Bonded body manufacturing method

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

Manufacturing method of the bonded body

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

[0002] In recent years, manufacturing methods for semiconductor devices such as IGBTs, which generate a large amount of heat when a large current is passed through them, have adopted a process of joining objects to be joined, such as semiconductor elements and circuit boards, using a joining material containing sinterable metal particles.

[0003] For example, Patent Document 1 describes a bonding material for bonding objects to be bonded at low temperatures, which has the following relationship between the temperature and the crystallite size during heating in an inert atmosphere: (a) the temperature at which the crystallite size ratio to the copper crystallite size at 30°C becomes 1.2 is 250°C or less, and (b) the change in the crystallite size ratio per unit temperature in the temperature range of 250°C to 350°C is 2.0 × 10 －３ Copper particles having the above properties are disclosed.

[0004] Japanese Patent Application Laid-Open No. 2019-2054

[0005] The copper particles described in Patent Document 1 can be said to have excellent sinterability, but tend to have large volume shrinkage, and 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 from above, cracks due to shrinkage are also noticeable at the end of the bonding layer (hereinafter also referred to as the "fillet portion") where the semiconductor element is not placed, and the bonding strength between the bonding layer and the substrate (bonded body) at the fillet portion is not fully exerted, resulting in the problem that the end of the bonding layer peels off from the substrate.

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

[0007] As a result of intensive research to solve the above problem, the inventors discovered 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 body to be bonded.

[0008] That is, the present invention provides a method for manufacturing a bonded body, which includes 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 to form a bonding layer, wherein the copper particles have an average primary particle diameter of 0.06 μm or more and 1 μm or less, and an increase rate (D2-D1) / D1×100 of crystallite diameter D2 (nm) at 250°C relative to crystallite diameter D1 (nm) at 150°C is 5% or more, and the coating film is held at a heating temperature of 150°C or more and 350°C or less for 45 minutes or less to sinter the copper particles.

[0009] Fig. 1 is a schematic diagram showing the steps of the method for producing a bonded body of the present invention, and Fig. 2 is a cross-sectional view of the bonded body obtained by the production method of the present invention.

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on preferred embodiments thereof. Fig. 1 is a process diagram illustrating a method for bonding a bonded body of the present invention, and Fig. 2 is a cross-sectional view of a bonded body obtained by the manufacturing method shown in Fig. 1.

[0011] 1(a), a paste containing copper particles is applied to a first object to be bonded 11 to form a coating film 12X. The method for applying the paste is not particularly limited, and examples thereof include screen printing, dispense printing, gravure printing, and offset printing.

[0012] The paste used in the present invention contains copper particles, an organic solvent, and an adjuster, as described below, as appropriate. 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 particularly preferably 0.3 μm or less. By having the average primary particle diameter of the copper particles be 0.06 μm or more, cracks in the bonding layer can be prevented when the paste containing the copper particles is coated and fired to form a bonding layer. This allows for excellent bonding strength between the bonded bodies (the first bonded body and the second bonded body), and increases the bonding strength between the bonding layer and the first bonded body at the fillet portion. Furthermore, by having the average primary particle diameter of the copper particles be 1 μm or less, the crystallite size increase ratio (D2-D1) / D1×100, as described below, can be easily adjusted to a suitable range.

[0013] Furthermore, the copper particles have an increase ratio (D2-D1) / D1 x 100 of the crystallite diameter D2 (nm) at 250 °C relative to the crystallite diameter D1 (nm) at 150 °C of 5% or more, preferably 6% or more, more preferably 7.5% or more, and even more preferably 8% or more. The increase ratio (D2-D1) / D1 x 100 is an indicator of the sinterability of the copper particles. When the copper particles have the above-mentioned average primary particle diameter in addition to the increase ratio, 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 bonding layer at the fillet portion does not peel from the first bonded body. In the following description, for simplicity, the term "increase ratio" refers to the value calculated from "(D2-D1) / D1 x 100". There is no particular limitation on the upper limit of the increase ratio, but it can be approximately 100%. Copper particles having an increase rate of 5% or more are not obtained by a special manufacturing method, and can be adjusted by the types of copper source, organic surface treatment agent, reducing agent, organic solvent, etc. used in the manufacture of the copper particles, as well as the reaction time and reaction temperature during manufacture. Alternatively, copper particles having an increase rate of 5% or more can be appropriately selected and used from commonly used copper particles.

[0014] By having the increase rate of 5% or more and the average primary particle diameter within the above-mentioned range, the sintering properties of the copper particles are good. Moreover, excessive volume shrinkage of the copper particles can be prevented, so that the bonding between the first bonded body and the second bonded body proceeds sufficiently without shrinkage cracking 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 bonded body at the fillet portion is excellent. The proportion of copper particles that satisfy the 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 calculated by randomly selecting 50 or more copper particles with clearly defined contours from a scanning electron microscope image of the copper particles magnified at a magnification of 10,000 times or more and 150,000 times or less, measuring the particle diameter (Heywood diameter) of the particles, and then calculating the volume of the particles assuming that they are true spheres from the obtained particle diameters.

[0016] The crystallite size of the copper particles in the present invention is determined by analyzing the X-ray diffraction pattern obtained by XRD measurement based on the high-temperature XRD (powder X-ray diffraction) method, and then calculating it using the Scherrer formula. The high-temperature XRD method involves placing the measurement sample in a high-temperature unit that can heat the sample, and performing XRD measurement while gradually heating it. The XRD measurement is performed using a fully automatic horizontal multipurpose X-ray diffractometer manufactured by Rigaku Corporation and a high-speed two-dimensional X-ray detector PILATUS100K / R manufactured by the same company 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° (X-ray diffraction intensity corresponding to 2θ = 38 to 48° can be obtained with the two-dimensional detector described above) Exposure time: 60 seconds Collimator: Φ0.2 mm Measurement atmosphere: Nitrogen Measurement temperature: 150, 250°C Heating rate: 10°C / min The measurement temperature is maintained without heating during XRD measurement (exposure time 60 seconds) at each measurement temperature.

[0017] Next, the crystallite diameter is calculated from the half-width of the X-ray diffraction pattern of the crystal plane (111) of the copper particle obtained by the above-mentioned XRD measurement using the following Scherrer formula: Scherrer formula: D = Kλ / β cos θ D: crystallite diameter K: Scherrer constant (0.94) λ: X-ray wavelength β: half-width [rad] θ: Bragg angle [rad]

[0018] The shape and properties of the copper particles are not particularly limited. For example, the shape may be spherical, polyhedral, flat, irregular, or a combination thereof. Among these, spherical, flat, or a combination thereof is preferred. The copper particles may be in the form of a powder, or may be in the form of a paste or slurry in which the copper particles are dispersed in an organic solvent.

[0019] The copper particles may have a surface treatment agent attached to their surfaces. By attaching a surface treatment agent to the surfaces of the copper particles, excessive aggregation of the copper particles can be suppressed.

[0020] The surface treatment agent is not particularly limited, and examples thereof include fatty acids, aliphatic amines, and complexes that have adsorption properties 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 or printing properties of the paste, the viscosity of the paste is measured at a shear rate of 10 s －１ The viscosity value at this time 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 conditions for measuring the viscosity of the paste are as follows: Measurement mode: Shear rate dependency measurement Sensor: Parallel type (Φ20 mm) Measurement temperature: 25°C Gap: 0.300 mm Shear rate: 0.05 to 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 a sufficient thickness of the bonding layer described below and sufficient bonding strength between the bonding layer and the bonded bodies. On the other hand, from the viewpoint of preventing cracks from occurring in the bonding layer during the process of baking the coating film 12X to form the bonding layer, which would reduce the bonding strength between the bonded bodies (the first bonded body and the second bonded body), or preventing the bonding layer at the fillet portion from peeling off from the first bonded body, the thickness is preferably 500 μm or less, more preferably 300 μm or less.

[0023] From the viewpoint of improving the applicability of the paste to the workpiece and the shape retention of the coating film 12X, the content of copper particles in the paste is preferably 60% by mass or more and 99% by mass or less, more preferably 65% ​​by mass or more and 95% by mass or less, and particularly preferably 70% by mass or more and 93% by mass or less.

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

[0025] As described above, the paste may contain an appropriate modifier for adjusting various properties, such as a reducing agent, a viscosity modifier, and a surface tension modifier.

[0026] The reducing agent is preferably one that promotes sintering of copper particles, and examples thereof include monoalcohols, polyhydric alcohols, amino alcohols, citric acid, oxalic acid, formic acid, ascorbic acid, aldehydes, hydrazine and its derivatives, hydroxylamine and its derivatives, dithiothreitol, phosphites, hydrophosphites, and phosphorous acid and its derivatives.

[0027] The viscosity adjuster is preferably one that can adjust the viscosity of the paste, preferably within the above-mentioned viscosity range, and examples thereof include ketones, esters, alcohols, glycols, hydrocarbons, and polymers.

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

[0029] Next, as shown in FIG. 1( b), the coating film 12X is dried at a temperature below the sintering temperature of the copper particles constituting the coating film 12X. The drying temperature must be a temperature that evaporates the organic solvent, adjusters, etc. in the coating film 12X, but does not sinter the copper particles as described above. Therefore, assuming that the drying temperature is lower than the sintering temperature described below, the drying temperature is preferably 50°C or higher and 160°C or lower, more preferably 60°C or higher and 150°C or lower. It is not necessary to remove the entire amount of the organic solvent; it is sufficient that the organic solvent is removed to the extent that the coating film 12X loses its fluidity. Therefore, the 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 film 12X can be dried in an inert atmosphere or in the air. Alternatively, the coating film 12X may be dried under reduced pressure. The drying time may be long enough to evaporate the organic solvent, adjusters, etc. in the coating film 12X and remove the organic solvent to the extent that the coating film 12X loses its fluidity, as described above.

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

[0032] There are no particular limitations on the types of the first bonded body 11 and the second bonded body 13. In general, it is preferable that both the first bonded body 11 and the second bonded body 13 contain a metal on the bonding surface thereof. For example, a member having a surface made of metal can be used as at least one of the first bonded body 11 and the second bonded body 13. Note that, as used herein, "metal" refers to a metal itself that does not form a compound with other elements, or an alloy of two or more metals. Examples of such metals include copper, silver, gold, aluminum, palladium, nickel, and alloys made of a combination of two or more of these.

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

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

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

[0036] Next, as shown in Figure 1 (d), the laminate 15 is sandwiched between a predetermined jig (not shown), and the laminate 15, i.e., the coating film 12X, is heated under pressure to 150 ° C or higher and 350 ° C or lower, preferably 170 ° C or higher and 330 ° C or lower, more preferably 190 ° C or higher and 310 ° C or lower. At this heating temperature, the temperature is maintained for preferably 45 minutes or less, more preferably 1 minute or higher and 40 minutes or lower, particularly preferably 2 minutes or higher and 35 minutes or lower, and even more preferably 2 minutes or higher and 20 minutes or lower, 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 bonded object from being damaged by heat and 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, and as shown in Fig. 2, the fillet portion 12A of the bonding layer 12 on which the second object to be bonded 13 is not placed also does not peel off from the first object to be bonded 11. As a result, the bonding layer 12 is bonded with high bonding strength not only to the second object to be bonded 13 but also to the first object to be bonded 11, and a laminate 15 can be obtained in which peeling does not occur.

[0038] 1 , the laminate 15 is pressurized using a jig to bond the first and second objects to be bonded 11 and 13 by the bonding layer 12. However, the first and second objects to be bonded 11 and 13 may be bonded by the bonding layer 12 without pressurizing the laminate 15. In this case, the bonding layer 12 at the fillet portion 12A does not peel from the first object to be bonded 11. As a result, the bonding layer 12 is bonded with high bonding strength not only to the second object to be bonded 13 but also to the first object to be bonded 11, thereby obtaining a laminate 15 that does not peel. When bonding the laminate 15 while pressurizing it as described above, it is preferable to apply a pressure of 0.1 MPa or more and 40 MPa or less from the viewpoint of sufficiently bonding the first and second objects to be bonded 11 and 13 via the bonding layer 12.

[0039] The bonded body obtained by the manufacturing method of the present invention is suitable for use in, for example, in-vehicle electronic circuits and electronic circuits equipped with power devices, taking advantage of the high bonding properties between the bonded body and the bonding layer at the fillet portion.

[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 such examples. Unless otherwise specified, "%" means "% by mass."

[0041] (Example 1) (1) Preparation of Bonding Paste Copper particles (Mitsui Mining & Smelting Co., Ltd. CH-0200L1, spherical, average primary particle diameter 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 (final gap 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 diameter D2 (nm) of the copper particles at 250 °C relative to the crystallite diameter D1 (nm) at 150 °C was 8.9%.

[0042] (2) Application of the bonding paste to the first bonded object: The bonding paste was printed on 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 in length, 10 mm in width, and 100 μm in thickness to form a rectangular coating film. This coating film was dried in the air at 90° C. for 20 minutes to remove the organic solvent.

[0043] (3) Placing the second bonded body on the dried coating film (forming a laminate) Assuming that the second bonded body was a model component of a semiconductor power device, an Ag-plated alumina chip (length 5.1 mm × width 5.1 mm × thickness 0.5 mm) was prepared. Next, this alumina chip was placed at the center of the dried coating film, and a laminate was formed in which the first bonded body, the coating film, and the second bonded body were laminated in this order.

[0044] (4) Sintering of the laminate (production of a 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 bonded bodies of the laminate to produce a bonded body. The temperature holding time and pressure holding time were 5 minutes. The temperature rise rate was 14°C / sec, and the pressure rise rate was 0.6 MPa / sec.

[0045] (Example 2) A bonding paste and a bonded body were produced in the same manner as in Example 1, except that the copper particles used in (1) of Example 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 the crystallite diameter D2 (nm) at 250 ° C relative to the crystallite diameter D1 (nm) at 150 ° C was 8.6%. The viscosity of the bonding paste was 70 Pa s.

[0046] (Example 3) A bonding paste and a bonded body were produced in the same manner as in Example 1, except that the copper particles used in (1) of Example 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 the crystallite diameter D2 (nm) at 250 ° C relative to the crystallite diameter D1 (nm) at 150 ° C was 6.4%. The viscosity of the bonding paste was 42 Pa s.

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

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

[0049] <Evaluation of Peelability at Fillet Portion> To evaluate peelability at the fillet portion, a bonded sample was prepared without a second bonded body. Specifically, after preparing a dried coating film as described above in (2), the sample was heated to 250°C in a nitrogen atmosphere without passing through (3). The temperature was maintained for 5 minutes, and the heating rate was 14°C / sec. A sample similar to the bonding layer portion exposed from the alumina chip in (4) was obtained. Peelability was evaluated based on a tape peeling test. Specifically, adhesive tape (Nichiban Co., Ltd.: Cellotape (registered trademark) No. 405) was applied 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 the tape. A load of 1.2 kg (including the mass of the copper plate) was applied for 20 seconds. The load application was then stopped, and the copper plate was removed. The adhesive tape covering the coating film was peeled off in a 180° direction at a speed of 0.1 to 1 mm / sec. The mass of the bonding layer attached to the adhesive tape was measured. It is believed that the smaller the mass of the attached bonding layer, the less likely the unpressurized portion of the bonding layer will peel off. The evaluation results of the samples of the examples and comparative examples are shown in Table 1. Those with a mass of the attached bonding layer of less than 0.1 mg are indicated as "<0.1" mg.

[0050]

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

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

Claims

1. A method for manufacturing a bonded body, which comprises 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 to form a bonding layer, wherein the copper particles have an average primary particle size of 0.06 μm or more and 1 μm or less, and the increase rate (D2 - D1) / D1 x 100 of the crystallite diameter D2 (nm) at 250°C relative to the crystallite diameter D1 (nm) at 150°C is 5% or more, and the coating film is held at a heating temperature of 150°C to 350°C for 45 minutes or less to sinter the copper particles.

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

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.

Images