Bonding layer, bonded body, and method for manufacturing bonded body

Abstract

To prevent a joint layer from decreasing in strength.SOLUTION: A joint layer 20 comprises sintered copper for joining members together. The joint layer 20 has a sintering density of 80% or more and contains phosphorus.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a bonding layer, a bonded body, and a method for manufacturing a bonded body.

Background Art

[0002] When joining two or more components, a bonding material is generally used. For example, Patent Document 1 describes that solder is used as a bonding material. In recent years, the heat resistance of non-bonded objects such as semiconductor elements has improved, and they are increasingly used in high-temperature environments such as an automobile engine room. Therefore, as shown in Patent Document 2, silver paste may be used as a bonding material in some cases. Silver paste can be sintered under relatively low-temperature conditions, and the melting point of the bonding layer formed after sintering is equivalent to that of silver. Therefore, the bonding layer composed of the sintered body of this silver paste is excellent in heat resistance and can be stably used even in high-temperature environments or high-current applications. On the other hand, from the perspective of material cost, as shown in Patent Document 3, copper paste may be used as a bonding material in some cases.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since copper is easily oxidized, the strength of the bonding layer composed of a sintered body of copper may decrease.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a bonding layer, a bonded body, and a method for manufacturing a bonded body in which a decrease in strength is suppressed.

Means for Solving the Problems

[0006] In order to solve the above problems, the bonding layer of the present disclosure is a sintered body of copper that bonds members to each other, has a sintering density of 80% or more, and contains phosphorus.

[0007] In order to solve the above problems, the method for manufacturing a bonded body of the present disclosure includes copper particles, a solvent, and an additive composed of a phosphate ester, and the content of the additive is 0.5% or more and 3.0% or less by mass ratio. A coating layer forming step of applying a bonding paste to at least one surface of a first member and a second member to form a coating layer, a superposing step of superposing the first member and the second member via the coating layer, and heating the first member and the second member superposed via the coating layer to form a bonded body. The heating step includes heating at a temperature of 200°C or more and 300°C or less for 1 minute or more and 10 minutes or less while applying a pressure of 0.5 MPa or more and 10 MPa or less to at least one of the first member and the second member in a non-reducing atmosphere.

Effects of the Invention

[0008] According to the present invention, it is possible to suppress a decrease in strength.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the following embodiments (hereinafter referred to as embodiments) for carrying out the present invention. Further, the constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art, substantially the same ones, and those within the so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate. Also, the range of rounding off is included for numerical values.

[0011] Figure 1 is a schematic diagram of the bonding paste according to this embodiment. The bonding paste of this embodiment is used for bonding members. As shown in Figure 1, the bonding paste 10 of this embodiment contains copper particles 12, a solvent 14, and an additive 16. Note that Figure 1 is a schematic diagram, and the actual shape of the bonding paste 10 is not limited to that shown in Figure 1.

[0012] (Copper particles) The BET diameter of the copper particles 12 is preferably 50 nm or more and 300 nm or less. The BET diameter is the particle diameter calculated from the BET specific surface area and the true density of the copper particles determined by the BET method assuming the copper particles 12 as a perfect sphere or a cube. Specifically, it can be determined by the method described in the examples described later.

[0013] When the BET diameter of the copper particles 12 is 50 nm or more, it is difficult to form strong aggregates. Therefore, the surface of the copper particles 12 can be uniformly coated with the solvent 14. On the other hand, when the BET diameter of the copper particles 12 is 300 nm or less, the reaction area is large and the sinterability by heating is high, so a strong bonding layer can be formed. The BET diameter of the copper particles 12 is preferably in the range of 80 nm or more and 200 nm or less, and particularly preferably in the range of 80 nm or more and 170 nm or less.

[0014] The BET specific surface area of the copper particles 12 is preferably in the range of 2.0 m 2 / g or more and 8.0 m 2 / g or less, more preferably in the range of 3.5 m 2 / g or more and 8.0 m 2 / g or less, and particularly preferably 4.0 m2 8.0 m or more per g 2 Particularly preferably, it is within the range of 8.0 m or less per g. Further, the shape of the copper particles 12 is not limited to spherical, and may be needle-shaped or flat plate-shaped.

[0015] The surface of the copper particles 12 is preferably coated with an organic protective film that is a film of an organic substance. By being coated with the organic protective film, oxidation of the copper particles 12 is suppressed, and it becomes even less likely for a decrease in sinterability due to oxidation of the copper particles 12 to occur. Note that it can be said that the organic protective film that coats the copper particles 12 is not formed by the solvent 14 and is not derived from the solvent 14. Also, it can be said that the organic protective film that coats the copper particles 12 is not a film of copper oxide formed by oxidation of copper.

[0016] That the copper particles 12 are coated with an organic protective film can be confirmed by analyzing the surface of the copper particles 12 using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Therefore, in the present embodiment, the copper particles 12 are detected by analyzing the surface using time-of-flight secondary ion mass spectrometry, and the Cu + ion detection amount to C3H3O3 - ion detection amount ratio (C3H3O3 - / Cu + ratio) is preferably 0.001 or more. The C3H3O3 - / Cu + ratio is more preferably within the range of 0.05 or more and 0.2 or less. Note that the surface of the copper particles 12 in this analysis refers to the surface of the copper particles 12 including the coating organic protective film (that is, the surface of the organic protective film), not the surface of the copper particles 12 when the organic protective film is removed from the copper particles 12.

[0017] The copper particles 12 may be analyzed for the surface using time-of-flight secondary ion mass spectrometry, and C3H4O2 - ions and ions of C5 or more may be detected. The C3H4O2 + ion detection amount to the Cu - ion detection amount ratio (C3H4O2 - / Cu +The ratio is preferably 0.001 or more. + The ratio of the amount of ions detected that are C5 or more to the amount of ions detected (C5 or more ions / Cu + It is preferable that the ratio is less than 0.005.

[0018] C3H3O3 detected by time-of-flight secondary ion mass spectrometry - Ions and C3H4O2 - The C3H3O3 ions and C5 or higher ions originate from the organic protective film that covers the surface of the copper particles 12. - / Cu + Ratio and C3H4O2 - / Cu + When each of the ratios is 0.001 or more, the surface of the copper particles 12 is less likely to be oxidized, and the copper particles 12 are less likely to aggregate. - / Cu + Ratio and C3H4O2 - / Cu + When the ratio is 0.2 or less, the oxidation and aggregation of the copper particles 12 can be suppressed without excessively decreasing the sinterability of the copper particles 12, and further, the generation of decomposition gas of the organic protective film during heating can be suppressed, so that a bonding layer with fewer voids can be formed. - / Cu + Ratio and C3H4O2 - / Cu + The ratio is preferably in the range of 0.08 to 0.16. + If the ratio is 0.005 or more, the particle surface will have a large amount of organic protective film with a relatively high desorption temperature, resulting in insufficient sintering and making it difficult to obtain a strong bonding layer. + Preferably, the ratio is less than 0.003.

[0019] The organic protective film is preferably derived from citric acid. A method for producing the copper particles 12 coated with the organic protective film derived from citric acid will be described later. The coating amount of the organic protective film on the copper particles 12 is preferably in the range of 0.5% by mass or more and 2.0% by mass or less, more preferably in the range of 0.8% by mass or more and 1.8% by mass or less, and even more preferably in the range of 0.8% by mass or more and 1.5% by mass or less with respect to 100% by mass of the copper particles. When the coating amount of the organic protective film is 0.5% by mass or more, the copper particles 12 can be uniformly coated with the organic protective film, and the oxidation of the copper particles 12 can be more reliably suppressed. Further, when the coating amount of the organic protective film is 2.0% by mass or less, it is possible to suppress the generation of voids in the sintered body (bonding layer) of the copper particles due to the gas generated by the decomposition of the organic protective film by heating. The coating amount of the organic protective film can be measured using a commercially available device. For example, the coating amount can be measured using a differential scanning calorimeter TG8120-SL (manufactured by Rigaku Corporation). In this case, for example, the sample uses copper particles from which moisture has been removed by freeze-drying. In order to suppress the oxidation of the copper particles, the measurement is performed in a nitrogen (G2 grade) gas atmosphere, the heating rate is 10 ° C / min, and the weight loss rate when heated from 250 ° C to 300 ° C can be defined as the coating amount of the organic protective film. That is, the coating amount = (weight of the sample after measurement) / (weight of the sample before measurement) × 100 (wt%). The measurement is performed three times for each copper particles of the same lot, and the arithmetic mean value may be used as the coating amount.

[0020] When the copper particles 12 are heated at a temperature of 300 ° C for 30 minutes in an inert gas atmosphere such as argon gas, it is preferable that 50% by mass or more of the organic protective film decomposes. The organic protective film derived from citric acid generates carbon dioxide gas, nitrogen gas, evaporation gas of acetone, and water vapor during decomposition.

[0021] The copper particles 12 coated with an organic protective film derived from citric acid can be produced, for example, as follows. First, a water dispersion of copper citrate is prepared, and a pH adjuster is added to this copper citrate water dispersion to adjust the pH to 2.0 or higher and 7.5 or lower. Next, in an inert gas atmosphere, a hydrazine compound in an amount of 1.0 to 1.2 times the equivalent amount capable of reducing copper ions is added as a reducing agent to the pH-adjusted copper citrate water dispersion and mixed. The resulting mixture is heated to a temperature of 60°C or higher and 80°C or lower and held for 1.5 hours or longer and 2.5 hours or shorter in an inert gas atmosphere. Thereby, the copper ions eluted from copper citrate are reduced to generate copper particles 12, and an organic protective film derived from citric acid is formed on the surface of the copper particles 12.

[0022] The water dispersion of copper citrate can be prepared by adding powdery copper citrate to pure water such as distilled water or ion-exchanged water so that the concentration becomes 25% by mass or higher and 40% by mass or lower, and stirring with a stirring blade to uniformly disperse it. Examples of the pH adjuster include ammonium citrate tribasic, ammonium hydrogen citrate, and citric acid. Among these, ammonium citrate tribasic is preferred because it is easy to adjust the pH mildly. The reason for setting the pH of the copper citrate water dispersion to 2.0 or higher is to increase the elution rate of copper ions eluted from copper citrate and to rapidly proceed with the formation of copper particles so as to obtain the target fine copper particles 12. Also, the reason for setting the pH to 7.5 or lower is to suppress the eluted copper ions from becoming copper(II) hydroxide and to increase the yield of the copper particles 12. Further, by setting the pH to 7.5 or lower, it is possible to suppress the reducing power of the hydrazine compound from becoming excessively high, and the target copper particles 12 can be easily obtained. The pH of the copper citrate water dispersion is preferably adjusted within the range of 4 or higher and 6 or lower.

[0023] The reduction of copper citrate with a hydrazine compound is carried out in an inert gas atmosphere. This is to prevent the oxidation of copper ions eluted in the liquid. Examples of inert gases include nitrogen gas, argon gas, etc. The hydrazine compound has advantages such as not producing residues after the reduction reaction, relatively high safety, and easy handling when reducing copper citrate under acidic conditions. Examples of this hydrazine compound include hydrazine monohydrate, anhydrous hydrazine, hydrazine hydrochloride, hydrazine sulfate, etc. Among these hydrazine compounds, hydrazine monohydrate and anhydrous hydrazine, which do not contain components that can become impurities such as sulfur and chlorine, are preferred.

[0024] Generally, copper generated in an acidic solution with a pH less than 7 will dissolve. However, in this embodiment, a hydrazine compound as a reducing agent is added and mixed into an acidic solution with a pH less than 7 to generate copper particles 12 in the resulting mixed solution. Therefore, the components derived from citric acid generated from copper citrate quickly coat the surface of the copper particles 12, suppressing the dissolution of the copper particles 12. The aqueous dispersion of copper citrate after adjusting the pH is preferably set at a temperature of 50°C or higher and 70°C or lower to facilitate the progress of the reduction reaction.

[0025] Mixing a hydrazine compound in an inert gas atmosphere and heating the resulting mixture to a temperature of 60°C or higher and 80°C or lower, and holding it for 1.5 hours or longer and 2.5 hours or shorter, is to generate copper particles 12 and form and coat an organic protective film on the surface of the generated copper particles 12. Heating and holding in an inert gas atmosphere is to prevent oxidation of the generated copper particles 12. Copper citrate, which is the starting material, usually contains about 35% by mass of a copper component. By adding a hydrazine compound, which is a reducing agent, to a copper citrate aqueous dispersion containing this amount of copper component, heating the mixture while raising the temperature to the above temperature, and holding it for the above time, the generation of copper particles 12 and the generation of an organic protective film on the surface of the copper particles 12 proceed in good balance. Thus, copper particles 12 can be obtained in which the coating amount of the organic protective film is in the range of 0.5% by mass or more and 2.0% by mass or less with respect to 100% by mass of the copper particles. If the heating temperature is less than 60°C and the holding time is less than 1.5 hours, copper citrate may not be completely reduced, the generation rate of copper particles 12 may become too slow, and the amount of the organic protective film coating the copper particles 12 may become excessive. Also, if the heating temperature exceeds 80°C and the holding time exceeds 2.5 hours, the generation rate of copper particles 12 may become too fast, and the amount of the organic protective film coating the copper particles 12 may become too small. The preferred heating temperature is 65°C or higher and 75°C or lower, and the preferred holding time is 2 hours or longer and 2.5 hours or shorter.

[0026] The copper particles 12 generated in the mixture are separated from the mixture in an inert gas atmosphere, for example, using a centrifuge, and dried by freeze-drying or vacuum drying to obtain copper particles 12 whose surfaces are coated with an organic protective film. Since the surfaces of these copper particles 12 are coated with an organic protective film, they are less likely to oxidize even when stored in the atmosphere until they are used as the bonding paste 10.

[0027] (Solvent) The solvent 14 acts as a binder for the copper particles 12. The solvent 14 is an organic solvent. Any substance may be used as the solvent 14, and examples thereof include alcohol solvents, glycol solvents, acetate solvents, hydrocarbon solvents, and amine solvents. Specific examples of alcohol solvents include α-terpineol and isopropyl alcohol. Specific examples of glycol solvents include ethylene glycol, diethylene glycol, and polyethylene glycol. A specific example of an acetate solvent is butyl acetate carbitol. Specific examples of hydrocarbon solvents include decane, dodecane, and tetradecane. Specific examples of amine solvents include hexylamine, octylamine, and dodecylamine.

[0028] (Additive) The additive 16 is a phosphate ester. Among organic phosphate compounds, an ester formed by dehydration condensation of phosphoric acid and alcohol may be referred to as a phosphate ester. The phosphate ester used as the additive 16 preferably has an average molecular weight of 1000 or more and 2000 or less, more preferably 1200 or more and 1800 or less, and even more preferably 1400 or more and 1600 or less. When the average molecular weight of the phosphate ester is 1000 or more, decomposition at room temperature is suppressed and storage stability is improved. When it is 2000 or less, decomposition and reaction at the target heating temperature (about 200 to 350 °C) become possible. The average molecular weight here refers to the weight average molecular weight. The average molecular weight can be measured, for example, by size exclusion chromatography.

[0029] The phosphate ester used for the additive 16 may be any one, and examples thereof include lauryl-n-phosphate, oleyl-n-phosphate, stearyl-n-phosphate (n is an integer), and the like. As the additive 16, one of these may be used, or two or more thereof may be used.

[0030] (Bonding paste) In this embodiment, the bonding paste 10 preferably contains no substances other than copper particles 12, a solvent 14, and an additive 16 composed of a phosphate ester, excluding inevitable impurities. However, it is not limited thereto, and the bonding paste 10 may contain an additive other than the copper particles 12, the solvent 14, and the additive 16 composed of a phosphate ester.

[0031] The content of the additive 16 in the bonding paste 10 is preferably 0.5% or more and 3.0% or less, more preferably 0.5% or more and 2.0% or less, and even more preferably 1.0% or more and 1.5% or less, by mass ratio with respect to the entire bonding paste 10. When the content of the additive 16 is within this range, oxidation of the copper particles 12 can be suppressed, and as a result, a decrease in the strength of the bonding layer when members are bonded using the bonding paste 10 in a non-reducing atmosphere can be appropriately suppressed.

[0032] The content of the solvent 14 in the bonding paste 10 is preferably 5% or more and 20% or less, more preferably 5% or more and 15% or less, and even more preferably 8% or more and 13% or less, by mass ratio with respect to the entire bonding paste 10. When the content of the solvent 14 is within this range, the copper particles 12 can be appropriately dispersed.

[0033] (Method for manufacturing the bonding paste) The bonding paste 10 is manufactured by performing a mixing step of mixing the copper particles 12, the solvent 14, and the additive 16. In this mixing step, the copper particles 12, the solvent 14, and the additive 16 are mixed so that the content of the additive 16 is 0.5% or more and 3.0% or less by mass ratio with respect to the entire bonding paste 10. Also, in the mixing step, the copper particles 12, the solvent 14, and the additive 16 are mixed so that the contents of the solvent 14 and the copper particles 12 with respect to the entire bonding paste 10 are also within the above ranges. Further, in the mixing step, the copper particles 12, the solvent 14, and the additive 16 may be mixed using a kneading device. As the kneading device, for example, a three-roll mill is used.

[0034] (Method for manufacturing the bonded body) FIG. 2 is a schematic diagram of the joined body according to the present embodiment. As shown in FIG. 2, in the present embodiment, the joining paste 10 is used as the joining layer 20 to join the first member 21 and the second member 22 to manufacture the joined body 30. The first member 21 and the second member 22 may be arbitrary. For example, one of the first member 21 and the second base material may be a substrate and the other may be an electronic component. That is, a semiconductor module in which a substrate and an electronic component are joined by the joining layer 20 may be manufactured as the joined body 30. The substrate is not particularly limited, and examples thereof include an oxygen-free copper plate, a copper molybdenum plate, a high heat dissipation insulating substrate (for example, DCB (Direct Copper Bond)), a substrate for mounting semiconductor elements such as an LED (Light Emitting Diode) package, and the like. Examples of the electronic component include semiconductor elements such as an IGBT (Insulated Gate Bipolar Transistor), a diode, a Schottky barrier diode, a MOS-FET (Metal Oxide Semiconductor Field Effect Transistor), a thyristor, a logic, a sensor, an analog integrated circuit, an LED, a semiconductor laser, and a transmitter.

[0035] In this manufacturing method, a coating layer forming step of applying the joining paste 10 to at least one surface of the first member 21 and the second member 22 to form a coating layer is performed. The coating method is not particularly limited, and examples thereof include a spin coating method, a metal mask method, a spray coating method, a dispenser coating method, a knife coating method, a slit coating method, an inkjet coating method, a screen printing method, an offset printing method, a die coating method, and the like. Next, a preheating step is performed at a temperature of 50°C to 150°C for 1 minute to 30 minutes to volatilize the solvent in the paste. Next, a superposing step of superposing the first member 21 and the second member 22 through the coating layer is performed.

[0036] Next, a heating step of heating the first member 21 and the second member 22 superposed via the coating layer is performed. In the heating step, in a non-reducing atmosphere, while applying a predetermined pressure to at least one of the superposed first member 21 and second member 22, heating is performed at a predetermined temperature for a predetermined time. By performing the heating step, the copper particles 12 in the coating layer are sintered to form the bonding layer 20, and a bonded body 30 in which the first member 21 and the second member 22 are bonded by the bonding layer 20 is manufactured.

[0037] The non-reducing atmosphere in the heating step refers to a state filled with a non-reducing gas and can also be called an inert gas atmosphere filled with an inert gas. Examples of the non-reducing gas include nitrogen and noble gases such as argon. For example, in the present embodiment, the heating step may be performed in a nitrogen atmosphere with an oxygen concentration of 1000 ppm. By performing the heating step in a non-reducing atmosphere, it is not necessary to use a reducing gas, and the heating step can be easily performed.

[0038] Also, the predetermined pressure applied to at least one of the first member 21 and the second member 22 is preferably 0.5 MPa or more and 10 MPa or less, more preferably 1 MPa or more and 5 MPa or less, and even more preferably 2 MPa or more and 5 MPa or less. By setting the applied pressure within such a relatively low range, while appropriately bonding the first member 21 and the second member 22, defective shape of the bonding layer 20 can be suppressed. Here, the pressure is applied in a direction in which the first member 21 and the second member 22 are relatively pressed against each other via the coating layer.

[0039] Also, the predetermined temperature, which is the heating temperature in the heating step, is preferably 200°C or more and 300°C or less, more preferably 230°C or more and 300°C or less, and even more preferably 250°C or more and 300°C or less. By setting the heating temperature within such a relatively low range, while appropriately sintering the copper particles 12, defective shape of the bonding layer 20 can be suppressed.

[0040] In addition, the predetermined time, which is the heating time in the heating step, is preferably 1 minute or more and 10 minutes or less, more preferably 1 minute or more and 5 minutes or less, and even more preferably 1 minute or more and 3 minutes or less. By setting the heating time within this range, the copper particles 12 can be appropriately sintered.

[0041] (Bonding layer) As described above, the bonding layer 20 in the present embodiment is formed by heating the bonding paste 10 and sintering the copper particles 12. The bonding layer 20 is located between the first member 21 and the second member 22 and bonds the first member 21 and the second member 22. It can be said that the bonding layer 20 is a sintered body of copper. The sintering density of the bonding layer 20 is preferably 80% or more, more preferably 85% or more and 95% or less, and even more preferably 85% or more and 90% or less. By setting the sintering density within this range, the bonding layer 20 can ensure electrical conductivity and thermal conductivity. Note that the sintering density refers to the ratio of the volume of the bonding layer 20 excluding open pores and closed pores to the total volume of the bonding layer 20 including open pores and closed pores. The sintering density is obtained by binarizing an image randomly acquired at a magnification of 50,000 times of the cross-section of the bonding layer with a SEM (Scanning Electron Microscope) using image processing software (ImageJ manufactured by the National Institutes of Health, USA), dividing it into a particle part and a pore part, and calculating the sintering density from the following formula. Sintering density (%) = (total area of particle part / (total area of particle part + total area of pore part)) × 100

[0042] In addition, the bonding layer 20 contains phosphorus. The phosphorus here refers to phosphorus as an element, including not only elemental phosphorus but also phosphorus contained in any compound. The content of phosphorus in the bonding layer 20 is preferably 100 ppm or more and 1000 ppm or less, more preferably 100 ppm or more and 500 ppm or less, and even more preferably 200 ppm or more and 500 ppm or less, in terms of mass ratio with respect to the entire bonding layer 20. When the content of phosphorus is within this range, the bonding layer 20 can suppress a decrease in strength even when formed, for example, in a non-reducing atmosphere. The content of phosphorus can be measured by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer). In this embodiment, the phosphorus contained in the bonding layer 20 is derived from the phosphate ester contained in the bonding paste 10.

[0043] Also, the thickness of the bonding layer 20 is preferably 10 μm or more and 200 μm or less, more preferably 20 μm or more and 150 μm or less, and even more preferably 50 μm or more and 100 μm or less. When the thickness of the bonding layer 20 is within this range, it is possible to maintain high heat dissipation while relaxing the stress due to the difference in the linear expansion coefficient between members caused by the temperature difference.

[0044] As described above, the bonding layer 20 according to this embodiment is a copper sintered body having a sintering density of 80% or more and containing phosphorus. Since the sintering density of the bonding layer 20 according to this embodiment is 80% or more, a decrease in strength is suppressed. Furthermore, since the oxidation of the copper particles 12 is suppressed by the origin of phosphorus (phosphate ester in this embodiment) contained in the bonding layer 20, as a result, the bonding layer 20 containing phosphorus suppresses a decrease in strength. Note that the bonding layer 20 in this embodiment is formed by heating the bonding paste 10 as described above, but the formation method of the bonding layer 20 may be arbitrary as long as it satisfies the above characteristics.

[0045] (Effect) As described above, the bonding layer 20 according to the present embodiment is a sintered body of copper that bonds members to each other, has a sintering density of 80% or more, and contains phosphorus. The bonding layer 20 according to the present embodiment has a sintering density of 80% or more, and oxidation of the copper particles 12 is suppressed by a phosphorus-derived substance (phosphoric acid ester in the present embodiment), so that a decrease in strength is suppressed.

[0046] Further, the method for manufacturing the bonded body 30 according to the present embodiment includes a coating layer forming step, a superposing step, and a heating step. In the coating layer forming step, a bonding paste 10 containing copper particles 12, a solvent 14, and an additive 16 composed of a phosphoric acid ester, and having a content of the additive 16 of 0.5% or more and 3.0% or less by mass ratio is applied to at least one surface of the first member 21 and the second member 22 to form a coating layer. In the superposing step, the first member 21 and the second member 22 are superposed via the coating layer. In the heating step, the first member 21 and the second member 22 superposed via the coating layer are heated to form the bonded body 30. In the heating step, in a non-reducing atmosphere, while applying a pressure of 0.5 MPa or more and 10 MPa or less to at least one of the first member 21 and the second member 22, heating is performed at a temperature of 200°C or more and 300°C or less for 1 minute or more and 10 minutes or less. According to this manufacturing method, by using the bonding paste 10 to which a phosphoric acid ester is added as an additive, oxidation of the copper particles 12 is suppressed, and as a result, even when the members are bonded to each other in a non-reducing atmosphere, a decrease in the strength of the bonding layer 20 can be suppressed.

[0047] (Example) Next, examples will be described.

[0048] (Example 1) In Example 1, copper particles having a BET diameter of 400 nm were prepared. The BET diameter was measured by measuring the nitrogen gas adsorption amount of the copper particles using a specific surface area measuring device (manufactured by Quantachrome Instruments, QUANTACHROME AUTOSORB-1), and the specific surface area of the copper particles was determined by the BET method. The obtained specific surface area S (m 2 / g) and the density ρ (g / cm 3) Using the following formula, the BET diameter was calculated. BET diameter (nm) = 6000 / (ρ (g / cm 3 ) × S (m 2 / g)) In Example 1, oleth-10 phosphate was prepared as the phosphate ester for the additive, and ethylene glycol was prepared as the solvent. In Example 1, the copper particles, the additive, and the solvent were mixed so that the content of the additive was 1% by mass and the content of the solvent was 10% by mass, with the remainder being copper particles, to obtain a joining paste. In Example 1, a joined body was manufactured using the obtained joining paste. Specifically, an opening of 3 mm was formed in a copper plate, and the joining paste of each example was printed with a metal mask having a thickness of 50 μm and a metal squeegee. Then, it was dried on a hot plate at 90 °C for 5 minutes, and a 2.5 mm × 2.5 mm silicon dummy chip having gold sputtered on the back surface with a thickness of 100 nm was placed thereon. While pressurizing at 5 MPa in a nitrogen atmosphere, it was heated at 250 °C for 3 minutes to heat the joining paste to form a joining layer, thereby obtaining a joined body. In Example 1, it was confirmed that the joining layer contained phosphorus. The confirmation of the inclusion of phosphorus was performed by ICP-OES. In Example 1, the sintering density of the joining layer was 91%. The sintering density was measured as follows. After the joining layer was sealed with an epoxy resin, the joining layer was cut in a horizontal direction with respect to the thickness direction of the joining layer. The cross-section of the joining layer was prepared by subjecting the cut surface of the joining layer to mechanical polishing and cross-polishing. Next, the cut surface of the joining layer was observed at 50,000 times magnification using an SEM (scanning electron microscope). The obtained SEM image was binarized using image processing software (ImageJ manufactured by the National Institutes of Health, USA) and divided into a particle portion and a pore portion, and the sintering density was calculated from the following formula. Sintering density (%) = (total area of particle portion / (total area of particle portion + total area of pore portion)) × 100 The sintering density was measured for 10 randomly taken SEM images. The values shown in Table 1 are the average values of the sintering density calculated from 10 SEM images.

[0049] (Example 2-7) In Example 2-7, a bonded body was obtained in the same manner as in Example 1, except that the bonding paste and test conditions were those shown in Table 1.

[0050] (Comparative Example 1) In Comparative Example 1, a bonded body was obtained in the same manner as in Example 1, except that the bonding paste was the one shown in Table 1. The bonded body of Comparative Example 1 did not contain phosphorus and had a sintered density of 76%.

[0051] (Evaluation) In the evaluation, the shear strength of the obtained bonded body (bonded silicon dummy chip and oxygen-free copper plate) was measured. If the shear strength was 40 MPa or more, it was rated as "excellent"; if it was 20 MPa or more and less than 40 MPa, it was rated as "good"; if it was 10 MPa or more and less than 20 MPa, it was rated as "fair"; if it was less than 10 MPa, it was rated as "poor". "Fair", "good", and "excellent" were considered as passing. The shear strength was measured by a method conforming to JIS Z 3198-7 (Lead-free solder test method - Part 7: Solder joint shear test method for chip components). Specifically, a load was applied to the silicon dummy chip using a tool of a bond tester (manufactured by Nordson DAGE, SERIES 4000), and the load (maximum shear load) when the silicon dummy chip peeled off from the copper bonding layer was measured. The moving speed of the tool was set at 50 μm / sec, and the gap between the tip of the tool and the oxygen-free copper substrate was set at 50 μm. The shear strength (unit: MPa) was obtained by converting the obtained maximum shear load into Newtons and dividing it by the area of the copper bonding layer (2.5 mm × 2.5 mm). Seven bonded bodies were fabricated, and the shear strength of each bonded body was measured. The values shown in Table 1 are the average of the shear strengths of the seven bonded bodies.

[0052]

Table 1

[0053] Table 1 is a table showing the evaluation results of each example. As shown in Table 1, in the examples, the share strength is qualified, and it can be seen that by using a joined body containing phosphorus and having a sintered density of 80% or more, a decrease in strength can be suppressed. On the other hand, in Comparative Example 1, it can be seen that when using a joined body that does not contain phosphorus and has a sintered density of less than 80%, a decrease in strength cannot be suppressed.

[0054] As described above, the embodiments of the present invention have been described, but the embodiments are not limited by the content of these embodiments. In addition, the above-described components include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or changes of the components can be made without departing from the gist of the above-described embodiments.

Explanation of Reference Numerals

[0055] 10 Joining paste 12 Copper particles 14 Solvent 16 Additive 20 Joining layer 21 First member 22 Second member 30 Joined body

Claims

1. A copper sintered body for joining members, The joining layer has a sintering density of 84% or more and 97% or less and contains phosphorus.

2. The joining layer according to claim 1, wherein the phosphorus content is 100 ppm or more and 1000 ppm or less by mass ratio with respect to the whole of the joining layer.

3. The joining layer according to claim 1 or 2, having a thickness of 10 μm or more and 200 μm or less.

4. A joined body including a first member, a second member, and the joining layer according to any one of claims 1 to 3 disposed between the first member and the second member. Joined body.

5. The joined body according to claim 4, wherein the first member is a substrate and the second member is an electronic component, and a semiconductor module is constituted.

6. A coating layer forming step of applying a joining paste containing copper particles, a solvent, and an additive composed of a phosphate ester having an average molecular weight of 1000 or more and 2000 or less, and having a content of the additive of 0.5% or more and 3.0% or less by mass ratio, to at least one surface of the first member and the second member to form a coating layer; An overlapping step of overlapping the first member and the second member through the coating layer; A heating step of heating the first member and the second member overlapped through the coating layer to form a joined body, In the heating step, in a non-reducing atmosphere, while applying a pressure of 0.5 MPa or more and 10 MPa or less to at least one of the first member and the second member, heating is performed at a temperature of 200°C or more and 300°C or less for 1 minute or more and 10 minutes or less. Method for manufacturing a joined body.

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