Cu pillar joint, and method for manufacturing a Cu pillar joint.

Abstract

To provide a Cu pillar joint that can form sufficient intermetallic compounds even under low temperature and short time conditions, and has excellent thermal reliability without leaving a large amount of solder layer remaining.SOLUTION: A Cu pillar joint 1 is formed by joining a first Cu pillar 11 and a second Cu pillar 21 via a joining layer 30, and the joining layer 30 has a porous Cu layer 31 formed on the first Cu pillar 11 side, a solder layer 32 formed on the second Cu pillar 21 side, and an intermetallic compound layer 33 formed between the porous Cu layer 31 and the solder layer 32, and the porosity of the porous Cu layer 31 is within the range of 5% or more and 80% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for joining a Cu pillar, specifically a Cu pillar that joins a first Cu pillar and a second Cu pillar. [Background technology]

[0002] In recent years, semiconductor devices have become increasingly high-performance, and the importance of micro-junction technology is growing. Flip-chip mounting is widely used as a mounting technology for IC chips, and as shown in Patent Document 1, for example, a method is provided in which a solder layer is formed on a protruding electrode and joined by solder.

[0003] Furthermore, to address the need for even narrower pitches, bonding technologies such as TLP (Transient Liquid Phase Diffusion Bonding) and SLID (Solid-Liquid Interdiffusion), which involve the mutual diffusion of solid and liquid phases during bonding, have been proposed. In the SLID method, as shown in Patent Documents 1 and 2, solder material is used as the material that forms the liquid phase. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-046148 [Patent Document 2] Patent No. 6061276 [Patent Document 3] Patent No. 6369620 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, while the SLID method uses solder material as described above, if a large amount of low-melting-point solder material remains after joining, it can lead to poor heat resistance, potentially resulting in insufficient thermal cycle reliability and thermal reliability. Forming intermetallic compounds by diffusing solder material requires prolonged heating, which leads to problems such as reduced production efficiency.

[0006] This invention has been made in view of the circumstances described above, and aims to provide a Cu pillar joint that can sufficiently form intermetallic compounds even under low temperature and short time conditions, has excellent thermal reliability without leaving a large solder layer, and a method for manufacturing a Cu pillar joint. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors conducted diligent research and found that by forming a porous Cu layer on the bonding surface of the Cu pillar, the surface area of ​​the bonding surface of the Cu pillar increases and the diffusion rate increases, promoting the formation of intermetallic compounds and suppressing the residue of a large amount of low-melting-point solder material after bonding.

[0008] The present invention is based on the above-mentioned findings, and an embodiment 1 of the present invention is a Cu pillar joint in which a first Cu pillar and a second Cu pillar are joined via a bonding layer, wherein the bonding layer comprises a porous Cu layer formed on the first Cu pillar side, a solder layer formed on the second Cu pillar side, and an intermetallic compound layer formed between the porous Cu layer and the solder layer, and the porosity of the porous Cu layer is in the range of 5% to 80%.

[0009] According to the Cu pillar joint of embodiment 1 of the present invention, the joint layer formed between the first Cu pillar and the second Cu pillar comprises a porous Cu layer formed on the first Cu pillar side, a solder layer formed on the second Cu pillar side, and an intermetallic compound layer formed between the porous Cu layer and the solder layer. Since the porosity of the porous Cu layer is in the range of 5% to 80%, even under low temperature and short time conditions, sufficient mutual diffusion occurs between the molten liquid phase of the solder layer and the solid phase of the porous Cu layer, promoting the formation of intermetallic compounds. This suppresses the retention of a large amount of low-melting-point solder material, resulting in excellent thermal reliability.

[0010] The Cu pillar joint according to aspect 2 of the present invention is characterized in that, in the method for joining Cu pillars according to aspect 1, a diffusion prevention layer is formed between the second Cu pillar and the solder layer. According to the Cu pillar joint of embodiment 2 of the present invention, since a diffusion prevention layer is formed between the second Cu pillar and the solder layer, the diffusion of metal elements constituting the solder layer into the second Cu pillar can be suppressed, allowing sufficient mutual diffusion between the molten liquid phase of the solder layer and the solid-phase porous Cu layer, and ensuring that the first Cu pillar and the second Cu pillar are reliably joined.

[0011] The Cu pillar joint according to embodiment 3 of the present invention is characterized in that, in the Cu pillar joint according to embodiment 1 or embodiment 2, a second porous Cu layer is formed between the second Cu pillar and the solder layer. According to the Cu pillar joint of embodiment 3 of the present invention, since a second porous Cu layer is formed between the second Cu pillar and the solder layer, the formation of intermetallic compounds can be promoted on the second porous Cu layer side as well, further suppressing the remaining amount of low-melting-point solder material, and enabling the production of a pillar joint with excellent thermal reliability.

[0012] The Cu pillar joint of embodiment 4 of the present invention is characterized in that, in any one of the Cu pillar joints of embodiment 1 to embodiment 3, the solder layer is composed of In or an In alloy. According to the Cu pillar joint of embodiment 4 of the present invention, since the solder layer is composed of In or an In alloy, joining can be performed under low temperature conditions of 200°C or less.

[0013] A method for manufacturing a Cu pillar joint according to aspect 5 of the present invention is a method for manufacturing a Cu pillar joint in which a first Cu pillar and a second Cu pillar are joined, characterized by comprising: a porous Cu layer forming step of forming a porous Cu layer having a porosity in the range of 5% to 80% on the joining surface of the first Cu pillar; a solder layer forming step of forming a solder layer on the joining surface of the second Cu pillar; a lamination step of laminating the first Cu pillar having the porous Cu layer formed on it and the second Cu pillar having the solder layer formed on it; and a joining step of heat-treating the laminated first Cu pillar and the second Cu pillar at a temperature of 120°C to 200°C to generate an intermetallic compound between the porous Cu layer and the solder layer, and joining the first Cu pillar and the second Cu pillar.

[0014] According to the method for manufacturing a Cu pillar joint of embodiment 5 of the present invention, a porous Cu layer having a porosity in the range of 5% to 80% is formed on the joining surface of the first Cu pillar, the first Cu pillar and the second Cu pillar are laminated via solder material, and the joint is heat-treated at a temperature of 120°C to 200°C. As a result, the liquid phase of the molten solder layer and the solid phase porous Cu layer sufficiently interdiffuse, promoting the formation of intermetallic compounds, suppressing the remaining amount of low-melting-point solder material, and making it possible to produce a pillar joint with excellent thermal reliability.

[0015] A method for manufacturing a Cu pillar joint according to aspect 6 of the present invention is characterized in that, in the method for manufacturing a Cu pillar joint according to aspect 5, a diffusion prevention layer formation step is included in which a diffusion prevention layer is formed on the joint surface of the second Cu pillar, and in the solder layer formation step, the solder layer is formed on the diffusion prevention layer. According to the method for producing a Cu pillar bonded body of aspect 6 of the present invention, since the method includes a diffusion prevention layer forming step of forming a diffusion prevention layer on the bonding surface of the second Cu pillar, diffusion of the metal elements constituting the solder layer into the second Cu pillar can be suppressed, the molten liquid phase of the solder layer and the solid-phase porous Cu layer can be sufficiently interdiffused, and the first Cu pillar and the second Cu pillar can be reliably bonded.

[0016] A method for producing a Cu pillar bonded body according to aspect 7 of the present invention is the method for producing a Cu pillar bonded body according to aspect 5 or aspect 6, wherein the method comprises a second porous Cu layer forming step of forming a second porous Cu layer on the bonding surface of the second Cu pillar, and in the solder layer forming step, the solder layer is formed on the second porous Cu layer. According to the method for producing a Cu pillar bonded body of aspect 7 of the present invention, since the method includes a second porous Cu layer forming step of forming a second porous Cu layer on the bonding surface of the second Cu pillar, the formation of intermetallic compounds can be promoted also on the side of the second porous Cu layer formed on the bonding surface of the second Cu pillar, and a pillar bonded body excellent in thermal reliability can be produced.

[0017] A method for producing a Cu pillar bonded body according to aspect 8 of the present invention is the method for producing a Cu pillar bonded body according to any one of aspects 5 to 7, wherein the solder layer forming step forms a solder layer composed of In or an In alloy. According to the method for producing a Cu pillar bonded body of aspect 8 of the present invention, since a solder layer composed of In or an In alloy is formed in the solder layer forming step, bonding can be performed under a low temperature condition of 200°C or lower. Effects of the Invention

[0018] According to the present invention, there can be provided a Cu pillar bonded body which can sufficiently form an intermetallic compound even under low-temperature and short-time conditions, does not leave a large amount of solder layer, and is excellent in thermal reliability, and a method for producing the Cu pillar bonded body. Brief Description of the Drawings

[0019] [Figure 1] This is an explanatory diagram of a Cu pillar joint according to one embodiment of the present invention. [Figure 2] This is a flowchart of a method for manufacturing a Cu pillar joint according to one embodiment of the present invention. [Figure 3] This is an explanatory diagram of a method for joining Cu pillars (manufacturing method for a Cu pillar joint) according to one embodiment of the present invention. [Figure 4] This is an explanatory diagram of a Cu pillar joint according to one embodiment of the present invention. [Modes for carrying out the invention]

[0020] Below, an embodiment of the present invention, a Cu pillar joint, and a method for manufacturing the Cu pillar joint, will be described with reference to the drawings.

[0021] The Cu pillar bonded body 1 according to this embodiment is, for example, a semiconductor device in which protruding electrodes (Cu pillars) formed on a semiconductor chip are joined together. As shown in Figure 1, the Cu pillar bonded body 1 in this embodiment has a structure in which a first Cu pillar 11 formed on a first wafer 10 and a second Cu pillar 21 formed on a second wafer 20 are bonded together via a bonding layer 30.

[0022] The bonding layer 30 comprises a porous Cu layer 31 formed on the first Cu pillar 11 side, a solder layer 32 formed on the second Cu pillar 21 side, and an intermetallic compound layer 33 formed between the porous Cu layer 31 and the solder layer 32.

[0023] Furthermore, the porous Cu layer 31 formed on the first Cu pillar 11 side is said to have nano-sized pores. Here, in the porous Cu layer 31, the average porosity P is ave The range is considered to be between 5% and 80%. Average porosity P aveThis is the average value of the porosity P calculated as follows. In this embodiment, the porosity P is calculated at three locations, and the average value of the porosity P is used as the average porosity P. ave It is calculating this. The porosity P is calculated by analyzing the cross-section of the porous Cu layer 31 using a scanning electron microscope to determine the total area S1 of the porous Cu layer 31 and the area S2 of the vacant portions within the porous Cu layer 31, and then using the following formula. Porosity P(%)=(S2 / S1)×100

[0024] On the other hand, in this embodiment, a diffusion prevention layer 22 is formed between the solder layer 32 formed on the second Cu pillar 21 side and the second Cu pillar 21.

[0025] The diffusion prevention layer 22 suppresses the diffusion of metal elements constituting the solder layer 23 towards the second Cu pillar 21. In this embodiment, the diffusion prevention layer 22 is made of Ni. In this case, the thickness of the diffusion prevention layer 22 is preferably within the range of 0.5 μm to 3 μm.

[0026] The solder layer 32 is composed of a solder material made of a metal with a low melting temperature, and it is preferable that its melting temperature is 200°C or lower. In this embodiment, the solder layer 32 is composed of In or an In alloy, specifically, the solder layer 32 is an In-Sn alloy (Sn concentration is 0 mass% or more and 75 mass% or less). Furthermore, it is preferable to use a low-alpha-ray material for the solder material constituting the solder layer 32, as this material generates less alpha radiation.

[0027] The intermetallic compound layer 33 formed between the solder layer 32 and the porous Cu layer 31 is formed by the mutual diffusion of the molten liquid phase of the solder layer 32 and the solid phase of the porous Cu layer 31. Here, it is preferable that the thickness of the bonding layer 30 (the total thickness of the porous Cu layer 31, the solder layer 32, and the intermetallic compound layer 33) be within the range of 3 μm to 20 μm. Furthermore, the area ratio occupied by the intermetallic compound layer 33 in the bonding layer 30 is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more.

[0028] Next, as shown in Figure 2, the manufacturing method for the Cu pillar joint 1 according to this embodiment comprises a pillar formation step S01, a porous Cu layer formation step S02, a diffusion prevention layer formation step S03, a solder material arrangement step S04, a lamination step S05, and a joining step S06.

[0029] <Pillar formation process S01> First, as shown in Figure 3, resist layers 41 and 51 are formed on one surface of the first wafer 10 and the second wafer 20. By performing Cu plating with the resist layers 41 and 51 formed, the first Cu pillar 11 and the second Cu pillar 21 are formed. Before forming the first Cu pillar 11 and the second Cu pillar 21, an adhesion layer (e.g., a Ti layer) and a seed layer (Cu layer) may be formed on one surface of the first wafer 10 and the second wafer 20.

[0030] <Porous Cu layer formation process S02> Next, as shown in Figure 3, a porous Cu layer 31 is formed on the bonding surface of the first Cu pillar 11. In this embodiment, with the resist layer 41 formed, the porous Cu layer formation step S02 is formed by plating as follows. Here, we will explain the method for forming the porous Cu layer 31. Examples of methods for forming the porous Cu layer 31 include the de-alloying method and the direct plating method.

[0031] (Dealloying method) In the de-alloying method, copper and a metal species electrochemically less noble than copper are co-deposited on the joint surface of the first Cu pillar 11 by electroplating to form a copper alloy plating film. Subsequently, the less noble metal species in the copper alloy plating film is de-alloyed to form a porous Cu layer 12. In this de-alloying method, a porous Cu layer 31 with a desired porosity and shape can be formed by controlling the deposition ratio and deposition morphology of copper and metal species less noble than copper.

[0032] Copper alloy plating is formed using a copper-zinc alloy plating solution containing, for example, copper salts, zinc salts, additives that control the deposition of copper and zinc, and a solvent. This copper alloy plating can be carried out by electroless plating or electrolytic plating. Metal species that are electrochemically less noble than copper (e.g., Fe, Mn, etc.) can also be selected as alloy species.

[0033] In copper-zinc alloy plating, copper sulfate, zinc sulfate, zinc pyrophosphate, zinc phosphate, etc., can be used as metal salts. The copper ions and zinc ions in the copper-zinc alloy plating solution are preferably each at 0.001 to 1.0 moles, and the molar ratio of copper ions to zinc ions is preferably within the range of Cu:Zn = 1:1 to 1:1000. The reason for making the zinc ion concentration higher than the copper ion concentration is that, due to the difference in standard oxidation-reduction potentials, copper is preferentially deposited compared to zinc.

[0034] Additionally, citric acid and pyrophosphate may be added as supporting salts (complexing agents). Examples of glossing agents include surfactants such as alkanolamines, glycine, serine, alanine, tyrosine aspartic acid, glutamic acid, histidine, or salts thereof. The pH of the plating solution should be 2.5 or higher to adjust the deposition balance of copper and zinc. Additionally, the cathode current density should be 0.3 A / dm 2 More than 0.8A / dm 2 Set it within the following range.

[0035] After forming a copper-zinc alloy plating film, the resist layer 41 is removed using a resist stripping solution, and then a de-alloying treatment is performed. Dealloying treatments for the formed copper-zinc alloy plating film include etching reactions using chemical solutions and electrochemical anodic reactions. In this embodiment, dealloying is performed using acid, and the copper alloy film is immersed and stirred for 30 minutes or more, depending on the thickness of the plating film, in a solution containing hydrochloric acid with a concentration of 0.002 mol / L to 0.5 mol / L at a temperature between 20°C and 35°C, thereby removing zinc from the copper-zinc alloy plating film. As a result, a porous Cu layer 31 is formed on the bonding surface of the first Cu pillar 11.

[0036] Next, the formed porous Cu layer 31 is washed with a cleaning solvent such as ethanol, water, or acetone, and then dried in the air using dry air. Furthermore, to prevent surface oxidation, it is preferable to immerse the product in a rust inhibitor mainly composed of benzotriazole and a surfactant for a predetermined time.

[0037] (Direct plating method) In the direct plating method, a porous Cu layer 31 with a porous structure is formed by electroplating the bonding surface of the first Cu pillar 11 using a Cu plating solution containing an azole-based additive, which is a copper ion electrodeposition inhibitor. After forming the porous Cu layer 31, the resist layer 41 is removed using a resist stripping solution. In this direct plating method, by controlling the type and amount of additives contained in the Cu plating solution and the plating conditions, it is possible to form a porous Cu layer 31 with a desired porosity and shape.

[0038] As the copper plating solution, an acidic electrolytic copper plating solution is used, which contains a soluble copper salt, an azole compound having 2 to 3 nitrogen atoms in a five-membered ring (which acts as a copper ion deposition inhibitor), an acid, and water. Brighteners, surfactants, antioxidants, etc., may be added as needed. Furthermore, the copper plating solution used has a copper concentration of 0.1 mol / L or higher, an azole compound concentration of 10 mmol / L or more and 50 mmol / L or less, and a chloride ion concentration of 10 ppm or less.

[0039] Specific examples of soluble copper salts include copper sulfate, copper oxide, copper carbonate; copper alkanesulfonates such as copper methanesulfonate and copper propanesulfonate; copper alkanolsulfonates such as copper isethionate and copper propanolsulfonate; and organic acid copper salts such as copper acetate, copper citrate and copper tartrate. These may be used alone or in a mixture of two or more thereof.

[0040] Further, examples of the acid include organic acids and inorganic acids. Illustrative examples thereof include sulfuric acid; alkanesulfonic acids such as methanesulfonic acid and propanesulfonic acid; alkanolsulfonic acids such as isethionic acid and propanolsulfonic acid; and organic acids such as citric acid and tartaric acid. These may be used alone or in a mixture of two or more thereof. Examples of the water include pure water such as ion-exchanged water and distilled water.

[0041] Further, as for plating conditions, for example, a DC power source is used, and the current density is set to 0.1 A / dm 2 to 5 A / dm 2 , preferably 0.4 A / dm 2 to 1.0 A / dm 2 , and a plating time that allows formation of a desired porous Cu layer 12 is selected. When Cu plating is performed under the above conditions, along with copper ions, the azole compound serving as a copper ion electrodeposition inhibitor is also adsorbed onto the cathode surface, which is the bonding surface of the first Cu pillar 11. The presence of the azole compound strongly suppresses the electrodeposition of copper ions, prioritizes copper nucleation, and forms a porous Cu layer 31 as a copper plating film on the cathode surface.

[0042] <Diffusion Prevention Layer Forming Step S03> A diffusion prevention layer 22 is formed on the bonding surface of the second Cu pillar 21. In the present embodiment, with the resist layer 51 formed, Ni plating is performed to form the diffusion prevention layer 22 made of Ni.

[0043] <Solder Layer Forming Step S04> Next, solder material is arranged to laminate onto the diffusion prevention layer 22 formed on the joint surface of the second Cu pillar 21 to form a solder layer 32. In this embodiment, the solder layer 32 is formed by plating with solder material while the resist layer 51 is formed. After the solder layer 32 is formed, the resist layer 51 is removed using a resist stripping solution. Here, it is preferable that the thickness of the solder layer 32 be within the range of 1 μm to 10 μm. Furthermore, the solder material is composed of In or an In alloy; specifically, the solder layer 32 is an In-Sn alloy (Sn concentration is between 0 mass% and 75 mass%). Furthermore, it is preferable to use a low-alpha-ray material for the solder material constituting the solder layer 32, as this material generates less alpha radiation.

[0044] <Lamination process S05> Next, as shown in Figure 3, a first Cu pillar 11 with a porous Cu layer 31 formed on its bonding surface and a second Cu pillar 21 with a diffusion prevention layer 22 and a solder layer 32 formed on its bonding surface are laminated together.

[0045] <Joining process S06> Next, as shown in Figure 3, the stacked first Cu pillar 11 and second Cu pillar 21 are heated while being pressurized in the stacking direction to join the first Cu pillar 11 and the second Cu pillar 21. This produces a pillar joint 1 in which the first Cu pillar 11 and the second Cu pillar 21 are joined.

[0046] In this embodiment, the first Cu pillar 11 and the second Cu pillar 21 are joined by the SLID method, in which the molten liquid phase of the solder layer 32 and the solid phase porous Cu layer 31 are joined by mutual diffusion. In other words, the intermetallic compound layer 33 is formed by the mutual diffusion of the molten liquid phase of the solder layer 32 and the solid phase porous Cu layer 31, thereby joining the first Cu pillar 11 and the second Cu pillar 21.

[0047] In this embodiment, it is preferable that the pressurized load in joining process S06 is within the range of 0.1 MPa to 20 MPa. Furthermore, in this embodiment, it is preferable that the bonding temperature in bonding step S06 is within the range of 120°C to 200°C. Furthermore, in this embodiment, it is preferable that the holding time at the bonding temperature in bonding step S06 is within the range of 10 seconds to 3 minutes.

[0048] According to the Cu pillar joint 1 of this embodiment, which has the above configuration, the joint layer 30 formed between the first Cu pillar 11 and the second Cu pillar 21 has a porous Cu layer 31 formed on the first Cu pillar 11 side, a solder layer 32 formed on the second Cu pillar 21 side, and an intermetallic compound layer 33 formed between the porous Cu layer 31 and the solder layer 32. Since the porosity of the porous Cu layer 31 is in the range of 5% to 80%, even under low temperature and short time conditions, the liquid phase of the molten solder layer 32 and the solid phase of the porous Cu layer 31 sufficiently interdiffuse, promoting the formation of intermetallic compounds, which suppresses the remaining amount of low-melting-point solder material and provides excellent thermal reliability.

[0049] In the Cu pillar joint 1 of this embodiment, when a diffusion prevention layer 22 is formed on the joining surface of the second Cu pillar 21, the diffusion of metal elements constituting the solder layer 13 toward the second Cu pillar 21 can be suppressed, and the liquid phase of the molten solder layer 32 and the solid phase porous Cu layer 31 can sufficiently mutually diffuse, promoting the formation of intermetallic compounds, and ensuring that the first Cu pillar 11 and the second Cu pillar 12 are reliably joined.

[0050] In the Cu pillar joint 1 of this embodiment, when the solder layer 32 is made of In or an In alloy, a liquid phase can be generated even under low temperature conditions of 200°C or less, and the first Cu pillar 11 and the second Cu pillar 12 can be reliably joined by the SLID method.

[0051] According to the manufacturing method of the Cu pillar joint 1 of this embodiment, a porous Cu layer 31 having a porosity in the range of 5% to 80% is formed on the joining surface of the first Cu pillar 11, the first Cu pillar 11 and the second Cu pillar 12 are laminated via a solder layer 32, and the joint is heat-treated at a temperature of 120°C to 200°C. As a result, the liquid phase of the molten solder layer 32 and the solid phase porous Cu layer 31 sufficiently interdiffuse with each other, promoting the formation of intermetallic compounds, suppressing the remaining amount of low-melting-point solder material, and making it possible to produce a pillar joint 1 with excellent thermal reliability.

[0052] In the manufacturing method of the Cu pillar joint 1 according to this embodiment, if the method includes a diffusion prevention layer formation step S03 in which a diffusion prevention layer 22 is formed on the joining surface of the second Cu pillar 21, the diffusion of metal elements constituting the solder layer 32 into the second Cu pillar 21 can be suppressed, and the first Cu pillar 11 and the second Cu pillar 21 can be reliably joined.

[0053] Furthermore, in this embodiment, if a low-alpha-ray material that generates less alpha rays is used as the solder material constituting the solder layer 32, the occurrence of soft errors in the semiconductor device equipped with the pillar joint 1 of this embodiment can be suppressed, and a stable semiconductor device can be constructed.

[0054] Although embodiments of the present invention have been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. For example, in this embodiment, a diffusion-blocking layer 22 made of Ni was described as being formed, but the invention is not limited to this, and a diffusion-blocking layer may not be formed.

[0055] Furthermore, although this embodiment has been described as having a porous Cu layer formed on the first Cu pillar side, it is not limited to this, and as shown in the pillar joint 101 in Figure 4, a second porous Cu layer 34 may be formed on the second Cu pillar 21 side, and a solder layer 31 may be formed in contact with this second porous Cu layer 34. In this case, a second intermetallic compound layer 35 will be formed between the solder layer 31 and the porous Cu layer 34. [Examples]

[0056] The results of the verification experiments conducted to confirm the effectiveness of the present invention are described below.

[0057] First, a Si wafer (thickness: 0.8 mm) with a seed layer formed on its surface was used. The seed layer consisted of a titanium layer (thickness: 100 nm) and a copper layer (thickness: 500 nm) formed on top of this titanium layer by sputtering. The surface of this Si wafer was patterned with photoresist to have a 75 μm diameter bump pattern (total number of bumps: 625), and a resist layer with openings was formed on the seed layer.

[0058] In Examples 1 to 12 of the present invention, the above-described wafer was used as the first wafer, and a first Cu pillar and a porous Cu layer were formed on one surface of this first wafer. In Comparative Example 1, however, no porous Cu layer was formed.

[0059] In Examples 1-6 and Comparative Example 2 of the present invention, a porous Cu layer was formed by a de-alloying method. Copper-zinc alloy electroplating was performed using a copper-zinc alloy electroplating solution. Table 1 shows the plating conditions for the de-alloying methods of Examples 1 to 7 of the present invention. After forming a copper-zinc alloy plating layer, the resist layer was dissolved and removed using a dry film resist stripping solution. Next, the seed layer in areas where the copper-zinc alloy plating layer was not formed was removed using an etching solution. Then, the copper-zinc alloy plating layer was immersed in a 27°C solution containing 1.00 mol / L hydrochloric acid and the solution was stirred for 70 minutes to remove zinc from the copper-zinc alloy plating layer and dealloy it.

[0060] [Table 1]

[0061] In Examples 7-12 and Comparative Example 3 of the present invention, a porous Cu layer was formed by a direct plating method. Copper plating was performed using a copper plating bath. Table 2 shows the plating conditions for the direct plating methods of Examples 7 to 12 and Comparative Example 3 of the present invention. In the direct plating method, after porous copper plating, the resist layer was dissolved and removed using a dry film resist stripping solution, and then the seed layer was etched.

[0062] [Table 2]

[0063] Furthermore, the aforementioned wafer was designated as a second wafer, and a second Cu pillar, a diffusion prevention layer made of Ni, and a solder material layer were formed on one surface of this second wafer by plating. The thicknesses of each layer are shown in Table 3.

[0064] Then, the first Cu pillar and the second Cu pillar shown in Table 3 were stacked, and after alignment was performed using a Treky high-precision flip-chip bonder T-300-PRO, the first Cu pillar and the second Cu pillar were joined by pressurizing them at a pressure of 0.1 MPa in a nitrogen atmosphere and heat treatment under the conditions of holding at the bonding temperature shown in Table 3 for 1 minute, thereby obtaining a pillar joint.

[0065] Here, the average porosity P in the formed porous Cu layerave This was calculated as follows: By analyzing images of the cross-section of the porous Cu layer using a scanning electron microscope, the total area S1 of the porous Cu layer and the area S2 of the vacancies within the porous Cu layer were determined, and the degree of porosity P was calculated using the following formula. Porosity P(%)=(S2 / S1)×100 Then, the porosity P is calculated at three locations, and the average porosity P is taken as the average value of the porosity P values. ave The result was calculated. The evaluation results are shown in Table 3.

[0066] Furthermore, the joint portion of the pillar joint was observed in cross-section, and the formation of metal compounds (IMC formation) at the joint portion was evaluated. The cross-section of the joint layer of the pillar joint was processed using CP (compression plasma) to obtain SEM images and EDS maps of Cu and the metals (In,Sn) in the solder material. The overlapping portion of the EDS maps of the metals (In,Sn) in the solder material and Cu was identified as the intermetallic compound. The area ratio (IMC ratio) of the metal compounds in the joint was then calculated using the following formula. IMC conversion rate (%) = (Overlap area of ​​EDS between solder material (In,Sn) and Cu) / (EDS area of ​​solder material (In,Sn)) × 100

[0067] As mentioned above, a percentage of 90% or higher was rated as "Good," a percentage of 50% or higher but less than 90% was rated as "Acceptable," and a percentage of less than 50% was rated as "Unacceptable." The evaluation results are shown in Table 3.

[0068] [Table 3]

[0069] In Comparative Example 1, where a porous Cu layer was not formed, under the conditions of 200°C for 1 minute, sufficient intermetallic compounds were not generated, and a large amount of low-melting-point solder layer remained. In Comparative Example 2, where the porosity of the porous Cu layer was set to 85%, under the conditions of 150°C for 1 minute, sufficient intermetallic compounds were not formed, and a large amount of low-melting-point solder layer remained. In Comparative Example 3, where the porous Cu layer had a porosity of 3%, under the conditions of 200°C for 1 minute, sufficient intermetallic compounds were not formed, and a large amount of low-melting-point solder layer remained.

[0070] In contrast, in Examples 1 to 12 of the present invention, in which a porous Cu layer with a porosity in the range of 5% to 80% was formed, intermetallic compounds were sufficiently generated, and the remaining low-melting-point solder layer was suppressed.

[0071] Based on the results of the above verification experiments, it has been confirmed that, according to the present invention, it is possible to provide a Cu pillar joint with excellent thermal reliability, where an intermetallic compound can be sufficiently formed even under low temperature and short time conditions, and where a large amount of solder layer remains. [Explanation of Symbols]

[0072] 1,101 Cu pillar joint 11. First Cu Pillar 21. Second Cu Pillar 30 Bonding layer 31 Porous Cu layer 32 solder layers 33 Intermetallic compound layer

Claims

1. A Cu pillar joint in which a first Cu pillar and a second Cu pillar are joined via a bonding layer, The bonding layer comprises a porous Cu layer formed on the first Cu pillar side, a solder layer formed on the second Cu pillar side, and an intermetallic compound layer formed between the porous Cu layer and the solder layer. A Cu pillar joint characterized in that the porosity of the porous Cu layer is in the range of 5% to 80%.

2. The Cu pillar joint according to claim 1, characterized in that a diffusion prevention layer is formed between the second Cu pillar and the solder layer.

3. The Cu pillar joint according to claim 1, characterized in that a second porous Cu layer is formed between the second Cu pillar and the solder layer.

4. The Cu pillar joint according to claim 1, characterized in that the solder layer is composed of In or an In alloy.

5. A method for manufacturing a Cu pillar joint in which a first Cu pillar and a second Cu pillar are joined together, A porous Cu layer formation step is to form a porous Cu layer having a porosity in the range of 5% to 80% on the bonding surface of the first Cu pillar, A solder layer formation step is performed to form a solder layer on the joint surface of the second Cu pillar, A lamination step of stacking the first Cu pillar on which the porous Cu layer is formed and the second Cu pillar on which the solder layer is formed, A bonding step is to heat-treat the stacked first Cu pillar and the second Cu pillar at a temperature of 120°C to 200°C to generate an intermetallic compound between the porous Cu layer and the solder layer, and to join the first Cu pillar and the second Cu pillar, A method for manufacturing a Cu pillar joint, characterized by comprising the following features.

6. The method for manufacturing a Cu pillar joint according to claim 5, comprising a diffusion prevention layer formation step of forming a diffusion prevention layer on the joint surface of the second Cu pillar, wherein in the solder layer formation step, the solder layer is formed on the diffusion prevention layer.

7. The method for manufacturing a Cu pillar joint according to claim 5, comprising a second porous Cu layer forming step of forming a second porous Cu layer on the joint surface of the second Cu pillar, wherein in the solder layer forming step, the solder layer is formed on the second porous Cu layer.

8. The method for manufacturing a Cu pillar joint according to claim 5, characterized in that the solder layer formation step involves forming a solder layer composed of In or an In alloy.

Images