Acidic electrolytic copper plating solution

Abstract

This acidic electrolytic copper plating solution is characterized by comprising a soluble copper salt, an azole compound, a carboxylic acid, water, and an acid, the azole compound content being 5-100 mmol / L, and the carboxylic acid content being 5-500 mg / L.

Description

Acidic electrolytic copper plating solution

[0001] The present invention relates to an acidic electrolytic copper plating solution used to form a porous copper layer on the surface of a member. This application claims priority to Japanese Patent Application No. 2024-036201, filed on March 8, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, the performance of semiconductor devices has been improving, and micro-bonding technology has become increasingly important. Flip-chip mounting is widely used as a mounting technology for IC chips, and a method of forming a solder layer on a protruding electrode and bonding it with solder, as disclosed in Patent Document 1, for example, has been proposed. Furthermore, as disclosed in Patent Documents 1 and 2, for example, bonding technologies such as the TLP method (Transient Liquid Phase Diffusion Bonding) and the SLID method (Solid-Liquid Interdiffusion) have been proposed, which bond solid and liquid phases by mutual diffusion.

[0003] As a next-generation packaging technology for even finer pitches, a technology for solid-phase diffusion bonding of copper members has been proposed. Here, when bonding substrates on which multiple Cu pillars are provided, the distance between the Cu pillars to be bonded must be precisely adjusted, and processing using CMP or the like is required. Furthermore, as shown in Patent Document 3, for example, a technology has been proposed in which a porous copper layer (preform layer) is formed on the bonding surface of the Cu pillars and the Cu pillars are bonded together using solid-phase diffusion bonding. When pressure is applied during bonding, the porous copper layer (preform layer) acts like a cushion, allowing the Cu pillars to be bonded to each other and be bonded even if there is variation in the height of the Cu pillars.

[0004] Japanese Patent No. 6061276 Japanese Patent No. 6369620 Japanese Patent Application Laid-Open No. 2018-046148

[0005] However, when joining Cu pillars together using a porous copper layer, in order to ensure reliable contact between the Cu pillars even when the Cu pillars have large height variations, it is necessary to further increase the porosity of the porous copper layer.Furthermore, in order to ensure the bonding strength after joining, it is necessary for the porous copper layer to have a fine crystal grain size.

[0006] The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide an acidic electrolytic copper plating solution that can stably form a porous copper layer having a high porosity and a small crystal grain size by a plating method.

[0007] In order to solve the above problems, an acidic electrolytic copper plating solution according to Aspect 1 of the present invention comprises a soluble copper salt, an azole compound, a carboxylic acid, water, and an acid, wherein the content of the azole compound is in the range of 5 mmol / L to 100 mmol / L, and the content of the carboxylic acid is in the range of 5 mg / L to 500 mg / L.

[0008] According to the acidic electrolytic copper plating solution of Aspect 1 of the present invention, the azole-based compound is contained in a range of 5 mmol / L to 100 mmol / L, and therefore, during electroplating, the azole-based compound is adsorbed onto the cathode surface together with copper ions, thereby strongly suppressing copper electrodeposition and favoring copper nucleation, resulting in the formation of a porous copper layer composed of copper particles on the cathode surface. Furthermore, the acidic electrolytic copper plating solution of Aspect 1 of the present invention contains a carboxylic acid in a range of 5 mg / L to 500 mg / L, and therefore the Cu ions and the carboxylic acid form a complex, further suppressing copper electrodeposition and increasing the porosity of the porous copper layer. Furthermore, the growth of deposited copper particles is suppressed, enabling the formation of a porous copper layer with a small crystal grain size. Therefore, even when the Cu pillars vary in height, for example, the Cu pillars to be joined can be brought into contact with each other and firmly joined.

[0009] The acidic electrolytic copper plating solution of Aspect 2 of the present invention is characterized in that, in the acidic electrolytic copper plating solution of Aspect 1, the azole compound is a compound represented by any of the following formulas (1) to (4) having two or more and three or less nitrogen atoms in a five-membered ring: In the above formulas (1) to (4), R1 to R4 may be the same or different from one another and are any of an alkyl group having 10 or less carbon atoms, an alkenyl group having 10 or less carbon atoms, an alkynyl group having 10 or less carbon atoms, an aryl group having 10 or less carbon atoms, an aralkyl group having 10 or less carbon atoms, and an alkoxy group having 10 or less carbon atoms; or a group in which the hydrogen atom of any of these groups is substituted with a halogen atom, a hydroxyl group, a carboxyl group, an amino group, an alkyl-substituted amino group having 5 or less carbon atoms, a hydroxyalkyl-substituted amino group having 5 or less carbon atoms in the alkyl chain, or a mercapto group; or any of an amino group, an alkyl-substituted amino group having 5 or less carbon atoms, a hydroxyalkyl-substituted amino group having 5 or less carbon atoms in the alkyl chain, a mercapto group, a hydroxyl group, a carboxyl group, a halogen atom, and a hydrogen atom.

[0010] The acidic electrolytic copper plating solution of Aspect 2 of the present invention contains the compounds having the structures shown in the above formulas (1) to (4) as azole compounds, thereby reliably suppressing copper electrodeposition and forming a porous copper layer composed of copper particles on the cathode surface. Furthermore, the acidic electrolytic copper plating solution contains carboxylic acid in a range of 5 mg / L to 500 mg / L, thereby reliably forming a porous copper layer with high porosity and small average particle size. Therefore, even if the Cu pillars vary in height, for example, the Cu pillars to be joined can be brought into contact with each other and joined more firmly.

[0011] According to the present invention, it is possible to provide an acidic electrolytic copper plating solution that can stably form a porous copper layer having high porosity and small crystal grain size by a plating method.

[0012] FIG. 1 is an explanatory view showing a method for forming a porous copper layer using an acidic electrolytic copper plating solution according to one embodiment of the present invention, and is a schematic diagram of an electrolytic copper plating apparatus. FIG. 2 is an explanatory view showing a method for forming a porous copper layer using an acidic electrolytic copper plating solution according to one embodiment of the present invention, and is a schematic side view of a substrate on which a porous copper layer is formed in a pattern. FIG. 3 is an enlarged side view of a porous copper layer formed using an acidic electrolytic copper plating solution according to one embodiment of the present invention. FIG. 4 is an explanatory view showing steps of a method for producing a bonded body using a porous copper layer. FIG. 5 is an explanatory view showing a method for producing a bonded body for measuring share strength in the Examples. FIG. 6 is a cross-sectional SEM (Scanning Electron Microscope) photograph of the porous copper layer observed in Example 1 of the Examples. FIG. 7 is a cross-sectional SEM photograph of the porous copper layer observed in Comparative Example 1 of the Examples. FIG. 8 is a cross-sectional SEM photograph of the porous copper layer observed in Comparative Example 2 of the Examples.

[0013] An acidic copper electroplating solution according to an embodiment of the present invention will be described below with reference to the drawings.

[0014] The acidic electrolytic copper plating solution according to this embodiment forms a porous copper layer that is used, for example, in a semiconductor device, when joining a plurality of protruding electrodes (Cu pillars) provided on a semiconductor chip or substrate.

[0015] The acidic electrolytic copper plating solution of this embodiment contains a soluble copper salt, an azole compound, a carboxylic acid, water, and an acid, with the azole compound content being in the range of 5 mmol / L to 100 mmol / L and the carboxylic acid content being in the range of 5 mg / L to 500 mg / L. Note that the acidic electrolytic copper plating solution of this embodiment may contain other components, such as a brightener, a surfactant, an antioxidant, etc., as needed.

[0016] Specific examples of soluble copper salts include copper sulfate, copper oxide, copper carbonate, copper alkanesulfonates such as copper methanesulfonate and copper propanoate, copper alkanolsulfonates such as copper isethionate and copper propanolsulfonate, and copper organic acids such as copper acetate, copper citrate, and copper tartrate. These can be used alone or in combination of two or more.

[0017] The acid may be an organic acid or an inorganic acid. The acid may be any acid other than carboxylic acid. Examples of the acid include sulfuric acid; alkanesulfonic acids such as methanesulfonic acid and propanesulfonic acid; and alkanolsulfonic acids such as isethionic acid and propanolsulfonic acid. These may be used alone or in combination. Examples of water include pure water such as ion-exchanged water and distilled water.

[0018] Examples of the azole compounds include imidazole, 2-aminoimidazole, pyrazole, 3-aminoimidazole, 1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, 3,5-diamino-1,2,4-triazole, 3-amino-5-methylthio-1H-1,2,4-triazole, etc. These azole compounds are compounds represented by the above formulas (1) to (4) having two to three nitrogen atoms in a five-membered ring.

[0019] The imidazole is a type of azole compound represented by the above formula (1) and is represented by the following formula (5). 2-Aminoimidazole is a type of azole compound represented by the above formula (1) and is represented by the following formula (6). Pyrazole is a type of azole compound represented by the above formula (2) and is represented by the following formula (7). 3-Aminoimidazole is a type of azole compound represented by the above formula (2) and is represented by the following formula (8). 1,2,3-triazole is a type of azole compound represented by the above formula (3) and is represented by the following formula (9).

[0020]

[0021] 1,2,4-Triazole is a type of azole compound represented by the above formula (4) and is represented by the following formula (10). 3-Amino-1,2,4-triazole is a type of azole compound represented by the above formula (4) and is represented by the following formula (11). 3,5-Diamino-1,2,4-triazole is a type of azole compound represented by the above formula (4) and is represented by the following formula (12). 3-Amino-5-methylthio-1H-1,2,4-triazole is a type of azole compound represented by the above formula (4) and is represented by the following formula (13).

[0022]

[0023] The azole compound adsorbs onto the cathode surface together with copper ions during electroplating, suppressing copper electrodeposition and functioning as a copper ion electrodeposition inhibitor. By suppressing copper electrodeposition in this way, copper nucleation is prioritized on the cathode surface, resulting in the formation of a porous copper layer composed of copper particles.

[0024] Examples of carboxylic acids include acetic acid, propionic acid, oxalic acid, citric acid, gluconic acid, and glycinic acid. Carboxylic acid forms a complex with Cu ions, which further inhibits copper electrodeposition and increases the porosity of the porous copper layer. Furthermore, the growth of deposited copper particles is inhibited, resulting in the formation of a porous copper layer with a small crystal grain size.

[0025] The acidic copper electroplating solution of the present embodiment can be prepared by mixing the soluble copper salt, the copper ion electrodeposition inhibitor, which is an azole compound having two to three nitrogen atoms in a five-membered ring, a carboxylic acid, an acid, and water.

[0026] Here, the content of the soluble copper salt in the prepared acidic electrolytic copper plating solution is preferably 0.01 mol / L or more. If the content of the soluble copper salt is 0.01 mol / L or more, a porous copper layer can be stably formed as a copper plating film. The upper limit of the content of the soluble copper salt is not particularly limited, but it may be 1 mol / L. In addition, the lower limit of the content of the azole-based compound in the acidic electrolytic copper plating solution is preferably 5 mmol / L or more, more preferably 10 mmol / L or more. The upper limit of the content of the azole-based compound is preferably 100 mmol / L or less, more preferably 30 mmol / L or less.

[0027] In the prepared acidic electrolytic copper plating solution, the content of the azole-based compound functioning as a copper ion electrodeposition inhibitor is set to be in the range of 5 mmol / L to 100 mmol / L. If the content of the azole-based compound is less than 5 mmol / L, the effect of inhibiting copper ion electrodeposition is poor, and a porous copper layer as a copper plating film cannot be stably formed. On the other hand, if the content of the azole-based compound exceeds 100 mmol / L, the electrodeposition of copper ions is excessively inhibited, resulting in a brittle copper plating film with significantly reduced strength. Alternatively, the azole-based compound is insoluble in the solution and precipitates.

[0028] In the prepared acidic electrolytic copper plating solution, the carboxylic acid content is within the range of 5 mg / L or more and 500 mg / L or less. If the carboxylic acid content is less than 5 mg / L or more than 500 mg / L, the porosity of the porous copper layer may not be improved, and the crystal grain size may not be refined. In addition, in the acidic electrolytic copper plating solution, the lower limit of the carboxylic acid content is preferably 10 mg / L or more, more preferably 50 mg / L or more. The upper limit of the carboxylic acid content is preferably 300 mg / L or less, more preferably 150 mg / L or less.

[0029] In the prepared acidic electrolytic copper plating solution, there are no particular restrictions on the concentrations of the above-mentioned soluble copper salt, azole compound, and components other than carboxylic acid, such as water and acid, but it is preferable to adjust the pH of the acidic electrolytic copper plating solution to be within the range of 0 to 5, and more preferably within the range of 1 to 3.

[0030] Next, a method for forming a patterned porous copper layer on the surface of a substrate using the acidic copper electrolytic plating solution of this embodiment will be described with reference to FIGS. 1A, 1B, and 2. FIG.

[0031] 1A and 1B , an acidic electrolytic copper plating solution 3 according to the present embodiment is placed in a plating tank 2 of an electrolytic copper plating apparatus 1. A substrate 4a having a copper or nickel surface and a patterned resist film 4b is placed in the acidic electrolytic copper plating solution 3. A copper material 5 is placed facing one side of the substrate 4a. The substrate 4a is then connected to a cathode 6 as a cathode, and the copper material 5 is connected to an anode 7 as a soluble anode, to perform electrolytic copper plating. A resist film 4b is formed on the surface of the substrate 4a in advance, with openings at predetermined intervals. As a result, a porous copper layer 8 composed of copper particles 12 is formed as a copper plating film within the openings in the resist film 4b formed on one side of the substrate 4a.

[0032] Here, the conditions for electrolytic copper plating in the acidic electrolytic copper plating solution 3 are, for example, to apply a current density of 0.1 A / dm2 to the substrate 4a to be plated using a DC power source. ２ ~5 A / dm ２ Approximately, preferably 0.4 A / dm ２ ~1.0 A / dm ２The solution is heated to a temperature of approximately 10°C to 60°C, preferably approximately 25°C to 50°C, and air and jet stirring or rocking stirring is performed. When electrolytic copper plating is performed under these conditions, the azole-based compound, which acts as a copper ion electrodeposition inhibitor, is adsorbed onto the cathode surface, which is the surface of the substrate 4a, along with copper ions. The presence of the azole-based compound strongly inhibits the electrodeposition of copper ions, favoring copper nucleation, and a porous copper layer 8 composed of copper particles 12 is formed on the cathode surface as a copper plating film. Furthermore, the carboxylic acid forms a complex with the copper ions, increasing the porosity of the porous copper layer 8 and reducing the crystal grain size.

[0033] After electrolytic copper plating, the substrate 4a with the porous copper layer 8 formed thereon is removed from the acidic electrolytic copper plating solution 3, and the resist film 4b is removed. The substrate 4a is then washed with a cleaning solvent such as ethanol, water, or acetone, and dried in the atmosphere using dry air. As a result, a patterned porous copper layer 8 is formed on one side of the substrate 4a, as shown in FIG. 1B . Cu pillars are bonded to each of the patterned porous copper layers 8. The substrate 4a with the porous copper layer 8 formed thereon is preferably immersed for a predetermined period of time in a rust inhibitor primarily composed of benzotriazole and a surfactant to prevent surface oxidation.

[0034] Here, the thickness of the porous copper layer 8 formed on the surface of the substrate 4a is preferably in the range of 15 μm to 50 μm. If the thickness of the porous copper layer 8 is 15 μm or more, the strength of the porous copper layer 8 itself is ensured and handling is easy. On the other hand, if the thickness of the porous copper layer 8 is 50 μm or less, the porous copper layer 8 conforms to the irregularities on the surfaces of the substrates or electronic components described below during bonding, improving the bonding strength of the bonded body.

[0035] As shown in FIG. 2 , the porous copper layer 8 is formed in the form of an aggregate of copper particles, in which copper particles 12 are stacked on the surface of the substrate 4 a. The porous copper layer 8 made of these copper particles 12 preferably has an average porosity in the range of 10% to 80%. If the average porosity is 10% or more, copper particles that contribute to the sintering of the porous copper layer 8 are secured, improving the sinterability of the copper particles. If the average porosity is 80% or less, the porosity within the porous copper layer 8 is not increased more than necessary, ensuring the strength of the porous copper layer 8 and the sinterability of the copper particles. It is more preferable that the average porosity is 15% or more. It is also more preferable that the average porosity is 70% or less.

[0036] The average porosity of the porous copper layer 8 described above is calculated by image analysis of a cross section of the porous copper layer 8 using a scanning electron microscope. The average porosity is defined as the arithmetic mean of the porosities (P) calculated by the following formula (A). Specifically, the measurement is performed three times with images taken from different fields of view, and the average value of the calculated porosities is defined as the average porosity. P (%) = (S2 / S1) × 100 (A) where, in formula (A), P is the porosity of the porous copper layer 8, S1 is the total area of ​​the porous copper layer 8, and S2 is the area of ​​the pores in the porous copper layer 8.

[0037] 2, the surfaces of the copper particles 12 are coated with copper nanoparticles 12a having an average particle size smaller than that of the copper particles 12. Copper plating is performed using the acidic electrolytic copper plating solution 3 of this embodiment, whereby an azole compound is adsorbed onto the copper surface and a complex with copper ions is formed by carboxylic acid, thereby suppressing copper electrodeposition, prioritizing nucleation, and forming copper nanoparticles 12a on the surfaces of the copper particles 12. Due to this characteristic structure, when the porous copper layer 8 is pressurized, the copper particles are easily sintered together to form a robust bonding layer.

[0038] Here, the average particle size of the copper nanoparticles is difficult to calculate from a microscope image because fine copper particles and nanoparticles even finer than the copper particles are combined, and the average particle size is calculated from BET measurement. Thus, the average particle size of the copper nanoparticles calculated from BET measurement is preferably 50 nm or more and 300 nm or less. If the average particle size of the copper nanoparticles is within this range, the copper particles will be easily sintered. It is more preferable that the average particle size of the copper nanoparticles is within the range of 50 nm or more and 200 nm or less.

[0039] The average particle size of the copper nanoparticles described above is measured by the BET method using the porous copper layer 8. In the BET method, the substrate 4a on which the porous copper layer 8 is formed is cut to a predetermined size, filled into a measurement cell, and measured using the BET single-point method. The mass of the substrate 4a is subtracted from the measured value, and the result is converted to the mass of the porous copper layer 8 itself. The particle size of the copper nanoparticles is calculated from the calculated BET measured value based on the following formula (B). Note that the coefficient 335.95 in the following formula (B) is a value calculated from the theoretical values ​​of the density of copper, the surface area of ​​the copper nanoparticles, and the volume of the copper nanoparticles. The average particle size (d) of the copper nanoparticles is the average value of three measurements made using the BET method. d (nm) = 335.95 / (BET measured value (m ２ / g)) (B)

[0040] Next, a method for manufacturing a bonded body using a substrate 4a having a porous copper layer 8 formed thereon is described. First, as shown in FIG. 3( a), a substrate 4a having a porous copper layer 8 formed thereon is prepared. An electronic component 17 (e.g., a silicon chip element, an LED chip element, etc.) is prepared as the member to be bonded. Next, as shown in FIG. 3( b), the electronic component 17 is placed on the porous copper layer 8 formed on the surface of the substrate 4a. In this state, the electronic component 17 and the substrate 4a, stacked via the porous copper layer 8, are heated in a nitrogen atmosphere at a temperature of 250°C to 350°C for 1 minute to 30 minutes in a heating furnace. In some cases, the substrate 4a and the electronic component 17 may be bonded while applying a pressure of 1 MPa to 20 MPa in the stacking direction. As a result, as shown in FIG. 3( c), the porous copper layer 8 becomes a bonding layer 15, and the substrate 4a and the electronic component 17 are bonded by this bonding layer 15 to produce a bonded body 18.

[0041] The acidic electrolytic copper plating solution of this embodiment, configured as described above, contains an azole-based compound in a range of 5 mmol / L to 100 mmol / L. During electrolytic plating, the azole-based compound adsorbs onto the cathode surface along with copper ions. This strongly suppresses copper electrodeposition, favoring copper nucleation and resulting in the formation of a porous copper layer composed of copper particles on the cathode surface. Furthermore, the acidic electrolytic copper plating solution of this embodiment contains a carboxylic acid in a range of 5 mg / L to 500 mg / L. This allows the Cu ions and the carboxylic acid to form a complex, further suppressing copper electrodeposition and increasing the porosity of the porous copper layer. Furthermore, the growth of deposited copper particles is suppressed, enabling the formation of a porous copper layer with a small crystal grain size. Therefore, even when the Cu pillars vary in height, the Cu pillars to be joined can be brought into contact with each other and firmly bonded.

[0042] In the acidic electrolytic copper plating solution of this embodiment, when the azole compound is a compound represented by any one of the above formulas (1) to (4) having two to three nitrogen atoms in a five-membered ring, copper electrodeposition can be reliably suppressed and a porous copper layer composed of copper particles can be formed on the cathode surface. Furthermore, since the solution contains 5 mg / L or more and 500 mg / L or less of carboxylic acid, a porous copper layer with high porosity and small average particle size can be reliably formed. Therefore, even if the Cu pillars vary in height, for example, the Cu pillars to be joined can be brought into contact with each other and joined more firmly.

[0043] While the present invention has been described above as an embodiment, it is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. For example, in the present embodiment, the porous copper layer 8 is formed in a pattern on the surface of the substrate 4 a, and the electronic component 17 is bonded via this porous copper layer 8. However, the present invention is not limited thereto and may be modified as long as the bonded members are bonded via the porous copper layer.

[0044] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0045] First, an acidic electrolytic copper plating solution containing copper sulfate pentahydrate as a soluble copper salt, an azole compound, and a carboxylic acid was prepared as shown in Tables 1 and 2. In addition to the copper sulfate pentahydrate, the azole compound, and the carboxylic acid, water and sulfuric acid were added to adjust the pH to 2.5.

[0046] A Si substrate was prepared, and a Ti layer (100 nm thick) and a Cu layer (500 nm thick) were sputter-deposited on the surface of the Si substrate in this order. The Si substrate with the Cu layer formed on its surface was electrolytically copper plated using the acidic electrolytic copper plating solution described above, to form a porous copper layer on the surface of the Si substrate with the Cu layer formed on its surface. The plating conditions were a bath temperature of 30°C, pH of 2.5, and a current density as shown in Tables 3 and 4. The plating time was adjusted so that the thickness of the porous copper layer was 2 μm.

[0047] To measure the bonding strength of the bonded structure, an oxygen-free copper substrate (5 mm × 5 mm, 3 mm thick) and a copper chip (1 mm × 1 mm, 2 mm thick) were prepared, and a porous copper layer was formed on the surface of the substrate and the copper chip using the acidic electrolytic copper plating solution described above. The plating conditions were a bath temperature of 30°C, pH of 2.5, and a current density shown in Tables 3 and 4. The plating time was adjusted so that the thickness of the porous copper layer was 2 μm.

[0048] Then, as shown in FIG. 4, the substrate and the copper chip were stacked so that the porous copper layer formed on the substrate and the porous copper layer formed on the copper chip were in contact with each other, and bonded using a pressure and heat bonding device (HTB-MM manufactured by Alpha Design) under the conditions of heating temperature: 300°C, heating time: 1 minute, pressure load: 10 MPa, and atmosphere: nitrogen, to obtain a bonded body.

[0049] The porosity and average particle size of the resulting porous copper layer and the shear strength of the bonded body were evaluated as follows.

[0050] (Porosity) Measurement samples were taken from Si substrates on which porous copper layers had been formed by electroplating, and cross sections along the thickness direction of the porous copper layer were subjected to CP (cross-section polishing) and cross-sectional SEM observation. The cross-sectional SEM images at 10,000 magnifications were binarized to calculate the porosity using formula (A). Cross-sectional SEM images of Inventive Example 1 and Comparative Examples 1 and 2 are shown in Figures 5A, 5B, and 5C. It is confirmed that a porous copper layer was formed in Inventive Example 1 (Figure 5A). On the other hand, it is confirmed that a porous copper layer was not formed in Comparative Example 1 (Figure 5B) and Comparative Example 2 (Figure 5C).

[0051] (Average particle size) Measurement by the BET method was carried out using a Macsorb HM-model-1201. The Si substrate on which the porous copper layer was formed was cut into 2 mm squares, filled into a measurement cell, and measured by the BET single-point method. The mass of the copper sheet was subtracted from the measured value, and the value was converted to the mass of the porous copper layer itself. From the calculated BET measured value, the particle size of the copper nanoparticles was calculated based on the following formula (B). The coefficient 335.95 in the following formula (B) is a value calculated from the theoretical values ​​of the density of copper, the surface area of ​​the copper nanoparticles, and the volume of the copper nanoparticles. The average particle size (d) of the copper nanoparticles was measured three times by the BET method and is the average value. d (nm) = 335.95 / (BET measured value (m ２ / g)

[0052] (Shear Strength) The shear strength of the bonded structure was measured using a shear strength evaluation tester (Bond Tester; Dage Series 4000, manufactured by Nordson Advanced Technologies Co., Ltd.). The shear strength was measured by fixing the substrate of the bonded structure horizontally, and pressing the copper chip horizontally from the side with a shear tool at a position 50 μm above the surface (upper surface) of the bonding layer, and measuring the strength when the copper chip broke. The shear tool was moved at a speed of 0.1 mm / sec.

[0053]

[0054]

[0055]

[0056]

[0057] In Comparative Example 1, an azole compound and a carboxylic acid were not contained, and a porous copper layer could not be formed. In Comparative Examples 2 to 4, an azole compound was not contained, and a porous copper layer could not be formed. In Comparative Examples 5 to 7 and 9 to 11, no carboxylic acid was contained, and compared with the inventive examples with the same current density, the porosity was smaller, the average particle size was larger, and the shear strength was lower.

[0058] In Comparative Example 8, the carboxylic acid content was as high as 600 mg / L, and the porosity was smaller, the average particle size was larger, and the shear strength was lower than in the Examples of the present invention with the same current density. In Comparative Example 12, the carboxylic acid content was as low as 1 mg / L, and the porosity was smaller, the average particle size was larger, and the shear strength was lower than in the Examples of the present invention with the same current density.

[0059] In contrast, in Examples 1 to 15 of the present invention, the porosity was higher, the average particle size was smaller, the shear strength was higher, and the bondability was excellent compared to the comparative examples with the same current density.

[0060] From the results of the above confirmatory experiments, it was confirmed that the present invention can provide an acidic electrolytic copper plating solution that can stably form a porous copper layer having a high porosity and a small crystal grain size by a plating method.

[0061] 4a Substrate 8 Porous copper layer

Claims

1. An acidic electrolytic copper plating solution comprising a soluble copper salt, an azole compound, a carboxylic acid, water, and an acid, wherein the content of the azole compound is in the range of 5 mmol / L to 100 mmol / L, and the content of the carboxylic acid is in the range of 5 mg / L to 500 mg / L.

2. The acidic copper electroplating solution according to claim 1, wherein the azole compound is a compound represented by the following formulas (1) to (4) having two or more and three or less nitrogen atoms in a five-membered ring. In the above formulas (1) to (4), R １ ~R ４ may be the same or different from each other, and are any of an alkyl group having 10 or less carbon atoms, an alkenyl group having 10 or less carbon atoms, an alkynyl group having 10 or less carbon atoms, an aryl group having 10 or less carbon atoms, an aralkyl group having 10 or less carbon atoms, or an alkoxy group having 10 or less carbon atoms, or a group in which the hydrogen atom of any of these groups is substituted with a halogen atom, a hydroxyl group, a carboxyl group, an amino group, an alkyl-substituted amino group having 5 or less carbon atoms, a hydroxyalkyl-substituted amino group having 5 or less carbon atoms in the alkyl chain, or a mercapto group, or any of an amino group, an alkyl-substituted amino group having 5 or less carbon atoms, a hydroxyalkyl-substituted amino group having 5 or less carbon atoms in the alkyl chain, a mercapto group, a hydroxyl group, a carboxyl group, a halogen atom, or a hydrogen atom.

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