Silver oxide particles, silver oxide powder, composition for bonding, silver oxide paste, method for producing semiconductor device using said composition for bonding or said silver oxide paste, and method for producing silver oxide particles or silver oxide powder

Abstract

The invention provides a bonding material which can obtain good bonding strength even in low-temperature bonding. Provided are silver oxide particles having a flake shape or a silver oxide powder containing the same. The average thickness of the silver oxide particles having the sheet shape is 10 to 100 nm, and the D50 is 100 to 350 nm. In addition, silver oxide particles having a flake shape or a silver oxide powder containing the same can be used as a paste for bonding a semiconductor substrate and, for example, a power semiconductor chip.

Description

Technical Field

[0001] This invention relates to silver oxide paste and a method for manufacturing semiconductor devices using the silver oxide paste. Background Technology

[0002] Power semiconductor devices have long been used in power control and motor control in automobiles, power transmission systems, railways, solar cells, and home appliances. While Si-based semiconductor devices are still the mainstream, the demand for higher current and higher voltage applications is driving research into power semiconductor devices using SiC, GaN, and other materials.

[0003] Power semiconductor devices operate at temperatures above 200°C, which is higher than the operating temperature of current mainstream Si-based semiconductor devices. Therefore, the bonding materials used in the past, such as solder alloys and epoxy-based conductive adhesives, cannot withstand these operating temperatures.

[0004] In recent years, silver-based bonding materials, such as silver oxide, have been studied as bonding materials with high-temperature durability above 200℃, low resistance, and high heat dissipation characteristics.

[0005] As a material for bonding semiconductor elements to the circuit layer in a power module, Patent Document 1 discloses that using silver oxide particles can suppress the bonding temperature on the semiconductor elements to a lower level, thereby reducing the thermal load on the semiconductor elements. Furthermore, Patent Document 1 discloses silver oxide particles ranging from 0.1 μm to 40 μm, and its embodiments demonstrate the use of micron-sized silver oxide particles. Typically, such tiny silver oxide particles are obtained by precipitation from a silver halide solution, and are generally spherical, nearly spherical, or other relatively isotropic shapes.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent document 1: Japanese Patent Application Publication No. 2014-96545. Summary of the Invention

[0009] The problem the invention aims to solve

[0010] It is known that in the bonding materials composed of spherical silver oxide particles studied above, the bonding strength is sometimes insufficient in relatively low-temperature bonding, such as around 250°C, and improvements are needed for practical application. The object of the present invention is to provide a bonding material such as silver oxide paste that can achieve good bonding strength even in low-temperature bonding.

[0011] Solution for solving the problem

[0012] The inventors focused on the nano-sizing of silver oxide particles and further discovered a bonding material that, by shaping the silver oxide particles into thin sheets, can provide good bonding strength without producing cracks or peeling caused by thermal shrinkage.

[0013] That is, one aspect of the present invention relates to thin sheet-like silver oxide particles with a thickness of nanometers or silver oxide powder containing such particles.

[0014] The present invention is as follows.

[0015] This invention (1-1) relates to silver oxide particles having a flake shape or silver oxide powder containing the same, characterized in that,

[0016] The average thickness of the aforementioned silver oxide particles with a flake shape is 1–100 nm, and the D50 is 100–350 nm.

[0017] The present invention (1-2) relates to the silver oxide particles having a flake shape or silver oxide powder containing the same as described in the present invention (1-1), wherein the average major diameter of the silver oxide particles having a flake shape is 300 to 1000 nm.

[0018] The present invention (1-3) relates to silver oxide particles having a sheet-like shape or silver oxide powder containing the sheet-like shape as described in the present invention (1-1) or (1-2), wherein, in the X-ray diffraction spectrum of the silver oxide particles having a sheet-like shape, the half-width of the diffraction peak from the (111) plane is 0.80 or more.

[0019] The present invention (1-4) relates to silver oxide particles having a flake shape or silver oxide powder containing the same as described in any one of the present invention (1-1) to (1-3), wherein at least a portion of the aforementioned silver oxide particles having a flake shape have a compound having a glycol ether backbone in the main chain and / or side chain on their surface.

[0020] The present invention (1-5) relates to a bonding composition, characterized in that it comprises:

[0021] Silver oxide particles having a flake shape or silver oxide powder containing the same as described in any one of (1-1) to (1-4) of the present invention;

[0022] Dispersants; and

[0023] Dispersion medium.

[0024] The present invention (1-6) relates to the bonding composition of the present invention (1-5), wherein the dispersant is a compound having a glycol ether backbone in the main chain and / or side chain.

[0025] The present invention (1-7) relates to the bonding composition described in (1-5) or (1-6) of the present invention, wherein the dispersion medium is a compound having an ethylene-based or propylene-based glycol ether skeleton.

[0026] The present invention (1-8) relates to a method for manufacturing silver oxide particles having a flake shape or silver oxide powder containing the same, characterized in that the method is the method for manufacturing silver oxide particles having a flake shape or silver oxide powder containing the same as described in any one of the present invention (1-1) to (1-4), wherein the silver oxide particles are bead-milled.

[0027] This invention (1-9) relates to a method for manufacturing silver oxide particles having a flake shape or silver oxide powder containing the same as described in this invention (1-8), wherein the above-mentioned bead milling and pulverization includes the following steps:

[0028] The process of supplying the aforementioned silver oxide particles, the aforementioned dispersant, and the aforementioned dispersion medium to an apparatus for bead milling; and

[0029] The process involves bead milling in the aforementioned apparatus to obtain a slurry containing silver oxide particles with a flake-like shape.

[0030] The present invention (1-10) relates to a method for manufacturing silver oxide particles having a flake shape or silver oxide powder containing the present invention (1-8) or (1-9), wherein the dispersant is a compound having a glycol ether backbone in the main chain and / or side chain.

[0031] This invention (1-11) relates to a method for manufacturing a semiconductor device, characterized by comprising the following steps:

[0032] Step (1): Apply the bonding composition of any one of (1-5) to (1-7) of the present invention onto a semiconductor substrate to form a layer of the bonding composition;

[0033] Step (2): Place a semiconductor chip on the layer of the above bonding composition to form a laminate;

[0034] Process (3): The obtained laminate is pressurized at 0-30 MPa and heated at 300°C to integrate it.

[0035] The present invention (1-12) relates to a method for manufacturing a semiconductor device according to the present invention (1-11), wherein a step of drying the layer of the bonding composition is further included between the above-mentioned step (1) and step (2).

[0036] The present invention (1-13) relates to a method for manufacturing the semiconductor device described in the present invention (1-11) or (1-12), wherein the semiconductor chip is a SiC semiconductor chip.

[0037] This invention (2-1) relates to a silver oxide paste, comprising:

[0038] Silver oxide particles with a flake-like shape;

[0039] Dispersants; and

[0040] Dispersion medium,

[0041] The average thickness of the silver oxide particles is 1–100 nm, and the D50 is 100–350 nm.

[0042] This invention (2-2) relates to the silver oxide paste described in this invention (2-1), wherein the silver oxide paste further comprises proton-based additives.

[0043] The present invention (2-3) relates to the silver oxide paste described in (2-1) or (2-2) of the present invention, wherein the dispersant is a compound having a glycol ether backbone in the main chain and / or side chain.

[0044] The present invention (2-4) relates to silver oxide paste as described in any one of the present invention (2-1) to (2-3), wherein the dispersion medium is a compound having an ethylene-based or propylene-based glycol ether skeleton.

[0045] The present invention (2-5) relates to the silver oxide paste of any one of the present invention (2-1) to (2-4), wherein the average major diameter of the silver oxide particles is 300 to 1000 nm.

[0046] The present invention (2-6) relates to the silver oxide paste described in any one of the present invention (2-1) to (2-5), wherein, in the X-ray diffraction spectrum of the above-mentioned silver oxide particles, the full width at half maximum (FWHM) of the diffraction peaks from the (111) plane is 0.80 or more.

[0047] The present invention (2-7) relates to silver oxide paste according to any one of the present invention (2-1) to (2-6), wherein the content of the above dispersant is 12% by mass or less relative to the total mass of the silver oxide paste.

[0048] This invention (2-8) relates to the silver oxide paste described in this invention (2-2), wherein the content of the above-mentioned proton-based additive is 0.5 to 10% by mass relative to the total mass of the silver oxide paste.

[0049] The present invention (2-9) relates to silver oxide paste as described in any one of the present invention (2-1) to (2-8), wherein the silver oxide paste is used for bonding purposes.

[0050] This invention (2-10) relates to a method for manufacturing a semiconductor device, comprising the following steps:

[0051] Step (1): Apply silver oxide paste as described in any one of (2-1) to (2-9) of the present invention onto a first substrate to form a layer of the silver oxide paste;

[0052] Step (2): Place a second substrate on the above silver oxide paste layer to form a laminate;

[0053] Process (3): The obtained laminate is pressurized at 0-30 MPa and heated at 300°C to integrate it.

[0054] The present invention (2-11) relates to a method for manufacturing a semiconductor device according to the present invention (2-10), wherein a step of drying the silver oxide paste layer is further included between the above-mentioned step (1) and the above-mentioned step (2).

[0055] This invention (2-12) relates to a method for manufacturing a semiconductor device as described in (2-10) or (2-11) of this invention, wherein the second substrate is a semiconductor chip.

[0056] Invention Effects

[0057] According to the present invention, bonding materials such as silver oxide paste can be provided that provide good bonding strength even in low-temperature bonding. Attached Figure Description

[0058] Figure 1 This is a diagram illustrating a bonding method for a power semiconductor using a paste containing silver oxide particles of the present invention in a sheet shape as a composition.

[0059] Figure 2 These are electron microscope images used to determine the (a) average major diameter and (b) average thickness of silver oxide particles with a flake-like shape.

[0060] Figure 3 The photographs are alternative illustrations of the raw material silver oxide particles (before dispersion treatment) used in Comparative Examples 2-5.

[0061] Figure 4 The photographs are alternative drawings showing cross-sections of the bonding layers of (a) Example 3 and (b) Comparative Example 6.

[0062] Figure 5 The photograph is a photograph showing a cross-section of the bonding layer of Embodiment 3, which is an alternative drawing. Detailed Implementation

[0063] The present invention will now be described in detail. The description of the structural elements described below is an example of an embodiment of the present invention and is not limited to these specific contents. Various modifications can be made within the scope of its spirit to implement the invention.

[0064] In this specification, unless otherwise specified, expressions such as "X~Y" in the description of numerical ranges mean X or more and Y or less. For example, "1~5% by mass" means "more than 1% by mass and less than 5% by mass".

[0065] The silver oxide paste of the present invention comprises silver oxide particles having a sheet shape, a dispersant, and a dispersion medium, wherein the average thickness of the silver oxide particles is 1 to 100 nm and the D50 is 100 to 350 nm.

[0066] Therefore, good bonding strength can be obtained even in low-temperature (e.g., 250°C) bonding.

[0067] The present invention will now be described in detail.

[0068] (Silver oxide particles or powder with a flake-like shape)

[0069] In this invention, the silver oxide particles with a flake shape constituting the silver oxide powder do not refer to individual silver oxide particles with a flake shape, but rather to a collection of silver oxide particles with a flake shape or a group of silver oxide particles with a flake shape.

[0070] The silver oxide powder of the present invention is characterized in that it comprises silver oxide particles having a flake shape, wherein the average thickness of the flake-shaped silver oxide particles is 1 to 100 nm and the D50 is 100 to 350 nm. Furthermore, "silver oxide particles having a flake shape" refers to silver oxide particles having a flake shape and showing the average thickness and D50 within the above-mentioned range.

[0071] According to the research of the inventors, by forming the silver oxide particles into the aforementioned flake-shaped silver oxide particles instead of the spherical shape that has been used in the past, good bonding strength can be obtained even at low temperatures.

[0072] Furthermore, in one aspect of the present invention, as the researchers of the present invention have shown, the smaller the particle size of silver oxide particles with a flake shape, the easier it is to be reduced in low-temperature regions below 250°C. On the other hand, the shrinkage during heating increases, making it easier to produce cracks, peeling, etc. It can be further considered that the aforementioned shrinkage also originates from the loss of oxygen caused by the reduction of silver oxide, and it is known that this tendency is more likely to occur when using silver oxide particles compared to using silver particles. Furthermore, while it becomes less prone to cracking and peeling with larger particle sizes, reduction in the aforementioned low-temperature regions becomes more difficult. One aspect of the present invention is to balance ease of reduction and suppression of cracking and peeling by making the silver oxide particles into a flake shape.

[0073] Furthermore, the silver oxide powder of the present invention may also contain silver oxide particles that are not in a flake shape, to a extent that it does not adversely affect various properties. The content of such silver oxide particles is not particularly limited; for example, it may be less than 30% by mass when the silver oxide powder is taken as 100%.

[0074] The aforementioned "sheet shape" refers to a non-spherical structure that has at least an upper surface, a lower surface, and a thickness, with the upper and lower surfaces being substantially flat. In this case, it is acceptable if the upper and lower surfaces are partially uneven or deformable, as long as it is a flat plate or a thin (thickness relatively small to length) cuboid when viewed as a whole. Alternatively, it can refer to a flat, plate-like shape, such as a sheet or scale (sheet-like: "plate-like shape" as described in JIS Z2500:2000).

[0075] More specifically, according to the method described in the measurement of average thickness described later, a sample that can be observed from the cross-sectional direction of the silver oxide particles is prepared, and the sample is observed by scanning electron microscopy. The distance between the upper and lower surfaces of the central part of a particle is taken as the thickness of the particle. If the length of the side intersecting the thickness direction of the particle is greater than the aforementioned thickness, it can be determined that the particle has a sheet-like shape.

[0076] By making the average thickness of the aforementioned silver oxide particles with a flake shape 1 to 100 nm, the ease of reduction (especially during bonding) at temperatures below 250 °C is improved, and the bonding strength is 30 MPa or higher. Furthermore, 5 to 90 nm is preferred, 10 to 50 nm is more preferred, and 15 to 40 nm is even more preferred.

[0077] The D50 of the aforementioned silver oxide particles with a flake shape represents the median particle size (median) when each particle is considered as a sphere. Good bonding strength can be obtained by setting the D50 to 100–350 nm. Furthermore, it is known that the aforementioned silver oxide particles tend to crack and peel at the joint due to thermal shrinkage as the particle size decreases. On the other hand, setting the D50 to 100–350 nm allows for both suppression of cracking and peeling at the joint and good bonding strength. From the viewpoint of more easily suppressing cracking and peeling at the joint, the D50 is preferably 180–350 nm, and more preferably 200–320 nm. Here, cracks and peeling caused by thermal shrinkage can occur in various processes involving heating, such as during the reduction of silver oxide, the drying of the silver oxide paste (hereinafter also simply referred to as paste), sintering, and bonding. Especially when D50 is above 200nm, even without the presence of components that help suppress cracks and peeling that occur during the reduction of silver oxide or the drying of the paste (such as plasticizers described later), the generation of the aforementioned cracks and peeling is easily suppressed, and therefore preferred.

[0078] From another perspective, the average length diameter (AMD) of the silver oxide particles with a flake shape can be, for example, 300–1000 nm, preferably 300–900 nm, more preferably 300–700 nm, and even more preferably 400–700 nm. If it is within the above range, it is preferred from the viewpoint of suppressing the generation of cracks and peeling at the joint.

[0079] Furthermore, from another perspective, the average length of the silver oxide particles with a sheet-like shape is preferably 300 to 1000 nm, and from the viewpoint of suppressing the generation of cracks and peeling at the joint, it is even more preferably 400 to 900 nm.

[0080] From another perspective, in the X-ray diffraction spectrum of silver oxide particles with a flake shape, the full width at half maximum (FWHM) of the diffraction peak from the (111) plane of silver oxide is preferably 0.80 or higher, more preferably 0.85 or higher. The upper limit is not particularly limited and can be, for example, 1.20 or lower, preferably 1.12 or lower. Furthermore, the (111) plane of the aforementioned silver oxide has a main peak at 32° to 33°.

[0081] When the full width at half maximum (FWHM) is within the aforementioned range, compared to spherical silver oxide particles with the same D50, there is a tendency to improve the bonding strength, which is preferable. It can be inferred that when the FWHM is above 0.80, the crystallinity of silver oxide is low, and the Ag-O bonding force constituting the crystal decreases, thus making it easier to undergo reduction at lower temperatures. It can be inferred that the decrease in the crystallinity of silver oxide is due to the pulverization process described later. It can be inferred that when the raw silver oxide particles are pulverized, although they become smaller to a certain size, they cannot be broken down further after miniaturization to the limit, thus undergoing plastic deformation into a sheet shape. It can be inferred that this plastic deformation leads to a decrease in crystallinity.

[0082] Furthermore, from the viewpoint of suppressing crack and peeling at the joint, the aspect ratio (l / t) of the average major diameter (l) to the average thickness (t) is preferably 8 to 20, and more preferably 14 to 18. This aspect ratio can also be a value calculated from the average thickness and average major diameter of the silver oxide particles having a flake shape.

[0083] Furthermore, if at least a portion of the silver oxide particles in the aforementioned silver oxide powder have a compound with a glycol ether backbone in the main chain and / or side chains, they are readily reduced at low temperatures, which is therefore preferable. This compound is the same as the dispersant in the composition described later. Furthermore, "on the surface" refers to a state where the silver oxide particles in the flake shape are attached to the surface through chemical bonds, physical adsorption, etc. More preferably, the silver oxide particles in the flake shape are attached to all the silver oxide particles constituting the silver oxide powder.

[0084] In addition, the shape of the particles, D50, average thickness, average major diameter, and half-width of the XRD can be confirmed or measured separately by the measurement methods described in detail below.

[0085] (Method for manufacturing silver oxide particles with a flake shape)

[0086] The flake-shaped silver oxide particles of the present invention can be obtained, for example, by pulverizing commercially available silver oxide particles (generally spherical or approximately spherical in shape, with a particle size of about 1 to 20 μm) using a bead mill. Typically, silver oxide particles with a particle size of less than a micrometer are spherical particles obtained by precipitation from a silver halide solution, as disclosed in Japanese Patent Application Publication No. 2005-104825. In contrast, the silver oxide particles of the present invention are formed by pulverizing using a bead mill, resulting in flake-shaped particles.

[0087] In the pulverization process using a bead mill, silver oxide particles (raw silver oxide particles) as raw material, along with a dispersant to inhibit particle aggregation and a dispersion medium, are introduced into the pulverization chamber of the bead mill. The stirring mechanism (rotor) rotates at high speed (high circumferential speed), causing the grinding beads, which serve as the pulverizing medium in the pulverization chamber, to collide with the raw silver oxide particles, thereby pulverizing them.

[0088] As for the dispersant used, there are no particular limitations as long as it can disperse the silver oxide particles as raw material, the pulverized silver oxide particles, and the pulverized silver oxide particles with a flake shape in the dispersion medium without particularly affecting the physical properties of the raw silver oxide particles. Various dispersants can be used. Furthermore, the dispersant typically adheres to the surface of at least a portion of the flake-shaped silver oxide particles and remains even after the solid components are separated and dried as described below, thus preventing strong agglomeration of the flake-shaped silver oxide particles. Commercially available dispersants such as polyacrylate-based, aliphatic-based, polyester-based, polyurethane-based, and polyether-based dispersants can be used. The dispersant can be used alone or in combination of two or more. Furthermore, compounds with a glycol ether backbone in the main chain and / or side chains, as described later, are also preferred as dispersants.

[0089] As a dispersion medium, since strong energy is applied to the raw silver oxide particles during grinding with grinding beads, a medium that does not react with silver oxide (e.g., through reduction reactions) is used. Furthermore, there are no particular limitations on the use of any medium that can maintain the raw silver oxide particles, the silver oxide particles during grinding, and the ground silver oxide particles with a flake-like shape in a dispersed state; various dispersion media can be used. Water, for example, can be used as such a dispersion medium. The dispersion medium can be used alone or in combination with two or more.

[0090] As for the grinding media (grinding beads), there are no particular restrictions on the media that have been used in the field of bead milling, and various grinding beads can be used. Such grinding beads can be made of materials such as glass, zirconium oxide, alumina, silica, and steel. These can be used alone or in combination of two or more. Since grinding beads that are too large or too small can easily lead to insufficient grinding, grinding beads with a diameter of 0.01 to 0.5 mm are preferred. By keeping the diameter of the grinding beads within the above range, it is possible to obtain thin, flake-shaped silver oxide particles with the desired size and shape.

[0091] Furthermore, the average thickness, D50 value, and average major diameter of the target flake-shaped silver oxide particles can be adjusted by appropriately regulating the grinding process time, rotor circumferential speed, and bead filling rate of the bead mill. While the processing time also depends on the desired size of the flake-shaped silver oxide powder, it can be, for example, around 100 to 500 minutes. As the processing time increases, the grinding process continues, and the D50 value tends to decrease. Additionally, the rotor circumferential speed is preferably around 5 to 20 m / s, and the bead filling rate is preferably around 70 to 95% by volume.

[0092] Anyone skilled in the art can confirm the particle morphology of the silver oxide particles with a flake shape described below under such conditions, thereby appropriately setting the conditions.

[0093] Furthermore, depending on the desired size of the silver oxide particles with a thin, flake-like shape, different grinding beads of varying diameters and types can be used to pulverize the particles in stages, reducing their size gradually, more than twice. Additionally, to prevent the grinding device and grinding chamber from becoming excessively hot, a known cooling mechanism or temperature control mechanism can be incorporated.

[0094] The amount of silver oxide particles used in the bead milling process is not particularly limited, as long as they can be sufficiently pulverized. For example, when the amount of material to be processed supplied to the milling chamber of the bead mill is 100, it can be set to 2-60% by mass, preferably 5-40% by mass. Furthermore, the dispersion medium can be, for example, 28-90% by mass, preferably 30-90% by mass, and more preferably 60-88% by mass.

[0095] Furthermore, the dispersant is not particularly limited as long as it can disperse the raw material silver oxide particles and the silver oxide particles have a flake shape. The dispersant can be 8 to 70% by mass relative to the raw material silver oxide particles used, preferably 10 to 70% by mass, and more preferably 15 to 60% by mass.

[0096] As described above, a slurry (hereinafter sometimes simply referred to as "slurry") containing silver oxide particles with a flake shape can be obtained. By separating the solid components from the slurry and drying it, silver oxide powder containing silver oxide particles with a flake shape can be obtained. Furthermore, in the case of preparing a composition for silver oxide paste (preferably a bonding composition), the liquid in the slurry can be replaced instead of drying the solid components, thereby obtaining the silver oxide paste described later.

[0097] As for the method of separating the above-mentioned solid components, there are no particular limitations as long as it does not impair the various properties of the silver oxide powder. For example, using the well-known centrifugation method to separate the solid components into a supernatant is relatively simple. When drying the solid components, there are no particular limitations as long as the reduction of silver oxide does not occur. For example, by removing the supernatant and then vacuum drying the solid components at room temperature, solid silver oxide powder can be obtained. Alternatively, to purify the flake-shaped silver oxide particles and remove residual dispersant, the solid components can be redispersed in a new dispersion medium, and the same operation repeated. Other drying methods include spray drying.

[0098] (A composition including a paste or the like (preferably a bonding composition) containing silver oxide particles in the shape of flakes)

[0099] The composition (e.g., the silver oxide paste of the present invention) comprises the above-mentioned silver oxide particles having a flake shape, a dispersion medium, and a dispersant. The dispersion medium and the dispersant may be used alone or in combination of two or more.

[0100] As described above, the dispersant used during manufacturing adheres to the surface of the silver oxide particles, which have a flake-like shape, and remains even after the solid components are separated and dried. When the dispersant is the dispersant for the paste described later, a composition (e.g., silver oxide paste) can be obtained simply by adding a dispersion medium for the paste. Alternatively, a composition (e.g., silver oxide paste) can be obtained by mixing a dispersion medium for the paste and a dispersant for the paste as needed into the silver oxide powder obtained by drying the slurry, followed by stirring, etc., to form a uniform dispersion.

[0101] When preparing a composition (e.g., silver oxide paste) from the above slurry without a drying process, it is preferable to centrifuge the slurry to separate it into solid components and a supernatant. The solid components obtained after removing the supernatant are then redispersed by adding a dispersion medium to obtain the desired composition. If a different dispersant is used than during manufacturing, the desired dispersant can be added simultaneously with the dispersion medium for replacement. Furthermore, the centrifugation, replacement of the dispersion medium or dispersant, and redispersion can be repeated multiple times to prepare the desired composition. By adding a predetermined amount of dispersion medium to the solid components obtained after the above operations and stirring, a composition containing silver oxide particles with a flake-like shape (e.g., silver oxide paste) can be prepared in the form of a uniform dispersion. Furthermore, a dispersant can be added further as needed. Thus, a composition (e.g., silver oxide paste) can be obtained in the form of a uniform dispersion, and the composition can be further stirred as needed.

[0102] When the above slurry is dried to obtain silver oxide powder, a composition (e.g., silver oxide paste) can be obtained in the form of a uniform dispersion by at least mixing and stirring the silver oxide powder with a dispersion medium for paste. Furthermore, any dispersant, dispersion medium, etc., may be further mixed as needed.

[0103] Mixing can be carried out using well-known dispersers and mixing devices for pastes and coatings, without causing further pulverization. Examples include various mixers, three-roll mills, and coating mixers.

[0104] Furthermore, the aforementioned silver oxide particles with a flake shape or silver oxide powder containing them can also be products after removing extremely large and extremely small particle sizes through known grading processes.

[0105] (Paste composition (preferably a bonding composition))

[0106] The following describes a paste composition (preferably a bonding composition) as one of the preferred embodiments of the present invention. However, the present invention is not limited to this embodiment.

[0107] The paste preferably contains: silver oxide particles having a flake shape; a compound having an ethylene-based or propylene-based glycol ether skeleton as a dispersion medium, the dispersion medium being a medium that holds the silver oxide particles having a flake shape in a dispersed state; and a compound having a glycol ether skeleton in the main chain and / or side chain as a dispersant for dispersing the silver oxide particles having a flake shape.

[0108] By preparing the above composition, a paste that does not undergo a reduction reaction at room temperature and promotes the reduction of silver oxide in a temperature range of 100–150°C can be produced. Furthermore, since no reduction reaction occurs at room temperature (around 20–30°C), it has a good shelf life and can be used after being stored for a certain period of time (e.g., more than one month) after preparation, rather than being used immediately after preparation.

[0109] The amount of flake-shaped silver oxide particles contained in the composition is not particularly limited, provided that it has suitable coatability for application, and is based on the total mass of the composition, for example, 70 to 95% by mass, preferably 75 to 85% by mass.

[0110] As the dispersion medium for the above-mentioned paste, any compound that has coatability suitable for application and has an ethylene- or propylene-based glycol ether backbone, and that can volatilize during the bonding process, is acceptable. Preferred examples include: diethylene glycol methyl ether (methyl carbitol), triethylene glycol methyl ether (methoxytriethylene glycol), diethylene glycol ethyl ether (carbitol), triethylene glycol ethyl ether (ethoxytriethylene glycol), ethylene glycol propyl ether (propyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether (butyl carbitol), triethylene glycol n-butyl ether (butoxytriethylene glycol), ethylene glycol hexyl ether (hexyl cellosolve), and diethylene glycol hexyl ether (hexyl carbitol). These include ethylene glycol (EPH), ethylene glycol n-butyl ether acetate (butyl cellosolve acetate), diethylene glycol n-butyl ether acetate (butyl carbitol acetate), ethylene glycol phenyl ether (EPh), 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, propylene glycol phenyl ether, etc. These can be used alone or in combination of two or more. Diethylene glycol monobutyl ether is particularly preferred.

[0111] The dispersion medium may be used in an amount of, for example, 8 to 30% by mass, preferably 10 to 25% by mass, and more preferably 13 to 20% by mass, relative to the total mass of the composition.

[0112] Here, when using two or more dispersion media, the above quantities refer to total quantities. The same applies to other similar records.

[0113] As a dispersant for the above-mentioned paste, compounds having a glycol ether backbone in the main chain and / or side chains are preferred. There are no particular limitations as long as the silver oxide particles with a flake shape can be maintained in a dispersed state in the dispersion medium; various dispersants can be used. Examples of such dispersants include polymers having a backbone of styrene, maleic acid, acrylic acid, methacrylic acid, aminoethyl methacrylate, etc., in the main chain, and having a glycol ether polymer with a molecular weight of 100 or more in the side chains. These can be used alone or in combination of two or more. The upper limit of the molecular weight of the above-mentioned dispersants can be, for example, 100,000 or less. Furthermore, the carboxyl groups of maleic acid, acrylic acid, and methacrylic acid in the main chain can be adjusted by forming salts with amine compounds to control the acid value and amine value. As such polymers, preferred trade names include, for example, BYK-190, BYK-194N, and BYK-2055 (all manufactured by BYK Chemie).

[0114] The dispersant may be present in an amount of, for example, 12% by mass or less relative to the total mass of the composition. It can be used in an amount preferably 5% by mass or less, more preferably 3.5% by mass or less. Furthermore, the lower limit is not particularly limited as long as it can be dispersed, and can be, for example, 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more. There is a tendency to obtain better bonding strength when the content of the dispersant is 3.5% by mass or less relative to the total mass of the composition.

[0115] Generally speaking, the reduction reaction of silver oxide powder usually proceeds as follows.

[0116] (1) Silver oxide reduction → (2) Sintering of Ag → (3) Grain growth (bonding; sintering and grain growth of Ag)

[0117] Generally speaking, silver oxide begins to decompose in the atmosphere at around 200°C, and heating to above 300°C is required to completely reduce it to metallic silver.

[0118] In low-temperature regions below 250°C, without the presence of a reducing agent, the reduction reaction of silver oxide ((1)→(2)) may not proceed sufficiently, and unreduced silver oxide may remain in the bonding layer and sintered layer obtained after treatment (3). If unreduced silver oxide remains, it may adversely affect the bonding strength, thermal conductivity, and electrical conductivity.

[0119] On the other hand, it is known that with the aid of a reducing agent, the reduction reaction (1) of silver oxide can proceed fully even in the aforementioned low-temperature region. In systems with strong reducing properties, the reduction reaction (1) proceeds slowly even when placed at room temperature. Furthermore, it is believed that if the system is subjected to a heating treatment for a specified time for drying purposes, the reaction will proceed to stage (3) of the above (1)→(2)→(3), making it difficult to terminate the reaction at the reduction stage.

[0120] In the invention described in Patent Document 1, a bonding layer exhibiting sufficient bonding strength is obtained by using a strong reducing agent such as diethylene glycol. However, if the coating layer containing the aforementioned paste is heated and dried, the reaction proceeds to (1)→(2)→(3), which may prevent the desired bonding from occurring even if a semiconductor chip or substrate to be bonded later is placed there. Consequently, it is necessary to either not heat-dry the paste containing the reducing agent or to remove the dispersion medium in order to prevent the reducing agent from evaporating, and to perform bonding in an insufficiently dried state. Compared to the case where the coating layer is dried, the bonding layer obtained in this way tends to have voids (pores) in the bonding layer due to the volatilization of the dispersion medium and reducing agent that occurs during bonding. This may adversely affect the stability of the semiconductor device during repeated use. Furthermore, when the paste contains a strong reducing agent such as diethylene glycol, there is also a problem that reduction occurs during the storage of the paste, rendering it unusable as a bonding material.

[0121] In one preferred embodiment of the present invention, the paste preferably does not contain a reducing agent. "The paste does not contain a reducing agent" means that no reducing agent is intentionally added to the paste, and even if it is assumed to be mixed in, it is less than 1% by mass, preferably less than 0.5% by mass.

[0122] The reducing agent is considered to be an organic compound with reducing properties, which in this invention is a polyol or an organic acid.

[0123] Examples of polyols include ethylene glycol, diethylene glycol, glycerol, 2,5-dimethyl-2,5-hexanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, 1,2,6-hexanetriol, and 1,10-decanediol.

[0124] Examples of organic acids include butyric acid, valeric 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 nonadecanoic acid, among other saturated fatty acids.

[0125] On the other hand, it is understood that in this invention, since the silver oxide is a thin sheet with a thickness of nanometers, it differs from the general silver oxide reduction reaction described above. Instead, it undergoes a process of (1) silver oxide reduction → (2) precipitation of nano-Ag → (3) sintering of nano-Ag → (4) grain growth (bonding; sintering and grain growth of Ag). Through the precipitation of nano-Ag during reduction, high bonding strength can be obtained even in low-temperature regions below 250°C through the sintering of Ag particles.

[0126] In one preferred embodiment of the present invention, a proton-based additive is preferably used instead of the known reducing agent used for silver oxide. Although the reduction reaction of silver oxide is facilitated by using a proton-based additive, the reduction reaction proceeds very slowly compared to the case where a reducing agent is used. Therefore, the paste can be heated and dried, and the dried coating layer can be bonded to chips or the like. As a result, pores are less likely to form in the bonding layer.

[0127] As described above, the paste preferably also contains proton-based additives. Therefore, even without a reducing agent, the reduction reaction of silver oxide becomes easier, reducing unreduced silver oxide within the bonding layer. Even if some unreduced silver oxide is present in the bonding layer, it will not significantly affect the bonding strength, but may negatively impact thermal and electrical conductivity. Furthermore, since the paste can be heated and dried, the dried coating layer can be bonded to chips, etc., reducing the likelihood of porosity within the bonding layer.

[0128] An example of the reduction reaction of silver oxide using a proton-based additive will be illustrated. For instance, the reduction reaction of silver oxide using water as the proton-based additive and diethylene glycol monobutyl ether (butyl carbitol) as the dispersion medium is presumably carried out as follows. Thus, it is predicted that the reduction reaction of silver oxide becomes easier to proceed in the presence of a proton-based additive such as water.

[0129] [Chemical Formula 1]

[0130]

[0131] As described above, in this invention, it is preferable to use a compound having an ethylene-based or propylene-based glycol ether skeleton as the dispersion medium for the above-mentioned paste. By using the dispersion medium (a compound having an ethylene-based or propylene-based glycol ether skeleton) in conjunction with a proton-based additive, the aldehyde generated from the glycol ether during the reaction is oxidized and releases electrons, thereby tending to allow the reduction reaction of silver oxide to proceed at a more appropriate rate.

[0132] As a proton-based additive, there are no particular limitations as long as it can release protons; various proton-based additives can be used. Examples of such proton-based additives include monohydric alcohols such as water, methanol, or ethanol, and hydrogen peroxide. These can be used alone or in combination of two or more. Water is particularly preferred.

[0133] The proton-based additive can be used in amounts, for example, 0.5 to 10% by mass, preferably 1 to 7% by mass, and more preferably 3 to 6% by mass, relative to the total mass of the composition.

[0134] For example, using water as the dispersion medium in manufacturing silver oxide particles with a flake shape, a slurry containing silver oxide particles with a flake shape obtained by bead milling is centrifuged to separate solid components and a supernatant. The supernatant is removed, and the obtained solid components are again dispersed by adding a medium containing water as a dispersion medium, thereby obtaining a composition. In this case, water, as a proton-based additive, is included in the composition. Furthermore, using water as the dispersion medium in manufacturing the aforementioned silver oxide particles, a slurry containing silver oxide particles with a flake shape obtained by bead milling is centrifuged to separate solid components and a supernatant. The supernatant is removed, and the obtained solid components are again dispersed by adding a dispersion medium different from that used in manufacturing, thereby replacing the dispersion medium and dispersing the solid components in a different dispersion medium, thereby obtaining a composition. In this case, since it is difficult to completely replace the original dispersion medium in the slurry, water, as a proton-based additive, is also included in the composition.

[0135] On the other hand, when a composition is obtained by mixing a dispersion medium and a dispersant in silver oxide powder obtained by drying the above-mentioned slurry and stirring, so as to obtain a uniform dispersion, since the dispersion medium in the original slurry has been removed, it is not included in the dispersion medium and dispersant used for paste. In this case, it is preferable to add a specified amount of proton-based additive.

[0136] The above composition may contain any other components without impairing its various properties. For example, by using known plasticizers (polyethylene glycol (PEG), dibutyl phthalate, benzyl butyl phthalate, etc.), cracks and peeling that occur during silver oxide reduction and paste drying can be easily reduced in silver oxide particles with a flake shape and a D50 of less than 200 nm.

[0137] In addition to the above, various fillers, known reducing agents, etc., may be included, provided that they do not impair the various properties of the composition. These may be used alone or in combination of two or more.

[0138] The total mass of the flake-shaped silver oxide particles, dispersant, and dispersion medium is preferably 90% by mass or more, more preferably 95% by mass or more, relative to the total mass of the composition. This results in a tendency to obtain better bonding strength even at low temperatures.

[0139] The total amount of the flake-shaped silver oxide particles, dispersant, dispersion medium, and proton-based additives relative to the overall mass of the composition is preferably 90% by mass or more, more preferably 95% by mass or more. This results in a tendency to obtain better bonding strength even at low temperatures, and also facilitates the reduction reaction of silver oxide.

[0140] The above composition exhibits good bonding strength even in low-temperature bonding, and is therefore preferably used for bonding applications. In other words, the above composition is preferably a bonding composition.

[0141] (Bonding method using silver oxide paste, semiconductor device manufacturing method)

[0142] Compositions obtained in this way (preferably compositions for bonding) are as follows: Figure 1 As shown, after being coated on the substrate 1, it is dried by heating to form a bonding layer 3. A semiconductor chip 2 is placed on the bonding layer 3. Then, the substrate 1 and the semiconductor chip 2 are processed under atmospheric pressure or pressure while the bonding layer 3 is clamped at a specified temperature, thereby enabling bonding between the bonded objects.

[0143] In this invention, it is preferable to dry the layer of the composition after it is applied to the first substrate and before placing the semiconductor chip, etc., which serves as the second substrate. This reduces porosity (void) within the bonding layer. Furthermore, provided good bonding is achieved, the layer of the composition may not be dried after application, and heating and pressure may be applied directly while the substrate 1 and the semiconductor chip 2 are clamped together. Additionally, the following uses... Figure 1 While this will be explained, any other substrate, such as a substrate with the semiconductor chip 2 bonded to it, may be used instead of the semiconductor chip 2 as the second substrate. Similarly, any other substrate, such as a substrate with the semiconductor chip 2 bonded to it, may be used instead of the semiconductor chip 1 as the first substrate.

[0144] The composition can be applied or coated onto the substrate 1 using various printing methods. Preferred printing methods include, for example, screen printing, dispensing, and applicator coating.

[0145] The amount of the composition used is based on the thickness after drying, for example, in an amount of 10 to 100 μm, preferably 20 to 50 μm.

[0146] The drying of the composition can be carried out at a temperature below the reduction temperature of the flake-shaped silver oxide particles and the temperature at which bonding is completed, for example, at a temperature of 80–150°C, preferably at 100–120°C. Furthermore, in the case of a paste containing the aforementioned proton-based additives, a rapid and temporary heating occurs in the temperature range of 100–150°C, thereby promoting the reduction reaction. Due to this heating, the dispersion medium volatilizes, so the drying temperature can also be set to the temperature at which the reduction reaction occurs. Specifically, 100–150°C is preferred, for example, and 100–120°C is also acceptable.

[0147] The drying time will vary depending on the drying temperature used, but it is generally 10 minutes to 1 hour, or it can be in the range of 20 minutes to 40 minutes.

[0148] If the bonding layer 3 is formed by drying the layers of the composition, at least a portion of the silver oxide in the bonding layer 3 is reduced to silver, and most of the dispersion medium is removed. Furthermore, if the reduction is sufficient before bonding is complete, a portion of unreduced silver oxide may remain, or if it can be removed before bonding is complete, a portion of the dispersion medium may remain.

[0149] Furthermore, it is known that when cracks or peeling occur in the bonding layer 3, voids from the cracks and unbonded portions from the peeling remain in the bonded layer after bonding. This can be attributed to the low bonding temperature and low pressure during semiconductor device manufacturing. Therefore, in order to prevent cracks or peeling from occurring in the bonding layer, it is preferable to suppress the formation of cracks or peeling in the bonding layer 3.

[0150] As a substrate, various substrates that have been used in the manufacture of semiconductor devices and power modules can be used. Examples of such substrates include, for example, copper substrates; alumina, silicon nitride, and aluminum nitride substrates; ceramic substrates; and various other heat dissipation substrates.

[0151] Furthermore, various semiconductor chips that have been used in the past can be used as semiconductor chips. Examples of such semiconductor chips include, for instance, Si semiconductor chips; SiC semiconductor chips; GaN semiconductor chips; and Ga2O3 semiconductor chips, which are commonly used in power semiconductors. SiC semiconductor chips are particularly preferred.

[0152] As the bonding pressure, a bonding pressure within the range required in the manufacture of power semiconductor devices can be appropriately adopted. In particular, the silver oxide powder of the present invention, due to its excellent bonding properties, can provide good bonding strength at lower pressures and lower temperatures.

[0153] The bonding pressure can be, for example, 0-30 MPa, 0-10 MPa, and is particularly preferably around 0-5 MPa, more preferably 0.5-5 MPa.

[0154] Furthermore, the bonding temperature can be appropriately adopted within the range required in the manufacture of power semiconductor devices. As a bonding temperature, it can be, for example, below 300°C, preferably below 250°C, more preferably below 230°C, and even more preferably below 210°C. In this invention, excellent bonding strength can be obtained even in a low-temperature region close to 230°C. The lower limit is not particularly limited as long as it is a temperature at which silver can be sintered, and can be, for example, greater than the drying temperature, preferably above 160°C, more preferably above 180°C.

[0155] The resulting bonding layer is composed of metallic silver formed by the reduction of silver oxide. By using the composition of the present invention (preferably the bonding composition), a bonding strength of 30 MPa or higher can be achieved. Furthermore, it is known that by using the silver oxide powder of the present invention, the generation of localized voids within the bonding layer can be suppressed.

[0156] (Methods for determining various properties)

[0157] (1) Determination of average major diameter

[0158] The composition prepared above was diluted 1000 times with butylcarbitol. 1 ml of the resulting diluted solution was spin-coated onto a smooth glass substrate (20×20 mm) using a spin-coating method (2000 rpm). The substrate was then vacuum-dried at room temperature to obtain an accumulation of silver oxide particles with a flake-like shape. Here, when the flake-shaped silver oxide particles are coated onto a glass substrate, their shape results in the planar portions of the flake shape being stacked in a vertically oriented manner.

[0159] Next, the aforementioned deposit was observed from above using a scanning electron microscope (Hitachi High Technology SU-8220). The major diameter of 20 particles was randomly measured, and the average value was calculated as the average major diameter of the silver oxide particles with a flake shape. Here, the longest diagonal line when the particles are observed from above is taken as the major diameter of the particles.

[0160] (2) Measurement of average thickness

[0161] 1 ml of the composition prepared above was screen-printed onto a smooth glass substrate (20 × 20 mm) and vacuum-dried at room temperature to obtain an accumulation of silver oxide particles with a flake shape. Next, the glass substrate was cut at the location containing the formed accumulation to create a sample that could be observed in cross-section of the flake-shaped silver oxide particles. Then, using a scanning electron microscope (Hitachi High Technology SU-8220), the thickness of 20 particles was randomly measured from the above-mentioned cross-section of the accumulation, and the average value was calculated as the average thickness of the flake-shaped silver oxide particles. Here, the distance between the upper and lower surfaces of the central portion of each particle was taken as the particle thickness.

[0162] (3) Determination of D50

[0163] The D50 value refers to the median particle size when each particle is considered as a sphere (the scattering intensity benchmark in dynamic light scattering). It is a statistical value in which half of the particles in a silver oxide particle with a flake shape or in a whole silver oxide powder containing such a particle are above this value and the other half are below it.

[0164] The D50 value was determined as follows: the composition prepared above was diluted 1000 times with butylcarbitol, and the diluted solution was measured using a dynamic light scattering analyzer (Malvern Panalytical Zetasizer Nano ZS).

[0165] (4) Powder X-ray diffraction (XRD) determination

[0166] The slurry prepared above is subjected to centrifugal separation (centrifugal force 20000×g) to separate it into solid components and supernatant. After removing the supernatant, the obtained solid components are vacuum dried at room temperature to obtain the dried silver oxide powder of the present invention.

[0167] The diffraction peaks of the dried powder were measured using a powder XRD apparatus (Rigaku MINIFLEX 600). The half-maximum width was calculated by fitting the data of the main peak (32°) of the (111) plane of the silver oxide particles with a thin sheet shape to the obtained diffraction peaks using a pseudo-voigt function.

[0168] (5) Cross-sectional observation of the joint

[0169] The bond was embedded in a two-component curable epoxy resin, cut after curing, and the cut surface was optically polished to create a sample for cross-sectional observation. The processed sample was then observed cross-sectionally using a scanning electron microscope (Hitachi High Technology SU-8220). The evaluation of crack formation in the bond layer was denoted by ×, △, and ○. × indicated severe crack formation, △ indicated that while not severe, cracks might reduce bond strength and stability, and ○ indicated no crack formation.

[0170] (6) Confirmation of dispersant

[0171] The slurry prepared above was centrifuged (centrifugal force 20000×g) to separate it into solid components and a supernatant. After removing the supernatant, the solid components were vacuum dried at room temperature to obtain a dry powder containing silver oxide particles with a flake-like shape. This dry powder was analyzed using a differential thermogravimetric-differential calorimeter (TG-DTA; Rigaku Thermoplus TG8120), and the content of the dispersant (adhered to the silver oxide) used was calculated based on the mass reduction rate.

[0172] Example

[0173] The present invention will be further described in detail below by way of examples and comparative examples, but the scope of the present invention is not limited by these examples and comparative examples. Furthermore, the following measured values ​​were obtained by the above-described measurement methods.

[0174] (Example 1)

[0175] Preparation of silver oxide particles with flake-like shape

[0176] The raw material used was micron-sized silver oxide (manufactured by DOWA ELECTRONICS, silver oxide PS) (spherical shape, particle size 10 μm). This raw silver oxide particle and water (dispersion medium) were mixed at a mass ratio of raw silver oxide:water = 10:90. A dispersant (DISPERBYK-190 from BYK Chemicals (a compound with a glycol ether backbone in the main chain and / or side chains)) was added at 30% by mass relative to the raw silver oxide. The mixture was then fed into the grinding chamber of a bead mill (Hiroshima Metal & Machinery Co., Ltd., Ultra Apex Mill UAM-015) for grinding to obtain a slurry containing silver oxide particles with a flake-like shape. In this grinding process, the grinding beads were spheres made of zirconium oxide (material) with a diameter of 0.1 mm, and the grinding time was 200 minutes.

[0177] Preparation of silver oxide paste

[0178] The slurry containing silver oxide particles with a flake shape obtained in Example 1 was centrifuged (centrifugal force 20000×g) to separate it into a solid component and a supernatant. The supernatant was removed to remove the remaining dispersant and water. Next, butylcarbitol was supplied to the obtained solid component as a dispersion medium to redisperse the solid component. Centrifugation (centrifugal force 20000×g) was then performed to separate it into a solid component and a supernatant. The supernatant was removed, thereby replacing the water in the dispersion with butylcarbitol.

[0179] Butylcarbitol was added to the obtained solid components in the manner shown in Table 1 below. After stirring with a rotary mixer without a pulverizing function, the mixture was dispersed using a three-roll mill to prepare a silver oxide paste containing silver oxide particles with a flake-like shape. The moisture content of the silver oxide paste was determined by gas chromatography. Furthermore, the moisture content of the silver oxide paste was 3% by mass.

[0180] (Example 2)

[0181] In the preparation of the slurry containing silver oxide particles with a flake shape, a dispersant (DISPERBYK-190 manufactured by BYK Chemical) was added at 20% by mass relative to the raw silver oxide, and the pulverization time was set to 300 minutes. Otherwise, the silver oxide paste was prepared in the same manner as in Example 1.

[0182] (Example 3)

[0183] In the preparation of a slurry containing silver oxide particles with a flake shape, the raw material silver oxide and water (dispersion medium) are mixed at a ratio of raw material silver oxide:water = 40:60 (by weight), and the pulverization time is set to 315 minutes. Otherwise, the silver oxide paste is prepared in the same manner as in Example 2.

[0184] (Example 4)

[0185] In the preparation of the slurry containing silver oxide particles with a flake shape, a slurry containing silver oxide particles with a flake shape was obtained in the same manner as in Example 2. Next, when butylcarbitol was added to the solid components after centrifugation and solvent replacement, a dispersant was added in such a way that the dispersant content in the paste was 4% by mass. Otherwise, the silver oxide paste was adjusted in the same manner as the paste adjustment method of Example 1.

[0186] (Example 5)

[0187] In the preparation of the slurry containing silver oxide particles with a flake shape, a dispersant is added in such a way that the dispersant content in the paste is 11% by mass, otherwise the silver oxide paste is prepared in the same manner as in Example 4.

[0188] (Example 6)

[0189] In the preparation of the slurry containing silver oxide particles with a flake shape, a slurry containing silver oxide particles with a flake shape was obtained in the same manner as in Example 2. Next, the obtained slurry was fed into a spray drying apparatus (a small spray dryer S-300 manufactured by BUCHI, Japan), and the dispersion medium was evaporated by heating, thereby obtaining a dried powder containing silver oxide particles with a flake shape.

[0190] Next, butylcarbitol was added to the obtained dry powder in the manner shown in Table 1 below. The mixture was stirred using a rotary mixer without a pulverizing function, and then dispersed using a three-roll mill to prepare silver oxide paste. Gas chromatography analysis of the obtained silver oxide paste showed that no moisture was detected in it.

[0191] (Example 7)

[0192] In the preparation of the slurry containing silver oxide particles with a flake-like shape, butylcarbitol and water were added to the obtained dry powder in such a manner as shown in Table 1 below. Otherwise, the silver oxide paste was prepared in the same manner as in Example 6. According to gas chromatography determination of the obtained silver oxide paste, the water content in the silver oxide paste was 2% by mass.

[0193] (Example 8)

[0194] In the preparation of the slurry containing silver oxide particles with a flake shape, water is added in a manner that is 3.5% by mass of the paste content. Otherwise, the silver oxide paste is prepared in the same manner as in Example 7.

[0195] (Example 9)

[0196] In the preparation of the slurry containing silver oxide particles with a flake shape, the water content in the paste is added in a manner that is 5% by mass. Otherwise, the silver oxide paste is prepared in the same manner as in Example 8.

[0197] (Example 10)

[0198] In the preparation of the slurry containing silver oxide particles with a flake shape, the water content in the paste is added in a manner that is 7% by mass. Otherwise, the silver oxide paste is prepared in the same manner as in Example 8.

[0199] (Example 11)

[0200] In the preparation of the slurry containing silver oxide particles with a flake shape, a dispersant (DISPERBYK-190 manufactured by BYK Chemical) was added at 20% by mass relative to the raw silver oxide, and the pulverization time was set to 360 minutes. Otherwise, the silver oxide paste was prepared in the same manner as in Example 2.

[0201] (Example 12)

[0202] In the preparation of the slurry containing silver oxide particles with a flake shape, BYK Chemicals' DISPERBYK-194N (a compound having a glycol ether backbone in the main chain and / or side chains) was used as a dispersant, and the pulverization time was set to 270 minutes. Otherwise, the silver oxide paste was prepared in the same manner as in Example 1.

[0203] (Example 13)

[0204] In the preparation of the slurry containing silver oxide particles with a flake shape, BYK Chemical's DISPERBYK-2055 (a compound having a glycol ether backbone in the main chain and / or side chains) was used as a dispersant, and the pulverization time was set to 160 minutes. Otherwise, the silver oxide paste was prepared in the same manner as in Example 1.

[0205] (Example 14)

[0206] Preparation of silver oxide particles with flake-like shape

[0207] The silver oxide particles used as raw materials were micron-sized silver oxide (manufactured by DOWA ELECTRONICS, silver oxide PS) (spherical shape, particle size 10μm). These raw silver oxide particles were mixed with water (dispersion liquid) at a ratio of raw silver oxide:water = 10:90 (mass ratio). A dispersant (DISPERBYK-190, manufactured by BYK Chemicals) was then added at 30% by mass relative to the raw silver oxide. The mixture was fed into the grinding chamber of a bead mill (Hiroshima Metal & Machinery Co., Ltd., Ultra Apex Mill UAM-015) for two grinding processes, yielding a slurry containing flake-shaped silver oxide powder. The processing conditions were as follows: The grinding beads for the first grinding process were spheres made of zirconium oxide (material) with a diameter of 0.1 mm, and the grinding time was 360 minutes. The grinding beads for the second grinding process were spheres made of zirconium oxide (material) with a diameter of 0.05 mm, and the grinding time was 30 minutes.

[0208] Preparation of silver oxide paste

[0209] The slurry containing silver oxide particles with a flake shape obtained in Example 14 was centrifuged (centrifugal force 20000×g) to separate it into a solid component and a supernatant. The supernatant was removed to remove the remaining dispersant and water. Next, butylcarbitol was supplied to the obtained solid component as a dispersion medium to redisperse the solid component. After centrifugation (centrifugal force 20000×g), it was separated into a solid component and a supernatant. The supernatant was removed, thereby replacing the water in the dispersion with butylcarbitol.

[0210] Butyl carbitol and polyethylene glycol (PEG400) as a plasticizer were added to the obtained solid components in a manner that makes them the composition shown in Table 1 below. After stirring with a rotary mixer, the mixture was dispersed with a three-roll mill to prepare a silver oxide paste containing silver oxide particles with a flake shape.

[0211] (Example 15)

[0212] In the preparation of the slurry containing silver oxide particles with flake shape, a dispersant (DISPERBYK-190 manufactured by BYK Chemical) was added in a manner of 50% by mass relative to the raw silver oxide, and the pulverization time of the second pulverization process was set to 150 minutes. Otherwise, the silver oxide paste was prepared in the same manner as in Example 7.

[0213] (Example 16)

[0214] Preparation of silver oxide particles with flake-like shape

[0215] In the manufacture of a slurry containing silver oxide particles with a flake shape, a slurry containing silver oxide particles with a flake shape is obtained in the same manner as in Example 2.

[0216] Preparation of silver oxide paste

[0217] The slurry containing silver oxide particles with a flake shape obtained in Example 16 was centrifuged (20,000 × g) to separate it into a solid component and a supernatant. The supernatant was removed to remove residual dispersant and water. Next, butylcarbitol was supplied to the obtained solid component as a dispersion medium to redisperse it. Centrifugation (20,000 × g) was then performed again to separate it into a solid component and a supernatant. The supernatant was removed, thereby replacing water in the dispersion with butylcarbitol. To further remove residual water from the obtained solid component, butylcarbitol was supplied again to redisperse it. Centrifugation (20,000 × g) was then performed again to separate it into a solid component and a supernatant. The supernatant was removed.

[0218] Butylcarbitol was added to the obtained solid components in a manner consistent with the composition shown in Table 1 below. The mixture was stirred using a rotary mixer without a pulverizing function, and then dispersed using a three-roll mill to prepare a silver oxide paste containing silver oxide particles with a flake-like shape. The moisture content of the silver oxide paste was determined by gas chromatography and was found to be 1.7% by mass.

[0219] (Example 17)

[0220] In the preparation of the paste as a bonding composition, to further remove residual moisture from the solid components, the solvent was replaced with butylcarbitol three times in total. Otherwise, the silver oxide paste was prepared in the same manner as in Example 16. Furthermore, the moisture content of the silver oxide paste was determined by gas chromatography, and the moisture content of the silver oxide paste was 0.8% by mass.

[0221] (Comparative Example 1)

[0222] In the preparation of the slurry containing silver oxide particles with a flake shape, a dispersant (DISPERBYK-190 manufactured by BYK Chemical) was added in a manner of 20% by mass relative to the raw silver oxide, and the pulverization time was set to 60 minutes. Otherwise, the silver oxide paste was prepared in the same manner as in Example 1.

[0223] (Comparative Example 2)

[0224] Using commercially available submicron-sized silver oxide particles (shape reference) Figure 3 The silver oxide particles were used as the raw materials. The silver oxide particles were mixed with water at a ratio of silver oxide particles:water = 10:90 (mass ratio), and a dispersant (DISPERBYK-190 manufactured by BYK Chemical) was added at a ratio of 30% by mass relative to the silver oxide particles. The mixture was then subjected to ultrasonic treatment for 280 minutes to obtain a slurry with uniformly dispersed silver oxide particles.

[0225] The slurry was first centrifuged (20000 × g) to separate it into solid components and a supernatant. The supernatant was removed, thereby removing the remaining dispersant and water. Electron micrographs of the silver oxide particles contained in the slurry were observed. Figure 3 The initial aggregated state is characterized by partial deagglomeration and consists entirely of spherical particles.

[0226] The obtained solid components are supplied with butylcarbitol as a dispersion medium to redisperse the solid components. Then, centrifugation is applied to separate the solid components and the supernatant. The supernatant is removed, thereby replacing the residual water with butylcarbitol.

[0227] The obtained solid components were mixed with butylcarbitol as a dispersion medium in a manner that resulted in the composition shown in Table 1 below. After stirring with a rotary mixer, the mixture was dispersed using a three-roll mill to prepare a paste.

[0228] (Comparative Example 3)

[0229] Use commercially available submicron-sized silver oxide particles (reference) Figure 3The silver oxide particles used were mixed with water at a ratio of silver oxide particles to water of 10:90 (mass ratio). A dispersant (DISPERBYK-190, manufactured by BYK Chemicals) was added at 30% by mass relative to the silver oxide particles. The mixture was dispersed for 5 minutes using a paint mixer (V-type, manufactured by Asada Iron Works Co., Ltd.), thereby partially deagglomerating the silver oxide particles and obtaining a slurry with uniformly dispersed silver oxide particles. The dispersion beads were spheres made of zirconium oxide (material) with a diameter of 0.3 mm, and the dispersion time was 5 minutes.

[0230] The slurry was first centrifuged (20000 × g) to separate it into solid components and a supernatant. The supernatant was removed, thereby removing the remaining dispersant and water. Electron micrographs of the silver oxide particles contained in the slurry were observed. Figure 3 The initial aggregated state is characterized by deagglomeration and consists entirely of spherical particles.

[0231] The obtained solid components are supplied with butylcarbitol as a dispersion medium to redisperse the solid components. Then, centrifugation is applied to separate the solid components and the supernatant. The supernatant is removed, thereby replacing the residual water with butylcarbitol.

[0232] The obtained solid components were mixed with butylcarbitol as a dispersion medium in a manner that resulted in the composition shown in Table 1 below. After stirring with a rotary mixer, the mixture was dispersed using a three-roll mill to prepare a paste.

[0233] (Comparative Example 4)

[0234] In the preparation of the slurry containing silver oxide particles, the dispersion time using a paint mixer was set to 15 minutes; otherwise, the paste was prepared in the same manner as in Example 3. Furthermore, the silver oxide particles contained in the obtained slurry were observed using an electron microscope, and the results showed… Figure 3 The initial aggregated state is characterized by deagglomeration and consists entirely of spherical particles.

[0235] (Comparative Example 5)

[0236] In the preparation of the slurry containing silver oxide particles, the dispersion time using a paint mixer was set to 30 minutes; otherwise, the paste was prepared in the same manner as in Example 3. Furthermore, the silver oxide particles contained in the obtained slurry were observed using an electron microscope, and the results showed… Figure 3 The initial aggregated state is characterized by deagglomeration and consists entirely of spherical particles.

[0237] (Comparative Example 6, Comparative Example 7)

[0238] A paste was prepared by mixing thin sheet-like silver particles (average major diameter: 6000 nm, average thickness: 100 nm) made by Fukuda Metal with butyl carbitol at a ratio of 90:10 (mass ratio).

[0239] The pastes of the embodiments and comparative examples obtained above were subjected to bonding tests by the following method.

[0240] like Figure 1 As shown, a Cu substrate with a Ni-Ag plating (the outermost layer being an Ag plating layer, with a surface size of 20×20 mm and a thickness of 3 mm) was prepared. The pastes of the examples and comparative examples were applied to the Ag plating layer via screen printing, and the substrate was heated at 100°C for 30 minutes to remove the dispersion medium. Furthermore, no cracks or peeling that could be visually observed were found in the dried bonding layer at this point.

[0241] Next, the Si chip (with an Ag sputtered film as the outermost layer, a surface size of 3×3 mm and a thickness of 625 μm) is placed in contact with the dried bonding layer. Pressure (1.5 MPa) and heating (set temperature 250 °C) are applied from above for 4 minutes to form the bonding layer, thereby bonding the Si chip to the Cu substrate.

[0242] (Cross-section observation)

[0243] The joints obtained in Examples 3 and 11, and Comparative Examples 6 and 7 were subjected to cross-sectional observation using the methods described in the "Methods for Determining Various Properties" section above. Figure 4 Cross-sectional photographs of the bonding layers of Example 3 and Comparative Example 6 are shown.

[0244] Furthermore, the joint obtained in Example 3 was subjected to cross-sectional observation using the method described in the "Methods for Measuring Various Properties" section above. Figure 5 A cross-sectional photograph of the bonding layer of Example 3 is shown.

[0245] (Joint strength test)

[0246] The obtained bond was subjected to a chip shear force test (shear) using a BondTester (DAGE4000Plus manufactured by Dage Japan) to determine the bond strength.

[0247] (Reduction after bonding)

[0248] For the bonded joints after shear peeling in the above-mentioned bond strength test, the color of the peeled surface is observed visually. Black areas indicate residual silver oxide, representing unreduced portions; silver-white areas indicate reduced silver oxide. The reducibility after bonding is evaluated using × and ○, with × indicating a portion of the peeled surface is black, and ○ indicating the entire peeled surface is silver-white.

[0249] The characteristics of the silver oxide particles or metallic silver particles used in the examples and comparative examples, as well as the composition of the pastes containing them, are described in Table 1 below.

[0250] Furthermore, for pastes obtained in this manner, the bonding strength, post-bonding reducibility, crack evaluation, and insights gained during bonding are described in Table 1 below. Additionally, "BC content" in Table 1 indicates the content of diethylene glycol monobutyl ether.

[0251] [Table 1]

[0252]

[0253] As shown in Table 1, when the silver oxide paste of the present invention is used to bond the substrates, an excellent bonding strength of over 30 MPa can be obtained. Furthermore, cross-sectional photographs of the bonded layer show no crack formation.

[0254] On the other hand, as shown in Comparative Example 1, in the preparation of the flake-shaped silver oxide particles used, when the pulverization time is short, the D50 of the flake-shaped silver oxide particles becomes larger. If a paste containing such flake-shaped silver oxide particles is used, the bonding strength becomes lower. Furthermore, it is known that if bonding is performed using a paste containing spherical silver oxide particles used in Comparative Examples 2-5, even if the D50 is within the scope of the present invention, the bonding strength is significantly reduced to below 20 MPa compared to the embodiments of the present invention. Moreover, observation of the peel surface after the bonding strength test reveals the presence of unreduced silver oxide.

[0255] Furthermore, although Example 6, which is anhydrous, has high bonding strength, some unreduced silver oxide remains on the peel surface after the bonding strength test, indicating low reducibility.

[0256] Furthermore, as shown in Comparative Examples 6 and 7, when bonding was performed using a paste containing commercially available flake-shaped silver particles, these particles had an average major diameter of 6000 nm and a micrometer size. As a result, voids were locally generated at the bonding interface and within the bonding layer. When these localized voids are generated, the bonding layer tends to become non-uniform, and the bonding stability tends to deteriorate. The mechanism of these voids is unclear, but it is speculated that they are due to the overlapping of large areas of flake-shaped silver particles, and that the voids cannot be eliminated at a low temperature of around 250°C.

[0257] As described above, the silver oxide paste of the present invention is useful in bonding semiconductor substrates and semiconductor chips with good bonding strength (without causing cracks).

[0258] Explanation of reference numerals in the attached figures

[0259] 1: Substrate;

[0260] 2: Semiconductor chips;

[0261] 3: A bonding layer comprising the silver oxide particles having a sheet shape according to the present invention.

Claims

1. A silver oxide particle having a flake shape or a silver oxide powder containing the same, characterized in that, The average thickness of the silver oxide particles with a flake shape is 1–100 nm, and the D50 is 100–350 nm.

2. The silver oxide particles having a flake shape or the silver oxide powder containing the same as described in claim 1, wherein, The average major axis of the silver oxide particles with a sheet-like shape is 300–1000 nm.

3. The silver oxide particles having a flake shape or the silver oxide powder containing the same as described in claim 1, wherein, In the X-ray diffraction spectrum of the silver oxide particles with the sheet-like shape, the full width at half maximum (FWHM) of the diffraction peaks from the (111) plane is greater than 0.

80.

4. The silver oxide particles having a flake shape or the silver oxide powder containing the same as described in claim 1, wherein, At least a portion of the silver oxide particles having a sheet-like shape have a compound on the surface of the main chain and / or side chain having a glycol ether backbone.

5. A bonding composition, characterized in that, have: Silver oxide particles having a flake shape or silver oxide powder containing the same as described in any one of claims 1 to 4; Dispersants; and Dispersion medium.

6. The joining composition according to claim 5, wherein, The dispersant is a compound having a glycol ether skeleton in the main chain and / or side chains.

7. The joining composition according to claim 5, wherein, The dispersion medium is a compound having an ethylene-based or propylene-based glycol ether skeleton.

8. A method for manufacturing silver oxide particles with a flake shape or silver oxide powder containing the same, characterized in that the method is the method for manufacturing silver oxide particles with a flake shape or silver oxide powder containing the same as described in claim 1. The silver oxide particles were ground into powder using a bead mill.

9. The method for manufacturing silver oxide particles having a flake shape or silver oxide powder containing the same as claimed in claim 8, wherein, The bead milling process includes the following steps: The process of supplying the silver oxide particles, the dispersant, and the dispersion medium to a bead milling apparatus; and The process involves bead milling within the apparatus to obtain a slurry containing silver oxide particles with a flake-like shape.

10. The method for manufacturing silver oxide particles having a flake shape or silver oxide powder containing the same as claimed in claim 8 or 9, wherein, The dispersant is a compound having a glycol ether skeleton in the main chain and / or side chains.

11. A method for manufacturing a semiconductor device, characterized in that the method comprises the following steps: Step (1): Applying the bonding composition of claim 5 onto a semiconductor substrate to form a layer of the bonding composition; Step (2): Place a semiconductor chip on the layer of the bonding composition to form a laminate; Process (3): The obtained laminate is pressurized at 0-30 MPa and heated at 300°C to integrate it.

12. The method for manufacturing a semiconductor device according to claim 11, wherein, Between steps (1) and (2), there is also a step of drying the layer of the bonding composition.

13. The method for manufacturing a semiconductor device according to claim 11, wherein, The semiconductor chip is a SiC semiconductor chip.

14. A silver oxide paste comprising: Silver oxide particles with a flake-like shape; Dispersants; and Dispersion medium, The average thickness of the silver oxide particles is 1–100 nm, and the D50 is 100–350 nm.

15. The silver oxide paste according to claim 14, wherein, The silver oxide paste also contains proton-based additives.

16. The silver oxide paste according to claim 14, wherein, The dispersant is a compound having a glycol ether skeleton in the main chain and / or side chains.

17. The silver oxide paste according to claim 14, wherein, The dispersion medium is a compound having an ethylene-based or propylene-based glycol ether skeleton.

18. The silver oxide paste according to claim 14, wherein, The average major diameter of the silver oxide particles is 300–1000 nm.

19. The silver oxide paste according to claim 14, wherein, In the X-ray diffraction spectrum of the silver oxide particles, the full width at half maximum (FWHM) of the diffraction peaks from the (111) plane is greater than 0.

80.

20. The silver oxide paste according to claim 14, wherein, The content of the dispersant is less than 12% by mass relative to the total mass of the silver oxide paste.

21. The silver oxide paste according to claim 15, wherein, The content of the proton-based additive is 0.5 to 10% of the total mass of the silver oxide paste.

22. The silver oxide paste according to claim 14, wherein, The silver oxide paste is used for bonding applications.

23. A method for manufacturing a semiconductor device, the method comprising the following steps: Step (1): Apply silver oxide paste according to any one of claims 14 to 22 onto the first substrate to form a layer of the silver oxide paste; Step (2): Place a second substrate on the silver oxide paste layer to form a laminate; Process (3): The obtained laminate is pressurized at 0-30 MPa and heated at 300°C to integrate it.

24. The method for manufacturing a semiconductor device according to claim 23, wherein, Between step (1) and step (2), there is also a step of drying the layer of silver oxide paste.

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

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