Cu pillar bonding method and Cu pillar bonded body manufacturing method

Abstract

To provide a method for joining Cu pillar capable of easily and surely joining Cu pillars to each other without requiring strict control of a shape of the Cu pillars to be joined.SOLUTION: A method for joining Cu pillar includes: a Cu-particle layer forming step S01 of forming a Cu-particle layer composed of a plurality of Cu particles on one of or both a joining surface of a first Cu pillar and a joining surface of a second Cu pillar; and a laminating step S02 of laminating the first Cu pillar and the second Cu pillar via the Cu-particle layer; and a joining step S03 of heating, while pressurizing, the laminated first Cu pillar and the second Cu pillar in the lamination direction, so as to solid-phase diffusion-join the first Cu pillar and the second Cu pillar. In the joining step S03, a deformation amount L (μm) in the lamination direction before and after the joining satisfies L≥1.4 μm, and the deformation amount L and a joining area A (μm2) of the first Cu pillar and the second Cu pillar are set to L / A≥0.0025.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a Cu pillar joining method for joining a first Cu pillar and a second Cu pillar, and a method for manufacturing a Cu pillar joined body. [Background technology]

[0002] In recent years, the performance of semiconductor devices has been improving, and the importance of micro-bonding technology has been increasing. Flip-chip mounting is a widely used mounting technique 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 the electrode is joined by soldering. However, since there is a limit to how narrow the pitch can be achieved with solder-based mounting techniques, a Cu-Cu bonding technique has been proposed as a solder-free joining technique, in which Cu pillars are bonded together by solid-phase diffusion, as shown in Patent Document 2, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-046148 [Patent Document 2] Japanese Patent Application Publication No. 2020-053569 Summary of the Invention [Problem to be solved by the invention]

[0004] When Cu-Cu bonding is performed, the shape of the Cu pillar to be bonded must be strictly controlled. Unlike solder bonding, Cu-Cu bonding does not generate a liquid phase during the bonding process, making it particularly important to improve the uniformity of Cu pillar height and achieve a high level of flatness on the bonding surface. In other words, the presence of a liquid phase in solder bonding allows it to fill in any differences in Cu pillar height and unevenness on the bonding surface. On the other hand, Cu-Cu bonding is a solid-state bonding process, which means it cannot fill in any differences in Cu electrode height or unevenness on the bonding surface, potentially resulting in poor bonding. Chemical Mechanical Polishing (CMP) technology is a method for controlling the shape of Cu pillars, but it requires extremely high-precision processing and has to address issues such as warping of the substrate.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a Cu pillar joining method that does not require strict control of the shape of the Cu pillars to be joined and that can easily and reliably join Cu pillars together, and a method for manufacturing a Cu pillar joined body. [Means for solving the problem]

[0006] In order to solve the above problems, the inventors conducted extensive research and discovered that by forming a porous Cu particle layer composed of nano-sized copper particles on the bonding surface of the Cu pillar, shape conformability is improved, differences in Cu pillar height and unevenness on the bonding surface can be absorbed, and Cu pillars can be bonded to each other satisfactorily.

[0007] The present invention has been made based on the above-mentioned findings, and a Cu pillar bonding method according to a first aspect of the present invention is a Cu pillar bonding method for bonding a first Cu pillar and a second Cu pillar, the method comprising: a Cu particle layer forming step of forming a Cu particle layer composed of a plurality of Cu particles on one or both of a bonding surface of the first Cu pillar and a bonding surface of the second Cu pillar; a stacking step of stacking the first Cu pillar and the second Cu pillar with the Cu particle layer interposed therebetween; and a bonding step of heating the stacked first Cu pillar and the second Cu pillar while applying pressure in the stacking direction to bond the first Cu pillar and the second Cu pillar by solid-phase diffusion bonding, wherein in the bonding step, a deformation amount L (μm) in the stacking direction before and after bonding is 1.4 μm or more, and a bonding area A (μm 2 ) and L / A≧0.0025.

[0008] The Cu pillar bonding method of the first aspect of the present invention includes a Cu particle layer forming step of forming a Cu particle layer on one or both of the bonding surfaces of the first Cu pillar and the second Cu pillar, a stacking step of stacking the first Cu pillar and the second Cu pillar with the Cu particle layer interposed therebetween, and a bonding step of heating the stacked first Cu pillar and the second Cu pillar while applying pressure in the stacking direction, wherein in the bonding step, a deformation amount L (μm) in the stacking direction before and after bonding is L≧1.4 μm, and a bonding area A (μm 2 ) and L / A≧0.0025, the Cu particle layer deforms sufficiently when pressure is applied in the bonding process, thereby absorbing differences in height of the Cu pillars and unevenness of the bonding surface, and enabling the first Cu pillar and the second Cu pillar to be reliably bonded.

[0009] A method for joining Cu pillars according to a second aspect of the present invention is the method for joining Cu pillars according to the first aspect, characterized in that the average porosity of the Cu particle layer is within the range of 5% to 71%. According to the Cu pillar joining method of aspect 2 of the present invention, the average porosity of the Cu particle layer is set to be within the range of 5% or more and 71% or less. Therefore, the Cu particle layer is sufficiently deformed in the joining process, and the strength of the Cu particle layer is ensured, thereby enabling the first Cu pillar and the second Cu pillar to be reliably joined.

[0010] A Cu pillar joining method according to a third aspect of the present invention is characterized in that in the Cu pillar joining method according to the first or second aspect, the Cu particle layer has a Vickers hardness of 95 HV or less. According to the Cu pillar joining method of aspect 3 of the present invention, the Vickers hardness of the Cu particle layer is set to 95 HV or less, and therefore the Cu particle layer is sufficiently deformed in the joining process to ensure sufficient shape followability, thereby enabling the first Cu pillar and the second Cu pillar to be reliably joined.

[0011] A fourth aspect of the present invention is a method for joining Cu pillars according to any one of the first to third aspects, characterized in that the pressure load in the joining step is 30 MPa or less. According to the Cu pillar bonding method of the fourth aspect of the present invention, the pressure load in the bonding step is set to 30 MPa or less, which can prevent the first Cu pillar and the second Cu pillar from having defective shapes after bonding.

[0012] A Cu pillar bonding method according to a fifth aspect of the present invention is the Cu pillar bonding method according to any one of the first to fourth aspects, characterized in that the bonding temperature in the bonding step is 370° C. or less. According to the Cu pillar joining method of aspect 5 of the present invention, the joining temperature in the joining step is set to 370°C or less, thereby suppressing deterioration of the substrate on which the first Cu pillar and second Cu pillar are formed after joining.

[0013] A sixth aspect of the present invention is a method for joining Cu pillars according to any one of the first to fifth aspects, characterized in that the load application time in the joining step is 10 minutes or less. According to the Cu pillar bonding method of the sixth aspect of the present invention, the load application time in the bonding step is set to 10 minutes or less, so that an improvement in throughput can be expected.

[0014] A Cu pillar joining method according to aspect 7 of the present invention is a Cu pillar joining method according to any one of aspects 1 to 6, characterized in that in the Cu particle layer forming step, the Cu particle layer is formed by an electroplating method. According to the Cu pillar joining method of the seventh aspect of the present invention, the Cu particle layer is formed by electroplating in the Cu particle layer forming step, so that the Cu particle layer composed of a plurality of Cu particles can be reliably formed. Furthermore, by controlling the electroplating conditions, it is possible to adjust the average porosity and Vickers hardness of the Cu particle layer.

[0015] The method for manufacturing a Cu pillar bonded body of aspect 8 of the present invention is a method for manufacturing a Cu pillar bonded body having a structure in which a first Cu pillar and a second Cu pillar are bonded, and is characterized in that the first Cu pillar and the second Cu pillar are bonded by the Cu pillar bonding method of any one of aspects 1 to 7.

[0016] According to the manufacturing method of the Cu pillar bonded body of aspect 8 of the present invention, the first Cu pillar and the second Cu pillar are bonded by the Cu pillar bonding method of any one of aspects 1 to 7, so that the first Cu pillar and the second Cu pillar can be reliably bonded, and a Cu pillar bonded body with excellent bonding reliability can be obtained. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a Cu pillar joining method that does not require strict control of the shape of the Cu pillars to be joined and that can easily and reliably join Cu pillars together, and a method for manufacturing a Cu pillar joined body. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is an explanatory diagram of a Cu pillar bonded body according to one embodiment of the present invention. [Figure 2] 1 is a flow diagram of a Cu pillar bonding method (a method for manufacturing a Cu pillar bonded body) according to one embodiment of the present invention. [Figure 3] 1A to 1C are explanatory diagrams of a Cu pillar bonding method (a method for manufacturing a Cu pillar bonded body) according to one embodiment of the present invention. [Figure 4] 1 is an explanatory view of a Cu particle layer formed in a Cu pillar bonding method (a method for manufacturing a Cu pillar bonded body) according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] A Cu pillar bonding method (a method for manufacturing a Cu pillar bonded body) according to an embodiment of the present invention will be described below with reference to the drawings.

[0020] The Cu pillar bonding method (method for manufacturing a Cu pillar bonded body) according to this embodiment is for bonding protruding electrodes (Cu pillars) formed on a semiconductor chip in a semiconductor device. As shown in FIG. 1, the pillar bonding body 1 in this embodiment has a structure in which a first Cu pillar 11 formed on a first semiconductor chip 10 and a second Cu pillar 21 formed on a second semiconductor chip 20 are bonded via a bonding layer 30. The thickness t1 of the bonding layer 30 is preferably within the range of 0.6 μm to 18 μm.

[0021] Next, a Cu pillar bonding method (a method for manufacturing a Cu pillar bonded body) according to this embodiment will be described with reference to FIGS. As shown in FIG. 2, the Cu pillar bonding method (method for manufacturing a Cu pillar bonded body) according to this embodiment includes a Cu particle layer forming step S01, a stacking step S02, and a bonding step S03.

[0022] (Cu particle layer formation step S01) 3, a Cu particle layer 40 is formed on one or both of the bonding surface of the first Cu pillar 11 and the bonding surface of the second Cu pillar 21. In FIG. 3, the Cu particle layers 40 (40A, 40B) are formed on both the bonding surface of the first Cu pillar 11 and the second Cu pillar 21. 4, the Cu particle layer 40 is configured in the form of an aggregate in which a plurality of Cu particles 41 are stacked one on top of another. Holes are formed between the Cu particles 41, and the Cu particle layer 40 has a porous structure.

[0023] In this embodiment, the average porosity P ave The average porosity P of the Cu particle layer 40 is preferably in the range of 5% to 71%. ave It is more preferable that the ratio is 45% or less. Average porosity P ave is the average value of the vacancy P calculated as follows. In this embodiment, the vacancy P is calculated at three locations, and the average value of the vacancy P is taken as the average vacancy P. ave is calculated.

[0024] The porosity P is calculated by determining the total area S1 of the Cu particle layer 40 and the area S2 of the pores in the Cu particle layer 40 through image analysis of the cross section of the Cu particle layer 40 using a scanning electron microscope, and then calculating the porosity P using the following formula: Porosity P(%)=(S2 / S1)×100

[0025] In this embodiment, the Cu particle layer 40 preferably has a Vickers hardness of 95 HV or less.

[0026] Furthermore, in this embodiment, the thickness of the Cu particle layer 40 is preferably within the range of 2 μm to 20 μm. The thickness of the Cu particle layer 40 is more preferably 3 μm or more, and even more preferably 4 μm or more. On the other hand, the thickness of the Cu particle layer 40 is more preferably 18 μm or less, and even more preferably 16 μm or less.

[0027] Here, a description will be given of a method for forming the Cu particle layer 40. Examples of the method for forming the Cu particle layer 40 include a dealloying method and a direct plating method.

[0028] In the dealloying method, copper and a metal species that is electrochemically less noble than copper are co-deposited by electroplating on the joining surfaces of the first Cu pillar 11 and the second Cu pillar 21 to form a copper alloy plating film, and then the less noble metal species in the copper alloy plating film are dealloyed to form a copper particle layer 40 with a porous structure. In this dealloying method, it is possible to form a Cu particle layer 40 having a desired porosity and shape by controlling the precipitation ratio and precipitation form of copper and metal species less noble than copper.

[0029] Next, the copper alloy plating and dealloying methods will be described in detail. Copper alloy plating is formed using a copper-zinc alloy plating solution containing, for example, copper salt, zinc salt, additives that control the deposition of copper and zinc, and a solvent. This copper alloy plating can be performed 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.

[0030] The copper ion concentration of the copper-zinc alloy plating solution is preferably in the range of 0.0025 mol / L to 0.1 mol / L, and the zinc ion concentration is preferably in the range of 0.1 mol / L to 0.8 mol / L. The zinc ion concentration is made higher than the copper ion concentration because copper is preferentially deposited over zinc due to the difference in standard oxidation-reduction potential. The pH of the plating solution is preferably 2.5 or higher to adjust the deposition balance between copper and zinc. In addition, the cathode current density is set to 0.3 A / dm 2 More than 0.8A / dm 2 Set within the following range.

[0031] The copper and zinc ion sources for copper alloy plating can be copper salts and zinc salts known as metal ion sources for plating systems. Examples include sulfates, pyrophosphates, acetates, chlorides, and sulfamates. Trisodium citrate and potassium pyrophosphate are used as conductive and supporting salts as additives for controlling the deposition of copper and zinc to form a copper-zinc alloy plating film with a smooth surface. Brighteners can include surfactants such as amino acids, compounds selected from their salts, and alkanolamines. An example of a surfactant is (ethylenedinitrilo)tetrakis(2-propanol). Amino acids can be used as long as they are water-soluble and do not cause precipitation with copper salts (copper ions) or zinc salts (zinc ions) at any concentration. Examples include glycine, serine, alanine, tyrosine, aspartic acid, glutamic acid, histidine, and the like, or their respective salts.

[0032] The dealloying of the formed copper-zinc alloy plating film can be achieved by, for example, an etching reaction using a chemical solution or an electrochemical anodic reaction. In this embodiment, acid dealloying is performed by immersing and stirring the copper alloy film in a solution containing hydrochloric acid at a concentration of 0.002 mol / L to 0.5 mol / L at a temperature ranging from 20°C to 35°C for 30 minutes or longer (depending on the thickness of the plating film). This results in the formation of a copper particle layer 40 with a porous structure composed of copper particles on the bonding surfaces of the first Cu pillar 11 and the second Cu pillar 21. It is preferable to dealloy the preform layer 13 after dealloying so that the zinc concentration measured by energy dispersive X-ray analysis (EDX) is 0.6 at% or less.

[0033] Next, the formed Cu particle layer 40 is washed with a washing solvent such as ethanol, water, or acetone, and dried in the atmosphere using dry air. In order to prevent surface oxidation, it is preferable to immerse the substrate for a predetermined period of time in a rust inhibitor containing benzotriazole and a surfactant as its main components.

[0034] In the direct plating method, a Cu plating solution containing an azole-based additive, which is a copper ion electrodeposition inhibitor, is used to perform electroplating on the bonding surfaces of the first Cu pillar 11 and the second Cu pillar 21, thereby forming a copper particle layer 40 with a porous structure. In this direct plating method, it is possible to form a Cu particle layer 40 having a desired porosity and shape by controlling the type and content of additives contained in the Cu plating solution and the plating conditions.

[0035] The Cu plating solution used is an acidic electrolytic copper plating solution containing a soluble copper salt, an azole compound having 2 to 3 nitrogen atoms in a five-membered ring, which is a copper ion electrodeposition inhibitor represented by the following formulas (1) to (4), an acid, and water. If necessary, a brightener, a surfactant, an antioxidant, etc. may also be added. The Cu plating solution used has a copper concentration of 0.1 mol / L or more, an azole compound concentration of 10 mmol / L or more and 50 mmol / L or less, and a chlorine chloride ion concentration of 10 ppm or less.

[0036] [ka]

[0037] In the above formulas (1) to (4), R1 to R4 may be the same or different from one another and are any of an alkyl group having 10 or less carbon atoms, an alkenyl group having 10 or less carbon atoms, an alkynyl group having 10 or less carbon atoms, an aryl group having 10 or less carbon atoms, an aralkyl group having 10 or less carbon atoms, and an alkoxy group having 10 or less carbon atoms, or a group in which the hydrogen atom of any of these groups is substituted with a halogen atom, a hydroxyl group, a carboxyl group, an amino group, an alkyl-substituted amino group having 5 or less carbon atoms, a hydroxyalkyl-substituted amino group having 5 or less carbon atoms in the alkyl chain, or a mercapto group, or any of an amino group, an alkyl-substituted amino group having 5 or less carbon atoms, a hydroxyalkyl-substituted amino group having 5 or less carbon atoms in the alkyl chain, a mercapto group, a hydroxyl group, a carboxyl group, a halogen atom, and a hydrogen atom.

[0038] Specific examples of soluble copper salts include copper sulfate, copper oxide, copper carbonate, copper alkanesulfonates such as copper methanesulfonate and copper propanoate, copper alkanolsulfonates such as copper isethionate and copper propanolsulfonate, and copper organic acids such as copper acetate, copper citrate, and copper tartrate, which can be used alone or in combination of two or more.

[0039] Furthermore, the acid may be an organic acid or an inorganic acid. Examples of these 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 combination of two or more. The water may be pure water such as ion-exchanged water or distilled water.

[0040] The plating conditions are, for example, a DC power supply with a current density of 0.1 A / dm 2 ~5A / dm 2 Approximately, preferably 0.4A / dm 2 ~1.0A / dm 2 and select a plating time that allows the desired copper particle layer 40 to be formed. When Cu plating is performed under the above conditions, not only copper ions but also the azole compound, which acts as a copper ion electrodeposition inhibitor, are adsorbed on the cathode surface, which is the joint surface of the first Cu pillar 11 and the joint surface of the second Cu pillar 21. The presence of the azole compound strongly suppresses the electrodeposition of copper ions, favoring copper nucleation, and a porous Cu particle layer 40 made of copper particles 41 is formed on the cathode surface as a copper plating film.

[0041] (Lamination process S02) Next, as shown in FIG. 3, a first Cu pillar 11 having a Cu particle layer 40A formed on its joining surface and a second Cu pillar 21 having a Cu particle layer 40B formed on its joining surface are stacked with the Cu particle layers 40A and 40B interposed between them. In this case, the thickness t0 of the Cu particle layer 40 in the laminate (the total thickness of the Cu particle layers 40A and 40B) is preferably within the range of 2 μm to 20 μm.

[0042] (Joining process S03) 3, the stacked first Cu pillar 11 and second Cu pillar 21 are heated while being pressurized in the stacking direction, to solid-phase diffusion bond the first Cu pillar 11 and the second Cu pillar 21. This produces a pillar bonded structure 1 in which the first Cu pillar 11 and the second Cu pillar 21 are bonded via the bonding layer 30. In this embodiment, since the Cu particle layer 40 (40A, 40B) is interposed between the first Cu pillar 11 and the second Cu pillar 21, the bonding layer 30 is formed by these Cu particle layers 40 (40A, 40B).

[0043] In the bonding step S03, the deformation amount L (μm) in the stacking direction before and after bonding is L≧1.4 μm, and the deformation amount L and the area A (μm 2 ) are said to have a relationship of L / A≧0.0025. In this embodiment, since the layers are stacked via the porous Cu particle layers 40 (40A, 40B), when pressure is applied in the stacking direction, the Cu particle layers 40 (40A, 40B) are mainly deformed in the stacking direction. Therefore, the deformation amount L is expressed as L=t0−t1, where t1 is the thickness of the bonding layer 30 and t0 is the thickness of the Cu particle layer 40 (40A, 40B).

[0044] In this embodiment, the pressure load in the joining step S03 is preferably 30 MPa or less. The pressure load in the joining step S03 is more preferably 24 MPa or less, and even more preferably 12 MPa or less. The lower limit of the applied pressure in the joining step S03 is preferably 1 MPa or more, and more preferably 5 MPa or more.

[0045] Furthermore, in this embodiment, the bonding temperature in the bonding step S03 is preferably 370° C. or less. The bonding temperature in the bonding step S03 is more preferably 320° C. or less, and even more preferably 280° C. or less. The lower limit of the bonding temperature in the bonding step S03 is preferably 100° C. or higher, and more preferably 150° C. or higher.

[0046] In this embodiment, the load application time in the joining step S03 is preferably 10 minutes or less. The load application time in the joining step S03 is more preferably 9 minutes or less, and even more preferably 7 minutes or less. The lower limit of the load application time in the joining step S03 is preferably 30 seconds or more, and more preferably 1 minute or more.

[0047] The Cu pillar bonding method (method for manufacturing a Cu pillar bonded body) of this embodiment configured as described above includes a Cu particle layer forming step S01 of forming a Cu particle layer 40 (40A, 40B) on one or both of the bonding surfaces of the first Cu pillar 11 and the second Cu pillar 21, a stacking step S02 of stacking the first Cu pillar 11 and the second Cu pillar 21 with the Cu particle layer 40 (40A, 40B) interposed therebetween, and a bonding step S03 of heating the stacked first Cu pillar 11 and the second Cu pillar 21 while applying pressure in the stacking direction. In the bonding step S03, the deformation amount L (μm) in the stacking direction before and after bonding is L≧1.4 μm, and the deformation amount L and the bonding area A (μm 2 ) and L / A≧0.0025, the Cu particle layer 40 (40A, 40B) deforms sufficiently when pressure is applied in the bonding process S03, thereby absorbing unevenness on the bonding surfaces of the first Cu pillar 11 and the second Cu pillar 21 and differences in height between the first Cu pillar 11 and the second Cu pillar 21, and making it possible to reliably bond the first Cu pillar 11 and the second Cu pillar 21 without strictly controlling the shape.

[0048] In this embodiment, the average porosity P aveWhen the difference is within the range of 5% or more and 71% or less, the Cu particle layer 40 (40A, 40B) is sufficiently deformed in the bonding step S03, and the strength of the Cu particle layer 40 (40A, 40B) is ensured, making it possible to reliably bond the first Cu pillar 11 and the second Cu pillar 21. That is, when the average porosity of the Cu particle layer 40 (40A, 40B) is 5% or more, the deformability of the Cu particle layer 40 (40A, 40B) is ensured, and the Cu particle layer 40 (40A, 40B) can be sufficiently deformed in the bonding step S03. Furthermore, when the average porosity of the Cu particle layer 40 (40A, 40B) is 71% or less, the strength is ensured. In this embodiment, in order to further ensure the deformability of the Cu particle layer 40 (40A, 40B), the average porosity P ave is more preferably 6% or more, and even more preferably 10% or more. On the other hand, in this embodiment, in order to further ensure the strength of the Cu particle layer 40, the average porosity P ave is more preferably 45% or less, and even more preferably 32% or less.

[0049] In the present embodiment, when the Vickers hardness of the Cu particle layer 40 (40A, 40B) is 95 HV or less, the Cu particle layer 40 (40A, 40B) is sufficiently deformed in the bonding step S03, thereby ensuring sufficient shape conformability and enabling the first Cu pillar 11 and the second Cu pillar 21 to be reliably bonded to each other. In this embodiment, in order to further ensure the shape conformability of the Cu particle layer 40, the Vickers hardness of the Cu particle layer 40 is more preferably 92 HV or less, and even more preferably 89 HV or less. Although there is no particular lower limit to the Vickers hardness of the Cu particle layer 40, it is practically 60 HV or more.

[0050] In this embodiment, when the pressure load in the bonding process S03 is set to 30 MPa or less, the pressure load is relatively low, which can suppress deformation of the first Cu pillar 11 and the second Cu pillar 21 during bonding, and can suppress the occurrence of defective shapes of the first Cu pillar 11 and the second Cu pillar 21 after bonding. In addition, in the joining process S03, since a porous Cu particle layer 40 is interposed between the first Cu pillar 11 and the second Cu pillar 21, even if the pressure load is 30 MPa or less, the deformation amount L in the stacking direction can be secured, and the first Cu pillar 11 and the second Cu pillar 21 can be reliably joined.

[0051] In this embodiment, when the bonding temperature in the bonding step S03 is set to 370°C or less, the bonding temperature is relatively low, and deterioration of the base materials on which the first Cu pillar 11 and the second Cu pillar 21 are formed after bonding can be suppressed. In addition, in the bonding process S03, a porous Cu particle layer 40 is interposed between the first Cu pillar 11 and the second Cu pillar 21, so even if the bonding temperature is 370°C or lower, the diffusion of Cu atoms can be promoted, and the first Cu pillar 11 and the second Cu pillar 21 can be reliably bonded.

[0052] In this embodiment, when the load application time in the bonding process S03 is set to 10 minutes or less, the load application time is relatively short, which is expected to improve throughput during bonding, and makes it possible to bond the first Cu pillar 11 and the second Cu pillar 21 after bonding in a short time. In addition, in the joining process S03, a porous Cu particle layer 40 is interposed between the first Cu pillar 11 and the second Cu pillar 21, so even if the load application time is 10 minutes or less, the deformation amount L in the stacking direction can be secured and the diffusion of Cu atoms can be promoted, making it possible to reliably join the first Cu pillar 11 and the second Cu pillar 21.

[0053] In the present embodiment, when the Cu particle layer 40 is formed by electroplating in the Cu particle layer forming step S01, the Cu particle layer 40 composed of a plurality of Cu particles 41 can be reliably formed. In addition, by controlling the electroplating conditions, the average porosity P ave It is also possible to adjust the Vickers hardness.

[0054] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. [Example]

[0055] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0056] First, a Ti layer was formed on a silicon wafer to a thickness of 100 nm, and then a Cu layer was formed as a seed layer to a thickness of 300 nm by sputtering. Next, bump patterns with diameters of 15 μm and 25 μm were formed using photoresist, and the resulting bump patterns were subjected to hydrophilization and pickling with 10% H2SO4.

[0057] Next, a copper sulfate-based plating solution for bump formation was used for plating, and Cu pillars were formed to a height of 10 μm. Thereafter, a Cu particle layer was formed on the bonding surface of the Cu pillar in Samples 1-9, as shown in Table 1. The Cu particle layer was formed by dealloying and direct plating, as shown in Table 1. Sample 10 was plated using a copper sulfate-based plating solution.

[0058] In the dealloying method, a Cu-Zn alloy was plated, and after plating, a dealloying treatment was performed using 2M HCl to form a Cu particle layer. In this embodiment, the following two types of plating solutions for dealloying (dealloying-1 and dealloying-2) were prepared.

[0059] (Dealloying-1) Copper sulfate pentahydrate (Cu 2+ as): 0.01 mol / L Zinc sulfate heptahydrate (Zn 2+ as): 0.25 mol / L Trisodium citrate dihydrate: 0.3 mol / L Glycine, an amino acid compound: 0.1 mol / L Ion-exchanged water: Remaining The pH of the plating solution is adjusted to 4.2 with citric acid.

[0060] (Dealloying-2) Copper sulfate pentahydrate (Cu 2+ as): 0.01 mol / L Zinc sulfate heptahydrate (Zn 2+ as): 0.25 mol / L Disodium citrate dihydrate: 0.3 mol / L Ion-exchanged water: Remaining Adjust the pH of the plating solution to 4.5 with citric acid

[0061] In the direct plating method, a Cu particle layer was formed by plating using a Cu plating solution containing an azole-based additive that strongly acts on the surface. In this embodiment, the following two types of plating solutions for the direct plating method (Direct Plating-1 and Direct Plating-2) were prepared.

[0062] (Direct plating-1) Copper sulfate pentahydrate (Cu 2+ as): 0.1 mol / L Copper ion electrodeposition inhibitor (3,5-diamino-1,2,4-triazole): 10mmol / L Chlorine: 0 ppm Ion-exchanged water: Remaining pH: 2.5

[0063] (Direct plating-2) Copper sulfate pentahydrate (Cu 2+ as): 0.1 mol / L Copper ion electrodeposition inhibitor (3,5-diamino-1,2,4-triazole): 5mmol / L Chlorine: 0 ppm Ion-exchanged water: Remaining pH: 2.5

[0064] The area of ​​the bonding surface of the formed Cu pillar was determined by measuring the shape of the Cu pillar surface with a white light interference microscope, calculating the surface area, and then calculating the average value of the areas measured for three bumps. Table 1 shows the current density during plating, the thickness of the Cu particle layer, the average porosity of the Cu particle layer, and Vickers hardness. Average porosity of the Cu particle layer, P ave was calculated as the arithmetic mean (n = 3) of the porosity (P) calculated by the following formula (1) based on the total area (S1) of the Cu particle layer calculated by image analysis of the cross section using a scanning electron microscope and the area (S2) of the pore portion in the Cu particle layer. P(%) = (S2 / S1) × 100 (1) The Vickers hardness of the Cu particle layer was measured using an ultra-microhardness tester.

[0065] [Table 1]

[0066] Next, the photoresist on the formed bump pattern was removed, and then a bonding test was carried out. Before the bonding test, the substrate was subjected to an acid cleaning treatment using 10% H2SO4. The bonding test was performed using a Tresky high-precision flip chip bonder T-3000-PRO, after aligning the top and bottom. The bonding process was performed in an N2 atmosphere, and the set bonding load, bonding temperature, and bonding time (load application time) are shown in Table 2.

[0067] The amount of deformation L before and after bonding was evaluated by measuring the total length of the protruding electrode, including the Cu pillar and Cu particle layer before bonding, and the distance between the chips after bonding after cross-section processing. The total length of the protruding electrodes before bonding was determined by first measuring the heights a and b of 10 random bumps on each side and calculating the average height. The distance between the chips after bonding was determined by cross-sectionally processing the bonded body and calculating the average value of the cross-sectional height (Z) measured at n=5. The value of (a+b)-Z was calculated as the deformation amount L.

[0068] To evaluate the bonded structure, the shear strength (bond strength) was measured using a shear strength evaluation tester (Bond Tester; Dage Series 4000, manufactured by Nordson Advanced Technologies Co., Ltd.). Specifically, the shear strength was measured as follows: the bonded structure was fixed horizontally, and the Si wafer with the chips was pressed horizontally from the side using a shear tool at a position 50 μm above the surface (top surface) of the bonding layer, and the strength was measured when the chips broke. During bonding, a pattern with 8100 bumps in the chip was used, and the bond strength per bump was calculated by dividing the obtained bond strength by the total area of ​​all 8100 bumps. The shear tool movement speed was 0.1 mm / sec. Strength tests were conducted three times per condition, and the arithmetic average of these values ​​was used as the measured bond strength.

[0069] In Examples 1 to 5 and 6-1 of the present invention and Comparative Example 1-4, Cu particle layers were formed on both the upper and lower Cu pillars, while in Example 6-2 of the present invention, only the lower Cu pillar was used and the upper Cu pillar was used with a Cu particle layer formed thereon. In addition, in order to easily measure the shear strength during bonding, the Si chip was diced to have an upper side measuring 6 mm square and a lower side measuring 10 mm square before mounting.

[0070] [Table 2]

[0071] In Comparative Example 1, the deformation amount L (μm) in the stacking direction before and after bonding was set to 1.0 μm in the bonding process, and the deformation amount L and the bonding area A (μm 2) was set to 0.0020, and the bonding strength of the pillar bonded body was 0.9 MPa. In Comparative Example 2, the deformation amount L (μm) in the stacking direction before and after bonding in the bonding step was 1.1 μm, and the bonding strength of the pillar bonded body was 1.5 MPa.

[0072] In Comparative Example 3, the deformation amount L (μm) in the stacking direction before and after bonding in the bonding process was set to 0.8 μm, and the deformation amount L and the bonding area A (μm 2 ) was 0.0016, and the bonding strength of the pillar bonded body was 0.8 MPa. In Comparative Example 4, no porous Cu particle layer was formed, and the bonding strength of the pillar bonded structure was 0.5 MPa.

[0073] In contrast, in the present invention example, the deformation amount L (μm) in the stacking direction before and after bonding in the bonding process was L≧1.4 μm, and the deformation amount L and the bonding area A (μm 2 ) is set to be 0.0025 or more, and the bonding strength of the pillar bonded structure is 2.4 MPa or more, which is improved compared to the comparative example.

[0074] From the results of the above confirmatory experiments, it was confirmed that the present invention can provide a Cu pillar joining method that does not require strict control of the shape of the Cu pillars to be joined, and that can easily and reliably join Cu pillars together, as well as a method for manufacturing a Cu pillar bonded body. [Explanation of symbols]

[0075] 1. Cu pillar junction 11 First Cu pillar 21 Second Cu pillar 30 Bonding layer 40 Cu particle layer 41 Cu particles S01 Cu particle layer formation process S02 Lamination process S03 Joining process

Claims

1. A Cu pillar joining method for joining a first Cu pillar and a second Cu pillar, comprising: a Cu particle layer forming step of forming a Cu particle layer composed of a plurality of Cu particles on one or both of the bonding surface of the first Cu pillar and the bonding surface of the second Cu pillar; a stacking step of stacking the first Cu pillar and the second Cu pillar with the Cu particle layer interposed therebetween; a bonding step of heating the stacked first Cu pillar and the second Cu pillar while applying pressure in the stacking direction, thereby solid-phase diffusion bonding the first Cu pillar and the second Cu pillar; It has In the bonding step, the deformation amount L (μm) in the stacking direction before and after bonding is L≧1.4 μm, and the deformation amount L and the bonding area A (μm ２ ) and L / A≧0.0025.

2. 2. The method for joining Cu pillars according to claim 1, wherein the average porosity of the Cu particle layer is in the range of 5% to 71%.

3. 2. The method for joining Cu pillars according to claim 1, wherein the Cu particle layer has a Vickers hardness of 95 HV or less.

4. 2. The Cu pillar joining method according to claim 1, wherein a pressure load in the joining step is 30 MPa or less.

5. 2. The Cu pillar bonding method according to claim 1, wherein the bonding temperature in the bonding step is 370° C. or less.

6. 2. The Cu pillar joining method according to claim 1, wherein the load application time in the joining step is 10 minutes or less.

7. 2. The Cu pillar joining method according to claim 1, wherein in the Cu particle layer forming step, the Cu particle layer is formed by electroplating.

8. A method for manufacturing a Cu pillar bonded body having a structure in which a first Cu pillar and a second Cu pillar are bonded, comprising: A method for manufacturing a Cu pillar bonded body, comprising bonding the first Cu pillar and the second Cu pillar by the Cu pillar bonding method according to any one of claims 1 to 7.

Images