicker bonding layer is advantageous from the perspective of stress relaxation. Based on this publicly known information, it is desirable that the thickness of the bonding layer exceed 20 μm.

[0008] On the other hand, as a result of further intensive research, the present inventors have newly discovered that when a silver oxide paste containing flake-shaped silver oxide particles (hereinafter simply referred to as flake-shaped silver oxide particles) having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm is used, shrinkage during drying and sintering is large, and the thickness of the bonding layer may become 20 μm or less.

[0009] The first disclosure of the present invention aims to provide a silver oxide paste that can obtain good bonding strength even when bonding at low temperatures and can achieve a bonding layer thickness of more than 20 μm.

[0010] Furthermore, as a result of intensive research by the present inventors, it was newly discovered that when a silver oxide paste containing flake-shaped silver oxide particles is used, slight air bubbles can be seen on the printed surface after screen printing before drying, depending on the equipment used and manufacturing conditions, and if the screen printing is carried out with these air bubbles or traces of degassing of the air bubbles still present, they may remain as linear marks (linear marks) on the printed surface after drying. If the above-mentioned air bubbles, degassing traces, or linear marks are present on the printed surface, they may be one of the causes of voids or cracks in the bonding layer, which may result in adverse effects on the bonding strength, thermal conductivity, and bonding reliability, and therefore it is desirable to improve this.

[0011] The second disclosure of the present invention aims to provide a silver oxide paste that can suppress the occurrence of linear scratches caused by air bubbles on the printed surface after screen printing while maintaining good bonding strength.

[0012] The present inventors have discovered that by using specific silver-containing particles together with flake-shaped silver oxide particles, it is possible to provide a silver oxide paste that can obtain good bonding strength even at low temperatures and achieve a bonding layer thickness of more than 20 μm, and have completed the first disclosure.

[0013] The present inventors further discovered that, for a silver oxide paste containing flake-shaped silver oxide particles and a dispersion medium, if the loss tangent tanδ measured by a predetermined method is 0.19 or more, it is possible to suppress the occurrence of linear scratches due to air bubbles on the printed surface after screen printing while maintaining good bonding strength, and thus completed a second disclosure.

[0014] The disclosures of the present invention (hereinafter sometimes referred to as "the present disclosure") are as follows.

[0015] The present disclosure (1) relates to a silver oxide paste comprising: flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm; and silver-containing particles having an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less.

[0016] The present disclosure (2) relates to a silver oxide paste comprising flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm, and a dispersion medium, wherein the silver oxide paste has a loss tangent tanδ of 0.19 or more at an angular frequency of 0.1 rad / s, as obtained by frequency dispersion measurement at a measurement temperature of 25°C.

[0017] The present disclosure (3) relates to the silver oxide paste according to the present disclosure (2), further comprising silver-containing particles.

[0018] The present disclosure (4) relates to the silver oxide paste according to any one of the present disclosures (1) to (3), wherein the aspect ratio of the flake-shaped silver oxide particles is 8.0 or more.

[0019] The present disclosure (5) relates to the silver oxide paste according to any one of the present disclosures (1) to (4), wherein the flake-shaped silver oxide particles have an average major axis of 300 to 1000 nm.

[0020] The present disclosure (6) relates to the silver oxide paste according to any one of the present disclosures (1) to (5), wherein in the X-ray diffraction spectrum of the flake-shaped silver oxide particles, the half-width of the diffraction peak derived from the (111) plane is 0.80 or more.

[0021] The present disclosure (7) relates to the silver oxide paste according to any one of the present disclosures (1) to (6), wherein the silver-containing particles are silver oxide particles and / or silver particles.

[0022] The present disclosure (8) relates to the silver oxide paste according to any one of the present disclosures (1) to (7), wherein the content of the silver-containing particles is 5 to 120 parts by mass per 100 parts by mass of the flake-shaped silver oxide particles.

[0023] The present disclosure (9) relates to the silver oxide paste according to any one of the present disclosures (1) to (8), further comprising a dispersant.

[0024] The present disclosure (10) relates to the silver oxide paste according to the present disclosure (9), wherein the dispersant is a compound having a glycol ether skeleton in the main chain and / or side chain.

[0025] The present disclosure (11) relates to the silver oxide paste according to any one of the present disclosures (1) to (10), further comprising a dispersion medium.

[0026] The present disclosure (12) relates to the silver oxide paste according to any one of the present disclosures (2) to (11), wherein the dispersion medium has a boiling point of 180°C or higher.

[0027] The present disclosure (13) relates to the silver oxide paste according to any one of the present disclosures (2) to (12), wherein the dispersion medium is a compound having an ethylene-based or propylene-based glycol ether skeleton.

[0028] The present disclosure (14) relates to the silver oxide paste according to any one of the present disclosures (2) to (13), wherein the dispersion medium is at least one selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, methyl carbitol, ethyl carbitol, isopropyl carbitol, butyl carbitol, isobutyl carbitol, hexyl carbitol, methyl triglycol, ethyl triglycol, butyl triglycol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether.

[0029] The present disclosure (15) relates to the silver oxide paste according to any one of the present disclosures (1) to (14), further comprising a proton-based additive.

[0030] The present disclosure (16) relates to a silver oxide paste according to any one of the present disclosures (2) to (15), in which the number of linear scratches measured by the following method is 20 or less. <Method for measuring the number of linear scratches> The silver oxide paste is stirred for 2 minutes using a stirring and degassing device under conditions of revolution: 2,000 rpm and rotation: 800 rpm, and the resulting paste is printed on a copper plate by screen printing (mask thickness: 80 μm, 4.6 × 4.6 mm pattern) and dried for 30 minutes at 130 °C using a hot air circulation dryer. The resulting printed surface is observed under an optical microscope (magnification: 35x), and linear scratches of 0.1 mm or more are counted. Evaluation is performed on eight printing patterns (n ​​number = 8), and the average number of linear scratches is calculated.

[0031] The present disclosure (17) relates to the silver oxide paste according to any one of the present disclosures (1) to (16), which is used for joining purposes.

[0032] The present disclosure (18) relates to a method for manufacturing a semiconductor device, comprising: (1) a step of applying the silver oxide paste according to any one of the present disclosures (1) to (17) onto a first substrate to form a bonding layer derived from the silver oxide paste; (2) a step of placing a second substrate on the bonding layer to form a laminate; and (3) a step of heating the obtained laminate to integrate it.

[0033] The present disclosure (19) relates to the method for manufacturing a semiconductor device according to the present disclosure (18), further comprising a step (1a) of drying the bonding layer between the step (1) and the step (2).

[0034] The present disclosure (20) relates to the method for manufacturing a semiconductor device according to the present disclosure (19), wherein the step (2) further includes a step (2a) of placing a second substrate on the bonding layer, and a step (2b) of temporarily bonding the second substrate to the first substrate via the bonding layer.

[0035] The present disclosure (21) relates to the method for manufacturing a semiconductor device according to any one of the present disclosures (18) to (20), wherein the heating temperature in the step (3) is 300° C. or less.

[0036] The present disclosure (22) relates to the method for manufacturing a semiconductor device according to any one of the present disclosures (18) to (21), wherein the step (3) further includes a step of pressurizing the laminate at 0 to 30 MPa, and the heating in the step (3) is heating the laminate while applying pressure.

[0037] The present disclosure (23) relates to a method for manufacturing a semiconductor device according to any one of the present disclosures (18) to (22), wherein the second substrate is a semiconductor chip.

[0038] The first aspect of the present invention provides a silver oxide paste that can achieve good bonding strength even at low temperatures and a bonding layer thickness of more than 20 μm. The second aspect of the present invention provides a silver oxide paste that can suppress the formation of linear scratches due to air bubbles on the printed surface after screen printing while maintaining good bonding strength.

[0039] 1 is a diagram showing an example of a method for bonding power semiconductors using a silver oxide paste according to the present disclosure; FIG. 2 is an electron microscope photograph used when measuring (a) the average major axis and (b) the average thickness of flake-shaped silver oxide particles; FIG. 3 is a photograph, in lieu of a drawing, of raw material silver oxide particles (before dispersion treatment) used in Reference Comparative Examples 2 to 5; FIG. 4 is a photograph, in lieu of a drawing, showing the cross section of the bonding layer of Reference Example 3 (a) and Reference Comparative Example 6 (b); FIG. 5 is a photograph, in lieu of a drawing, showing the cross section of the bonding layer of Reference Example 3; and FIG. 6 is a photograph, in lieu of a drawing, showing an SEM image of the film surface after sintering of a material in which each metal component is mixed.

[0040] The first disclosure (First Present Disclosure) and second disclosure (Second Present Disclosure) of the present invention will be described in detail below, but the description of the constituent elements described below is an example of an embodiment of the present disclosure and is not limited to these specific contents. Various modifications can be made within the scope of the gist. Furthermore, in the following specification, when simply referring to "the present disclosure," it is intended to mean matters common to the first and second present disclosures.

[0041] In this specification, the expression "X to Y" in the description of a numerical range means X or more and Y or less, unless otherwise specified. For example, "1 to 5 mass %" means "1 mass % or more and 5 mass % or less." Furthermore, in this specification, the term "metal component" refers to a solid metal regardless of shape. Note that, depending on the type of metal component (for example, when the metal component is silver oxide particles or silver-containing particles having a flake shape as disclosed herein), sintering may occur in step (3) of the present disclosure, but such solids whose original shape becomes unrecognizable as a result of use in the process of the present disclosure are also included in the metal component.

[0042] The silver oxide paste of the first present disclosure comprises flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm, and silver-containing particles having an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less. This allows for good bonding strength even at low temperatures (e.g., 250°C) and enables a bonding layer thickness of more than 20 μm to be achieved.

[0043] While the reason why the above-described effects are achieved in the first disclosure is not entirely clear, it is believed to be due to the following mechanism. The present inventors conducted extensive research into the cause of increased shrinkage during drying and sintering when using a silver oxide paste containing flake-shaped silver oxide particles, and as a result, they discovered the following: Due to the flake structure of the silver oxide particles, when the silver oxide paste is printed, the flake-shaped silver oxide particles are oriented in the silver oxide paste, forming a mille-feuille structure in which the flake-shaped silver oxide particles are stacked. This is believed to result in increased shrinkage in the thickness direction when the silver oxide paste is dried and sintered, resulting in a thinner bonding layer compared to general particulate materials. Therefore, as a countermeasure against shrinkage in the thickness direction, they attempted to add a metal component with an aspect ratio of a specific value or less. They found that the presence of a metal component with an aspect ratio of a specific value or less between layers of flake-shaped silver oxide particles formed wedges, suppressing shrinkage in the thickness direction during drying and sintering. It has been newly discovered that metal components with an aspect ratio of a specific value or less may result in a decrease in bonding strength. After extensive investigation into this newly discovered problem, it has been found that using silver-containing particles with a D50 of a specific value or less suppresses shrinkage in the thickness direction and achieves good bonding strength. It is presumed that the aspect ratio of a specific value or less suppresses shrinkage in the thickness direction, and the silver-containing particles with a D50 of a specific value or less sufficiently promote reaction with the flake-shaped silver oxide particles, resulting in good bonding strength. Even when using only flake-shaped silver oxide particles without adding a metal component with an aspect ratio of a specific value or less as a countermeasure against shrinkage in the thickness direction, it is possible to achieve the desired bonding layer thickness by applying a thick silver oxide paste in consideration of shrinkage during drying and sintering, but this increases the amount of silver oxide paste used. In the present disclosure, the combination of flake-shaped silver oxide particles and specific silver-containing particles allows the desired bonding layer thickness to be achieved without increasing the amount of silver oxide paste used.

[0044] A second silver oxide paste of the present disclosure is a silver oxide paste comprising flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm, and a dispersion medium, wherein the silver oxide paste has a loss tangent tanδ of 0.19 or greater at an angular frequency of 0.1 rad / s, as obtained by frequency dispersion measurement at a measurement temperature of 25° C. This makes it possible to suppress the occurrence of linear scratches due to air bubbles on the printed surface after screen printing, even when flake-shaped silver oxide particles are used.

[0045] Generally, when a paste containing particles is printed, shear stress is applied, which breaks the interactions between the particles contained in the paste, increasing its fluidity. After filling a mask or applying the paste to a desired location, the interactions are restored over time, resulting in a decrease in fluidity. Furthermore, if bubbles are present on the printed surface after application, they are degassed and the degassing marks disappear before the interactions are restored. When a silver oxide paste containing flake-shaped silver oxide particles of the present disclosure is printed, the flake-shaped silver oxide particles are oriented within the printed paste, forming a mille-feuille structure in which the flake-shaped silver oxide particles are stacked. The inventors' investigations have shown that pastes containing flake-shaped silver oxide particles of the present disclosure tend to have difficulty degassing bubbles depending on the printing conditions, and also tend to have higher thixotropy than pastes using materials with non-flake-shaped particles (e.g., spherical particles). This is presumably due to some interaction between particles resulting from the mille-feuille structure, shortening the time it takes for fluidity to decrease after printing. In contrast, by making the loss tangent tanδ of the silver oxide paste 0.19 or more as measured by the above method, it is possible to weaken the interactions between the flake-shaped silver oxide particles, although the mechanism is not clear, and it is presumed that this reduces the thixotropy of the paste and makes it possible to suppress the occurrence of linear scratches caused by air bubbles on the printed surface after screen printing.

[0046] The loss tangent tanδ at an angular frequency of 0.1 rad / s measured by the above method in the silver oxide paste of the second present disclosure is preferably 0.2 or more, more preferably 0.23 or more, and even more preferably 0.25 or more. In addition, the loss tangent tanδ is preferably 1.5 or less.

[0047] The silver oxide paste of the second present disclosure preferably has 20 or fewer linear scratches measured by the following method. The number of linear scratches is more preferably 15 or fewer, even more preferably 12 or fewer, even more preferably 10 or fewer, and particularly preferably 8 or fewer. Keeping the number within the above range is advantageous because it makes it easier to suppress voids and cracks in the bonding layer after bonding. <Method for measuring the number of linear scratches> The silver oxide paste was stirred for 2 minutes using a stirring and degassing device under conditions of revolution: 2,000 rpm and rotation: 800 rpm, and the resulting paste was printed on a copper plate by screen printing (mask thickness: 80 μm, 4.6 × 4.6 mm pattern) and dried for 30 minutes at 130 ° C using a hot air circulation dryer. The resulting printed surface was observed under an optical microscope (magnification: 35x), and linear scratches of 0.1 mm or more were counted. Evaluation was performed on eight printing patterns (n ​​number = 8), and the average number of linear scratches was calculated.

[0048] In this specification, "linear marks" refers to linear marks caused by air bubbles that appear on the printed surface after printing. If there are air bubbles on the printed surface before drying, or defoaming marks that appear as the air bubbles defoam, the surface will level over time and the defoaming and defoaming marks will disappear. However, the fluidity of the paste may decrease before the defoaming marks have completely disappeared, or the dispersion medium may volatilize before the printed surface has dried and the defoaming marks have completely disappeared, leaving linear marks. Alternatively, as the defoaming marks disappear due to leveling, linear marks may appear around the locations where the defoaming marks were present. In this specification, such linear marks will be referred to as "linear marks."

[0049] The silver oxide paste of the second present disclosure preferably has a printing bubble count of 30 or less, as measured by the following method. This allows for more sufficient suppression of the number of linear scratches after printing and drying. The printing bubble count is more preferably 20 or less. <Method for Measuring the Number of Bubbles During Printing> The silver oxide paste is stirred for 2 minutes using a stirring and degassing device under conditions of revolution: 2,000 rpm and rotation: 800 rpm, and the resulting paste is printed on a copper plate by screen printing (mask thickness: 80 μm, 4.6 × 4.6 mm pattern). The resulting printed surface is observed under an optical microscope (magnification: 35x), and bubbles with a diameter of 0.2 mm or more and bubbles with a diameter of 0.05 mm or more but less than 0.2 mm are counted. Evaluation is performed on eight printing patterns (n ​​= 8), and the average number of bubbles generated is calculated.

[0050] The present disclosure will be described in detail below. (Silver oxide particles having a flake shape) In the present disclosure, "silver oxide particles having a flake shape" does not mean individual silver oxide particles having a flake shape, but rather means silver oxide particles having a flake shape as an aggregate or a group of silver oxide particles having a flake shape. The flake-shaped silver oxide particles of the present disclosure are characterized by having an average thickness (average thickness) of 1 to 100 nm and a D50 of 100 to 350 nm. Note that "silver oxide particles having a flake shape" refers to silver oxide particles that have a flake shape and have an average thickness and D50 within the above ranges. By using silver oxide particles having the above flake shape, good bonding strength can be obtained even at low temperatures.

[0051] The term "flake-shaped" refers to a non-spherical structure having at least an upper surface, a lower surface, and a thickness, with the upper and lower surfaces being substantially flat. In this case, the upper and lower surfaces may be partially uneven or deformed, and the overall structure may be a flat plate or a thin rectangular parallelepiped (thickness smaller than length). It may also refer to a flat, plate-like shape such as a flake or scale shape (flaky: "plate-like shape" as defined in JIS Z2500:2000). More specifically, a sample that can be observed from the cross-sectional direction of silver oxide particles is prepared according to the method described in the measurement of average thickness below, and the sample is observed with a scanning electron microscope. The distance between the upper and lower surfaces of the central part of a particle is defined as the particle thickness. If the length of the side intersecting the thickness direction of the particle is greater than the thickness, the particle can be determined to have a flake shape.

[0052] The average thickness of the flake-shaped silver oxide particles is set to 1 to 100 nm, which makes it possible to improve the ease of reduction at 250° C. or less and achieve a bonding strength of 30 MPa or more. The average thickness may also be set to preferably 5 to 90 nm, more preferably 10 to 50 nm, and even more preferably 15 to 40 nm.

[0053] The D50 of the flake-shaped silver oxide particles is a value indicating the median diameter (center value) when each particle is considered as a sphere. By setting the D50 to 100 to 350 nm, good bonding strength can be obtained. Furthermore, as the particle size of the silver oxide particles decreases, cracking and peeling at the bonded portion due to thermal shrinkage tend to occur more easily. Therefore, from the viewpoint of easily suppressing these problems, a diameter of 180 to 350 nm may be preferable, and a diameter of 200 to 320 nm may be more preferable. Here, cracking and peeling due to thermal shrinkage can occur during various heating processes, such as the reduction of silver oxide, drying of the silver oxide paste (hereinafter also simply referred to as paste), sintering, and bonding. A D50 of 200 nm or more is particularly preferable because it facilitates suppression of cracking and peeling even without the inclusion of components (such as plasticizers, described below) that help suppress cracking and peeling during the reduction of silver oxide or the drying of the paste.

[0054] From another perspective, the average length of the major axes of the flake-shaped silver oxide particles (average major axis) may be, for example, 300 to 1000 nm, preferably 300 to 900 nm, more preferably 300 to 700 nm, and even more preferably 400 to 700 nm. A size within the above range is suitable from the viewpoint of suppressing cracking and peeling at the joints.

[0055] From another perspective, in the X-ray diffraction spectrum of flake-shaped silver oxide particles, the half-width of the diffraction peak derived from the (111) plane of silver oxide is preferably 0.80 or more, and more preferably 0.85 or more. The upper limit is not particularly limited, but may be, for example, 1.20 or less, preferably 1.12 or less. Furthermore, the (111) plane of the silver oxide has a main peak at 32° to 33°. When the half-width is within the above range, the bonding strength tends to be improved compared to spherical silver oxide particles with a similar D50, which is preferable. This is because when the half-width is 0.80 or more, the crystallinity of the silver oxide is low, and the bonding strength of the Ag—O that constitutes the crystal is thought to be reduced, making reduction more likely to occur at lower temperatures. The decrease in crystallinity of the silver oxide is thought to be due to the milling process described below. When raw silver oxide particles are crushed, they become smaller to a certain size, but once they reach the limit, they become indestructible and undergo plastic deformation into flakes, and it is believed that this plastic deformation reduces the crystallinity.

[0056] From the viewpoint of suppressing cracking and peeling at joints, the aspect ratio of the flake-shaped silver oxide particles is preferably 8.0 or more, more preferably 8.0 to 20, and even more preferably 13 to 18. In this specification, the aspect ratio of the particles can be measured by the measurement method described in detail below.

[0057] Furthermore, it is preferable that the surfaces of at least some of the flake-shaped silver oxide particles contain a compound having a glycol ether skeleton in the main chain and / or side chain, since this facilitates reduction at low temperatures. The compound is the same compound as the dispersant described below. Furthermore, "having on the surface" refers to a state in which the compound is attached to the surface of the flake-shaped silver oxide particles by chemical bonding, physical adsorption, or the like. It is more preferable that the compound is attached to all of the flake-shaped silver oxide particles. The particle shape, D50, average thickness, average major axis, XRD half-width, and aspect ratio can be confirmed or measured by the measurement methods described in detail below.

[0058] (Method for producing flake-shaped silver oxide particles) The flake-shaped silver oxide particles of the present disclosure can be obtained, for example, by pulverizing commercially available silver oxide particles (which are generally spherical or nearly spherical and have a particle size of about 1 to 20 μm) using a bead mill as a raw material. Typically, silver oxide particles having a particle size of a microparticle or less are spherical particles obtained by precipitation from a silver salt solution, as disclosed in JP 2005-104825 A. In contrast, the silver oxide particles of the present disclosure are formed by pulverizing using a bead mill, and the particles are obtained in a flake shape.

[0059] In the grinding process using a bead mill, raw silver oxide particles (raw silver oxide particles) are introduced into a grinding chamber in the bead mill together with a dispersant and a dispersion medium that suppress particle aggregation, and the raw silver oxide particles are ground by rotating the stirring mechanism (rotor) at high speed (high peripheral speed) and causing beads, which serve as grinding media in the grinding chamber, to collide with the raw silver oxide particles.

[0060] The dispersant used is not particularly limited, and various dispersants can be used as long as they can disperse the raw silver oxide particles, the silver oxide particles being pulverized, and the flaky silver oxide particles after pulverization in the dispersion medium and do not particularly affect the physical properties of the raw silver oxide particles. Furthermore, the dispersant typically adheres to the surface of at least some of the flaky silver oxide particles and remains thereon even after the solids are separated and dried, as described below, thereby preventing the flaky silver oxide particles from agglomerating under strong forces. Examples of such dispersants include commercially available dispersants based on polyacrylates, aliphatics, polyesters, polyurethanes, and polyethers. Dispersants may be used alone or in combination of two or more.

[0061] As the dispersion medium, a medium that does not react with silver oxide (e.g., reduction reaction) is used because strong energy is applied to the raw silver oxide particles when milling with beads. Furthermore, various dispersion media can be used without particular limitations as long as they can maintain the raw silver oxide particles, the silver oxide particles during milling, and the flake-shaped silver oxide particles after milling in a dispersed state. For example, water can be used as such a dispersion medium. The dispersion media may be used alone or in combination of two or more.

[0062] The milling media (beads) used are not particularly limited, and various types of beads can be used as long as they are conventionally used in the field of bead mill milling. Examples of such beads include beads made from materials such as glass, zirconia, alumina, silica, and steel. These may be used alone or in combination of two or more types. Since bead sizes that are too large or too small tend to result in insufficient milling, it is desirable to use beads with a diameter of 0.01 to 0.5 mm. By ensuring the diameter falls within the above range, silver oxide particles having a flake shape of the desired size and shape can be obtained.

[0063] The average thickness, D50 value, average major axis, and aspect ratio of the intended flake-shaped silver oxide particles can be adjusted by appropriately adjusting the grinding time using a bead mill, the rotor circumferential speed, the bead packing ratio, and the like. The grinding time depends on the desired size of the flake-shaped silver oxide particles, but may be, for example, about 100 to 500 minutes. As the grinding time increases, the grinding progresses and the D50 value tends to decrease. Furthermore, a rotor circumferential speed of, for example, about 5 to 20 m / s is preferred, and a bead packing ratio of, for example, about 70 to 95% by volume is preferred. Those skilled in the art can set the grinding conditions appropriately by confirming the particle morphology of the flake-shaped silver oxide particles described below under these conditions. Depending on the desired size of the flake-shaped silver oxide particles, grinding may be performed in stages, using beads of different diameters and types, two or more times to gradually reduce the size. In addition, in order to prevent the bead mill device or the inside of the grinding chamber from becoming excessively hot, a known cooling mechanism or temperature control mechanism may be provided.

[0064] The amount of raw silver oxide particles to be bead milled is not particularly limited, as long as it is sufficiently pulverizable. For example, when the material to be processed supplied to the milling chamber of the bead mill device is taken as 100% by mass, it may be 2 to 60% by mass, preferably 5 to 40% by mass. The dispersion medium may be, for example, 28 to 90% by mass, preferably 60 to 88% by mass. The dispersant is not particularly limited as long as it can disperse raw silver oxide particles and flake-shaped silver oxide particles. The dispersant may be 8 to 70% by mass, preferably 15 to 60% by mass, based on the raw silver oxide particles used. On the other hand, by using a dispersant amount of 5% by mass or less based on the raw silver oxide particles used, it is possible to prepare silver oxide particles with an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less, rather than flake-shaped silver oxide particles. These silver oxide particles can be used as silver-containing particles, as described below. In this way, a slurry containing flake-shaped silver oxide particles (hereinafter, sometimes simply referred to as "slurry") is obtained, and the solid content is separated from the slurry and dried to obtain flake-shaped silver oxide particles. Furthermore, when preparing a silver oxide paste, the liquid in the slurry may be replaced without going through the step of drying the solid content to obtain the silver oxide paste described below.

[0065] The method for separating the solids is not particularly limited as long as it does not impair the various properties of the flake-shaped silver oxide particles. For example, a simple method is to separate the solids from the supernatant using a known centrifugation method. The method for drying the solids is not particularly limited as long as it does not cause reduction of silver oxide. For example, after removing the supernatant, the solids are vacuum-dried at room temperature to obtain solid flake-shaped silver oxide particles. Note that in order to purify the flake-shaped silver oxide particles or remove excess dispersant, the solids may be dispersed again in a new dispersion medium and the same procedure may be repeated. Other drying methods, such as spray drying, may also be used.

[0066] (Dispersion Medium) The silver oxide paste of the first present disclosure contains the flake-shaped silver oxide particles and the silver-containing particles, and may further contain a dispersion medium that maintains these particles in a dispersed state. The dispersion medium used in the silver oxide paste of the first present disclosure is a compound that has coatability suitable for application, has an ethylene-based or propylene-based glycol ether skeleton, and is volatilizable during the process of drying the paste or bonding. Examples of the dispersion medium include diethylene glycol methyl ether (methyl carbitol), triethylene glycol methyl ether (methoxy triglycol), diethylene glycol methyl ether (carbitol), triethylene glycol methyl ether (ethoxy glycol), ethylene glycol propyl ether (propyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether (butyl carbitol), triethylene glycol n-butyl ether (butoxy triglycol), ethylene glycol hexyl ether (hexyl cellosolve), diethylene glycol hexyl ether (hexyl carbitol), ethylene glycol n-butyl ether acetate (butyl cellosolve), and the like. Suitable examples of the propylene glycol methyl ether include propylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol diacetate, and propylene glycol phenyl ether. These may be used alone or in combination of two or more. Of these, diethylene glycol monobutyl ether is preferred.

[0067] The dispersion medium contained in the silver oxide paste of the second present disclosure is not particularly limited as long as the loss tangent tanδ of the silver oxide paste is 0.19 or higher. However, since a tendency has been observed that linear scratches are more easily suppressed when the boiling point of the dispersion medium is higher than a certain level, the boiling point is preferably 180°C or higher. The boiling point of the dispersion medium is more preferably 200°C or higher, even more preferably 210°C or higher, and particularly preferably 215°C or higher. The upper limit is not particularly limited as long as it can be removed during drying, but it may be preferably 280°C or lower, more preferably 250°C or lower. The boiling point is a value at 1 atmosphere (atmospheric pressure) and can be measured by a commonly used method.

[0068] The dispersion medium contained in the silver oxide paste of the second present disclosure can be the preferred dispersion medium described above in the first present disclosure. Preferably, it is a compound having an ethylene- or propylene-based glycol ether skeleton, more preferably diethylene glycol, triethylene glycol, tetraethylene glycol, methyl carbitol, ethyl carbitol, isopropyl carbitol, butyl carbitol, isobutyl carbitol, hexyl carbitol, methyl triglycol, ethyl triglycol, butyl triglycol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, etc. These may be used alone or in combination of two or more. More preferred are butyl carbitol, isobutyl carbitol, methyl triglycol, dipropylene glycol, ethyl carbitol, and isopropyl carbitol. Particularly preferred are butyl carbitol, isobutyl carbitol, methyl triglycol, and dipropylene glycol, and most preferably isobutyl carbitol. The silver oxide paste of the first present disclosure may contain the preferred dispersion medium of the second present disclosure.

[0069] The content of the dispersion medium in the silver oxide paste of the present disclosure is not particularly limited, but may be, for example, 8 to 30% by mass, preferably 10 to 25% by mass, and more preferably 13 to 20% by mass, based on the mass of the entire paste. When two or more types of dispersion medium are used, the above amount refers to the total amount. The same applies to other similar descriptions.

[0070] (Method for Producing Silver Oxide Paste) The silver oxide paste of the first disclosure is a paste comprising a mixture of at least the flake-shaped silver oxide particles and the silver-containing particles described below, and may additionally contain the dispersion medium described above and the dispersant described below. The silver oxide paste of the second disclosure is a paste comprising a mixture of flake-shaped silver oxide particles and a dispersion medium, and may additionally contain the silver-containing particles and the dispersant described below. The dispersion medium and the dispersant may each be used alone, or two or more types may be used in combination. As mentioned above, the dispersant used during production may adhere to the surface of the flake-shaped silver oxide particles and remain even after the solids are separated and dried. When this dispersant is a dispersant for the paste described below, a silver oxide paste may be obtained by adding a dispersion medium for the paste. Alternatively, the flake-shaped silver oxide particles obtained by drying the slurry may be mixed with silver-containing particles, a dispersion medium for the paste, and, if necessary, a dispersant for the paste, and the mixture may be stirred to obtain a uniform dispersion of the silver oxide paste.

[0071] When preparing a silver oxide paste from the slurry without a drying step, it is preferable to separate the slurry into a solids portion and a supernatant by centrifugation, remove the supernatant, and then add the dispersion medium again to the solids obtained. If silver-containing particles are used, additional silver-containing particles are added to redisperse the solids, thereby obtaining the desired silver oxide paste. If a dispersant different from that used during production is used, the desired dispersant may be added simultaneously with the dispersion medium for replacement. Alternatively, the desired silver oxide paste may be prepared by repeating the centrifugation, replacement of the dispersion medium or dispersant, and redispersion multiple times. As an example, the above procedure produces a uniformly dispersed silver oxide paste, but the silver oxide paste may be further stirred as needed.

[0072] When the slurry is dried to obtain flake-shaped silver oxide particles, at least the silver oxide particles, and if silver-containing particles are used, the silver-containing particles and a dispersion medium for the paste may be mixed and stirred to obtain a silver oxide paste as a uniform dispersion. If necessary, any dispersant, dispersion medium, etc. may be further added. The viscosity of the silver oxide paste is not particularly limited, but it is preferably adjusted so that the viscosity at 25°C and a shear speed of 10 m / sec is 5 to 25 Pa s. The viscosity of the silver oxide paste is more preferably 10 to 18 Pa s. The viscosity of the paste can be measured using a B-type viscometer.

[0073] The stirring may be carried out using a disperser or kneading device known to be used for pastes or paints under conditions that do not cause further pulverization, such as various mixers, three-roll mills, paint shakers, etc. The flake-shaped silver oxide particles and the silver-containing particles described below may be used after removing extremely large or small particles by known classification or the like.

[0074] The amount of flake-shaped silver oxide particles contained in the silver oxide paste of the present disclosure does not need to be particularly limited as long as it has suitable coatability during application, but a suitable amount is, for example, 40 to 90 mass %, preferably 50 to 85 mass %, based on the mass of the entire silver oxide paste.

[0075] (Silver-Containing Particles) The silver oxide paste of the second present disclosure may further contain silver-containing particles. The silver-containing particles are not particularly limited as long as they contain silver, and examples thereof include silver particles, silver-containing alloy particles, silver compound particles such as silver oxide and silver nitrate, and composite particles coated with silver. These may be used alone or in combination of two or more. The alloy particles may contain metals other than silver, such as copper, nickel, tin, bismuth, aluminum, and silicon. Examples of base particles for the composite particles include copper particles, nickel particles, tin particles, bismuth particles, aluminum particles, and silicon particles. A preferred embodiment of the silver oxide paste of the second present disclosure includes the silver-containing particles. This can further increase the loss tangent tanδ of the silver oxide paste and more effectively suppress linear scratches from forming on the printed surface after drying. The particle size of the silver-containing particles that may be contained in the silver oxide paste of the second present disclosure is not particularly limited, but it is preferable that the D50 be 10 μm or less. It is more preferably 5 μm or less, even more preferably 2.0 μm or less, even more preferably 1.5 μm or less, and particularly preferably 1.0 μm or less. There is no particular restriction on the lower limit of the D50, but it is, for example, 0.05 μm or more, preferably 0.1 μm or more. In this specification, the D50 of the silver-containing particles can be measured by the measurement method described in detail below.

[0076] The aspect ratio of the silver-containing particles that may be contained in the silver oxide paste of the second present disclosure is not particularly limited, but is preferably in the same range as the aspect ratio of the silver-containing particles contained in the silver oxide paste of the first present disclosure described below.

[0077] The silver oxide paste of the first present disclosure contains, in addition to the flake-shaped silver oxide particles, silver-containing particles having an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less. The silver-containing particles are not particularly limited as long as they have an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less (particles containing silver). As described in the second present disclosure, examples of the silver-containing particles include silver particles, silver-containing alloy particles, silver compound particles such as silver oxide and silver nitrate, and composite particles coated with silver. These may be used alone or in combination of two or more. The metal other than silver in the alloy particles and the base particles of the composite particles are also as described in the second present disclosure.

[0078] The aspect ratio of the silver-containing particles is 6.0 or less, preferably 5.0 or less, more preferably 4.0 or less, even more preferably 3.0 or less, and particularly preferably 2.0 or less. The lower limit is not particularly limited, but is, for example, 1.0 or more. This makes it possible to more suitably achieve a bonding layer thickness of more than 20 μm.

[0079] The D50 of the silver-containing particles is 2.0 μm or less, preferably 1.5 μm or less, more preferably 1.0 μm or less. The lower limit is not particularly limited, but is, for example, 0.05 μm or more, preferably 0.1 μm or more. This allows for both better bonding strength and thicker film thickness of the bonding layer. In this specification, the D50 of the silver-containing particles can be measured by the measurement method described in detail below.

[0080] The silver-containing particles are not particularly limited as long as they contain silver, but are preferably silver oxide particles and / or silver particles, and are more preferably silver particles because they can more efficiently achieve a bonding layer thickness of more than 20 μm relative to the amount of silver oxide paste added. Since silver particles do not generate oxygen due to the silver particles, it is presumed that they can more effectively suppress a reduction in the bonding layer thickness due to gas generation, and more preferably achieve a bonding layer thickness of more than 20 μm.

[0081] The silver-containing particles may be commercially available products or may be appropriately manufactured. The silver-containing particles may be manufactured by a known method, such as a mechanical pulverization method in which a solid raw material is pulverized to obtain the particles, or a liquid-phase synthesis method in which a fine raw material is grown in a liquid phase to obtain the particles. Furthermore, when the silver-containing particles are silver oxide particles, for example, as explained in the explanation of the method for manufacturing flake-shaped silver oxide particles, by reducing the amount of dispersant used during production, silver oxide particles having an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less can be prepared.

[0082] When using the silver-containing particles, they may be mixed into the silver oxide paste or the slurry by a known method as long as the desired silver oxide paste can be obtained. Specifically, commercially available products or prepared products may be mixed as is, or may be mixed after various pretreatments. Examples of the pretreatment include, when the raw material is a dispersion of silver-containing particles in a liquid such as a slurry, a pretreatment in which a desired dispersant or dispersion medium is supplied after drying, or a pretreatment in which the dispersant or dispersion medium is replaced with a desired one without drying. Furthermore, when the silver-containing particles are a powder raw material, a treatment in which the particles are mixed with an optional dispersant or dispersion medium before being mixed into the silver oxide paste can be used to improve dispersibility in the paste.

[0083] In the silver oxide paste of the present disclosure, the content of the silver-containing particles is preferably 5 to 120 parts by mass, more preferably 8 to 100 parts by mass, and even more preferably 10 to 60 parts by mass per 100 parts by mass of the flake-shaped silver oxide particles. This tends to result in better bonding strength even at low temperatures (e.g., 250°C), and also makes it more suitable to achieve a bonding layer thickness of more than 20 μm. From the viewpoint of more adequately suppressing linear scratches on the printed surface after screen printing, in one embodiment, the content of the silver-containing particles is preferably 5 to 100 parts by mass per 100 parts by mass of the flake-shaped silver oxide particles. It is more preferably 10 to 80 parts by mass, and even more preferably 20 to 60 parts by mass.

[0084] (Other Components) The first silver oxide paste of the present disclosure preferably contains the flake-shaped silver oxide particles, the silver-containing particles, and a compound having an ethylene- or propylene-based glycol ether skeleton as a dispersion medium that maintains these particles in a dispersed state, and further contains a compound having a glycol ether skeleton in the main chain and / or side chain as a dispersant for dispersing the particles. By forming the silver oxide paste of the present disclosure into the above composition, it is possible to obtain a paste that does not undergo a reduction reaction at room temperature and promotes the reduction of silver oxide in a temperature range of 100 to 150°C. Furthermore, since the reduction reaction does not occur at room temperature (approximately 20 to 30°C), the paste has a good pot life and can be used after storage for a certain period of time (e.g., one month or more) after preparation, rather than immediately after preparation. The second silver oxide paste of the present disclosure also preferably contains the flake-shaped silver oxide particles, the dispersion medium, and the silver-containing particles, and more preferably contains a compound having a glycol ether skeleton in the main chain and / or side chain as a dispersant for dispersing the particles.

[0085] <Dispersant> The dispersant used in the paste is preferably a compound having a glycol ether-based skeleton in the main chain and / or side chain. Various dispersants can be used without particular limitation, as long as they can maintain the flake-shaped silver oxide particles in a dispersed state in the dispersion medium. Furthermore, a dispersant may be used as needed to maintain the dispersion state of the silver-containing particles in the dispersion medium. The dispersant used in this case may be the same as or different from the dispersant used for the flake-shaped silver oxide particles, as long as it does not impair the various performance properties of the silver oxide paste. Examples of such dispersants include polymer compounds having a skeleton of styrene, maleic acid, acrylic acid, methacrylic acid, aminoethyl methacrylate, or the like in the main chain and a glycol ether-based polymer with a molecular weight of 100 or more in the side chain. These may be used alone or in combination of two or more. The upper limit of the molecular weight of the dispersant may be, for example, 100,000. The carboxyl groups of maleic acid, acrylic acid, and methacrylic acid in the main chain may form salts with an amine compound to adjust the acid value and amine value. Suitable examples of such polymer compounds include those available under the trade names BYK-190, BYK-194N, and BYK-2055 (all manufactured by BYK-Chemie).

[0086] The dispersant may be contained in an amount of, for example, 12% by mass or less relative to the mass of the entire paste. It may be used in an amount of preferably 5% by mass or less, more preferably 3.5% by mass or less. Furthermore, as long as dispersion is possible, the lower limit is not particularly limited, but may be, for example, 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more. When the dispersant content is 3.5% by mass or less relative to the mass of the entire paste, better bonding strength tends to be obtained.

[0087] <Reducing Agent> Generally, the reduction reaction of silver oxide particles proceeds as follows: (1) Reduction of silver oxide → (2) Sintering of Ag → (3) Grain growth (bonding; sintering and grain growth of Ag). Generally, silver oxide begins to decompose in the atmosphere at approximately 200°C, and heating to 300°C or higher is required for complete reduction to metallic silver. If a reducing agent is not added at low temperatures below 250°C, the reduction reaction of silver oxide ((1) → (2)) does not proceed sufficiently, and there is a risk of unreduced silver oxide remaining in the bonded layer or sintered layer obtained after the treatment for (3). Residual unreduced silver oxide may adversely affect bonding strength, thermal conductivity, and electrical conductivity. On the other hand, when a reducing agent is added, the reduction reaction (1) of silver oxide can proceed sufficiently even at the low temperature range described above. However, in systems with strong reducing properties, the reduction reaction (1) proceeds gradually even when left at room temperature. If this system is subjected to a heat treatment for a predetermined time for drying or the like, the reaction proceeds up to the step (3) of the above-mentioned (1) → (2) → (3), and it is said to be difficult to stop the reaction at the reduction reaction step.

[0088] In the invention described in Patent Document 1, a strong reducing agent such as diethylene glycol is used to obtain a bonding layer exhibiting sufficient bonding strength. However, if the coating layer after applying the paste described above is heated and dried, the reaction proceeds from (1) to (2) to (3), and even if the semiconductor chip or substrate to be bonded is then placed, the desired bonding may not be achieved. Therefore, pastes containing reducing agents have either not been heated and dried, or bonding has had to be performed in an insufficiently dried state in order to remove the dispersion medium to a degree that does not volatilize the reducing agent. The bonding layer obtained in this manner tends to have voids (gaps) in the bonding layer due to the volatilization of the dispersion medium and reducing agent that occurs during bonding, compared to when the coating layer is dried. This may adversely affect the stability of the semiconductor device during repeated use. Furthermore, if a paste contains a strong reducing agent such as diethylene glycol, reduction may progress during storage, rendering the paste unusable as a bonding material.

[0089] In one preferred embodiment of the present disclosure, it is preferable that the paste does not contain a reducing agent. "No reducing agent in the paste" means that no reducing agent is intentionally added to the paste. Even if a reducing agent is mixed in, the content of the reducing agent is 1% by mass or less, preferably 0.5% by mass or less, assuming that the mass of the entire paste is 100. The reducing agent is considered to be an organic substance having reducing properties, and in the present disclosure, is a polyhydric alcohol or an organic acid. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, glycerin, 2,5-dimethyl-2,5-hexanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, 1,2,6-hexanetriol, and 1,10-decanediol. Examples of organic acids include saturated fatty acids such as butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, and nonanedecanoic acid.

[0090] <Proton-Based Additive> Meanwhile, in the present disclosure, a silver oxide paste contains nano-sized flake-shaped silver oxide. It has been found that the flake-shaped silver oxide undergoes the following process, unlike the reduction reaction of typical silver oxide described above: (1) reduction of silver oxide → (2) precipitation of nano Ag → (3) sintering of nano Ag → (4) grain growth (bonding; Ag sintering and grain growth). The precipitation of nano Ag during reduction promotes sintering of Ag particles, resulting in high bonding strength even at low temperatures below 250°C. In one preferred embodiment of the present disclosure, a proton-based additive is preferably used instead of a known reducing agent for silver oxide. While the use of a proton-based additive facilitates the reduction reaction of silver oxide, the reduction reaction proceeds much more slowly than when using a reducing agent. Therefore, the paste can be heated and dried, and the dried bonding layer can be used to bond a chip or the like. This reduces the likelihood of voids forming in the bonding layer.

[0091] As described above, it is preferable that the paste further contains a proton-based additive. This facilitates the reduction reaction of silver oxide even without the addition of a reducing agent, thereby reducing the amount of unreduced silver oxide in the bonding layer. Even if a small amount of unreduced silver oxide is present in the bonding layer, it does not significantly affect the bonding strength, but it may have a negative effect on thermal conduction and electrical conductivity. Furthermore, since the paste can be heated and dried, the dried coating layer can be used to bond to a chip or the like, making it less likely that voids will form in the bonding layer.

[0092] An example of the reduction reaction of silver oxide when a proton-based additive is used will be described below. For example, when water is used as the proton-based additive and diethylene glycol monobutyl ether (butyl carbitol) is used as the dispersion medium, the reduction reaction of silver oxide is expected to proceed as follows. In this way, the presence of a proton-based additive such as water is expected to make the reduction reaction of silver oxide more likely to proceed.

[0093] As described above, in the present disclosure, a compound having an ethylene- or propylene-based glycol ether skeleton is preferably used as the dispersion medium used in the paste. By using a dispersion medium (a compound having an ethylene- or propylene-based glycol ether skeleton) together with a proton-based additive, the aldehyde generated from the glycol ether during the reaction is oxidized and releases electrons, which tends to cause the reduction reaction of silver oxide to proceed at a more moderate rate.

[0094] The proton-based additive is not particularly limited as long as it can release a proton, and various proton-based additives can be used. Examples of such proton-based additives include water, monohydric alcohols such as methanol and ethanol, and hydrogen peroxide solution. These may be used alone or in combination of two or more. Of these, water is preferred. The proton-based additive may be used in an amount of, for example, 0.5 to 10% by mass, preferably 1 to 7% by mass, and more preferably 3 to 6% by mass, based on the total mass of the paste.

[0095] For example, when a paste is obtained by using water as a dispersion medium in producing flake-shaped silver oxide particles, separating a slurry containing flake-shaped silver oxide particles obtained by bead milling into a solid content and a supernatant by centrifugation, removing the supernatant, and again adding a water-containing dispersion medium to the obtained solid content to disperse the solid content, the paste contains water as a proton-based additive.Furthermore, when a paste is obtained by using water as a dispersion medium in producing the above-mentioned flake-shaped silver oxide particles, separating a slurry containing flake-shaped silver oxide particles obtained by bead milling into a solid content and a supernatant by centrifugation, removing the supernatant, and again adding a dispersion medium different from that used in production to the obtained solid content to replace the dispersion medium and disperse the solid content in a dispersion medium different from that used in production, the paste also contains water as a proton-based additive because complete replacement of the dispersion medium in the original slurry is difficult. On the other hand, when flake-shaped silver oxide particles obtained by drying the slurry are mixed with the silver-containing particles, a dispersion medium, and a dispersant, and the mixture is stirred to obtain a paste as a uniform dispersion, the dispersion medium in the original slurry is removed. Therefore, if the proton-based additive is not contained in the dispersion medium or dispersant for the paste, it is preferable to add a predetermined amount of the proton-based additive.

[0096] <Other Optional Components> The paste may contain other optional components as long as they do not impair the various properties of the paste. For example, by using a known plasticizer (polyethylene glycol (PEG), dibutyl phthalate, butyl benzyl phthalate, etc.), it is possible to more easily reduce the occurrence of cracks and peeling that occur during the reduction of silver oxide or paste drying in flake-shaped silver oxide particles having a D50 of less than 200 nm. In addition to the above, various metal components other than the flake-shaped silver oxide particles and silver-containing particles described above may be contained as long as they do not impair the various properties of the paste. Examples of such metal components include copper particles, nickel particles, tin particles, bismuth particles, aluminum particles, and silicon particles. These may be used alone or in combination of two or more. In the silver oxide paste of the present disclosure, the total amount of the flake-shaped silver oxide particles and the silver-containing particles in 100% by mass of the metal component is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may even be 100% by mass.

[0097] The total amount of the flake-shaped silver oxide particles, the silver-containing particles, the dispersant, and the dispersion medium relative to the mass of the entire paste is preferably 90% by mass or more, more preferably 95% by mass or more. This tends to provide better bonding strength even at low temperatures, and to enable a bonding layer thickness of more than 20 μm. The total amount of the flake-shaped silver oxide particles, the silver-containing particles, the dispersant, the dispersion medium, and the proton-based additive relative to the mass of the entire paste is preferably 90% by mass or more, more preferably 95% by mass or more. This tends to provide better bonding strength even at low temperatures, to facilitate the reduction reaction of silver oxide, and to enable a bonding layer thickness of more than 20 μm.

[0098] (Uses of Silver Oxide Paste) The paste is suitable for use in bonding applications because it can provide good bonding strength even at low temperatures. That is, the silver oxide paste is preferably a bonding composition. One embodiment of the present disclosure is also a method of using the paste, which includes a step of bonding a first substrate and a second substrate using the paste. Another embodiment of the present disclosure is also a use of the paste for bonding a first substrate and a second substrate.

[0099] (Bonding Method Using Silver Oxide Paste, Semiconductor Device Manufacturing Method) An example of a bonding method and a semiconductor device manufacturing method using the silver oxide paste of the present disclosure is described below. As shown in FIG. 1 , the silver oxide paste of the present disclosure is applied to a first substrate (hereinafter also referred to as "substrate 1") to form a bonding layer derived from the silver oxide paste (step (1)). Then, a second substrate such as a semiconductor chip 2 is placed on the bonding layer to form a laminate (step (2)). The laminate is then heated and integrated (step (3)). This enables bonding using the silver oxide paste and further enables the manufacturing of a semiconductor device. Note that the "bonding layer" mentioned above may be derived from the applied silver oxide paste, and the component ratio of the layer immediately after application may be the same as or different from the component ratio of the layer immediately before and after the placement of the semiconductor chip 2. For example, if the flake-shaped silver oxide particles, which are components of the layer, and the silver-containing particles, if any, are not all sintered, the "bonding layer" also includes a layer in which at least a portion of the dispersion medium has evaporated, a layer after the bonding layer derived from the silver oxide paste has dried as described below (dried film 3, which will be described later, and may also be referred to as a "dried bonding layer"), a layer after a temporary bonding process before step (3) (which may also be referred to as a "temporarily bonded bonding layer"), and the like. In this specification, the term "bonding layer" refers to all of the above layers. The bonding layer becomes the bonding layer after undergoing step (3).

[0100] In addition, the present disclosure preferably further includes a step (1a) of drying the bonding layer between the steps (1) and (2). This makes it possible to reduce voids in the bonding layer. That is, it is preferable that the silver oxide paste of the present disclosure is applied to a substrate 1 to form a bonding layer derived from the silver oxide paste (step (1)), the bonding layer is dried to form a dried film 3 (step (1a)), a second substrate such as a semiconductor chip 2 is placed on the dried film 3 to form a laminate (step (2)), and then the laminate is heated to be integrated (step (3)).

[0101] In addition, in the present disclosure, the step (2) further includes a step (2a) of placing a second substrate on the bonding layer, and a step (2b) of temporarily bonding the second substrate to the first substrate via the bonding layer, specifically, after forming a dry film 3 (dried bonding layer) by drying the bonding layer in the step (1a), the second substrate is preferably placed on the dry film 3 and temporary bonding is performed in this state. The temporary bonding process described above can prevent the fixing positions of the substrates from shifting in the subsequent step (3). That is, it is preferable that the silver oxide paste of the present disclosure is applied to a substrate 1 to form a bonding layer derived from the silver oxide paste (step (1)), the bonding layer is dried to form a dry film 3 (step (1a)), a second substrate such as a semiconductor chip 2 is placed on the dry film 3 (step (2a)), the second substrate is temporarily bonded to the first substrate via the dry film 3 (step (2b)), and a laminate in which the second substrate is placed on the dry film 3 is formed (step (2)), and then the laminate is heated to be integrated (step (3)).

[0102] 1, any other substrate or a substrate to which the semiconductor chip 2 is bonded may be used as the second substrate instead of the semiconductor chip 2. Similarly, any other substrate or a substrate to which the semiconductor chip 2 is bonded may be used as the first substrate instead of the substrate 1 which is a semiconductor substrate.

[0103] (Step (1)) In step (1), the silver oxide paste of the present disclosure is applied to a first substrate to form a bonding layer derived from the silver oxide paste. Specifically, for example, the silver oxide paste of the present disclosure can be painted or coated on substrate 1 using various printing methods to form a bonding layer derived from the silver oxide paste. Suitable printing methods include screen printing, dispense coating, and applicator coating. In step (1), if the number of bubbles during printing measured by the above-mentioned method is kept to 20 or less, the occurrence of linear scratches on the printed surface after drying can be more sufficiently suppressed. Specifically, the number of bubbles can be easily suppressed by appropriately adjusting the stirring speed of the silver oxide paste before coating, the coating speed, etc. The amount of silver oxide paste used (coated) is not particularly limited and may be selected appropriately depending on the thickness of the resulting bonding layer. In the first present disclosure, the amount of the paste used may be appropriately selected so that the thickness of the resulting bonding layer exceeds 20 μm. For example, it is preferable to use an amount such that the thickness after drying is preferably more than 30 μm and not more than 100 μm, more preferably 40 μm to 60 μm. For example, when using screen printing, the thicker the mask and the more paste used, the thicker the thickness after drying tends to be. The silver oxide paste of the first present disclosure is preferable because, compared to pastes that do not contain silver-containing particles, the desired thickness can be obtained even if the mask thickness is thinned and the amount of paste used is reduced.

[0104] (Step (1a)) In step (1a), the bonding layer derived from the silver oxide paste formed in step (1) is dried to form a dried film 3 (dried bonding layer). The drying of the bonding layer derived from the silver oxide paste is not particularly limited as long as it can dry the layer, but is preferably performed by heat treatment. The temperature may be at least lower than the temperature at which bonding is completed, for example, 70 to 150°C, preferably 70 to 130°C, and more preferably 80 to 100°C. The drying time varies depending on the drying temperature used, but is generally 10 minutes to 1 hour, and may be in the range of 20 to 40 minutes. When the dried film 3 (dried bonding layer) is formed by drying the bonding layer, at least a portion of the silver oxide has been reduced to silver, and most of the dispersion medium has been removed in the dried film 3. Furthermore, some unreduced silver oxide may remain as long as it is reducible by the time bonding is completed, and some dispersion medium may remain as long as it is removable by the time bonding is completed. It has also been found that when cracks or peeling occur in the dry film 3, voids resulting from the cracks or unbonded portions resulting from the peeling tend to remain in the bonding layer after bonding. Therefore, it is preferable to suppress the occurrence of cracks or peeling in the dry film 3 in order to prevent cracks or peeling from occurring in the bonding layer.

[0105] (Step (2)) In step (2), a second substrate is placed on the bonding layer to form a laminate. The step of placing a second substrate on the bonding layer to form a laminate may be performed by any known method and is not particularly limited. Furthermore, in order to prevent unintended reduction reactions and silver grain growth before step (3) described below, step (2) is preferably performed at 150°C or less in an atmospheric environment. Furthermore, when step (1a) is performed before step (2), the temperatures of substrate 1 and dried film 3 may be above room temperature (5 to 35°C), and may be lowered to a workable temperature before step 2.

[0106] As the substrate, various substrates conventionally used when manufacturing semiconductor devices and power modules can be used. Suitable examples of such substrates include copper substrates, alumina, silicon nitride, aluminum nitride substrates, ceramic substrates, and various other heat dissipation substrates. Furthermore, when a semiconductor chip is used as the second substrate, various semiconductor chips conventionally employed can be used as the semiconductor chip. Examples of such semiconductor chips include Si semiconductor chips, SiC semiconductor chips, GaN semiconductor chips, and Ga ２ O ３ Suitable examples include semiconductor chips used in power semiconductors, and among these, SiC semiconductor chips are preferred.

[0107] The laminate refers to a state in which a bonding layer made of silver oxide paste is sandwiched between a first substrate and a second substrate (semiconductor chip 2 in FIG. 1 ). In this laminate state, the bonding layer is not necessarily a bonding layer, and each substrate may or may not be fixed to the bonding layer. The laminate may also have any layer or member between the first substrate and the bonding layer, or between the bonding layer and the second substrate. However, it is desirable that the bonding layer is in at least partial contact with the first substrate and the second substrate. The state in which the bonding layer is not a bonding layer refers to a state in which the particles break apart when the bonding layer is tested according to the method specified in JIS K 5600-5-6:1999 "General Test Methods for Paints, Section 6: Adhesion (Cross-Cut Method)," as described below. The state in which the laminate is fixed refers to a state in which the laminate can be separated by manual force or slight external force (e.g., a temporary bonded state), and the bond strength in the fixed state is not as strong as that of the actual bond described below. Furthermore, the "temporarily bonded" state specifically means a state in which particles break apart when the bonding layer is tested by the method specified in JIS K 5600-5-6:1999 "General test methods for paints, Section 6: Adhesion (cross-cut method)" as described below, and also a state in which the bonding layer corresponds to a dried film after temporary bonding as described below.

[0108] When the step (1a) has been carried out, it is preferable to further carry out the following temporary bonding treatment (steps (2a) and (2b)).

[0109] (Step (2a)) In step (2a), a second substrate is placed on the bonding layer (the dry film 3 (dried bonding layer) formed in step (1a)). In step (2a) of placing the second substrate, the position at which the second substrate is placed is not particularly limited as long as it is on the dry film 3 and is a position where the dry film 3 and the second substrate can come into contact with each other, and the second substrate can be provided at any location. For example, the second substrate may be placed on the surface of the dry film 3 formed on the first substrate 1 opposite to the first substrate 1, or the second substrate may be provided on the surface of the dry film 3 formed on the first substrate 1 that is perpendicular to the first substrate 1.

[0110] When the second substrate is a semiconductor chip, the semiconductor chip can be mounted using known devices such as a flip chip bonder, a die bonder, a chip mounter, etc. These may be used alone or in combination of two or more.

[0111] (Step (2b)) In step (2b), the second substrate is temporarily bonded to the first substrate via the bonding layer (the dry film 3 (dried bonding layer) formed in step (1a)). Specifically, in step (2a), the second substrate is placed on the bonding layer (the dry film 3 (dried bonding layer) formed in step (1a)), and then the second substrate is temporarily bonded to the first substrate via the bonding layer (the dry film 3 (dried bonding layer) formed in step (1a)). In step (2a), the second substrate is placed in contact with the dry film 3. By proceeding with the temporary bonding in this state, the second substrate is temporarily bonded to the first substrate 1 via the dry film 3.

[0112] Step (2b) (hereinafter sometimes referred to as the "temporary bonding step") is preferably a step of temporarily bonding the second substrate to the first substrate 1 via the dry film 3 by heating (preferably by applying pressure and heat) while the second substrate is in contact with the dry film 3 formed on the first substrate 1, and more preferably a step of placing the second substrate on the surface of the dry film 3 formed on the first substrate 1 opposite the first substrate 1, and then heating (preferably by applying pressure and heat) to temporarily bond the second substrate to the first substrate 1 via the bonding layer. Sintering progresses in part by heating, and this sintering fixes the second substrate to the first substrate 1 via the temporarily bonded dry film 3.

[0113] Regarding the temperature in the temporary bonding step, it is preferable to heat the first substrate 1 to a temperature of preferably 60 to 150°C, more preferably 70 to 120°C, and even more preferably 80 to 100°C, and the second substrate to a temperature of preferably 100 to 250°C, more preferably 150 to 230°C, and even more preferably 200 to 220°C. Generally, a substrate made of copper or a composite with a copper material is often used as the first substrate 1, and from the viewpoint of preventing oxidation of copper, it is preferable to set the temperature of the first substrate 1 lower than the temperature of the second substrate (e.g., a semiconductor chip).

[0114] When pressure is applied in the temporary bonding step, the second substrate is pressed toward the dry film 3. At this time, the pressure applied is not particularly limited as long as it is a pressure that does not cause visually noticeable cracks or breakage in the dry film 3. Furthermore, deformation of the dry film 3 is acceptable as long as it is a pressure that does not cause breakage in the dry film 3, such as causing the second substrate to sink into the dry film 3. The pressure in the temporary bonding step may be preferably 0.1 to 5 MPa, more preferably 1 to 3.5 MPa, and even more preferably 1.5 to 3.5 MPa. Note that the above pressure refers to a pressure applied to a member provided on the main surface of the first substrate in a direction perpendicular to the main surface of the first substrate.

[0115] The process time (pressure and heat time) in the temporary bonding step may be preferably 0.1 to 5 seconds, more preferably 0.5 to 4 seconds.

[0116] The temporary bonding step may be carried out in the atmosphere or in an inert gas atmosphere, but is preferably carried out in the atmosphere for the reason that the process is simpler.

[0117] The temporary bonding strength between the first substrate and the second substrate after the temporary bonding step is preferably 0.5 N or more, more preferably 0.8 N or more, and even more preferably 1.0 N or more, and the upper limit is not particularly limited, but is, for example, 50 N or less. The temporary bonding strength can be determined by the following procedure. (Measurement of temporary bonding strength) A substrate in which a second substrate is temporarily bonded to a first substrate is prepared, and a die shear test (shear, load cell: S50 kg, measurement range: 5 kgf, shear speed: 10 μm / s) is performed using a bond tester (DAGE4000Plus manufactured by DAGE Japan) to determine the temporary bonding strength.

[0118] (Step (3)) In step (3), the laminate is heated to be integrated. The bonding of the laminate (hereinafter sometimes referred to as "main bonding") may be performed, for example, by heating at a temperature at which the bonding layer can be sintered. The silver oxide paste of the present disclosure can be heated at, for example, 300°C or less. At this time, a step of applying pressure to shorten the distance between the first substrate 1 and the second substrate may be further included. However, for the purpose of preventing misalignment of the components of the laminate, the laminate may be heated at a predetermined temperature while being pressurized with a predetermined pressure. The pressure applied externally during bonding (bonding pressure) can be appropriately selected within the range required for the manufacture of power semiconductor devices. In particular, the silver oxide paste of the present disclosure has excellent bonding properties and can provide good bonding strength even at lower pressures and temperatures. The bonding pressure may be, for example, 0 to 30 MPa or 0 to 10 MPa, preferably approximately 0 to 5 MPa, and more preferably 0.5 to 5 MPa. The pressure referred to here refers to pressure applied from the outside. "0 MPa" means that no intentional pressure is applied from the outside, and a minimum pressure, such as that due to the weight of the laminate or a fixing tool to prevent the laminate from shifting, may be applied. When no pressure is applied (hereinafter sometimes referred to as pressureless bonding), a pressure mechanism is not required, and known heating devices (e.g., various reflow furnaces, hot plates, box-type furnaces, etc.) can be used. When pressure bonding is performed in step (3), the heating time can be shortened compared to pressureless bonding, and there is a tendency for the bonding strength to be easily improved. On the other hand, pressureless bonding is preferred from the viewpoint of preventing cracking of semiconductor chips, etc.

[0119] Furthermore, the heating temperature (bonding temperature) during bonding can be appropriately selected from the range of bonding temperatures required in the manufacture of power semiconductor devices. The bonding temperature may be, for example, 300°C or less, preferably 250°C or less, more preferably 230°C or less, and particularly preferably 210°C or less. In the present disclosure, excellent bonding strength can be obtained even in a low temperature range close to 230°C. The lower limit is not particularly limited as long as it is a temperature at which silver can be sintered, but it may be, for example, higher than the drying temperature, preferably 160°C or more, more preferably 180°C or more.

[0120] When pressureless bonding is performed in step (3), the heating temperature may be the temperature described above. The process time (heating time) in step (3) is not particularly limited as long as bonding is possible when processed at the above temperature, but is preferably 15 to 60 minutes, more preferably 30 to 60 minutes. Depending on the shape, thickness, warpage, etc. of each substrate, breakage may occur easily during the bonding process or it may be difficult to apply strong pressure. However, performing step (3) with pressureless bonding enables bonding of a wider variety of substrates. Note that, in this specification, "no pressure" and "pressureless bonding" refer to the absence of intentional manipulation, such as applying pressure to reduce the distance between the first substrate 1 and the second substrate in the thickness direction of the temporary bonding layer. However, pressure due to the weight of the first substrate 1 or the second substrate, or the attachment of a fixing jig that is not intended to apply pressure, are included in the "no pressure" state and "pressureless bonding." Furthermore, as mentioned above, even in "pressureless bonding," slight pressure may be generated due to the weight of the laminate, etc. Therefore, pressureless bonding may be bonding in which the main bonding of the first substrate 1 and the second substrate is performed at a pressure of 0.5 MPa or less. The pressure is more preferably 0.1 MPa or less, and particularly preferably 0.01 MPa or less.

[0121] The resulting bonding layer is composed of metallic silver formed by the reduction of silver oxide. Even when observing the cross section of the resulting bonding layer, the shape of each particle and the boundaries between particles are barely visible. This is thought to be because, in the case of flake-shaped silver oxide particles and silver-containing particles present in the original bonding layer, most of the silver-containing particles have sintered and grown into an integrated silver layer. By using the silver oxide paste of the first present disclosure, it is possible to achieve a thickness of more than 20 μm and a bonding strength of 30 MPa or more. It has also been found that the use of the silver oxide paste of the first present disclosure can suppress the occurrence of localized voids in the bonding layer.

[0122] Furthermore, step (2b) may be performed under conditions in which sintering partially proceeds. On the other hand, step (3) may be performed under conditions in which sintering and grain growth proceed. Therefore, step (3) is usually performed under at least higher temperature conditions than step (2b). This tends to more favorably achieve both temporary bonding strength and final bonding strength. Therefore, it is preferable that the bonding temperature for final bonding in step (3) is higher than the temperature for temporary bonding in step (2b). For the same reason, the pressure for final bonding may be higher than the pressure for temporary bonding.

[0123] Below, we will briefly explain the differences between the dry film before temporary bonding (dried bonding layer), the dry film after temporary bonding (temporarily bonded bonding layer), and the bonding layer after permanent bonding. When the dry film before temporary bonding or the dry film after temporary bonding is lightly scratched with something, the structure of the accumulated particles collapses and the individual particles break apart. On the other hand, in the bonding layer after permanent bonding, the particles are firmly bonded, so they do not break apart. Here, breaking apart of particles means that the particles flow (move).

[0124] Therefore, for example, when each layer is tested according to the method specified in JIS K 5600-5-6:1999 "General Test Methods for Paints, Section 6: Adhesion (Cross-Cut Method)," if the particles do not disintegrate, it corresponds to a bonded layer after permanent bonding. On the other hand, if the particles disintegrate when tested according to the above method, it corresponds to either a dried film before temporary bonding or a dried film after temporary bonding. Furthermore, of the dried films before temporary bonding and dried films after temporary bonding, those in which sintering has progressed in part and the second substrate is fixed to the first substrate correspond to dried films after temporary bonding, while those in which the second substrate is not fixed (e.g., those in which sintering has not progressed at all, or those in which sintering has progressed in part but the second substrate is not fixed) correspond to dried films before temporary bonding. Whether sintering has progressed in the film and whether the second substrate is fixed can be determined by direct observation with a scanning electron microscope, etc.

[0125] (Methods for measuring various properties) (1) Measurement of the average major axis of flake-shaped silver oxide particles: A paste containing only flake-shaped silver oxide particles as the metal component was prepared, and this paste was diluted 1000 times with butyl carbitol. 1 ml of the resulting diluted solution was applied to a smooth glass substrate (20 × 20 mm) by spin coating (2000 rpm) and vacuum dried at room temperature to obtain a deposit of flake-shaped silver oxide particles. Here, when the flake-shaped silver oxide particles are applied to a glass substrate or the like, they are deposited with the flat portions of the flakes oriented vertically due to their shape. Next, the deposit was observed from above using a scanning electron microscope (SU-8220 manufactured by Hitachi High-Technologies Corporation) (for example, an image similar to the electron microscope photograph in Figure 2(a) was observed), and the major axis of 20 randomly selected particles was measured. The average value obtained was calculated as the average major axis of the flake-shaped silver oxide particles. Here, the longest diagonal line when observing the particles from above is taken as the major axis of the particle. (2) Measurement of the average thickness of flake-shaped silver oxide particles: A paste containing only flake-shaped silver oxide particles as the metal component was prepared, and 1 ml of this paste was applied by screen printing to a smooth glass substrate (20 x 20 mm) and vacuum dried at room temperature to obtain a deposit of flake-shaped silver oxide particles. Next, the glass substrate was cut at a position including the formed deposit to obtain a sample that could be observed from the cross-sectional direction of the flake-shaped silver oxide particles. Next, a scanning electron microscope (SU-8220 manufactured by Hitachi High-Technologies Corporation) was used to obtain an image of the cross-section of the deposit, as shown in the electron micrograph of Figure 2(b), and the thicknesses of 20 particles randomly selected from the cross-sectional deposit were measured, and the average value was calculated from the obtained values, which was taken as the average thickness of the flake-shaped silver oxide particles. Here, the distance between the top and bottom surfaces of the central part of each particle was taken as the particle thickness.

[0126] (3) Measurement of D50 of flake-shaped silver oxide particlesThe D50 value of flake-shaped silver oxide particles means the median diameter (center value) when each particle is considered to be a sphere (based on scattering intensity in dynamic light scattering), and is a statistical value where half of all flake-shaped silver oxide particles lie above this value and the remaining half lie below this value.The D50 value of flake-shaped silver oxide particles is measured by preparing a paste containing only flake-shaped silver oxide particles as the metal component, diluting this paste 1000 times with butyl carbitol, and measuring the resulting diluted solution using a dynamic light scattering measuring instrument (Zetasizer Nano ZS, manufactured by Malvern Panalytical).

[0127] (4) Powder X-ray diffraction (XRD) measurement of flake-shaped silver oxide particles: A paste containing only flake-shaped silver oxide particles as the metal component was prepared, and the paste was centrifuged (centrifugal force 20,000 × g) to separate it into a solid fraction and a supernatant. After removing the supernatant, the resulting solid fraction was vacuum-dried at room temperature to obtain a dry powder of flake-shaped silver oxide particles according to the present disclosure. The diffraction peaks of this dry powder were measured using a powder XRD measurement device (MINIFLEX 600 manufactured by Rigaku Corporation). The data for the main peak (32°) of the (111) plane of the flake-shaped silver oxide particles were fitted to the obtained diffraction peaks using a pseudo-Voigt function to calculate the half-width.

[0128] (5) Measurement of Particle Aspect Ratio: A paste containing only flake-shaped silver oxide particles as the metal component and a paste containing only silver-containing particles as the metal component were prepared. 1 ml of each of the resulting pastes was applied by screen printing to a smooth glass substrate (20 × 20 mm) and vacuum dried at room temperature to obtain deposits of flake-shaped silver oxide particles and deposits of silver-containing particles, respectively, which were used as measurement samples. The resulting samples were embedded in a two-component curing epoxy resin, then cross-sectioned, and the particle cross-sections were exposed by ion milling. Next, the exposed particle cross-sections were observed using a scanning electron microscope (SU-8220 manufactured by Hitachi High-Technologies Corporation). The aspect ratio was calculated as the ratio (major axis / minor axis) of the longest straight line connecting the ends of the particles, defined as the major axis, to the longest straight line connecting the ends of the particles perpendicular to the major axis, defined as the minor axis. The measurement is carried out on 20 particles selected at random, and the average value is taken as the aspect ratio of each particle.

[0129] (6) Measurement of D50 of Silver-Containing Particles The D50 value of silver-containing particles means the median diameter (center value) when each particle is considered to be a sphere (volume basis in laser diffraction method, particle transmittance: reflection mode), and is a statistical value where half of the silver-containing particles are above this value and the remaining half are below this value. The D50 of the silver-containing particles is the D50 value measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300 EXII, manufactured by Microtrac-Bell Co., Ltd.) after adding 0.1 g of silver-containing particles to a glass bottle containing 5 g of isopropyl alcohol (IPA) and dispersing the particles in an ultrasonic cleaner for 5 minutes.

[0130] In the above explanation, the methods for measuring the properties of flake-shaped silver oxide particles and silver-containing particles have been described. However, the properties of particles other than flake-shaped silver oxide particles and silver-containing particles can also be measured in the same manner using a paste or the like containing only the particles as the metal component.

[0131] (7) Cross-sectional observation of the bonded structure: The bonded structure was embedded in a two-component curing epoxy resin, cut after curing, and the cut surface was optically polished to prepare a sample for observing the bonded cross-section. Next, the processed sample was subjected to cross-sectional observation using a scanning electron microscope (SU-8220 manufactured by Hitachi High-Technologies Corporation). The occurrence of cracks in the bonding layer was evaluated using ×, △, or ○, with × indicating serious cracking, △ indicating that the cracking was not serious but that it may have a negative impact on the bond strength or bond stability, and ○ indicating that no cracking occurred.

[0132] (8) Confirmation of dispersant content in flake-shaped silver oxide particles: A paste containing only flake-shaped silver oxide particles as the metal component was prepared, and the paste was centrifuged (centrifugal force 20,000 × g) to separate the solids and the supernatant. After removing the supernatant, the solids were vacuum-dried at room temperature to obtain a dry powder of flake-shaped silver oxide particles. This dry powder was analyzed using a differential thermogravimetry / differential thermal analyzer (TG-DTA; Thermoplus TG8120, manufactured by Rigaku), and the content of the dispersant used (adhered to the silver oxide) was calculated from the mass loss rate. The dispersant content of other metal components can be calculated in a similar manner. The dispersant content in the paste can then be calculated based on the content of the dispersant attached to each metal component and the amount of dispersant added separately when preparing the paste.

[0133] (9) Method for Measuring Loss Tangent tanδ of Silver Oxide Paste Rheology measurements were performed on the silver oxide paste using a rheometer (MCR92, manufactured by Anton Paar) under the following conditions to measure the loss tangent tanδ at angular frequencies of 0.1 rad / s and 0.01 rad / s. <Measurement Conditions> Measurement temperature: 25°C, Shear strain: 1%, Frequency: 0.01 to 100 [rad / s]

[0134] (10) Method for measuring the number of bubbles during printing: A silver oxide paste was stirred for 2 minutes using a stirring and degassing device under conditions of revolution: 2,000 rpm, rotation: 800 rpm, and the resulting paste was printed on a copper plate by screen printing (mask thickness: 80 μm, 4.6 × 4.6 mm pattern). The resulting printed surface was observed under an optical microscope (magnification: 35x), and bubbles with a diameter of 0.2 mm or more and bubbles with a diameter of 0.05 mm or more but less than 0.2 mm were counted. Evaluation was performed at eight printing patterns (n ​​= 8), and the average number of bubbles generated was calculated.

[0135] (11) Method for measuring the number of linear scratches: Using a stirring and degassing device, the silver oxide paste was stirred for 2 minutes under conditions of revolution: 2,000 rpm, rotation: 800 rpm, and the resulting paste was printed on a copper plate by screen printing (mask thickness: 80 μm, 4.6 × 4.6 mm pattern) and dried for 30 minutes at 130 ° C. using a hot air circulation dryer. The printed surface obtained in this way was observed under an optical microscope (magnification: 35 times), and linear scratches of 0.1 mm or more were counted. Evaluation was performed on 8 printing patterns (n ​​number = 8), and the average number of linear scratches was calculated.

[0136] The present disclosure will be described in further detail below with reference to examples and comparative examples, but the scope of the present disclosure is not limited by these examples and comparative examples. The following measured values ​​were obtained by the respective measurement methods described above.

[0137] <Examples and Comparative Examples of the Prior Application> In order to demonstrate that flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm can provide good bonding strength without causing cracks or peeling due to thermal shrinkage, examples and comparative examples of Japanese Patent Application No. 2023-175174, which has already been filed, will be shown as a Reference Example and a Reference Comparative Example, respectively, before presenting the Examples and Comparative Examples of the present application.

[0138] Reference Example 1 The raw silver oxide particles used as a raw material for preparing flake-shaped silver oxide particles were micro silver oxide (Silver Oxide PS, manufactured by DOWA Electronics) (spherical in shape, particle size: 10 μm). These raw silver oxide particles and water (dispersion medium) were mixed at a mass ratio of raw silver oxide:water = 10:90, and a dispersant (DISPERBYK-190, manufactured by BYK (a compound having a glycol ether-based skeleton in the main chain and / or side chain)) was added to the raw silver oxide in an amount of 30 mass% based on the raw silver oxide. The mixture was then placed in the grinding chamber of a bead mill (Ultra Apex Mill UAM-015, manufactured by Hiroshima Metal & Machinery) and ground to obtain a slurry containing flake-shaped silver oxide particles. In this grinding process, the beads used were spherical and made of zirconia (material), with a diameter of 0.1 mm, and the grinding process time was 200 minutes.

[0139] Preparation of Silver Oxide Paste: The slurry containing flake-shaped silver oxide particles obtained in Reference Example 1 was centrifuged (centrifugal force: 20,000 × g) to separate the solids and the supernatant. The supernatant was then removed to remove excess dispersant and water. Next, butyl carbitol was added to the resulting solids as a dispersion medium, and the solids were re-dispersed. The mixture was then centrifuged (centrifugal force: 20,000 × g) to separate the solids and the supernatant. The supernatant was then removed, and the water in the dispersion was replaced with butyl carbitol. Butyl carbitol was added to the resulting solids to achieve the composition shown in Table 1 below. The mixture was stirred in a planetary centrifugal mixer without a grinding function and then dispersed in a three-roll mill to prepare a silver oxide paste containing flake-shaped silver oxide particles. The moisture content of the silver oxide paste was measured by gas chromatography. The moisture content of the silver oxide paste was 3% by mass.

[0140] Reference Example 2 A silver oxide paste was prepared in the same manner as in Reference Example 1, except that in the production of a slurry containing flake-shaped silver oxide particles, a dispersant (DISPERBYK-190 manufactured by BYK) was added in an amount of 20% by mass relative to the raw silver oxide, and the grinding time was set to 300 minutes. Reference Example 3 A silver oxide paste was prepared in the same manner as in Reference Example 2, except that in the production of a slurry containing flake-shaped silver oxide particles, raw silver oxide and water (dispersion medium) were mixed in a raw silver oxide:water ratio of 40:60 (by mass), and the grinding time was set to 315 minutes. Reference Example 4 A slurry containing flake-shaped silver oxide particles was obtained in the same manner as in Reference Example 2. Next, a silver oxide paste was prepared in the same manner as in Reference Example 1, except that when butyl carbitol was blended with the solid content obtained by centrifugation and solvent substitution, a dispersant was added so that the dispersant content in the paste was 4% by mass.

[0141] Reference Example 5 A silver oxide paste was prepared in the same manner as in Reference Example 4, except that in the production of a slurry containing flake-shaped silver oxide particles, a dispersant was added so that the amount of dispersant in the paste was 11 mass %.

[0142] Reference Example 6: A slurry containing flake-shaped silver oxide particles was prepared in the same manner as in Reference Example 2. The resulting slurry was then placed in a spray dryer (Mini Spray Dryer S-300, manufactured by Nippon Buchi Co., Ltd.), and the dispersion medium was evaporated by heating to obtain a dry powder containing flake-shaped silver oxide particles. Butyl carbitol was then blended with the resulting dry powder to achieve the composition shown in Table 1 below. The mixture was stirred using a planetary centrifugal mixer without a grinding function, and then dispersed using a three-roll mill to prepare a silver oxide paste. Gas chromatography analysis of the resulting silver oxide paste revealed no moisture content in the silver oxide paste. Reference Example 7: A silver oxide paste was prepared in the same manner as Reference Example 6, except that water was blended with butyl carbitol in addition to the resulting dry powder to achieve the composition shown in Table 1 below. Gas chromatography analysis of the resulting silver oxide paste revealed that the moisture content in the silver oxide paste was 2% by mass. (Reference Example 8) A silver oxide paste was prepared in the same manner as in Reference Example 7, except that in the production of a slurry containing flake-shaped silver oxide particles, butyl carbitol and water were blended so that the water content in the paste was 3.5% by mass. (Reference Example 9) A silver oxide paste was prepared in the same manner as in Reference Example 8, except that in the production of a slurry containing flake-shaped silver oxide particles, butyl carbitol and water were blended so that the water content in the paste was 5% by mass. (Reference Example 10) A silver oxide paste was prepared in the same manner as in Reference Example 8, except that in the production of a slurry containing flake-shaped silver oxide particles, butyl carbitol and water were blended so that the water content in the paste was 7% by mass.

[0143] (Reference Example 11) A silver oxide paste was prepared in the same manner as in Reference Example 2, except that in the production of a slurry containing flake-shaped silver oxide particles, a dispersant (DISPERBYK-190 manufactured by BYK) was added in an amount of 20 mass% relative to the raw silver oxide, and the grinding time was set to 360 minutes. (Reference Example 12) A silver oxide paste was prepared in the same manner as in Reference Example 1, except that in the production of a slurry containing flake-shaped silver oxide particles, a dispersant manufactured by BYK (a compound having a glycol ether-based skeleton in the main chain and / or side chain) was used, and the grinding time was set to 270 minutes. (Reference Example 13) A silver oxide paste was prepared in the same manner as in Reference Example 1, except that in the production of a slurry containing flake-shaped silver oxide particles, a dispersant manufactured by BYK (a compound having a glycol ether-based skeleton in the main chain and / or side chain) was used, and the grinding time was set to 160 minutes.

[0144] Reference Example 14 The silver oxide particles used as a raw material for preparing flake-shaped silver oxide particles were micro silver oxide (Silver Oxide PS, manufactured by DOWA Electronics) (spherical in shape, particle size: 10 μm). These raw silver oxide particles and water (dispersion liquid) were mixed at a mass ratio of raw silver oxide:water = 10:90, and a dispersant (DISPERBYK-190, manufactured by BYK-Chemie) was added to the mixture so that the mass ratio was 30% relative to the raw silver oxide. The mixture was then placed in the grinding chamber of a bead mill (Ultra Apex Mill UAM-015, manufactured by Hiroshima Metal & Machinery). The grinding process was carried out twice to obtain a slurry containing flake-shaped silver oxide powder. The processing conditions were as follows: In the first grinding process, the beads were spherical and made of zirconia (material), with a diameter of 0.1 mm, and the grinding process time was 360 minutes. In the second crushing treatment, the beads were spherical and made of zirconia (material), with a diameter of 0.05 mm, and the crushing treatment time was 30 minutes.

[0145] Preparation of Silver Oxide Paste: The slurry containing flake-shaped silver oxide particles obtained in Reference Example 14 was centrifuged (centrifugal force 20,000 × g) to separate the solids and the supernatant, and the supernatant was removed to remove excess dispersant and water. Next, butyl carbitol was added as a dispersion medium to the obtained solids, and the solids were re-dispersed. Then, the mixture was centrifuged (centrifugal force 20,000 × g) to separate the solids and the supernatant, and the supernatant was removed. The water in the dispersion was replaced with butyl carbitol. The obtained solids were blended with butyl carbitol and polyethylene glycol (PEG 400) as a plasticizer to obtain the composition shown in Table 1 below. The mixture was stirred in a planetary centrifugal mixer and then dispersed in a three-roll mill to prepare a silver oxide paste containing flake-shaped silver oxide particles.

[0146] (Reference Example 15) In the production of a slurry containing flake-shaped silver oxide particles, a dispersant (DISPERBYK-190 manufactured by BYK) was added in an amount of 50 mass% relative to the raw silver oxide, and the grinding time for the second grinding treatment was set to 150 minutes. (Reference Example 16) - Preparation of flake-shaped silver oxide particles In the production of a slurry containing flake-shaped silver oxide particles, a slurry containing flake-shaped silver oxide particles was obtained in the same manner as in Reference Example 2. - Preparation of silver oxide paste The slurry containing flake-shaped silver oxide particles obtained in Reference Example 16 was centrifuged (centrifugal force 20,000 × g) to separate it into a solid content and a supernatant, and the supernatant was removed to remove excess dispersant and water. Next, butyl carbitol was added as a dispersion medium to the obtained solids, and the solids were re-dispersed. The mixture was then centrifuged (centrifugal force: 20,000 × g) to separate the solids and the supernatant, and the supernatant was removed. The water in the dispersion was replaced with butyl carbitol. To further remove residual moisture from the obtained solids, butyl carbitol was added, the solids were re-dispersed, and the mixture was then centrifuged (centrifugal force: 20,000 × g) to separate the solids and the supernatant, and the supernatant was removed. Butyl carbitol was added to the obtained solids to obtain the composition shown in Table 1 below. The mixture was stirred in a planetary centrifugal mixer without a grinding function and then dispersed in a three-roll mill to prepare a silver oxide paste containing flake-shaped silver oxide particles. The water content of the silver oxide paste was measured by gas chromatography and found to be 1.7% by mass. (Reference Example 17) A silver oxide paste was prepared in the same manner as in Reference Example 16, except that in preparing a paste as a bonding composition, solvent substitution with butyl carbitol was repeated a total of three times for the purpose of removing residual moisture from the solid content. The moisture content in the silver oxide paste was measured by gas chromatography and was found to be 0.8% by mass.

[0147] (Reference Comparative Example 1) A silver oxide paste was prepared in the same manner as in Reference Example 1, except that in the production of a slurry containing flake-shaped silver oxide particles, a dispersant (DISPERBYK-190 manufactured by BYK-Chemie) was added in an amount of 20 mass % relative to the raw material silver oxide, and the grinding time was set to 60 minutes.

[0148] (Reference Comparative Example 2) Commercially available submicron-sized silver oxide particles (see Figure 3 for the shape) were used as the silver oxide particles. Silver oxide particles were mixed with water at a mass ratio of 10:90, and a dispersant (DISPERBYK-190 manufactured by BYK) was added to the mixture at a concentration of 30% by mass relative to the silver oxide particles. Ultrasonic treatment was then performed for 280 minutes to obtain a slurry in which the silver oxide particles were uniformly dispersed. The slurry was first centrifuged (centrifugal force: 20,000 x g) to separate the solids from the supernatant, and the supernatant was removed, thereby removing excess dispersant and water. An electron microscope photograph of the silver oxide particles contained in the slurry revealed that the initial aggregates shown in Figure 3 had only partially disintegrated, and all particles were spherical. Butyl carbitol was added as a dispersion medium to the obtained solids, and the solids were dispersed again. The solids were then centrifuged to separate the solids from the supernatant, and the supernatant was removed, thereby replacing the remaining water with butyl carbitol. Butyl carbitol was added as a dispersion medium to the obtained solids so as to obtain the composition shown in Table 1 below. The mixture was stirred with a planetary centrifugal mixer and then dispersed with a three-roll mill to prepare a paste.

[0149] (Reference Comparative Example 3) Commercially available submicron-sized silver oxide particles (see Figure 3) were used as the silver oxide particles. The silver oxide particles were mixed with water at a mass ratio of 10:90, and a dispersant (DISPERBYK-190 manufactured by BYK) was added to the mixture at a mass ratio of 30% relative to the silver oxide particles. The mixture was dispersed in a paint shaker (V-type manufactured by Asada Iron Works Co., Ltd.) for 5 minutes to partially disintegrate the aggregates of the silver oxide particles, resulting in a slurry in which the silver oxide particles were uniformly dispersed. The dispersion treatment involved the use of spherical beads made of zirconia (material) with a diameter of 0.3 mm, and the dispersion treatment time was 5 minutes. The slurry was first centrifuged (centrifugal force 20,000 x g) to separate the solids from the supernatant, and the supernatant was removed, thereby removing excess dispersant and water. When an electron microscope photograph of the silver oxide particles contained in the slurry was observed, the initial agglomeration state shown in Figure 3 had been broken down, and all spherical particles were observed. Butyl carbitol was added as a dispersion medium to the obtained solid content, and the solid content was dispersed again. The solid content was then separated from the supernatant by centrifugation, and the supernatant was removed, thereby replacing the remaining water with butyl carbitol. Butyl carbitol was added as a dispersion medium to the obtained solid content so as to obtain the composition shown in Table 1 below. The mixture was stirred in a planetary centrifugal mixer and then dispersed in a three-roll mill to prepare a paste.

[0150] (Reference Comparative Example 4) A paste was prepared in the same manner as Reference Comparative Example 3, except that in the production of a slurry containing silver oxide particles, the time for dispersion treatment in a paint shaker was changed to 15 minutes. Furthermore, when the silver oxide particles contained in the obtained slurry were observed under an electron microscope, the initial agglomerated state shown in Figure 3 had only slightly disintegrated, and all particles were observed to be spherical.

[0151] (Reference Comparative Example 5) A paste was prepared in the same manner as Reference Comparative Example 3, except that in the production of a slurry containing silver oxide particles, the time for dispersion treatment in a paint shaker was changed to 30 minutes. Furthermore, when the silver oxide particles contained in the obtained slurry were observed under an electron microscope, the initial agglomerated state shown in Figure 3 had only slightly disintegrated, and all particles were observed to be spherical.

[0152] Comparative Examples 6 and 7 Flake-shaped silver particles (average major axis: 6000 nm, average thickness: 100 nm) manufactured by Fukuda Metal Foil & Powder Co., Ltd. and butyl carbitol were mixed in a mass ratio of 90:10 to prepare a paste.

[0153] A bonding test was performed on the pastes of the Reference Example and Reference Comparative Example obtained above using the following method. As shown in FIG. 1 , a Cu substrate (with an Ag-plated outermost layer, surface dimensions of 20 × 20 mm, and thickness of 3 mm) with Ni—Ag plating was prepared. The pastes of the Reference Example and Reference Comparative Example were applied to the Ag-plated layer by screen printing, and the substrate was heated at 100°C for 30 minutes to remove the dispersion medium. No visible cracks or peeling occurred in the dried bonding layer. Next, a Si chip (with an Ag-sputtered outermost layer, surface dimensions of 3 × 3 mm, and thickness of 625 μm) was placed on the dried bonding layer so that the Ag-sputtered layer was in contact with the Si chip. Pressure (1.5 MPa) and heating (set temperature 250°C or 230°C) were applied from above for 4 minutes, and the Si chip and the Cu substrate were bonded using the bonding layer as a bonding layer.

[0154] (Cross-section observation) The bonded bodies obtained in Reference Examples 3 and 11 and Reference Comparative Examples 6 and 7 were subjected to cross-section observation by the method described above in the section "Method for measuring various properties." Cross-section photographs of Reference Example 3 and Reference Comparative Example 6 are shown in FIG. 4. Furthermore, the bonded body obtained in Reference Example 3 was subjected to cross-section observation by the method described above in the section "Method for measuring various properties." A cross-section photograph of Reference Example 3 is shown in FIG. 5.

[0155] (Bonding Strength Test) The bonded structure was subjected to a die shear test (shear, evaluation height 100 μm, shear speed 100 μm / s) using a bond tester (DAGE4000Plus manufactured by DAGE Japan) to determine the bonding strength. The bonding strength was calculated as the maximum load when the Si chip peeled off from the bonding layer.

[0156] (Post-bonding reduction property) The color of the peeled surface of the bonded body after shear peeling in the bonding strength test was visually observed. Black areas were judged to be areas where silver oxide remained and there were unreduced parts, and silvery-white areas were judged to be areas where silver oxide had been reduced to silver. The post-bonding reduction property was evaluated with x or ◯, with x being judged to be the case where even a part of the peeled surface was black, and ◯ being judged to be the case where the entire peeled surface was silvery-white.

[0157] The properties of the silver oxide particles or metallic silver particles used in the Reference Examples and Reference Comparative Examples, and the compositions of the pastes containing them, are shown in Table 1 below. Furthermore, the bonding strength, post-bonding reducibility, crack evaluation, and findings during bonding for the pastes obtained in this manner are also shown in Table 1 below. Note that the "BC content" in Table 1 refers to the content of diethylene glycol monobutyl ether.

[0158]

[0159] Table 1 shows that bonding between bonded objects using the silver oxide paste according to the Reference Examples of the present disclosure achieved excellent bonding strength of 30 MPa or more. Furthermore, cross-sectional photographs of the bonding layer revealed that no cracks occurred. On the other hand, as shown in Reference Comparative Example 1, when the pulverization time was short in the preparation of the flake-shaped silver oxide particles used, the D50 of the flake-shaped silver oxide particles increased, and the use of a paste containing such flake-shaped silver oxide particles resulted in low bonding strength. Furthermore, when bonding was performed using a paste containing spherical silver oxide particles used in Reference Comparative Examples 2 to 5, even when the D50 was within the range of the present disclosure, the bonding strength was significantly lower, at 20 MPa or less, compared to the Reference Examples of the present disclosure. Furthermore, observation of the peeled surface after the bonding strength test revealed that unreduced silver oxide remained.

[0160] In addition, Reference Example 6, which did not contain water, had high bonding strength, but some unreduced silver oxide remained on the peeled surface after the bonding strength test, resulting in low reducibility. Furthermore, as shown in Reference Comparative Examples 6 and 7, when bonding was performed using a paste containing commercially available flaky silver particles, the commercially available flaky silver particles had an average major axis of 6000 nm, which is micron-sized. As a result, local voids occurred at the bonding interface and within the bonding layer. The occurrence of local voids makes the bonding layer uneven, which tends to result in poor bonding stability. The mechanism by which these voids occurred is unknown, but it is presumed that they were due to the overlapping of large-area flaky silver particles, and that the voids could not be eliminated at temperatures as low as 250 °C.

[0161] As described above, the silver oxide paste according to the reference examples of the present disclosure is useful for bonding a semiconductor substrate and a semiconductor chip with good bonding strength.

[0162] <Examples and Comparative Examples of the Present Application> Next, examples and comparative examples of the present application are shown. Examples 1-1 to 1-8 and Examples 1-1', 1-2', and 1-4' correspond to the first disclosure of the present invention, and Examples 2-1 to 2-12 and Examples 2-3', 2-5', 2-8', and 2-11' correspond to the second disclosure of the present invention.

[0163] (Production Example 1) The raw silver oxide particles used as a raw material for preparing silver oxide particles having an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less were micro silver oxide (Silver Oxide PS, manufactured by DOWA Electronics) (spherical in shape, particle size of 10 μm). These raw silver oxide particles and water (dispersion medium) were mixed at a mass ratio of raw silver oxide:water of 55:45, and a dispersant (DISPERBYK-190, manufactured by BYK (a compound having a glycol ether skeleton in the main chain and / or side chain)) was added in an amount of 3 mass% relative to the raw silver oxide. The mixture was then placed in the milling chamber of a bead mill (Ultra Apex Mill UAM-015, manufactured by Hiroshima Metal & Machinery) and milled to obtain a slurry containing silver oxide particles having an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less. The beads used in this milling process were spherical zirconia beads with a diameter of 0.1 mm, and the milling process time was 120 minutes. The resulting silver oxide particles had a D50 of 0.3 μm and an aspect ratio of 3.1.

[0164] In the following Examples 1-1 to 1-8, Examples 1-1', 1-2', and 1-4', and Comparative Examples 1-1 to 1-6, and Comparative Examples 1-1', 1-2', 1-4', and 1-6', the flake-shaped silver oxide particles obtained in Reference Example 3 (referred to as nano silver oxide flakes in Table 2, aspect ratio: 17) were used as the flake-shaped silver oxide particles, the silver oxide particles obtained in Production Example 1 (referred to as nano silver oxide particles in Table 2) and commercially available products with the product numbers listed in Table 2 were used as the silver-containing particles, and the commercially available products with the product numbers listed in Table 2 were used as the non-silver-containing particles. In Table 2, metal components other than the nano silver oxide flakes, such as the silver-containing particles, are referred to as "added metal components," and the amount of added metal component in Table 2 means the amount added relative to the blend amount of nano silver oxide flakes.

[0165] Comparative Example 1-1: Preparation of Silver Oxide Paste: The slurry containing flake-shaped silver oxide particles obtained in Reference Example 3 was centrifuged (centrifugal force: 20,000 × g) to separate the solids and the supernatant. The supernatant was then removed to remove excess dispersant and water. Next, butyl carbitol was added as a dispersion medium to the resulting solids, and the solids were re-dispersed. The mixture was then centrifuged (centrifugal force: 20,000 × g) to separate the solids and the supernatant. The supernatant was then removed, and the water in the dispersion was replaced with butyl carbitol. Butyl carbitol was added to the resulting solids to achieve the composition of Reference Example 3 shown in Table 1. The mixture was stirred in a planetary centrifugal mixer without a grinding function and then dispersed in a three-roll mill to prepare a silver oxide paste containing flake-shaped silver oxide particles. The moisture content of the silver oxide paste was measured by gas chromatography. The moisture content of the silver oxide paste was 3% by mass. Therefore, the composition of the obtained silver oxide paste was 80% by mass of flake-shaped silver oxide particles, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0166] Example 1-1 A paste containing flaky silver oxide particles and silver oxide particles having an aspect ratio of 3.1 and a D50 of 0.3 μm was prepared in the same manner as in Comparative Example 1-1, except that the silver oxide particles produced in Production Example 1 were added as silver-containing particles in an amount of 100% by mass relative to the blending amount of flaky silver oxide particles. Gas chromatography measurement of the obtained silver oxide paste revealed that the water content in the silver oxide paste was 3% by mass. Therefore, the composition of the obtained silver oxide paste was 40% by mass of flaky silver oxide particles, 40% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0167] Example 1-2 A paste containing flake-shaped silver oxide particles and silver-containing particles was prepared in the same manner as in Comparative Example 1-1, except that 43% by mass of AgC-164H (aspect ratio: 1.1, D50: 0.5 μm) manufactured by Fukuda Metal Foil & Powder Co., Ltd. was added as silver-containing particles relative to the amount of flake-shaped silver oxide particles. Gas chromatography measurement of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 56% by mass of flake-shaped silver oxide particles, 24% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0168] Example 1-3 A paste containing flake-shaped silver oxide particles and silver-containing particles was prepared in the same manner as in Comparative Example 1-1, except that 11% by mass of AG-2-1C (aspect ratio: 1.2, D50: 0.9 μm) manufactured by DOWA Electronics was added as silver-containing particles relative to the amount of flake-shaped silver oxide particles. Gas chromatography of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 72% by mass of flake-shaped silver oxide particles, 8% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0169] Example 1-4 A paste containing flake-shaped silver oxide particles and silver-containing particles was prepared in the same manner as in Comparative Example 1-1, except that 43% by mass of AG-2-1C (aspect ratio: 1.2, D50: 0.9 μm) manufactured by DOWA Electronics was added as silver-containing particles relative to the amount of flake-shaped silver oxide particles. Gas chromatography analysis of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 56% by mass of flake-shaped silver oxide particles, 24% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0170] Example 1-5 A paste containing flake-shaped silver oxide particles and silver-containing particles was prepared in the same manner as in Comparative Example 1-1, except that 43% by mass of AgC-162IT (aspect ratio: 1.1, D50: 1.3 μm) manufactured by Fukuda Metal Foil & Powder Co., Ltd. was added as silver-containing particles relative to the amount of flake-shaped silver oxide particles. Gas chromatography of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 56% by mass of flake-shaped silver oxide particles, 24% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0171] Example 1-6 A paste containing flake-shaped silver oxide particles and silver-containing particles was prepared in the same manner as in Comparative Example 1-1, except that 43% by mass of AgC-1632T (aspect ratio: 1.2, D50: 1.8 μm) manufactured by Fukuda Metal Foil & Powder Co., Ltd. was added as silver-containing particles relative to the amount of flake-shaped silver oxide particles. Gas chromatography measurement of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 56% by mass of flake-shaped silver oxide particles, 24% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0172] Example 1-7 A paste containing flake-shaped silver oxide particles and silver oxide particles having an aspect ratio of 3.1 and a D50 of 0.3 μm was prepared in the same manner as in Comparative Example 1-1, except that 25% by mass of the silver oxide particles produced in Production Example 1 was added as silver-containing particles relative to the blending amount of flake-shaped silver oxide particles. Gas chromatography measurement of the obtained silver oxide paste revealed that the water content in the silver oxide paste was 3% by mass. Therefore, the composition of the obtained silver oxide paste was 64% by mass of flake-shaped silver oxide particles, 16% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0173] Example 1-8 A paste containing flaky silver oxide particles and silver-containing particles was prepared in the same manner as in Comparative Example 1-1, except that 100% by mass of AG-2-1C (aspect ratio: 1.2, D50: 0.9 μm) manufactured by DOWA Electronics was added as silver-containing particles relative to the amount of flaky silver oxide particles. Gas chromatography of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 40% by mass of flaky silver oxide particles, 40% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0174] Comparative Example 1-2 Silver oxide particles having an aspect ratio of 6.3 and a D50 of 0.4 μm were obtained by the same method as in Production Example 1, except that the milling treatment time was 80 minutes. Next, a paste containing flake-shaped silver oxide particles and silver oxide particles having an aspect ratio of 6.3 and a D50 of 0.4 μm was prepared by the same method as in Comparative Example 1-1, except that 100% by mass of the silver oxide particles prepared above was added as silver-containing particles relative to the amount of flake-shaped silver oxide particles. Gas chromatography analysis of the resulting silver oxide paste revealed that the water content in the silver oxide paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 40% by mass of flake-shaped silver oxide particles, 40% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0175] (Comparative Example 1-3) A paste containing flaky silver oxide particles and silver-containing particles was prepared in the same manner as in Comparative Example 1-1, except that 43% by mass of AG-5-7F (aspect ratio: 1.1, D50: 2.7 μm) manufactured by DOWA Electronics was added as silver-containing particles relative to the amount of flaky silver oxide particles. Gas chromatography measurement of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 56% by mass of flaky silver oxide particles, 24% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0176] (Comparative Example 1-4) A paste containing flake-shaped silver oxide particles and silver-containing particles was prepared in the same manner as in Comparative Example 1-1, except that 25% by mass of FA-D-6 (aspect ratio: 8.9, D50: 9.4 μm) manufactured by Dowa Electronics was added as silver-containing particles relative to the amount of flake-shaped silver oxide particles. Gas chromatography analysis of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 64% by mass of flake-shaped silver oxide particles, 16% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0177] (Comparative Example 1-5) A paste containing flake-shaped silver oxide particles and copper particles was prepared in the same manner as in Comparative Example 1-1, except that 43% by mass of HXR-CU (component: Cu, aspect ratio: 1.1, D50: 4.3 μm) manufactured by Nippon Atomize Kako was added relative to the amount of flake-shaped silver oxide particles. Gas chromatography of the resulting paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the resulting silver oxide paste was 56% by mass of flake-shaped silver oxide particles, 24% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0178] (Comparative Example 1-6) A paste containing flake-shaped silver oxide particles and nickel particles was prepared in the same manner as in Comparative Example 1-1, except that 43% by mass of NF32 (component: Ni, aspect ratio: 1.0, D50: 0.7 μm) manufactured by Toho Titanium was added relative to the amount of flake-shaped silver oxide particles. Gas chromatography measurement of the obtained paste revealed that the water content in the paste was 3% by mass. Therefore, the composition of the obtained silver oxide paste was 56% by mass of flake-shaped silver oxide particles, 24% by mass of added metal component, 3% by mass of dispersant, 14% by mass of butyl carbitol, and 3% by mass of water.

[0179] (Examples 1-1 to 1-8, Comparative Examples 1-1 to 1-6) A bonding test was performed on the pastes of Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-6 obtained above by the following method. As shown in Figure 1, a Cu substrate (the outermost layer was an Ag plating layer, the surface size was 70 × 35 mm, and the thickness was 1 mm) with Ni-Ag plating was prepared, and the pastes of Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-6 were applied to the Ag plating layer by screen printing (mask thickness: 80 μm, 4.6 × 4.6 mm pattern), heated at 100 °C for 30 minutes, the dispersion medium was removed, and a dried bonding layer was obtained. Next, a Si chip (the outermost layer of which was an Ag sputtered film, the surface size of which was 4 × 4 mm, and the thickness of which was 625 μm) was placed on the dried bonding layer so that the Ag sputtered layer was in contact with it, and pressure (10 MPa) and heating (set temperature 250°C) were applied from above for 3 minutes, thereby bonding the Si chip and the Cu substrate using the bonding layer as a bonding layer.

[0180] (Examples 1-1', 1-2', 1-4' and Comparative Examples 1-1', 1-2', 1-4', 1-6') Bonding tests were carried out in the same manner as in Examples 1-1, 1-2, 1-4 and Comparative Examples 1-1, 1-2, 1-4, 1-6 above, except that after the Si chip was placed, a temporary bonding step was carried out under the following conditions to temporarily fix the substrate and the Si chip. Temporary Fixing Conditions Upper heater: 200°C Lower heater: 100°C Time: 3 seconds Pressure: 3 MPa The temperature of the upper heater corresponds to the Si chip temperature, and the temperature of the lower heater corresponds to the substrate temperature. The pressure (pressure) refers to the pressure applied to the Si chip provided on the main surface of the substrate in a direction perpendicular to the main surface of the substrate.

[0181] (Measurement of bonding layer thickness) Next, the three-dimensional shape of the bonded portion of the bonded sample was measured using a one-shot 3D shape measuring instrument VR-3000 manufactured by Keyence Corp. Then, the Cu substrate surface was used as the reference plane (zero point), and the thickness of the bonding layer (the length of the bonding layer present between the Cu substrate and the Si chip from the Cu substrate surface to the Si chip surface) was calculated by subtracting the thickness of the Si chip from the average height of the bonded Si chip surface.

[0182] (Bonding Strength Test) The bonded body was subjected to a die shear test (shear, evaluation height 100 μm, shear speed 100 μm / s) using a bond tester (DAGE4000Plus manufactured by DAGE Japan) to determine the bonding strength. In the test, the maximum strength when the Si chip completely broke was calculated as the bonding strength.

[0183] The measured thickness and bonding strength of the bonding layer, along with the characteristics of the particles (referred to as added metal components in Table 2) used in Examples 1-1 to 1-8, Examples 1-1', 1-2', and 1-4', and Comparative Examples 1-1 to 1-6, and Comparative Examples 1-1', 1-2', 1-4', and 1-6', are shown in Table 2 below.

[0184]

[0185] From Table 2, it can be seen that, from the viewpoint of suppressing shrinkage in the thickness of the bonding layer, it is possible to increase the thickness by adding a metal component having a specific aspect ratio, regardless of the composition of the added metal component, and it was confirmed that a bonding layer thickness exceeding the target 20 μm can be achieved.

[0186] On the other hand, in terms of bonding strength as a sintering material (bonding material), high bonding strength was obtained only with silver-containing particles with small particle diameters (nanosilver oxide particles, AG-2-1C, AgC-164H, AgC-162IT, AgC-1632T), and the other particles showed very low values ​​of 10 MPa or less.

[0187] Figure 6 shows SEM images of the film surface (in the area not bonded to the Si chip) after sintering for materials containing each metal component. Note that the term "metal component" in Figure 6 refers to metal components other than the nano-silver oxide flakes. AG-2-1C, AgC-164H, AgC-162IT, and AgC-1632T, which have high bonding strength, contain silver. Because their particle sizes are very small, they sinter (react) with the silver precipitated by reduction from the nano-silver oxide flakes, even at low temperatures and short sintering times of 250°C for 180 seconds. On the other hand, other silver particles (AG-5-7F, FA-D-6), which have large particle sizes, exhibit low sintering (reactivity) and no sintering between particles. Copper and nickel particles, which have different compositions, also exhibit low reactivity and therefore no sintering with silver particles. Nickel particles NF32, despite having a particle size similar to that of AG-2-1C, did not sinter, indicating that the sintering characteristics at low temperatures such as 250°C are inherent to silver.

[0188] From Table 2, it can be seen that the silver oxide paste of the first present disclosure, which contains flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm, and silver-containing particles having an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less, provides good bonding strength even when bonding at low temperatures (e.g., 250°C), and can achieve a bonding layer thickness of more than 20 μm.

[0189] In the following Examples 2-1 to 2-12 and Comparative Examples 2-1 and 2-2, the flake-shaped silver oxide particles obtained in Reference Example 3 (referred to as nano silver oxide flakes in Table 3, aspect ratio: 17) were used as the flake-shaped silver oxide particles. In Examples 2-1 to 2-10, AG-2-1C (aspect ratio: 1.2, D50: 0.9 μm) manufactured by Dowa Electronics (referred to as Ag particles in Table 3) was used as the silver-containing particles. In Table 3, metal components other than nano silver oxide flakes, such as silver-containing particles, are referred to as "added metal components," and the amount of added metal component in Table 3 refers to the amount added relative to the blend amount of nano silver oxide flakes. The dispersion media abbreviated in Table 3 are as follows: BC: Butyl carbitol, IBC: Isobutyl carbitol, MTG: Methyl triglycol, DPG: Dipropylene glycol, EC: Ethyl carbitol, IPC: Isopropyl carbitol

[0190] Comparative Example 2-1 The slurry containing flake-shaped silver oxide particles obtained in Reference Example 3 was centrifuged (centrifugal force 20,000 × g) to separate it into a solid fraction and a supernatant, and the supernatant was removed to remove excess dispersant and water. Next, butyl carbitol was added as a dispersion medium to the obtained solid fraction, and the solid fraction was re-dispersed. Then, the mixture was centrifuged (centrifugal force 20,000 × g) to separate it into a solid fraction and a supernatant, and the supernatant was removed. Thus, the water in the dispersion was replaced with butyl carbitol. Butyl carbitol was added to the obtained solid fraction so as to obtain the composition of Reference Example 3 shown in Table 1. The mixture was stirred with a planetary centrifugal mixer without a grinding function, and then dispersed with a three-roll mill. Butyl carbitol was added so as to obtain a paste viscosity of 15-20 Pa s (shear speed 10 m / sec), thereby preparing a silver oxide paste containing flake-shaped silver oxide particles.

[0191] Examples 2-1 to 2-10 Silver oxide pastes were prepared in the same manner as in Comparative Example 2-1, except that AG-2-1C manufactured by Dowa Electronics was used as the silver-containing particles in the proportions shown in Table 3 (proportions relative to 100% by mass of flake-shaped silver oxide particles) and the type of dispersion medium was changed to a dispersion medium shown in Table 3.

[0192] Examples 2-11 and 2-12, Comparative Example 2-2 Silver oxide pastes were prepared in the same manner as in Comparative Example 2-1, except that the type of dispersion medium was changed to one shown in Table 3.

[0193] The pastes of Examples 2-1 to 2-12 and Comparative Examples 2-1 and 2-2 obtained above were measured for the number of bubbles and linear scratches during printing by the above-mentioned methods. The results are shown in Table 3.

[0194] For the pastes of Examples 2-1 to 2-12 and Comparative Examples 2-1 and 2-2 obtained above, as shown in Figure 1, a Cu substrate (the outermost layer is an Ag plating layer, the surface size is 70 x 35 mm, the thickness is 1 mm) with Ni-Ag plating applied to the surface was prepared, and the pastes of Examples 2-1 to 2-12 and Comparative Examples 2-1 and 2-2 were applied to the Ag plating layer by screen printing (mask thickness: 80 μm, 4.6 x 4.6 mm pattern), heated at 130 ° C. for 30 minutes, the dispersion medium was removed, and a dried bonding layer was obtained. Next, a Si chip (the outermost layer is an Ag sputtered film, the surface size is 3 x 3 mm, the thickness is 625 μm) was placed on the dried bonding layer so that the Ag sputtered layer was in contact with it, and pressure (10 MPa) and heating (set temperature 250 ° C.) were applied from above for 3 minutes, and the bonding layer was used as a bonding layer, and the Si chip and the Cu substrate were bonded.

[0195] (Examples 2-3', 2-5', 2-8', 2-11' and Comparative Example 2-1') Bonding tests were carried out in the same manner as in Examples 2-3, 2-5, 2-8, 2-11 and Comparative Example 2-1 above, except that after the Si chip was placed, a temporary bonding step was carried out under the following conditions to temporarily fix the substrate and the Si chip. Temporary Fixing Conditions Upper heater: 200°C Lower heater: 100°C Time: 3 seconds Pressure: 3 MPa The temperature of the upper heater corresponds to the Si chip temperature, and the temperature of the lower heater corresponds to the substrate temperature. Furthermore, the pressure (pressure) refers to the pressure applied to the Si chip provided on the main surface of the substrate in a direction perpendicular to the main surface of the substrate.

[0196] The bonded structure was subjected to a die shear test (shear, evaluation height 100 μm, shear speed 100 μm / s) using a bond tester (DAGE4000Plus manufactured by DAGE Japan) to determine the bond strength. The maximum strength at which the Si chip completely broke in the test was calculated as the bond strength. The results are shown in Table 3.

[0197]

[0198] Table 3 shows that the second silver oxide paste of the present disclosure, which contains flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm, a dispersion medium, and has a loss tangent tanδ of 0.19 or greater, can suppress the formation of linear scratches caused by air bubbles on the printed surface after screen printing while maintaining good bonding strength (20 MPa or greater).

[0199] As described above, the silver oxide paste of the present disclosure is useful for bonding a semiconductor substrate and a semiconductor chip with good bonding strength and high reliability. The silver oxide paste of the present disclosure is also useful for forming wiring.

[0200] 1. Substrate 2. Semiconductor 3. Dry film

Claims

1. A silver oxide paste comprising: flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm; and silver-containing particles having an aspect ratio of 6.0 or less and a D50 of 2.0 μm or less.

2. A silver oxide paste comprising flake-shaped silver oxide particles having an average thickness of 1 to 100 nm and a D50 of 100 to 350 nm, and a dispersion medium, wherein the silver oxide paste has a loss tangent tanδ of 0.19 or greater at an angular frequency of 0.1 rad / s, as determined by frequency dispersion measurement at a measurement temperature of 25°C.

3. The silver oxide paste of claim 2, further comprising silver-containing particles.

4. The silver oxide paste according to claim 1 or 2, wherein the aspect ratio of the flake-shaped silver oxide particles is 8.0 or more.

5. The silver oxide paste according to claim 1 or 2, wherein the flake-shaped silver oxide particles have an average major axis of 300 to 1,000 nm.

6. The silver oxide paste according to claim 1 or 2, wherein in the X-ray diffraction spectrum of the flake-shaped silver oxide particles, the half-value width of the diffraction peak derived from the (111) plane is 0.80 or more.

7. The silver oxide paste according to claim 1 or 3, wherein the silver-containing particles are silver oxide particles and / or silver particles.

8. The silver oxide paste according to claim 1 or 3, wherein the content of the silver-containing particles is 5 to 120 parts by mass per 100 parts by mass of the flake-shaped silver oxide particles.

9. The silver oxide paste according to claim 1 or 2, further comprising a dispersant.

10. The silver oxide paste according to claim 9, wherein the dispersant is a compound having a glycol ether skeleton in the main chain and / or side chain.

11. The silver oxide paste of claim 1, further comprising a dispersing medium.

12. The silver oxide paste according to claim 2 or 11, wherein the dispersing medium has a boiling point of 180°C or higher.

13. The silver oxide paste according to claim 2 or 11, wherein the dispersion medium is a compound having an ethylene-based or propylene-based glycol ether skeleton.

14. The silver oxide paste according to claim 2 or 11, wherein the dispersion medium is at least one selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, methyl carbitol, ethyl carbitol, isopropyl carbitol, butyl carbitol, isobutyl carbitol, hexyl carbitol, methyl triglycol, ethyl triglycol, butyl triglycol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether.

15. The silver oxide paste according to claim 1 or 2, further comprising a proton-based additive.

16. The silver oxide paste according to claim 2, wherein the number of linear scratches measured by the following method is 20 or less. <Method for measuring the number of linear scratches> The silver oxide paste is stirred for 2 minutes using a stirring and degassing device under conditions of revolution: 2,000 rpm and rotation: 800 rpm, and the resulting paste is printed on a copper plate by screen printing (mask thickness: 80 μm, 4.6 × 4.6 mm pattern) and dried for 30 minutes at 130°C using a hot air circulation dryer. The resulting printed surface is observed under an optical microscope (magnification: 35x), and linear scratches of 0.1 mm or more are counted. Evaluation is performed on eight printed patterns (n ​​= 8), and the average number of linear scratches is calculated.

17. The silver oxide paste according to claim 1 or 2, which is used for joining purposes.

18. A method for manufacturing a semiconductor device, comprising: (1) a step of applying the silver oxide paste according to claim 1 or 2 onto a first substrate to form a bonding layer derived from the silver oxide paste; (2) a step of placing a second substrate on the bonding layer to form a laminate; and (3) a step of heating the obtained laminate to integrate it.

19. The method for manufacturing a semiconductor device according to claim 18, further comprising a step (1a) of drying the bonding layer between the step (1) and the step (2).

20. The method for manufacturing a semiconductor device described in claim 19, wherein step (2) further includes step (2a) of placing a second substrate on the bonding layer, and step (2b) of temporarily bonding the second substrate to the first substrate via the bonding layer.

21. The method for producing a semiconductor device according to claim 18, wherein the heating temperature in step (3) is 300° C. or less.

22. The method for manufacturing a semiconductor device according to claim 18, wherein step (3) further comprises a step of pressurizing the stack at 0 to 30 MPa, and the heating in step (3) comprises heating the stack while applying pressure.

23. The method for manufacturing a semiconductor device according to claim 18, wherein the second substrate is a semiconductor chip.

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