Electric connection and method of manufacturing the same

Abstract

An electric connection is provided, and has a first copper (Cu) layer, a second Cu layer, and a composite metal layer disposed between the first Cu layer and the second Cu layer. The composite metal layer has 0.01 wt. %gallium (Ga)20 wt. %, 0.01 wt. %copper (Cu)50 wt. %, and 30 wt. %nickel (Ni)99.98 wt. %. Moreover, a method of manufacturing the electric connection is provided, and has the steps of: (1) providing a first Cu layer and a second Cu layer; (2) forming a first Ni layer on the first Cu layer; (3) forming a second Ni layer on the second Cu layer; (4) forming a Ga layer on the first Ni layer; and (5) keeping the second Ni layer in contact with the Ga layer and carrying out a thermo-compress bonding therebetween to form the electric connection.

Claims

1. An electric connection, comprising: a first Cu layer; a second Cu layer; and a composite metal layer disposed between the first Cu layer and the second Cu layer, wherein the first Cu layer and the second Cu layer are connected with the composite metal layer, wherein the composite metal layer consists essentially of: 0.01 wt. %Ga20 wt. %; 0.01 wt. %Cu50 wt. %; and 30 wt. %Ni99.98 wt. %, and wherein the composite metal layer comprises no intermetallic compound, and the composite metal layer has a face-centered cubic crystal structure.

2. The electric connection according to claim 1, wherein the composite metal layer comprises 0.01 wt. % to 10 wt. % of Ga, 0.01 wt. % to 10 wt. % of Cu, and 80 wt. % to 99.98 wt. % of Ni.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of an electric connection according to one embodiment of the present invention.

(2) FIGS. 2a to 2d are schematic views of a flow chart of a method of manufacturing an electric connection according to one embodiment of the present invention.

(3) FIG. 3 is an image of an electric connection observed by a Metallographic Microscope according to one embodiment of the present invention.

(4) FIG. 4 is an image of an electric connection observed by a Metallographic Microscope after being analyzed by a Vickers Hardness Tester according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The structure and the technical means adopted by the present invention to achieve the above and other objectives can be best understood by referring to the following detailed description of the preferred embodiments. In addition, directional terms described by the present invention, such as upper, lower, front, back, left, right, inner, outer, side, etc., are only directions by referring to the accompanying drawings, and thus the directional terms are used to describe and understand the present invention, but the present invention is not limited thereto. Furthermore, if there is no specific description in the invention, singular terms such as a, one, and the include the plural number. For example, a compound or at least one compound may include a plurality of compounds, and the mixtures thereof. If there is no specific description in the invention, the % means weight percentage (wt. %), and the numerical range (e.g. 10%11% of A) contains the upper and lower limit (i.e. 10%A11%). If the lower limit is not defined in the range (e.g. less than, or below 0.2% of B), it means that the lower limit is 0 (i.e. 0%B0.2%). The proportion of weight percent of each component can be replaced by the proportion of weight portion thereof. The above-mentioned terms are used to describe and understand the present invention, but the present invention is not limited thereto.

(6) Referring to FIG. 1, an electric connection 1 according to one embodiment of the present invention mainly comprises a first Cu layer 11, a second Cu layer 12, and a composite metal layer 41. The composite metal layer 41 is disposed between the first Cu layer 11 and the second Cu layer 12, and comprises 0.01 wt. %Ga20 wt. %, 0.01 wt. %Cu50 wt. %, and 30 wt. %Ni99.98 wt. %. Preferably, the composite metal layer 41 comprises 0.01 wt. % to 10 wt. % of Ga, 0.01 wt. % to 10 wt. % of Cu, and 80 wt. % to 99.98 wt. % of Ni, such as 0.8 wt. % of Ga, 1.1 wt. % of Cu, and 98.1 wt % of Ni, but it is not limited thereto. Furthermore, the composite metal layer 41 has a face-centered cubic (FCC) crystal structure.

(7) Referring to FIGS. 2a to 2d, a method of manufacturing an electric connection 1 according to one embodiment of the present invention mainly comprises steps of (S1) providing a first Cu layer 11 and a second Cu layer 12; (S2) forming a first Ni layer 21 on the first Cu layer 11; (S3) forming a second Ni layer 22 on the second Cu layer 12; (S4) forming a Ga layer 31 on the first Ni layer 21; and (S5) contacting the second Ni layer 22 with the Ga layer 31 to perform a thermal pressing connection there-between. The principle and the implementation details of each step in this embodiment of the present invention will be described in detail hereinafter.

(8) First, as shown in FIG. 2a, the method of manufacturing an electric connection 1 according to one embodiment of the present invention is to execute the step (S1): providing a first Cu layer 11 and a second Cu layer 12. The first Cu layer 11 and the second Cu layer 12 are for example the Cu pads in TSVs. By the electric connection between one copper pad and another copper pad, a 3D IC integration assembly can be achieved.

(9) Next, referring to FIG. 2b, the method of manufacturing an electric connection 1 according to one embodiment of the present invention is to execute the step (S2): forming a first Ni layer 21 on the first Cu layer 11; and (S3): forming a second Ni layer 22 on the second Cu layer 12. Preferably, before the step (S2), the method can further comprise a step (S1a): carrying out a surface treatment of the first Cu layer 11. Similarly, before the step (S3), the method can further comprise a step (S1b): carrying out a surface treatment of the second Cu layer 12. In the step (S1a) or (S1b), the surface treatment is to clean the first Cu layer 11 or the second Cu layer 12 by grinding or by using an acidic solution and a solvent. The acidic solution is for example hydrochloric acid, nitric acid, or acetic acid, but it is not limited thereto. The solvent is for example acetone, methanol, or ethanol, but it is not limited thereto. In addition, the step (S2) is to form the first Ni layer 21 by an electroplating process or an evaporation deposition process. The step (S3) is to form the second Ni layer 22 by an electroplating process or an evaporation deposition process. Preferably, the first Ni layer 21 and the second Ni layer 22 are formed at the same time by the same method, i.e. electroplating or evaporation deposition, so as to simplify the production process. For example, when the first nickel layer 21 and the second nickel layer 22 are formed by electroplating. The electroplating solution is a standard Watts' Nickel Solution containing 300 g/L nickel sulfate hexahydrate (NiSO.sub.4.6H.sub.2O), 45 g/L nickel(II) chloride hexahydrate (NiCl.sub.2.6H.sub.2O), and 40 g/L boric acid (H.sub.3BO.sub.3), and the electroplating process is performed by using a pure Cu as a cathode at pH 3.8, a temperature of 50 C., and a current density of 2 A/dm.sup.2.

(10) Next, referring to FIG. 2c, the method of manufacturing an electric connection 1 according to one embodiment of the present invention is to execute the step (S4): forming a Ga layer 31 on the first Ni layer 21. In this step, the Ga layer 31 is formed on the first Ni layer 21 by an electroplating process or an evaporation deposition process. For example, when the Ga layer 31 is formed by electroplating, a platinum electrode can be used as a counter electrode, a Hg|Hg.sub.2Cl.sub.2 (Saturated Calomel Electrode, SCE) can be used as a reference electrode, the electrolytic solution contains 0.25 M of Ga ions and 0.5 M sodium citrate with pH more than 10, the voltage is controlled with a current density of 10 mA/cm.sup.2, and the electroplating process of the Ga layer is performed at room temperature.

(11) Next, referring to FIG. 2d, the method of manufacturing an electric connection 1 according to one embodiment of the present invention is to execute the step (S5): contacting the second Ni layer 22 with the Ga layer 31 to perform a thermal pressing connection between the second Ni layer 22 and the Ga layer 31. In this step, a temperature of the thermal pressing connection is 300-400 C., for example 300 C., but it is not limited thereto. A pressure of the thermal pressing connection is 4-8 bars. After the thermal pressing connection is finished, the electric connection 1 mentioned above can be formed.

(12) Furthermore, in the method of manufacturing an electric connection 1 according to one embodiment of the present invention, a thickness ratio of the first Ni layer 21, the second Ni layer 22, and the Ga layer 31 is 0.520:0.520:0.015. Preferably, the first Ni layer 21 has a thickness ranged from 0.5 to 20 microns (m), such as 0.5, 5, 10, or 15 microns, but it is not limited thereto. Preferably, the second Ni layer 22 has a thickness ranged from 0.5 to 20 microns, such as 0.5, 5, 10, or 15 microns, but it is not limited thereto. Preferably, the Ga layer 31 has a thickness ranged from 0.01 to 5 microns (m), such as 0.5, 1.5, 3, or 4.5 microns, but it is not limited thereto.

(13) To make the electric connection and the method of manufacturing the electric connection provided by the present invention more definite, please refer to the experiment process described in the following.

(14) First, a pure Cu substrate is prepared and grinded by using a silicon carbide papers and then polished with 1 m alumina powders. Next, a pure Ni layer is coated on the Cu substrate by electroplating. The electroplating bath is formed of an acidic solution of nickel sulfate. Subsequently, a pure Ga metal is disposed between two pieces of Cu substrates with the Ni layer coated thereon, and then the sandwich structure is placed in a vacuum tube furnace to perform a thermal pressing connection for at least 30 minutes.

(15) When a 10 m-thick Ni layer is coated, the structure as shown in FIG. 3 can be formed at 300 C. It can be seen from FIG. 3 that only an extensive Ni-rich solid solution phase with FCC crystal structure is formed between the two pieces of copper substrates. The reason for this result is that Ga and Cu both are soluble in the Ni-rich FCC phase (Ni-FCC).

(16) Furthermore, the mechanical properties of the above-mentioned structure are analyzed by a Vickers Hardness Tester, and the result is shown in FIG. 4. From FIG. 4, the notch on the Ni-FCC is smaller than that on the Cu substrates under 10 gf of load. In addition, average hardness values measured at different positions of the structure are respectively 2749.62 MPa in Ni-FCC and 715.62 MPa in Cu. Moreover, the same analyses is performed for pure Ni and its hardness is 2121.26 MPa. The result of the hardness tests shows that the electric connection according to the embodiment of the present invention has superior mechanical properties. Generally, in conventional solder joints, the tensile strength and the peel strength are decreased with growth of the interfacial IMCs. In this invention, while there is no IMC formation and only the solid solution phase with FCC crystal structure forms in the connection according to the embodiment, thus it is predictable that the mechanical properties of the FCC structure without IMC are better than that of any conventional connection structure with IMCs, and has better reliability. The above experiment and analysis results demonstrate that the electric connection and the manufacturing method thereof provided by the present invention can avoid the brittle IMC formation within the Cu-to-Cu connection, and obtain a Cu-to-Cu connection with high ductility and thus high reliability and a wide rage of applications.

(17) Compared with traditional technologies, the electric connection and the manufacturing method thereof according to the present invention can achieve a formation of a composite metal layer with solid solution phase and high ductility. Since there is no IMC, the reliability problem of Cu-to-Cu connection can be resolved. In addition, moderate processing temperature and pressure are adequate for forming this Cu-to-Cu interconnection, which may directly reflect on the costs of processes as well as materials compatibility. It has the potential for mass production.

(18) The present invention has been described with preferred embodiments thereof and it is understood that many changes and modifications to the described embodiments can be carried out without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims.