ACIDIC ELECTROLYTIC COPPER PLATING LIQUID, METHOD FOR FORMING PREFORM LAYER, METHOD FOR PRODUCING JOINING SHEET, METHOD FOR PRODUCING JOINING SUBSTRATE, AND METHOD FOR PRODUCING JOINED BODY

Abstract

This acidic electrolytic copper plating solution contains a soluble copper salt, an azole compound which has 2 or 3 nitrogen atoms in a five-membered ring and serves as a copper ion electrodeposition inhibitor, an acid, and water, in which a copper concentration is 0.1 mol/L or more, an azole compound concentration is 10 mmol/L or more and 50 mmol/L or less, and a chloride ion concentration is 10 ppm or less.

Description

TECHNICAL FIELD

The present invention relates to an acidic electrolytic copper plating solution for forming a porous preform layer for bonding two members used in the assembly, implementation, or other processes of electronic components. In addition, the present invention relates to a method for forming a preform layer using this acidic electrolytic copper plating solution. Furthermore, the present invention relates to a method for producing a bonding sheet formed of a copper sheet with a preform layer, a method for producing a bonding substrate formed of a substrate with a preform layer, and a method for producing a bonded body using the bonding sheet or the bonding substrate.

The present application claims priority on Japanese Patent Application No. 2021-181970 filed on Nov. 8, 2021, the content of which is incorporated herein by reference.

BACKGROUND ART

In the related art, as a method for producing this type of a porous material, a technique for producing a film is disclosed, and the technique includes causing electrolytic deposition on a film (hereinafter, simply referred to as electrodeposition) by a composite plating method using polymer fine particles as a dispersant to produce a porous film through decomposition and desorption of the polymer fine particles (see Non Patent Document 1). In this method for producing a porous material, nickel plating using a Watt bath is employed as a matrix of a composite plating, and highly crosslinked type acrylic polymer fine particles are added to the bath as a dispersant. In this producing method, a soft iron plate of which one surface has been coated is used as a base material, the base material is subjected to a pre-treatment of alkali degreasing, and then nickel plating is performed in a plating bath containing nickel sulfate, nickel chloride, and boric acid. The plated film is subjected to a pore-forming treatment after co-deposition by heat treatment in the atmosphere at 500° C. for 1 hour to obtain a porous material.

In the above-described method for producing a porous film in the related art, processing for removing polymer fine particles from the desired metal is complicated, and there is an issue in that the remaining of these polymer fine particles is concerned even though the polymer fine particles have been removed.

CITATION LIST

Patent Document

[Non Patent Document 1]

• • Tomohiko Nakamura, Minoru Matsuda, Development of Porous Material Using Plating Technology, Kyoto Prefectural Technology Center for Small and Medium Enterprises, technical report, No. 31, pages 36 to 38, 2003

SUMMARY OF INVENTION

Technical Problem

A first objective of the present invention is to provide an acidic electrolytic copper plating solution capable of forming a porous preform layer with a simple process. A second objective of the present invention is to provide a method for forming a preform layer using this acidic electrolytic copper plating solution. A third objective of the present invention is to provide a method for producing a bonding sheet formed of a copper sheet with a preform layer. A fourth objective of the present invention is to provide a method for producing a bonding substrate formed of a substrate with a preform layer. Furthermore, a fifth objective of the present invention is to provide a method for producing a bonded body using the bonding sheet or the bonding substrate.

Solution to Problem

[1] An acidic electrolytic copper plating solution containing:

• • a soluble copper salt;
  • an azole compound which has 2 or more and 3 or less nitrogen atoms in a five-membered ring represented by Formulae (1) to (4) and serves as a copper ion electrodeposition inhibitor;
  • an acid; and
  • water,
  • in which a copper concentration is 0.1 mol/L or more, an azole compound concentration is 10 mmol/L or more and 50 mmol/L or less, and a chloride ion concentration is 10 ppm or less,

• • in Formulae (1) to (4), R₁ to R₄ may be the same as or different from each other, and are any one 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 a hydrogen atom of these groups is substituted with any one of 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 an alkyl chain, or a mercapto group, or any one 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 an alkyl chain, a mercapto group, a hydroxyl group, a carboxyl group, a halogen atom, or a hydrogen atom.

[2] A method for forming a preform layer, the method including:

• • a step of placing a copper sheet or a substrate on a cathode side in the acidic electrolytic copper plating solution according to [1] and performing acidic electrolytic copper plating (hereinafter, sometimes simply referred to as “electrolytic copper plating”) to form a porous preform layer on one surface or both surfaces of the copper sheet or the substrate, in which the porous preform layer serves as a copper plating film, contains copper particles, and has an average porosity of 11% to 78%,
  • in which the surface of the copper particle is coated with copper nanoparticles with a particle size smaller than an average grain size of the copper particles,
  • in which an average grain size calculated using a BET value of the copper nanoparticles is 9.59 nm or more and 850 nm or less, and
  • in which the average porosity of the preform layer is an arithmetic average of a porosity (P) determined by Equation (A) based on a total area (S₁) of the preform layer and an area (S₂) of a void portion in the preform layer, which is calculated by image analysis of a cross-section of the preform layer using an electron scanning microscope,

$\begin{array}{cc}P\left(\%\right)=\left(S_2/S_1\right)\times 100.& \left(A\right)\end{array}$

[3] A method for producing a bonding sheet, the method including: a step of forming a porous preform layer on one surface or both surfaces of a copper sheet by the method for forming a preform layer according to [2].

[4] A method for producing a bonded body, the method including:

• • a step of laminating a base material, an electronic component, and the bonding sheet produced by the method for producing a bonding sheet according to [3] so that the bonding sheet is disposed between the base material and the electronic component; and
  • a step of heating the base material and the electronic component under pressure in a laminating direction to produce a bonded body.

[5] A method for producing a bonding substrate, the method including: a step of forming a porous preform layer on one surface of a substrate by the method for forming a preform layer according to [2].

[6] A method for producing a bonded body, the method including:

• • a step of laminating the bonding substrate produced by the method for producing a bonding substrate according to [5] and an electronic component so that the porous preform layer is disposed between the bonding substrate and the electronic component; and
  • a step of heating the bonding substrate and the electronic component under pressure in a laminating direction to produce a bonded body.

Advantageous Effects of Invention

The acidic electrolytic copper plating solution according to the aspect of [1] contains a soluble copper salt, a specific azole compound which serves as a copper ion electrodeposition inhibitor including two or more nitrogen atoms, an acid, and water. Therefore, in a case where electrolytic plating is carried out, the azole compound, which serves as a copper ion electrodeposition inhibitor, also adsorbs to a cathode surface together with copper ions. Accordingly, the electrodeposition of copper ions is strongly suppressed, the nucleation of copper is given priority, and a porous preform layer including copper particles is formed as a copper plating film on the cathode surface.

In the method for forming a preform layer according to the aspect of [2], the copper sheet or substrate is disposed on the cathode side in the acidic electrolytic copper plating solution according to the aspect of [1], and electrolytic copper plating is carried out. Therefore, unlike the conventional method for producing a porous film, as a copper plating film, the porous preform layer including copper particles of which the surfaces are coated with copper nanoparticles and having an average porosity of 11% to 78% can be formed on one surface or both surfaces of the copper sheet or the substrate with a simple process.

In the method for producing a bonding sheet according to the aspect of [3], the bonding sheet, which includes the porous preform layer on one surface or both surfaces of the copper sheet with a high strength of the sheet itself, can be produced with a simple process.

In the method for producing a bonded body according to the aspect of [4], the base material, the electronic component, and the bonding sheet produced by the method according to the aspect of [3] are laminated so that the bonding sheet is disposed between the base material and the electronic component, and the base material and the electronic component are heated under pressure in the laminating direction; and thereby, the bonded body is produced. Therefore, since the preform layer serves as a bonding layer, the bonded body with a high bonding strength can be produced.

In the method for producing a bonding substrate according to the aspect of [5], the porous preform layer is formed on one surface of the substrate by the method according to the aspect of [2]. Therefore, the bonding substrate having a high strength when bonded can be produced.

In the method for producing a bonded body according to the aspect of [6], the bonding substrate produced by the method according to the aspect of [5] and the electronic component are laminated, and the bonding substrate and the electronic component are heated under pressure in the laminating direction; and thereby, the bonded body is produced. Therefore, since the preform layer serves as a bonding layer, the bonded body including the bonding substrate and the electronic component, which are firmly bonded, can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a situation in which porous preform layers are formed on both surfaces of a copper sheet by an electrolytic copper plating method of the present embodiment.

FIG. 2 is a diagram schematically showing a bonding sheet including the copper sheet with the porous preform layers formed on both surfaces of the copper sheet of the present embodiment.

FIG. 3A is a diagram showing a situation in which porous preform layers are formed on one surface of a substrate whose surface is made of copper or nickel by an electrolytic copper plating method of the present embodiment.

FIG. 3B is a diagram schematically showing a bonding substrate with the porous preform layers formed on one surface of the substrate.

FIG. 4 is a diagram showing a first method for producing a bonded body by using the bonding sheet of the present embodiment; FIG. 4 (a) is a diagram showing a state in which the bonding sheet is placed on a base material; FIG. 4 (b) is a diagram showing a step of placing an electronic component on the bonding sheet and then carrying out heating under pressure; and FIG. 4 (c) is a diagram showing a bonded body produced by the heating under pressure.

FIG. 5 is a diagram showing a second method for producing a bonded body by using the bonding substrate of the present embodiment; FIGS. 5 (a) to (d) are diagrams showing a step of forming preform layers on a part of the substrate by electrolytic copper plating to produce the bonding substrate; and FIGS. 5 (e) to (h) are diagrams showing a step of placing an electronic component on the preform layers of the bonding substrate and then carrying out heating under pressure to produce the bonded body.

FIG. 6A is an electron scanning microscope image obtained by imaging a preform layer of Example 1 of the present invention at a magnification of 50000 times.

FIG. 6B is an electron scanning microscope image obtained by imaging a preform layer of Example 1 of the present invention at a magnification of 100000 times.

DESCRIPTION OF EMBODIMENTS

Next, embodiments for implementing the present invention will be described with reference to the drawings.

[Acidic Electrolytic Copper Plating Solution]

An acidic electrolytic copper plating solution of the present embodiment contains a soluble copper salt, an azole compound which has 2 or more and 3 or less nitrogen atoms in a five-membered ring represented by Formulae (1) to (4) and serves as a copper ion electrodeposition inhibitor, an acid, and water. Any solution can be used as long as these components are contained. As necessary, a brightening agent, a surfactant, an antioxidant, and other agents can be added.

Specific examples of the soluble copper salt include copper sulfate, copper oxide, and copper carbonate; copper alkane sulfonates such as copper methane sulfonate and copper propanoate; copper alkanol sulfonates such as copper isethionate and copper propanol sulfonate; organic acid coppers such as copper acetate, copper citrate, and copper tartrate, and the like. One of these or a combination of two or more kinds thereof can be used.

Furthermore, examples of the acid include an organic acid and an inorganic acid. Specific examples of the acids include sulfuric acid; alkanesulfonic acids such as methanesulfonic acid and propanesulfonic acid; alkanolsulfonic acids such as isethionic acid and propanolsulfonic acid; organic acids such as citric acid, tartaric acid, and formic acid, and the like. One of these or a combination of two or more kinds thereof can be used. Examples of water include pure water such as ion exchange water and distilled water.

Next, the azole compound, which has two or more and three or less nitrogen atoms in a five-membered ring and serves as a copper ion electrodeposition inhibitor, will be described. Specific examples of the azole compound represented by Formulae (1) to (4) 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, and the like.

The imidazole is a kind of the azole compound represented by Formula (1), and is represented by Formula (5). 2-Aminoimidazole is a kind of the azole compound represented by Formula (1), and is represented by Formula (6). Pyrazole is a kind of the azole compound represented by Formula (2), and is represented by Formula (7). 3-Aminoimidazole is a kind of the azole compound represented by Formula (2), and is represented by Formula (8). 1,2,3-Triazole is a kind of the azole compound represented by Formula (3), and is represented by Formula (9).

1,2,4-Triazole is a kind of the azole compound represented by Formula (4), and is represented by Formula (10). 3-Amino-1,2,4-triazole is a kind of the azole compound represented by Formula (4), and is represented by Formula (11). 3,5-Diamino-1,2,4-triazole is a kind of the azole compound represented by Formula (4), and is represented by Formula (12). 3-Amino-5-methylthio-1H-1,2,4-triazole is a kind of the azole compound represented by Formula (4), and is represented by Formula (13).

[Method for Producing Acidic Electrolytic Copper Plating Solution]

The acidic electrolytic copper plating solution of the present embodiment can be prepared by mixing the above-described soluble copper salt, the azole compound which has 2 or more and 3 or less nitrogen atoms in a five-membered ring and serves as the copper ion electrodeposition inhibitor described above, an acid, and water.

The prepared acidic electrolytic copper plating solution has a soluble copper salt concentration of 0.1 mol/L or more, and preferably 0.1 mol/L or more and 1.0 mol/L or less. In a case where the soluble copper salt concentration is less than 0.1 mol/L, the preform layer as the copper plating film cannot be formed. In addition, a concentration of the azole compound, serving as the copper ion electrodeposition inhibitor, is 10 mmol/L or more and 50 mmol/L or less and preferably 10 mmol/L or more and 30 mmol/L or less. In a case where the azole compound concentration is less than 10 mmol/L, the effect of suppressing electrodeposition of copper ions is defective, and the preform layer as the copper plating film is not porous. In addition, in a case where the concentration of the azole compound is more than 50 mmol/L, the electrodeposition of copper ions is excessively suppressed. Therefore, the copper plating film becomes brittle, and the strength significantly deteriorates. Alternatively, the azole compound cannot be dissolved in the solution and is precipitated. In addition, an acid concentration is not particularly limited, but is preferably pH 0 to 5, and more preferably pH 1 to 3. Furthermore, a chloride ion concentration is 10 ppm or less and preferably 5 ppm or less. In a case where the chloride ion concentration is more than 10 ppm, the chloride ions adsorb to the copper surface, and the formation of the preform layer as the copper plating film is impaired.

[Method for Producing Porous Preform Layer and Bonding Sheet]

A method for producing a bonding sheet including a copper sheet with a preform layer will be described, and the method includes forming the preform layers on one surface or both surfaces of the copper sheet by using the acidic electrolytic copper plating solution described above.

As shown in FIG. 1, an acidic electrolytic copper plating solution 3, which is as described above, is put into a plating tank 2 of an electrolytic copper plating apparatus 1, and in this acidic electrolytic copper plating solution 3, a copper sheet 4 to be plated and two copper materials 5 and 5, which are respectively made of electrolytic copper and oxygen-free copper, are disposed so that one of the copper materials 5 and 5 faces one surface of the copper sheet 4 and the other of the copper materials 5 and 5 faces the other surface of the copper sheet 4. As shown in the figure, the copper sheet 4 is connected to a negative electrode 6 as a cathode, and the two copper materials 5 and 5 are connected to a positive electrode 7 as soluble anodes. A voltage is applied to the copper sheet 4 and the copper materials 5 and 5 to form preform layers 8 as copper plating films on both surfaces of the copper sheet 4. In this embodiment, this copper sheet 4 is a copper foil, and the thickness of the copper sheet 4 is exaggerated in FIG. 1. As the copper foil constituting the copper sheet 4, pure copper or a copper alloy can be used. For example, oxygen-free copper, tough pitch copper, phosphorous deoxidized copper, or other coppers can be used. As the copper foil, a rolled copper foil obtained by rolling such a copper material, or an electrolytic copper foil produced by an electrolytic copper plating method, or other ways can be used. Although the copper materials 5 are used as the soluble anodes herein, an insoluble anode such as Pt/Ti can be used instead of the copper materials 5. Although not shown in the figure, it is also possible to produce a bonding sheet including a preform layer on one surface of the copper sheet 4 by allowing the copper material 5 to face only one surface of the copper sheet 4.

[Method for Producing Porous Preform Layer and Bonding Substrate]

Another electrolytic copper plating method is shown in FIG. 3A. In FIG. 3A, the same elements as those shown in FIG. 1 are designated by the same reference numerals. As shown in FIG. 3A, a substrate 4a whose surface is made of copper or nickel is disposed in the acidic electrolytic copper plating solution 3 of the electrolytic copper plating apparatus 1, and the copper material 5 is disposed to face one surface of this substrate 4a to perform electrolytic copper plating in the same manner as the electrolytic copper plating shown in FIG. 1. A resist film 4b is formed on the surface of the substrate 4a in advance to have openings at predetermined intervals. As a result, the porous preform layers 8 containing copper particles 12 are formed as copper plating films in the openings of the resist film 4b formed on one surface of the substrate 4a.

Regarding the conditions for the electrolytic copper plating in the acidic electrolytic copper plating solution 3 shown in FIG. 1 or FIG. 3A, a current density in the copper sheet 4 or substrate 4a to be plated is set to about 0.1 A/dm² to 5 A/dm², preferably 0.4 A/dm² to 1.0 A/dm² by using a direct current supply, and air and jet stirring or rocking stirring is then performed for about 30 minutes to 150 minutes and preferably about 60 minutes to 120 minutes, for example.

When the electrolytic copper plating is carried out under the above-described conditions, the azole compound, which serves as a copper ion electrodeposition inhibitor, also adsorbs to the cathode surface, which is the surface of the copper sheet 4 or substrate 4a, together with copper ions. The electrodeposition of copper ions is strongly suppressed due to the presence of the azole compound, the nucleation of copper is given priority, and the porous preform layers 8 containing the copper particles 12 are formed as copper plating films on the cathode surface.

After the electrolytic copper plating is carried out, the copper sheet 4 on which the preform layers 8 shown in FIG. 1 have been formed is taken out from the acidic electrolytic copper plating solution 3. In addition, the substrate 4a on which the preform layers shown in FIG. 3A have been formed is taken out from the acidic electrolytic copper plating solution 3, and the resist film 4b is removed.

Thereafter, the copper sheet 4 or the substrate 4a is cleaned with a cleaning solvent such as ethanol, water, or acetone, and dried in the atmosphere with a dry air. As shown in FIG. 2, a bonding sheet 10 including the porous preform layers 8 on both surfaces of the copper sheet 4 is thus obtained. In addition, as shown in FIG. 3B, a bonding substrate 20 including the porous preform layers 8 on one surface of the substrate 4a is obtained. The obtained bonding sheet 10 or bonding substrate 20 is preferably immersed in a rust preventive agent containing benzotriazole and a surfactant as main components for a predetermined time in order to prevent surface oxidation.

The thickness of each porous preform layer 8 on the copper sheet 4 or substrate 4a is preferably 15 μm to 50 μm. In a case where the thickness of each preform layer is less than 15 μm, the strength of each preform layer itself is decreased, and the preform layer is difficult to handle. In a case where the thickness of the preform layer is more than 50 μm, the preform layer is difficult to follow irregularities of each surface of the base material or electronic component described later during the bonding, and the bonding strength of the bonded body may decrease.

[Bonding Sheet]

The total thickness of the bonding sheet 10 obtained as described above is at least 25 μm. In other words, the thickness of the bonding sheet 10 is 25 μm or more. The total thickness is preferably 25 μm to 140 μm. In a case where the total thickness is less than the lower limit of 25 μm, the strength of the bonding sheet itself may decrease. In a case where the total thickness is more than 140 μm, provided that the base material is a substrate, and the substrate to which the electronic component is bonded has warpage, the warpage may not be mitigated. The total thickness of the bonding sheet is measured as follows. The bonding sheet is completely coated with an epoxy resin, and then cut in a direction perpendicular to a surface direction of the bonding sheet, and the cut surface is polished with an argon ion beam. Next, the processed surface subjected to polishing is observed with an electron scanning microscope (SEM), the thicknesses of the bonding sheet are randomly measured at 100 or more points, and an average value thereof is defined as the thickness of the bonding sheet.

The bonding sheet 10 including the copper sheet 4 with the porous preform layers 8 formed on both surfaces of the copper sheet 4 shown in FIG. 2 will be described in detail. The porous preform layers 8 are formed in the form of an aggregate of the copper particles 12, which are accumulated on both surfaces of the copper sheet 4. The preform layers 8 containing the copper particles 12 each have an average porosity of 11% or more and 78% or less. In a case where the average porosity is less than 11%, the amount of the copper particles 12 that contribute to the sintering of the porous preform layers 8 is small, and the sinterability of the copper particles 12 decreases. In a case where the average porosity is more than 78%, the percentage of voids in the porous preform layers 8 increases; and thereby, the preform layers 8 are brittle, and the sinterability of the copper particles 12 decreases. The average porosity of the preform layers 8 is preferably 11% or more and 17% or less.

In addition, as shown in an enlarged view of FIG. 2, each of the surfaces of the copper particles 12 is coated with copper nanoparticles 12a having an average grain size smaller than the average grain size of the copper particles 12. Therefore, each of the porous preform layers 8 is composed of the copper particles 12 and the copper nanoparticles 12a with which each of the surface of the copper particles 12 is coated. Copper plating is carried out with the acidic electrolytic copper plating solution that is characteristic of the present embodiment to cause the azole compound to adsorb to a copper surface. Accordingly, the electrodeposition of copper is suppressed, and nucleation is given priority; and as a result, the copper nanoparticles 12a are formed on a surface of each copper particle 12. By employing the structure with such characteristics, the copper particles 12 are easily sintered together when the porous preform layer 8 is pressurized to facilitate the formation of the robust bonding layer. It is difficult to calculate the average grain size of the copper nanoparticles 12a by the microscopic image because the fine copper particles 12 and the copper nanoparticles 12a, which are finer than the copper particles 12 are composited. Thus, the average grain size is calculated from a BET measurement value. As described above, the average grain size of the copper nanoparticles 12a calculated from the BET measurement value is 9.59 nm or more and 850 nm or less. In a case where the average grain size of the copper nanoparticles 12a is out of this range, it is difficult to facilitate sintering of the copper particles 12. The average grain size of the copper nanoparticles 12a is preferably within a range of 50 nm or more and 300 nm or less.

The above-described average porosity of the preform layer 8 is calculated by image analysis of a cross-section of the preform layer 8 using an electron scanning microscope. The arithmetic average of the porosity (P) determined by Equation (A) is defined as an average porosity. Specifically, imaging is performed three times in different visual fields, and an average value of the calculated porosity is defined as an average porosity.

$\begin{array}{cc}P\left(\%\right)=\left(S_2/S_1\right)\times 100& \left(A\right)\end{array}$

In Equation (A), P is a porosity of the preform layer 8, S₁ is the total area of the preform layer 8, and S₂ is an area of void portions in the preform layer 8.

In addition, the above-described average grain size of the copper nanoparticles 12a is calculated from the specific surface area of the porous preform layer 8 measured by the BET method. The measurement by the BET method is performed using Macsorb HM-model-1201 manufactured by MOUNTECH. The copper sheet 4 with the preform layers 8 is cut into a size of 2 mm square, and a measurement cell is filled with the cut sheets to measure the specific surface area by a single-point BET method. The mass of the copper sheet 4 is subtracted from a measurement value, and the value is converted into the mass of the preform layer 8 itself. The grain size of the copper nanoparticles 12a is calculated from the calculated BET measurement value from Equation (B). A coefficient of 335.95 in Equation (B) is a value calculated from theoretical values of the density of copper, the surface area of the copper nanoparticles 12a, and the volume of the copper nanoparticles 12a. The average grain size (d) of the copper nanoparticles 12a is an average value of the values obtained by performing measurement three times by the BET method.

$\begin{array}{cc}d\left(\mathrm{nm}\right)=335.95/\left(\mathrm{BET}\mathrm{measurement}\mathrm{value}\left(m^2/g\right)\right)& \left(B\right)\end{array}$

[First Method of Producing Bonded Body with Bonding Sheet]

A first method for producing a bonded body with the above-described bonding sheet 10 will be described.

As shown in FIG. 4 (a), first, a substrate, such as an oxygen-free copper plate, various heat dissipation boards, a flame retardant type 4 (FR4) board, or a substrate such as kovar, is prepared as a base material 16, and an electronic component, such as a silicon chip device or an LED chip device, is prepared as an electronic component 17. Next, the bonding sheet 10 is disposed at a predetermined position on the base material 16, and as shown in FIG. 4 (b), the electronic component 17 is disposed on the bonding sheet 10. In this state, the base material 16 and the electronic component 17 are held at a nitrogen atmosphere in a heating furnace at a temperature of 250° C. to 350° C. for 1 minute to 30 minutes under a pressure of 1 MPa to 20 MPa in a laminating direction, so that the base material 16 and the electronic component 17 are bonded. Accordingly, as shown in FIG. 4 (c), the bonding sheet 10 becomes a bonding layer 15, and the electronic component 17 is bonded to the base material 16 via this bonding layer 15 to obtain a bonded body 18.

[Second Method for Producing Bonded Body with Bonding Substrate]

A second method for producing a bonded body with a bonding substrate will be described.

As shown in FIG. 5, in this method, a bonding substrate 40 including a substrate 46 with porous preform layers 8 formed on a surface of the substrate 46 is used to form a bonded body 44.

The porous preform layers 8 shown in FIG. 5 are the same as the porous preform layers 8 shown in FIG. 2. The substrate surface of the substrate 46 is made of copper or nickel. For example, this substrate 46 is an oxygen-free copper plate, or a Si substrate whose surface is metallized with copper, or an oxygen-free copper plate provided with a Ni plating layer on a substrate surface. The electronic component 47 shown in FIG. 5 is the same as the electronic component 17 shown in FIG. 4.

First, as shown in FIG. 5 (a), the substrate 46 of which a substrate surface is made of copper or nickel is prepared. As shown in FIG. 5 (b), the surface of the substrate 46 is masked and patterned with a resist film 41 to have openings 46a at predetermined intervals. In this state, electrolytic copper plating is carried out in the acidic electrolytic copper plating solution 3 described above to form the porous preform layers 8 in the openings 46a as shown in FIG. 5 (c). Thereafter, as shown in FIG. 5 (d), the resist film 41 is removed to produce the bonding substrate 40 with the porous preform layers 8 formed on the substrate 46. This electrolytic copper plating can be performed by the method described above. In the above description, although the preform layers 8 are formed only on the openings 46a, the preform layers 8 may be formed on the entire surface of the substrate 46 without providing the resist film 41.

As shown in FIG. 5 (e) to (g), the electronic component 47 is bonded onto the porous preform layers 8 of the bonding substrate 40. Specifically, as shown in FIG. 5 (e), the bonding substrate 40 on which the porous preform layers 8 are formed is placed on a pressurizing plate 42. As shown in FIG. 5 (f), the electronic component 47 is placed on the preform layers 8 to obtain a laminate. Next, as shown in FIG. 5 (g), the laminate including the bonding substrate 40 and the electronic component 47 is heated while being pressurized by the pressurizing plate 42 and a pressurizing plate 43 in the laminating direction. The pressurizing and heating conditions are the same as the pressurizing and heating conditions for the base material 16 and electronic component 17 shown in FIG. 4 (a). Accordingly, as shown in FIG. 5 (h), the preform layers 8 become bonding layers 45, and the bonding substrate 40 and the electronic component 47 are bonded to obtain the bonded body 44.

Although not shown in the figure, an oxygen-free copper plate with no preform layer on a surface thereof or a substrate whose bonding surface is metallized with copper may be prepared as the substrate, and a preform layer may be formed on a bonding surface of the electronic component. In addition, although not shown in the figure, a preform layer may be formed on the substrate, and a preform layer may be further formed on the bonding surface of the electronic component. Since the preform layers are formed on both the substrate and the electronic component, the bonding strength between the substrate and the electronic component can be further increased, which is preferred.

EXAMPLES

Next, Examples of the present invention will be described in detail together with Comparative Examples. In Examples 1 to 20 and Comparative Examples 1 to 10 shown below, electrolytic copper plating was carried out on a Si wafer patterned by the method shown in FIG. 5.

First, types, structural formulae, and compound names of the copper ion electrodeposition inhibitors used in Examples 1 to 20 and Comparative Examples 1 to 10 are shown in Table 1.

TABLE 1
Copper ion electrodeposition inhibitor
	Structural
Type	formula	Compound name
No. 1	Formula (5)	Imidazole
No. 2	Formula (6)	2-Aminoimidazole
No. 3	Formula (7)	Pyrazole
No. 4	Formula (8)	3-Aminoimidazole
No. 5	Formula (9)	1,2,3-Triazole
No. 6	Formula (10)	1,2,4-Triazole
No. 7	Formula (11)	3-Amino-1,2,4-triazole
No. 8	Formula (12)	3,5-Diamino-1,2,4-triazole
No. 9	Formula (13)	3-Amino-5-methylthio-1H-1,2,4-triazole
No. 10	Formula (14)	Tetrazole
No. 11	Formula (15)	5-Amino-1H-tetrazole
No. 12	—	Additive containing 50 ppm of disodium
		3,3-dithiobis(1-propanesulfonate) and 300
		ppm of polyethylene glycol (Mw: 3400)

In Table 1, a copper ion electrodeposition inhibitor, which is tetrazole with a type No. 10, and a copper ion electrodeposition inhibitor, which is 5-amino-1H-tetrazole with a type No. 11, are represented by Formulae (14) and (15), respectively. These azole compounds do not belong to Formulae (1) to (4) described above.

Example 1

First, a copper layer having a thickness of about 500 nm was formed on an Si wafer (thickness: 1.2 mm) by a sputtering method and the Si wafer was used. The surface of the Si wafer that included this copper layer (hereinafter, also simply referred to as the Si wafer) was patterned with a photoresist to provide 6002 perfectly circular openings with a diameter of 75 μm per die (15 mm square). As a pre-treatment before electrolytic copper plating on this Si wafer, a hydrophilization treatment with a plasma cleaner was performed. Next, the Si wafer was pre-wet with pure water, then immersed in a sulfuric acid aqueous solution having a concentration of 10% by mass to conduct acid cleaning. The acid-cleaned Si wafer was washed with water. Electrolytic copper plating was carried out on one surface (patterned surface) of the Si wafer by using the plating apparatus 1 shown in FIG. 3A containing the following copper plating solution.

A copper plating bath was prepared with the following solution composition. The plating conditions are also shown together. Characteristic items out of the compositions of the plating bath and the plating conditions of Example 1 are shown in Table 2. In Example 1, as the copper ion electrodeposition inhibitor, 3,5-diamino-1,2,4-triazole (No. 8 shown in Table 1) represented by Formula (12) described above was used.

[Plating Bath Composition]

• • Copper sulfate pentahydrate (as Cu²⁺): 0.1 mol/L
  • Copper ion electrodeposition inhibitor (3,5-diamino-1,2,4-triazole): 10 mmol/L
  • Chloride ions: 0 ppm
  • Ion exchange water: Balance

[Plating Conditions]

• • Bath temperature: 26° C.
  • pH in bath: 2.5
  • Current density of cathode: 0.4 A/dm²

The Si wafer was immersed in the above-described copper plating solution, and electrolytic copper plating was carried out under the above-described plating conditions to form a porous preform layer including copper particles on the Si wafer. FIGS. 6A and 6B show electron scanning microscope images of the surface of the preform layer of Example 1.

	TABLE 2
	Acidic electrolytic copper plating solution		Evaluation
		Copper ion electrodeposition	Chloride	Plating	Average	Average
	Copper	inhibitor	ion	condition	porosity	grain size
	sulfate			Concen-	concen-	Current	of preform	of copper	Bonding	Determi-
	pentahydrate		Structural	tration	tration	density	layer	nanoparticles	strength	nation
	(mol/L)	Type	formula	(mol/L)	(ppm)	(A/dm2)	(%)	(nm)	(MPa)	result
Example 1	0.1	No. 8	Formula (12)	10	0	0.4	12	103	19.3	Good
Example 2	0.1	No. 8	Formula (12)	10	0	0.2	15	56	23.7	Good
Example 3	0.1	No. 8	Formula (12)	10	0	1.0	37	149	30.2	Good
Example 4	1.0	No. 8	Formula (12)	10	0	1.0	58	184	17.3	Good
Example 5	0.1	No. 8	Formula (12)	25	0	0.4	21	82	25.8	Good
Example 6	0.1	No. 8	Formula (12)	50	0	0.4	26	63	27.6	Good
Example 7	0.1	No. 8	Formula (12)	10	5	0.4	12	132	18.7	Good
Example 8	0.1	No. 8	Formula (12)	10	10	0.4	11	154	17.2	Good
Example 9	0.1	No. 6	Formula (10)	10	0	0.4	15	198	22.4	Good
Example 10	0.5	No. 6	Formula (10)	50	0	2.5	62	239	18.3	Good
Example 11	0.1	No. 7	Formula (11)	10	0	0.4	11	89	24.1	Good
Example 12	0.1	No. 7	Formula (11)	20	0	0.4	13	72	20.0	Good
Example 13	0.1	No. 9	Formula (13)	10	0	0.4	14	262	22.3	Good
Example 14	0.1	No. 9	Formula (13)	25	0	0.4	15	166	23.7	Good
Example 15	0.1	No. 1	Formula (5)	10	0	0.4	12	89	24.2	Good
Example 16	0.1	No. 1	Formula (5)	25	0	0.4	18	123	25.3	Good
Example 17	0.1	No. 2	Formula (6)	10	0	0.4	13	84	20.5	Good
Example 18	0.1	No. 4	Formula (8)	20	0	0.4	15	106	21.3	Good
Example 19	0.1	No. 3	Formula (7)	10	0	0.4	12	98	19.5	Good
Example 20	0.1	No. 5	Formula (9)	10	0	0.4	16	213	20.5	Good

Examples 2 to 20 and Comparative Examples 4 to 10

In Examples 2 to 20 and Comparative Examples 4 to 10, any of the concentration of the copper sulfate pentahydrate, the type of the copper ion electrodeposition inhibitor, the concentration of the copper ion electrodeposition inhibitor, or the chloride ion concentration was set to the same as or changed from those in Example 1. The current density of cathode during the plating was also the same as or changed from that in Example 1. Electrolytic copper plating was carried out in the same manner as in Example 1 except the above-described matters. Characteristic items out of the compositions of the plating baths and the plating conditions in Examples 2 to 20 and Comparative Examples 4 to 10 are shown in each of Table 2 described above and Table 3 described below.

Electrolytic copper plating was carried out in the same manner as in Example 1 to form porous preform layers containing copper particles as copper plating films on the Si wafers in Examples 2 to 20 and Comparative Examples 4 and 5. In Comparative Examples 6 to 10, since the electrodeposition of copper ions was defective, copper plating films were not uniformly formed on the Si wafers.

	TABLE 3
	Acidic electrolytic copper plating solution		Evaluation
		Copper ion electrodeposition	Chloride	Plating	Average	Average
	Copper	inhibitor	ion	condition	porosity	grain size
	sulfate			Concen-	concen-	Current	of preform	of copper	Bonding	Determi-
	pentahydrate		Structural	tration	tration	density	layer	nanoparticles	strength	nation
	(mol/L)	Type	formula	(mol/L)	(ppm)	(A/dm2)	(%)	(nm)	(MPa)	result
Comparative	1.0	—	—	—	80	3.0	0	—	—	Defective
Example 1
Comparative	1.0	—	—	—	5	3.0	0	—	—	Defective
Example 2
Comparative	1.0	No. 12	—	(See Table 1)	80	3.0	0	—	12.4	Slightly
Example 3										defective
Comparative	0.01	No. 8	Formula	10	0	0.4	8	42	9.2	Slightly
Example 4			(12)							defective
Comparative	0.1	No. 8	Formula	5	0	0.4	5	77	6.3	Slightly
Example 5			(12)							defective
Comparative	0.1	No. 8	Formula	75	0	0.4	—	—	—	Defective
Example 6			(12)
Comparative	0.1	No. 8	Formula	10	25	0.4	—	—	—	Defective
Example 7			(12)
Comparative	0.0	No. 8	Formula	0.15	50	0.4	—	—	—	Defective
Example 8			(12)
Comparative	0.1	No. 10	Formula	10	0	0.4	—	—	—	Defective
Example 9			(14)
Comparative	0.1	No. 11	Formula	10	0	0.4	—	—	—	Defective
Example 10			(15)

Comparative Example 1

In Comparative Example 1, the concentration of the copper sulfate pentahydrate was set to 1.0 mol/L, the cathode current density during the plating was set to 3.0 A/dm², and copper plating was carried out on the Si wafer in the same manner as in Example 1. In Comparative Example 1, the copper ion electrodeposition inhibitor was not used. The chloride ion concentration was 80 ppm in the copper plating solution.

Comparative Example 2

In Comparative Example 2, the concentration of the copper sulfate pentahydrate was set to 1.0 mol/L, the cathode current density during the plating was set to 3.0 A/dm², and copper plating was carried out on the Si wafer in the same manner as in Example 1. In Comparative Example 1, the copper ion electrodeposition inhibitor was not used. The chloride ion concentration was 5 ppm in the copper plating solution.

Comparative Example 3

In Comparative Example 3, the concentration of the copper sulfate pentahydrate was set to 1.0 mol/L, the cathode current density during the plating was set to 3.0 A/dm², and copper plating was carried out on the Si wafer in the same manner as in Example 1. In Comparative Example 3, in order to compare the azole compounds with organic compounds other than the azole compounds, as the copper ion electrodeposition inhibitor, a common additive containing 50 ppm of disodium 3,3-dithiobis(1-propanesulfonate) and 300 ppm of polyethylene glycol (Mw: 3400) was used. The chloride ion concentration was 80 ppm in the copper plating solution.

<Comparative Evaluation>

<Measurement of Chloride Ion Concentration>

The chloride ion concentration in the copper plating solution after bath preparation was measured by an ion chromatography method (manufactured by Thermo SCIENTIFIC, apparatus name: Dionex ICS-2100, separation column: Dionex IonPac™ AS12A (4×200 mm)).

<Average Porosity of Porous Preform Layer and Average Grain Size of Copper Nanoparticles>

The average porosity of the porous preform layers of 25 types of the bonding substrates obtained in Examples 1 to 20 and Comparative Examples 1 to 5, and the average grain size of the copper nanoparticles with which each of the copper particles constituting the preform layer was coated were determined by the methods described above. The results are shown in Table 2 and Table 3 described above.

<Producing of Bonded Body>

As shown in FIG. 5 (f), the chip 47 was disposed on the preform layers 8 of 25 types of the bonding substrates 40 obtained in Examples 1 to 20 and Comparative Examples 1 to 5, and as shown in FIG. 5 (g), heating was carried out under pressure to obtain each bonded body 44. The chip 47 was formed of a 2.5 mm square Si wafer (thickness: 1.2 mm) in which an uppermost surface was subjected to copper metallization.

This bonding was carried out by holding the bonded body 44 at a temperature of 300° C. under a pressure of 30 MPa for 30 minutes in a nitrogen atmosphere by using a pressurizing and heating bonding apparatus (manufactured by ALPHA-DESIGN Co., Ltd.; HTB-MM). The shear strengths of 25 types of the bonded bodies were measured as follows.

<Method for Measuring Shear Strength of Bonded Body>

The shear strength of the bonded body was measured by using a shear strength evaluation tester (bond tester manufactured by Nordson Corporation; Dage series 4000). Specifically, the measurement of the shear strength was carried out by fixing the Si wafer serving as a substrate of the bonded body horizontally, pressing the chip from the side in a horizontal direction by a shear tool at a position 50 μm above the surface (upper surface) of the bonding layer to measure the strength when the chip was broken. The moving speed of the share tool was set to 0.1 mm/sec. The strength test was performed three times per condition, and the arithmetic average value of the obtained values was used as the measurement value of the bonding strength. The shear strengths of 25 types of the bonded bodies are shown in Tables 2 and 3 described above. In a case where the bonding strength was 15 MPa or more, the bonding strength was evaluated as “good”, in a case where the bonding strength was 1.7 MPa or more and less than 15 MPa, the bonding strength was evaluated as “slightly defective”, and in a case where the bonding strength was less than 1.7 MPa, the bonding strength was evaluated as “defective”. In the bonding strengths in Tables 2 and 3, “-” indicates a case where the chip 47 and the bonding substrate 40 were not bonded even though an attempt was made to bond the chip 47 and the bonding substrate 40, or a case where the chip 47 was peeled off before the bonding strength was measured. The results are shown in Tables 2 and 3.

As is clear from Tables 2 and 3, in Comparative Example 1 and Comparative Example 2, the copper ion electrodeposition inhibitors functioning to form the porous copper plating films were not contained. In Comparative Example 3, the added copper ion electrodeposition inhibitor did not function to form the porous copper plating film. Therefore, in Comparative Examples 1 to 3, although copper plating films were formed, the average porosity was “0%” in each of Comparative Examples, and the copper plating films were not porous. Therefore, in each of Comparative Examples 1 and 2, the chip and the bonding substrate were not bonded to each other, and the bonding strength was determined as “defective”. In addition, in Comparative Example 3, the bonding strength was as low as “12.4 MPa”, and determined as “slightly defective”.

In Comparative Example 4, since the concentration of copper ions was too low as “0.01 mol/L”, the sufficient electrodeposition did not occur, the average porosity was as low as “8%”, and the average grain size of the copper nanoparticles was 42 nm; and as a result, the preform layer had a low degree of porosity as the copper plating film. Therefore, the bonding strength was as low as “9.2 MPa”, and determined as “slightly defective”.

In Comparative Example 5, since the concentration of 3,5-diamino-1,2,4-triazole serving as the copper ion electrodeposition inhibitor was too low as “5 mmol/L”, the electrodeposition of copper ions was not sufficiently suppressed, the average porosity was as low as “5%”, and the average grain size of the copper nanoparticles was 77 nm; and as a result, the preform layer had a low degree of porosity as the copper plating film. Therefore, the bonding strength was as low as “6.3 MPa”, and determined as “slightly defective”.

In Comparative Example 6, since the concentration of 3,5-diamino-1,2,4-triazole serving as the copper ion electrodeposition inhibitor was as high as “75 mmol/L”, the electrodeposition of copper ions hardly occurred. As a result, the copper plating film was not formed. Therefore, the bonding strength was not measured. The bonding strength was determined as “defective”.

In Comparative Example 7, the chloride ion concentration was too high as “25 ppm”. Therefore, the chloride ions adsorbed onto the copper surface to inhibit the adsorption of the azole compound for forming porous onto the copper surface. As a result, the porous copper plating film was not formed. Therefore, the bonding strength was not measured. The bonding strength was determined as “defective”.

In Comparative Example 8, the chloride ion concentration was too high as “50 ppm”. Therefore, the chloride ions adsorbed to the copper surface to inhibit the formation of the preform layer as the copper plating film. In addition, since the concentration of 3,5-diamino-1,2,4-triazole serving as the copper ion electrodeposition inhibitor was too low as “0.15 mmol/L”. As a result, sufficient surface adsorption to form the porous copper plating film was not obtained; and thereby, the porous copper plating film was not formed. Therefore, the bonding strength was not measured. The bonding strength was determined as “defective”.

In Comparative Examples 9 and 10, since tetrazole (No. 10, Formula (14)) and 5-amino-1H-tetrazole (No. 11, Formula (15)), which did not belong to Formulae (1) to (4) were used as the copper ion electrodeposition inhibitors, the adsorption of the copper ion electrodeposition inhibitor onto the copper surface was too strong, and the electrodeposition of copper ions hardly occurred. As a result, the copper plating film was not formed. Therefore, the bonding strength was not measured. The bonding strength was determined as “defective”.

On the other hand, in each of Examples 1 to 20, the average porosity of the preform layer and the average grain size calculated from the BET value were appropriately controlled. The average porosity of the preform layer formed on the Si wafer was within a range of 11% or more and 78% or less as described above. In addition, the porous preform layer formed of the copper particles with the copper nanoparticles having the average grain size within a range of 9.59 nm to 850 nm as described above, which was calculated from the BET value, was formed. As a result, when the bonding substrate in each of Examples 1 to 20 and the chip were bonded, the bonding substrate and the chip were firmly bonded, and all bonding evaluations were “good.”

INDUSTRIAL APPLICABILITY

In the assembly and mounting of electronic components, the acidic electrolytic copper plating solution of the present embodiment can be used in the step of forming the porous preform layer for bonding two members to each other.

REFERENCE SIGNS LIST

• • 3: Acidic electrolytic copper plating solution
  • 4: Copper sheet
  • 4a, 46: Substrate (Si wafer)
  • 8: Preform layer
  • 10: Bonding sheet
  • 12: Copper particle
  • 12a: Copper nanoparticle
  • 15, 45: Bonding layer
  • 16: Base material
  • 17, 47: Electronic component
  • 18, 44: Bonded body
  • 20, 40: Bonding substrate

Claims

1. An acidic electrolytic copper plating solution comprising:

a soluble copper salt;

an azole compound which has 2 or more and 3 or less nitrogen atoms in a five-membered ring represented by Formulae (1) to (4) and serves as a copper ion electrodeposition inhibitor;

an acid; and

water,

wherein a copper concentration is 0.1 mol/L or more, an azole compound concentration is 10 mmol/L or more and 50 mmol/L or less, and a chloride ion concentration is 10 ppm or less,

in Formulae (1) to (4), R1 to R4 may be the same as or different from each other, and are any one 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 a hydrogen atom of these groups is substituted with any one of 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 an alkyl chain, or a mercapto group, or any one 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 an alkyl chain, a mercapto group, a hydroxyl group, a carboxyl group, a halogen atom, or a hydrogen atom.

2. A method for forming a preform layer, the method comprising:

a step of placing a copper sheet or a substrate on a cathode side in the acidic electrolytic copper plating solution according to claim 1 and performing acidic electrolytic copper plating to form a porous preform layer on one surface or both surfaces of the copper sheet or the substrate, wherein the porous preform layer serves as a copper plating film, contains copper particles, and has an average porosity of 11% to 78%,

wherein the surface of the copper particle is coated with copper nanoparticles with a particle size smaller than an average grain size of the copper particles,

wherein an average grain size calculated using a BET value of the copper nanoparticles is 9.59 nm or more and 850 nm or less, and

wherein the average porosity of the preform layer is an arithmetic average of a porosity (P) determined by Equation (A) based on a total area (S1) of the preform layer and an area (S2) of a void portion in the preform layer, which is calculated by image analysis of a cross-section of the preform layer using an electron scanning microscope, P (%)=(S2/S1)×100  (A).

3. A method for producing a bonding sheet, the method comprising:

a step of forming a porous preform layer on one surface or both surfaces of a copper sheet by the method for forming a preform layer according to claim 2.

4. A method for producing a bonded body, the method comprising:

a step of laminating a base material, an electronic component, and the bonding sheet produced by the method for producing a bonding sheet according to claim 3 so that the bonding sheet is disposed between the base material and the electronic component; and

a step of heating the base material and the electronic component under pressure in a laminating direction to produce a bonded body.

5. A method for producing a bonding substrate, the method comprising:

a step of forming a porous preform layer on one surface of a substrate by the method for forming a preform layer according to claim 2.

6. A method for producing a bonded body, the method comprising:

a step of laminating the bonding substrate produced by the method for producing a bonding substrate according to claim 5 and an electronic component so that the porous preform layer is disposed between the bonding substrate and the electronic component; and

a step of heating the bonding substrate and the electronic component under pressure in a laminating direction to produce a bonded body.