Manufacturing method of the joint

Abstract

A bonded body manufacturing method that forms a bonding layer by forming, between a body to be bonded and a second body to be bonded, a coating film of paste containing copper particles and then heating the coating film so as to sinter the copper particles, wherein: said copper particles include particles having an average primary particle diameter of between 0.06 μm and 1.0 μm inclusive, and a percentage increase of 5% or more from the crystalline diameter D1 (nm) at 150°C to the crystalline diameter D2 (nm) at 250°C ((D2-D1) / D1×100); and the coating film is maintained at a heating temperature of between 150°C and 350°C inclusive for 45 minutes or less to sinter the copper particles.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a bonded body.

Background Art

[0002] In recent years, in a method for manufacturing a semiconductor device in which a large current such as an IGBT is energized and the amount of heat generated increases, a step of joining a bonded body such as a semiconductor element or a circuit board using a joining material containing sinterable metal particles has been adopted.

[0003] For example, in Patent Document 1, as one of the joining materials for joining a bonded body at a low temperature, in the relationship between each temperature and the crystallite size while raising the temperature in an inert atmosphere, (a) the temperature at which the crystallite size ratio to the crystallite size of copper at 30°C is 1.2 is 250°C or lower, and (b) the change amount of the crystallite size ratio per unit temperature in the temperature range of 250°C or higher and 350°C or lower is 2.0×10 The above copper particles are disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Although the copper particles described in Patent Document 1 can be said to have excellent sinterability, they tend to have a large volume shrinkage. When a paste containing the copper particles is fired to form a bonded body, there is a problem that shrinkage cracks are likely to occur inside the bonding layer. Similarly, when the bonding layer is viewed in plan, cracks due to shrinkage are also prominent at the end of the bonding layer where the semiconductor element is not placed (hereinafter also referred to as the "fillet portion"), and the bonding strength between the bonding layer and the substrate (bonded body) at the fillet portion is not sufficiently exhibited, and there is a problem that the end of the bonding layer peels off from the substrate.

[0006] Therefore, the object of the present invention is to provide a method for manufacturing a bonded body in which the bonding layer in the fillet portion is less likely to peel off from the body to be bonded.

[0007] As a result of diligent research to solve the above problems, the present inventors have found that by using copper particles having a specific particle size and crystallite size as sinterable metal particles, and sintering the copper particles under specific sintering temperature conditions, the bonding layer in the fillet portion becomes less likely to peel off from the bonded object.

[0008] In other words, the present invention is a method for manufacturing a bonded body in which a bonded layer is formed by first forming a coating film of a paste containing copper particles between a first body to be bonded and a second body to be bonded, and then heating the coating film to sinter the copper particles, The copper particles include those with an average primary particle diameter of 0.06 μm or more and 1 μm or less, and whose increase ratio (D2-D1) / D1×100 from the crystallite size D1 (nm) at 150°C to the crystallite size D2 (nm) at 250°C is 5% or more. The present invention provides a method for manufacturing a bonded body, wherein the aforementioned coating film is held at a heating temperature of 150°C to 350°C for 45 minutes or less to sinter the copper particles. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing the steps of the manufacturing method for the jointed body according to the present invention. [Figure 2] Figure 2 is a cross-sectional view of the joint obtained by the manufacturing method of the present invention. [Modes for carrying out the invention]

[0010] The present invention will be described below based on its preferred embodiments. Figure 1 shows the joint of the present invention. manufacturing Figure 2 is a process diagram illustrating the method, and Figure 2 is a cross-sectional view of the joint obtained by the manufacturing method shown in Figure 1.

[0011] First, as shown in Figure 1(a), a paste containing copper particles is applied to the first workpiece 11 to form a coating film 12X. The method of applying the paste is not particularly limited, but for example, screen printing, dispensing printing, gravure printing, offset printing, etc., can be used.

[0012] The paste used in this invention appropriately contains copper particles, an organic solvent described later, and a adjusting agent. The copper particles preferably have an average primary particle diameter of 0.06 μm or more, more preferably 0.08 μm or more, and particularly preferably 0.1 μm or more. On the other hand, the average primary particle diameter is preferably 1 μm or less, more preferably 0.8 μm or less, particularly preferably 0.5 μm or less, and especially preferably 0.3 μm or less. By having an average primary particle diameter of 0.06 μm or more for the copper particles, it is possible to prevent cracking in the bonding layer during the process of coating the paste containing the copper particles and firing it to form a bonding layer, resulting in excellent bonding strength between the bonded objects (first bonded object and second bonded object), and increasing the bonding strength between the bonding layer and the first bonded object in the fillet portion. Furthermore, by having an average primary particle diameter of 1 μm or less for the copper particles, it becomes easier to set the crystallite size increase rate (D2-D1) / D1×100, which will be described later, within a suitable range.

[0013] Furthermore, the copper particles have an increase ratio (D2-D1) / D1×100 of the crystallite size D2 (nm) at 250°C relative to the crystallite size D1 (nm) at 150°C, which is 5% or more, preferably 6% or more, more preferably 7.5% or more, and more preferably 8% or more. The increase ratio (D2-D1) / D1×100 serves as an indicator of the sinterability of the copper particles. In addition to the increase ratio, the copper particles also possess the average primary particle size described above, and together, the bonded body obtained by this manufacturing method has excellent bonding strength between the bonded bodies (first bonded body and second bonded body), and the bonded layer in the fillet portion does not peel off from the first bonded body. In the following explanation, for simplicity of explanation, when "increase ratio" is used, it refers to the value calculated from "(D2-D1) / D1×100". There is no particular upper limit to the increase ratio, but it can be around 100%. Copper particles with an increase of 5% or more are not obtained by a special manufacturing method, but can be adjusted by the type of copper source, organic surface treatment agent, reducing agent, and organic solvent used in the production of the copper particles, as well as the reaction time and reaction temperature during production. Alternatively, copper particles with an increase of 5% or more can be appropriately selected from commonly available copper particles and used.

[0014] When the aforementioned increase rate is 5% or more, and the average primary particle diameter is within the above range, the sinterability between copper particles is good. Moreover, since excessive volume shrinkage of the copper particles can be prevented, the bonding between the first and second objects to be bonded proceeds sufficiently without shrinkage cracks occurring during the process of forming the bonding layer by firing the coating film 12X. Furthermore, the bonding strength between the bonding layer and the first object to be bonded in the fillet portion becomes excellent. The proportion of copper particles that satisfy the aforementioned increase rate of 5% or more is preferably 10% by mass or more of the total copper particles, and more preferably 15% by mass or more.

[0015] The average primary particle diameter in the present invention refers to the volume cumulative particle diameter at 50% by volume of the cumulative volume, which is obtained by randomly selecting 50 or more particles with clear contours from the scanning electron microscope image of copper particles within the range of 10,000 times or more and 150,000 times or less, measuring the particle diameter (Heywood diameter), and then calculating the volume assuming the particles are perfect spheres from the obtained particle diameters.

[0016] The crystallite diameter of the copper particles in the present invention is calculated by analyzing the X-ray diffraction pattern obtained by XRD measurement based on the high-temperature XRD (powder X-ray diffraction) method and then using Scherrer's formula. The high-temperature XRD method is a method in which the measurement sample is placed in a high-temperature unit capable of heating the sample, and XRD measurement is performed while gradually heating. The XRD measurement is performed using a Rigaku fully automatic horizontal multi-purpose X-ray diffractometer and the company's high-speed two-dimensional X-ray detector PILATUS100K / R as the detector. The measurement conditions for the X-ray diffraction pattern are as follows. Optical system: Parallel beam X-ray source: CuKα ray Measurement mode: Still mode, fixed at 2θ = 42° (The X-ray diffraction intensity corresponding to 2θ = 38 - 48° can be obtained with the above two-dimensional detector) Exposure time: 60 seconds Collimator: Φ0.2 mm Measurement atmosphere: Nitrogen Measurement temperature: 150, 250 °C Heating rate: 10 °C / min During the XRD measurement (exposure time 60 seconds) at each measurement temperature, the temperature is maintained without heating.

[0017] Next, the crystallite diameter is calculated from the full width at half maximum of the X-ray diffraction pattern of the crystal plane (111) of the copper particles obtained by the above XRD measurement using the following Scherrer's formula. Scherrer's formula: D = Kλ / βcosθ D: Crystallite diameter K: Scherrer constant (0.94) λ: Wavelength of X-ray β: Half-value width [rad] θ: Bragg angle [rad]

[0018] There are no particular restrictions on the shape and properties of the copper particles. For example, regarding the shape, it may be spherical, polyhedral, flat, amorphous, or a combination thereof. Among these, spherical, flat, or a combination thereof is preferable. Regarding the properties of the copper particles, they may be in powder form, or in paste or slurry form in which the copper particles are dispersed in an organic solvent.

[0019] A surface treatment agent may adhere to the surface of the copper particles. By adhering a surface treatment agent to the surface of the copper particles, excessive aggregation of the copper particles can be suppressed.

[0020] The surface treatment agent is not particularly limited, and examples include fatty acids, aliphatic amines, and complexes having an adsorptivity to copper.

[0021] The viscosity of the paste can be measured using a rheometer MARS III manufactured by Thermo Scientific. From the viewpoint of improving the coating property or printability of the paste, the viscosity value at a shear rate of 10 s -1 is preferably 10 Pa·s or more and 200 Pa·s or less, more preferably 15 Pa·s or more and 200 Pa·s or less, and even more preferably 30 Pa·s or more and 90 Pa·s or less. The measurement conditions for the viscosity of the paste are as follows. Measurement mode: Shear rate dependence measurement Sensor: Parallel type (Φ20 mm) Measurement temperature: 25°C Gap: 0.300 mm Shear rate: 0.05 - 120.01 s -1 Measurement time: 2 minutes

[0022] The thickness of the coating film 12X is preferably 1 μm or more, more preferably 5 μm or more, and particularly preferably 10 μm or more, from the viewpoint of ensuring sufficient thickness of the bonding layer described later and sufficient bonding strength between the bonding layer and the objects to be bonded. On the other hand, from the viewpoint of preventing cracks from occurring in the bonding layer during the process of firing the coating film 12X to form the bonding layer, which would reduce the bonding strength between the objects to be bonded (the first object to be bonded and the second object to be bonded), or the bonding layer at the fillet portion from peeling off from the first object to be bonded, the thickness is preferably 500 μm or less, and more preferably 300 μm or less.

[0023] The copper particle content in the paste is preferably 60% by mass or more and 99% by mass or less, from the viewpoint of improving the applicability of the paste to the bonded object and the shape retention of the coating film 12X, and preferably 65% ​​by mass or more and 95% by mass or less. below It is more preferable that the amount be 70% by mass or more and 93% by mass or less.

[0024] Examples of organic solvents include monoalcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, esters, nitrogen-containing heterocyclic compounds, amides, amines, and saturated hydrocarbons. These organic solvents can be used individually or in combination of two or more.

[0025] As mentioned above, the paste may contain modifiers to adjust various properties as appropriate. Examples of modifiers include reducing agents, viscosity modifiers, and surface tension modifiers.

[0026] Suitable reducing agents include those that promote the sintering of copper particles, such as monoalcohols, polyhydric alcohols, aminoalcohols, citric acid, oxalic acid, formic acid, ascorbic acid, aldehydes, hydrazines and their derivatives, hydroxylamines and their derivatives, dithiothreitol, phosphites, hydrophosphites, and phosphorous acid and its derivatives.

[0027] Viscosity modifiers are preferably those that can adjust the viscosity of the paste to be within the above viscosity range, and examples include ketones, esters, alcohols, glycols, hydrocarbons, and polymers.

[0028] The surface tension modifier can be any agent capable of adjusting the surface tension of the coating film 12X, and examples include polymers such as acrylic surfactants, silicone surfactants, alkyl polyoxyethylene ethers, and fatty acid glycerol esters, as well as monomers such as alcohol-based, hydrocarbon-based, ester-based, and glycol-based agents.

[0029] Next, as shown in Figure 1(b), the coating 12X is dried at a temperature below the sintering temperature of the copper particles constituting the coating 12X. The drying temperature must be such that the organic solvent and adjusting agents in the coating 12X evaporate, and the copper particles do not sinter, as described above. Therefore, assuming that it is lower than the sintering temperature described later, it is preferably 50°C to 160°C, and more preferably 60°C to 150°C. The entire amount of the organic solvent does not need to be removed; it is sufficient for the organic solvent to be removed to the extent that the coating film 12X loses its fluidity. Therefore, some organic solvent may remain in the coating film 12X, and its content may be, for example, 50% by mass or less, and particularly 30% by mass or less.

[0030] The coating 12X can be dried in an inert atmosphere or under atmospheric pressure. Alternatively, the coating 12X may be dried under reduced pressure. The drying time should be sufficient to evaporate the organic solvents and modifiers in the coating 12X, and remove enough organic solvents so that the coating 12X loses its fluidity, as described above.

[0031] Next, as shown in Figure 1(c), the second object to be bonded 13 is placed on the dried coating 12X to form the laminate 15.

[0032] There are no particular restrictions on the types of the first to be joined 11 and the second to be joined 13. Generally, it is preferable that both the first to be joined 11 and the second to be joined 13 contain metal on their joining surfaces. For example, at least one of the first to be joined 11 and the second to be joined 13 can be a member having a metal surface. In this specification, "metal" refers to metal itself that does not form compounds with other elements, or an alloy of two or more metals. Examples of such metals include copper, silver, gold, aluminum, palladium, nickel, or alloys consisting of two or more of these.

[0033] Furthermore, a dried paste containing metal fine particles and an organic solvent can be used as at least one of the first to be bonded body 11 and the second to be bonded body 13. Specifically, a member having a metal surface can be used as the first to be bonded body 11, and a dried paste containing metal fine particles and an organic solvent can be used as the second to be bonded body 13. When using a dried paste, it is preferable to apply the paste to a support substrate made of metal such as copper and dry it to produce the dried paste.

[0034] Specific examples of the first to be bonded 11 and the second to be bonded 13 include, independently, spacers, heat sinks, semiconductor elements, and substrates having at least one of the above-mentioned metals on their surface. As the substrate, for example, an insulating substrate having a metal layer such as copper on the surface of a ceramic or aluminum nitride plate can be used. When a semiconductor element is used as the to be bonded, the semiconductor element contains one or more elements such as Si, Ga, Ge, C, N, and As. The first to be bonded 11 is preferably a substrate. The second to be bonded 13 is preferably a spacer, a heat sink, or a semiconductor element.

[0035] If at least one of the first joined body 11 and the second joined body 13 is a member having a surface made of metal, the metal surface may be made of one type of metal, or it may be made of two or more types of metals. If it is made of two or more types of metals, the surface may be an alloy. The metal surface is generally preferably flat, but it may be curved in some cases.

[0036] Next, as shown in Figure 1(d), the laminate 15 is held by a predetermined jig (not shown), and the laminate 15, i.e., the coating film 12X, is heated under pressure at a temperature of 150°C to 350°C, preferably 170°C to 330°C, more preferably 190°C to 310°C. At this heating temperature, the temperature is maintained preferably for 45 minutes or less, more preferably 1 minute to 40 minutes, particularly preferably 2 minutes to 35 minutes, and even more preferably 2 minutes to 20 minutes, to sinter the copper particles and form the bonding layer 12. By maintaining the above heating temperature for 45 minutes or less, it is possible to prevent the workpiece from being damaged by heat and to improve productivity.

[0037] According to this manufacturing method, the bonding strength between the bonding layer 12 and the first object to be bonded 11 is increased, so that, as shown in Figure 2, the fillet portion 12A of the bonding layer 12 on which the second object to be bonded 13 is not placed will not peel off from the first object to be bonded 11. As a result, a laminate 15 can be obtained in which the bonding layer 12 bonds not only the second object to be bonded 13 but also the first object to be bonded 11 with high bonding strength, and no peeling occurs.

[0038] In Figure 1, the laminate 15 is pressurized using a jig to join the first object to be joined 11 and the second object to be joined 13 by the joining layer 12. However, the first object to be joined 11 and the second object to be joined 13 by the joining layer 12 without pressurizing the laminate 15. In this case as well, the joining layer 12 in the fillet portion 12A will not peel off from the first object to be joined 11. As a result, the joining layer 12 will join not only the second object to be joined 13 but also the first object to be joined 11 with high bonding strength, and a laminate 15 can be obtained in which peeling does not occur. As described above, when joining the laminate 15 under pressure, it is preferable to apply pressure of 0.1 MPa to 40 MPa, from the viewpoint of sufficiently joining the first body to be joined 11 and the second body to be joined 13 via the joining layer 12.

[0039] The bonded body obtained by the manufacturing method of the present invention is suitable for use in applications such as automotive electronic circuits and electronic circuits on which power devices are mounted, taking advantage of the high bonding characteristics between the workpiece and the bonding layer in the fillet portion. [Examples]

[0040] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0041] (Example 1) (1) Preparation of bonding paste Copper particles (CH-0200L1, manufactured by Mitsui Mining & Smelting Co., Ltd., spherical, average primary particle size 0.16 μm) and terpineol as an organic solvent were stirred in a rotary mixer. The resulting mixture was kneaded in a three-roll mill (with a final gap of 10 μm) to obtain a bonding paste. The proportion of copper particles in the bonding paste was 82%, and the proportion of terpineol was 18%. The viscosity of the bonding paste was 44 Pa·s. Furthermore, the increase in the crystallite size D2 (nm) of the copper particles at 250°C compared to the crystallite size D1 (nm) at 150°C was 8.9%.

[0042] (2) Application of bonding paste to the first object to be bonded A bonding paste was printed onto the center of a copper plate measuring 20 mm in length, 20 mm in width, and 2 mm in thickness using a metal mask measuring 10 mm vertically, 10 mm horizontally, and 100 μm thick, forming a rectangular coating. This coating was then dried in an air atmosphere at 90°C for 20 minutes to remove the organic solvent.

[0043] (3) Placing the second object to be bonded onto the dried coating (formation of a laminate) As the second substrate to be bonded, an Ag-plated alumina chip was prepared (5.1 mm long x 5.1 mm wide x 0.5 mm thick), assuming a model component of a semiconductor power device. Next, this alumina chip was placed in the center of the dried coating film, forming a laminate in which the first substrate, the coating film, and the second substrate were stacked in that order.

[0044] (4) Sintering of the laminate (manufacturing of the bonded body) Next, the laminate was heated to 250°C in a nitrogen atmosphere, and a pressure of 9 MPa was applied between the first and second parts to be joined to the laminate to produce a bonded structure. The temperature holding time and pressure holding time were set to 5 minutes. The heating rate was 14°C / second, and the pressure increasing rate was 0.6 MPa / second.

[0045] (Example 2) The bonding paste and bonded body were manufactured in the same manner as in Example 1, except that the copper particles used in Example 1(1) were replaced with other copper particles (CH-0200L1, manufactured by Mitsui Mining & Smelting Co., Ltd., spherical, average primary particle diameter = 0.14 μm). The increase in crystallite size D2 (nm) at 250°C compared to crystallite size D1 (nm) at 150°C was 8.6%. The viscosity of the bonding paste was 70 Pa·s.

[0046] (Example 3) The bonding paste and bonded body were manufactured in the same manner as in Example 1, except that the copper particles used in Example 1(1) were replaced with other copper particles (CH-0200, manufactured by Mitsui Mining & Smelting Co., Ltd., spherical, average primary particle diameter = 0.17 μm). The increase in crystallite size D2 (nm) at 250°C compared to crystallite size D1 (nm) at 150°C was 6.4%. The viscosity of the bonding paste was 42 Pa·s.

[0047] (Comparative Example 1) The bonding paste and bonded body were manufactured in the same manner as in Example 1, except that the copper particles used in Example 1(1) were replaced with other copper particles (spherical, average primary particle diameter = 0.76 μm). The increase in crystallite size D2 (nm) at 250°C compared to crystallite size D1 (nm) at 150°C was 4.4%. The viscosity of the bonding paste was 35 Pa·s.

[0048] (Comparative Example 2) The bonding paste and bonded body were manufactured in the same manner as in Example 1, except that the copper particles used in Example 1(1) were replaced with copper particles (spherical, average primary particle diameter = 0.05 μm). The increase in crystallite size D2 (nm) at 250°C compared to crystallite size D1 (nm) at 150°C was 53.7%. The viscosity of the bonding paste was 61 Pa·s.

[0049] <Evaluation of peelability in the fillet area> To evaluate the peelability at the fillet portion, a sample of a bonded material without a second bonded material was fabricated. Specifically, after preparing the dried coating in (2) above, it was heated to 250°C in a nitrogen atmosphere without going through (3). The temperature holding time was 5 minutes, and the heating rate was 14°C / second, to obtain a sample in a state similar to the bonded layer portion exposed from the alumina chip in (4). The peelability was evaluated based on a tape peel test. Specifically, adhesive tape (Nichiban Co., Ltd.: Cellotape® No. 405) was applied so as to cover the bonding layer of the prepared sample, a copper plate measuring 20 mm in length, 20 mm in width, and 2 mm in thickness was placed on top of it, and a load of 1.2 kg (including the mass of the copper plate) was applied from above for 20 seconds. After that, the load application was stopped and the copper plate was removed. The adhesive tape covering the coating was peeled off in a 180° direction at a speed of 0.1 to 1 mm / second. The mass of the bonding layer attached to the adhesive tape was measured. It is considered that the less mass of the bonding layer attached, the more difficult it is for the unpressurized portion of the bonding layer to peel off. The evaluation results of the samples for the examples and comparative examples are shown in Table 1. If the mass of the attached bonding layer is less than 0.1 mg, it will be indicated as "<0.1" mg.

[0050] [Table 1]

[0051] The bonded bodies produced using the bonding pastes of Examples 1 to 3 used copper particles with an average primary particle diameter of 0.06 μm to 1.0 μm, and an increase ratio of 5% or more in the crystallite size D2 (nm) at 250°C compared to the crystallite size D1 (nm) at 150°C. The coating film was heated at 150°C to 350°C for 45 minutes or less to sinter the copper particles, resulting in a bonded layer in the fillet portion that was less likely to peel off from the first bonded body. [Industrial applicability]

[0052] According to the present invention, it is possible to provide a method for manufacturing a bonded body in which the bonding layer in the fillet portion is less likely to peel off from the bonded body.

Claims

1. A method for manufacturing a bonded body, comprising forming a bonded layer by heating the coating film containing copper particles between a first body to be bonded and a second body to be bonded, thereby sintering the copper particles, The copper particles include those having an average primary particle diameter of 0.1 μm or more and 0.3 μm or less, and a ratio of increase in crystallite size D2 (nm) at 250°C relative to crystallite size D1 (nm) at 150°C (D2 - D1) / D1 × 100 of 6% or more and 8.9% or less. A method for manufacturing a bonded body, comprising holding the aforementioned coating film at a heating temperature of 150°C to 350°C for 1 minute to 45 minutes to sinter the copper particles.

2. The method for manufacturing a bonded body according to claim 1, wherein the aforementioned increase rate (D2 - D1) / D1 × 100 is 7.5% or more and 8.9% or less.

3. The method for manufacturing a bonded body according to claim 1 or 2, wherein the paste contains 60% by mass or more and 99% by mass or less of the copper particles.

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