US20220259754A1

US20220259754A1 - Twinned copper layer, substrate having the same and method for preparing the same

Info

Publication number: US20220259754A1
Application number: US17/574,151
Authority: US
Inventors: Chih Chen; Wei-You HSU
Original assignee: National Yang Ming Chiao Tung University NYCU
Current assignee: National Yang Ming Chiao Tung University NYCU
Priority date: 2021-02-17
Filing date: 2022-01-12
Publication date: 2022-08-18
Also published as: TW202233895A

Abstract

A twinned copper layer is disclosed, wherein 35% or more in volume of the twinned copper layer comprises plural twinned grains, 30% or more of the twinned grains are flake twinned grains, and a ratio of a length to a thickness of at least a part of the flake twinned grains is greater than or equal to 2. In addition, a substrate having the aforesaid twinned copper layer and a method for preparing the aforesaid twinned copper layer are also disclosed.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefits of the Taiwan Patent Application Serial Number 110105280, filed on Feb. 17, 2021, the subject matter of which is incorporated herein by reference.

BACKGROUND

1. Field

The present disclosure relates to a twinned copper layer, a substrate having the same and a method for preparing the same. More specifically, the present disclosure relates to a twinned copper layer with enhanced strength, a substrate having the same and a method for preparing the same.

2. Description of Related Art

Conventionally, the mechanical property of copper can be enhanced by rolling or doping with other metal such as Ti, Ni or Zn, but the conventional method still has its disadvantage.
If the copper film comprising copper grains is enhanced by rolling, the pure copper grains may be deformed. Even though the mechanical property of the copper film can be enhanced by rolling, the resistance thereof may be increased and the thermal conductivity thereof may be decreased. In addition, the copper film doped with other metal may cause the resistance of the copper film increased. Furthermore, the strength of the twinned copper film has high strength. If the strength of the twinned copper film is enhanced by grain refining, the obtained twinned copper film may have the problem of poor thermal stability.
Therefore, it is desirable to provide a novel twinned copper layer, wherein the strength thereof can be increased and the property thereof can be maintained, so this twinned copper layer can be applied to various electronic device.

SUMMARY

An object of the present disclosure is to provide a twinned copper layer, which have excellent hardness and/or thermal stability.
In the twinned copper layer of the present disclosure, 35% or more in volume of the twinned copper layer comprises plural twinned grains, 30% or more of the plural twinned grains are flake twinned grains, and a ratio of a length to a thickness of at least a part of the flake twinned grains is greater than or equal to 2. Herein, the proportion (expressed as the percentage) of the twinned grains and the proportion (expressed as the percentage) of the flake twinned grains can be observed or measured by any cross-section of the twinned copper layer.
In addition, the present disclosure further provides a substrate having the aforesaid twinned copper layer, which comprises: a substrate; and the aforesaid twinned copper layer disposed on the substrate or embedded into the substrate.
Furthermore, the present disclosure further provides a method for preparing the aforesaid twinned copper layer, which comprises the following steps: providing an electrodeposition device, comprising an anode, a cathode, a plating solution and a power supply, wherein the power supply is respectively connected to the cathode and the anode, and the cathode and the anode are immersed into the plating solution; and performing an electrodeposition process with the electrodeposition device to grow the aforesaid twinned copper layer on a surface of the cathode. Herein, the plating solution comprises a copper salt and an acid, and the plating solution does not comprise a chloride ion. In addition, the power supply provides electrical power to perform the electrodeposition process.
In the method for preparing the twinned copper layer of the present disclosure, the twinned copper layer with a specific structure can be prepared when the plating solution does not comprise a chloride ion. More specifically, in the twinned copper layer or the substrate comprising the same of the present disclosure, twinned grains may be flake twinned grains, and the flake twinned grains have a significant length to thickness ratio. Compared with the conventional nano-twinned copper layer including columnar twinned grains, the strength of the twinned copper layer of the present disclosure can be improved by 60% or more. In addition, most of the twinned grains in the twinned copper layer of the present disclosure can still be maintained when the twinned copper layer of the present disclosure is annealed at high temperature. Thus, the twinned copper layer of the present disclosure may have excellent thermal stability and can be applied to various electronic devices, for example, a connector of the electronic device.
In the present disclosure, 30% or more of the twinned grains may be flake twinned grains. In one embodiment of the present disclosure, for example, 30% to 100%, 30% to 99%, 30% to 95%, 35% to 95%, 35% to 90%, 40% to 90%, 40% to 85%, 45% to 85%, 45% to 80% or 50% to 80% of the twinned grains may be flake twinned grains, but the present disclosure is not limited thereto.
In the present disclosure, a ratio of a length to a thickness of at least a part of the flake twinned grains may be greater than or equal to 2. In one embodiment of the present disclosure, the ratio of the length (L) to the thickness (T) of at least a part of the flake twinned grains may be: 2≤LT≤10, 2≤L/T≤9, 2≤L/T≤8, 2≤L/T≤7, 2≤L/T≤6 or 2≤L/T≤5, but the present disclosure is not limited thereto. In the present disclosure, a thickness direction of the flake twinned grain may be a twin direction of the flake twinned grain. More specifically, the thickness direction of the flake twinned grain may be a stacking direction of the twins or the twin boundaries of the flake twinned grain.
In the present disclosure, 35% or more in volume of the twinned copper layer may comprise plural twinned grains. In one embodiment of the present disclosure, 35% to 99%, 35% to 95%, 35% to 90%, 40% to 90%, 40% to 85%, 45% to 85%, 45% to 80% or 50% to 80% in volume of the twinned copper layer may comprise plural twinned grains, but the present disclosure is not limited thereto.
In the present disclosure, an included angle between a twin boundary of at least a part of the plural twinned grains and a thickness direction of the twinned copper layer may be ranged from 0 degree to 30 degrees. In addition, in the present disclosure, an included angle between a twin boundary of at least a part of the plural twinned grains and a surface of the substrate may be ranged from 60 degrees to 90 degrees. Herein, a specific angle is included between the twin boundary of the twinned grain and the thickness direction of the twinned copper layer and/or between twin boundary of the twinned grain and the surface of the substrate. Thus, the arrangement of the twinned grains is non-uniform or irregular. Compared with the conventional nano-twinned copper layer in which the included angle between the twin boundary of the twinned grain and the thickness direction of the twinned copper layer is approximately 90 degrees or the twin boundary of the twinned grains is parallel to the surface of the substrate, the strength of the twinned copper layer of the present disclosure can be improved by 60% or more.
In the present disclosure, the twinned copper layer may comprise: 0.05 at % to 20 at % of at least one element selected from the group consisting of Ag, Ni, Zn, Pb, Al, Au, Pt, Mg and Cd; and rest of Cu. In the present disclosure, when a specific proportion of metal element other than copper is added, a twinned copper alloy layer can be obtained. This twinned copper alloy layer also has improved hardness or excellent thermal stability. When a twinned copper layer comprising the metal element other than copper is to be formed, the plating solution used in the method of the present disclosure may further comprise a salt of the at least one element. The addition amount of the salt of the at least one element can be added according to the content (expressed as the percentage) of the at least one element in the twinned copper layer.
In one embodiment of the present disclosure, the plating solution may further comprise a silver salt, for example, AgNO₃. When silver ions are added into the plating solution, the formed twinned copper layer may further comprise Ag. The electrical conductivity and the thermal conductivity of silver are better than those of copper, and silver does not react with copper. Thus, little amount of silver added into the twinned copper layer can greatly improve the hardness of the twinned copper layer, but does not cause the electrical conductivity and the thermal conductivity of the twinned copper layer reduced.
In the present disclosure, the addition amount of the metal element other than copper may be 0.05 at % to 20 at % based on the total elements of the twinned copper layer. In one embodiment of the present disclosure, the addition amount of the metal element other than copper may be, for example, 0.1 at % to 20 at %, 0.1 at % to 15 at %, 0.1 at % to 10 at %, 0.1 at % to 5 at %, 0.1 at % to 3 at % or 0.1 at % to 1 at %, but the present disclosure is not limited thereto.
In the present disclosure, a length of the at least a part of the flake twinned grains may be ranged from 0.5 μm to 20 μm. In one embodiment of the present disclosure, the length of the flake twinned grain may be ranged from, for example, 0.5 μm to 15 μm, 0.5 μm to 10 μm, 1 μm to 10 μm, 1 μm to 5 μm or 2 μm to 5 μm, but the present disclosure is not limited thereto. In one embodiment of the present disclosure, 30% or more of the flake twinned grains may have lengths with the aforesaid ranges. For example, 30% to 99%, 30% to 95%, 30% to 90%, 35% to 90%, 40% to 90%, 40% to 85%, 40% to 80%, 45% to 80% or 50% to 80% of the flake twinned grains may have lengths with the aforesaid ranges, but the present disclosure is not limited thereto. In the present disclosure, the lengths of the flake twinned grains can be the lengths of the flake twinned grains measured at a direction substantially perpendicular to the twin direction of the flake twinned grains. More specifically, the lengths of the flake twinned grains can be the lengths (for example, maximum lengths) of the flake twinned grains measured at a direction substantially perpendicular to the lamination direction of the twins or the twin boundaries (i.e. the extension direction of the twin boundary).
In the present disclosure, a thickness of the at least a part of the flake twinned grains may be ranged from 0.01 μm to 10 μm, 0.01 μm to 9 μm, 0.05 μm to 9 μm, 0.05 μm to 8 μm, 0.1 μm to 8 μm, 0.1 μm to 7 μm, 0.15 μm to 7, 0.15 μm to 6 μm, 0.2 μm to 6 μm or 0.2 μm to 5 μm, but the present disclosure is not limited thereto. In one embodiment of the present disclosure, 30% or more of the flake twinned grains may have thicknesses with the aforesaid ranges. For example, 30% to 99%, 30% to 95%, 30% to 90%, 35% to 90%, 40% to 90%, 40% to 85%, 40% to 80%, 45% to 80% or 50% to 80% of the flake twinned grains may have thicknesses with the aforesaid ranges, but the present disclosure is not limited thereto. In the present disclosure, the thicknesses of the flake twinned grains can be the thicknesses of the flake twinned grains measured at the twin direction of the flake twinned grains. More specifically, the thicknesses of the flake twinned grains can be the thicknesses (for example, maximum thicknesses) of the flake twinned grains measured at the lamination direction of the twins or the twin boundaries.
In the twinned copper layer of the present disclosure, two adjacent twinned grains of the plural twinned grains may be intersected. Herein, the included angle between twin directions of two adjacent twinned grains may be ranged from 5 degrees to 60 degrees. The intersection structure formed by two adjacent twinned grains may improve the mechanical strength of the twinned copper layer.
In the twinned copper layer of the present disclosure, 30% or more of the area of a surface of the twinned copper layer may expose the twin boundaries of at least a part of the twinned grains. In one embodiment of the present disclosure, the area of the exposed twin boundaries on the surface of the twinned copper layer may be, for example, 30% to 99%, 35% to 99%, 35% to 95%, 35% to 90%, 35% to 85%, 35% to 80%, 35% to 75%, 35% to 70%, 35% to 65%, 35% to 60%, 35% to 55%, 40% to 55% or 40% to 50% of the total area of the surface of the twinned copper layer, but the present disclosure is not limited thereto.
In the twinned copper layer of the present disclosure, 20% or more of the area of a surface of the twinned copper layer may expose the (111) surface of at least a part of the twinned grains. In one embodiment of the present disclosure, the (111) surface of the twinned grains exposed on the surface of the twinned copper layer may be, for example, 20% to 50%, 20% to 45%, 25% to 45%, 25% to 40%, 30% to 40% or 30% to 35% of the total area of the surface of the twinned copper layer, but the present disclosure is not limited thereto. In addition, in the twinned copper layer of the present disclosure, 10% or more of the area of a surface of the twinned copper layer may expose the (211) surface of at least a part of the twinned grains. In one embodiment of the present disclosure, the (211) surface of the twinned grains exposed on the surface of the twinned copper layer may be, for example, 10% to 40%, 10% to 35%, 10% to 30%, 15% to 30%, 15% to 25% or 15% to 20% of the total area of the surface of the twinned copper layer, but the present disclosure is not limited thereto. Herein, the preferred direction of the twinned grains on the surface of the twinned copper layer can be measured by electron backscatter diffraction (EBSD).
In the present disclosure, the thickness of the twinned copper layer may be adjusted according to the need. In one embodiment of the present disclosure, the thickness of the twined copper layer may be ranged from, for example, 0.1 μm to 500 μm, 0.1 μm to 400 μm, 0.1 μm to 300 μm, 0.1 μm to 200 m 0.1 μm to 100 μm, 0.1 μm to 80 μm, 0.1 μm to 50 m 1 μm to 50 μm, 2 μm to 50 μm, 3 μm to 50 μm, 4 μm to 50 μm, 5 μm to 50 μm, 5 μm to 40 μm, 5 μm to 35 μm, 5 μm to 30 μm or 5 μm to 25 μm, but the present disclosure is not limited thereto.
In the present disclosure, the substrate for electrodeposition may be a substrate with a metal layer formed thereon or a metal substrate. The substrate may be a silicon substrate, a glass substrate, a quartz substrate, a metal substrate, a plastic substrate, a print circuit board, a III-IV group substrate or a lamination substrate thereof. In addition, the substrate may have a single layer or a multi-layer structure.
In the present disclosure, “the twin direction of the twinned grain” or “the twin direction of the flake twinned grain” refers to the lamination direction of the twins or the twin boundaries in the twinned grains or the flake twinned grains, and in other words, the thickness direction of the twinned grains or the flake twinned grains. Herein, the twin boundaries of the twinned grains or the flake twinned grains may be substantially perpendicular to the lamination direction of the twins or the twin boundaries. In the present disclosure, the twinned grains are formed by staking plural twins along a [111] crystal axis. In the present disclosure, the term “substantially perpendicular” refers to that the included angle between two units may be ranged from 80 degrees to 100 degrees, 85 degrees to 95 degrees or 88 degrees to 92 degrees.
In the present disclosure, the included angle between the twin boundary of the twinned grain and the thickness direction of the twinned copper layer or the included angle between the twin boundary of the twinned grain and the surface of the substrate may be measured in a cross-section of the twinned copper layer. Similarly, the features such as the thickness of the twinned copper layer, and the length or the thickness of the twinned grains/the flake twinned grains may also be measured in a cross-section of the twinned copper layer. Alternatively, the length or the thickness of the twinned grains/the flake twinned grains may also be measured from the surface of the twinned copper layer. In the present disclosure, the measurement method is not particularly limited, and may be performed with scanning electron microscope (SEM), transmission electron microscope (TEM), focus ion beam (FIB) or other suitable measurement manners.
In the method of the present disclosure, examples of the copper salt comprised in the plating solution may comprise, but are not limited to, copper sulfate, methyl sulfonic copper or a combination thereof. Examples of the acid comprised in the plating solution may comprise, but are not limited to, sulfuric acid, methane sulfonic acid or a combination thereof. In addition, the plating solution may further comprise an additive, such as gelatin, surfactants, lattice modification agents or a combination thereof.
In the method of the present disclosure, the electrodeposition process may be performed with direct current electrodeposition, high-speed pulse electrodeposition, or direct current electrodeposition and high-speed pulse electrodeposition interchangeably. In one embodiment of the present disclosure, the twinned copper layer is prepared by direct current electrodeposition. The current density used in the direct current electrodeposition may be ranged from, for example, 0.5 ASD to 20 ASD, 0.5 ASD to 15 ASD, 0.5 ASD to 10 ASD, 0.5 ASD to 5 ASD, 1 ASD to 5 ASD, 1 ASD to 3 ASD or 1 ASD to 2 ASD, but the present disclosure is not limited thereto.
The shape of the twinned copper layer provided by the present disclosure is not particularly limited, and may be a foil, a film, a line or a bulk; but the present disclosure is not limited thereto. In addition, the twinned copper layer provided by the present disclosure may have a single layer or a multi-layered structure. Furthermore, the twinned copper layer provided by the present disclosure may be combined with other material to form a multi-layered composite structure.
The twinned copper layer provided by the present disclosure may be applied to various electronic products, for example, a through hole or via of a three-dimensional integrated circuit (3D-IC), a pin through hole of a packaging substrate, a metal interconnect, a substrate circuit or a connector, but the present disclosure is not limited thereto.
Other novel features of the disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an EBSD photo of a twinned copper layer according to Embodiment 1 of the present disclosure.

FIG. 2 is a FIB photo of a twinned copper layer according to Embodiment 1 of the present disclosure.

FIG. 3 is an EBSD photo of a twinned copper layer after annealing according to Embodiment 2 of the present disclosure.

FIG. 4 is a FIB photo of a twinned copper layer after annealing according to Embodiment 2 of the present disclosure.

FIG. 5 is an EBSD photo of a twinned copper layer before annealing according to Embodiment 4 of the present disclosure.

FIG. 6 is a FIB photo of a twinned copper layer before annealing according to Embodiment 4 of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENT

Different embodiments of the present disclosure are provided in the following description. These embodiments are meant to explain the technical content of the present disclosure, but not meant to limit the scope of the present disclosure. A feature described in an embodiment may be applied to other embodiments by suitable modification, substitution, combination, or separation.
It should be noted that, in the present specification, when a component is described to have an element, it means that the component may have one or more of the elements, and it does not mean that the component has only one of the element, except otherwise specified.
In the present specification, except otherwise specified, the feature A “or” or “and/or” the feature B means the existence of the feature A, the existence of the feature B, or the existence of both the features A and B. The feature A “and” the feature B means the existence of both the features A and B. The term “comprise(s)”, “comprising”, “include(s)”, “including”, “have”, “has” and “having” means “comprise(s)/comprising but is/are/being not limited to”.
Moreover, in the present specification, when an element is described to be arranged “on” another element, it does not essentially means that the elements contact the other element, except otherwise specified. Such interpretation is applied to other cases similar to the case of “on”.
Moreover, in the present specification, a value may be interpreted to cover a range within ±10% of the value, and in particular, a range within ±5% of the value, except otherwise specified; a range may be interpreted to be composed of a plurality of subranges defined by a smaller endpoint, a smaller quartile, a median, a greater quartile, and a greater endpoint, except otherwise specified.

Embodiment 1—Twinned Copper Layer Comprising 0.1 at % of Ag

A 12-inch silicon wafer coated with 100 nm Ti/200 nm Cu was broken into 2 cm×3 cm specimens. The specimen was washed with citric acid to remove oxides, and the electrodeposition region was defined with the acid alkaline resistant tape. The area of the total electrodeposition region was 2 cm×2 cm.
The plating solution used in the present embodiment was formulated by CuSO₄.5H₂O, H₂SO₄, AgNO₃aqueous solution and an additive provided by Chemleader Corporation (DP-101L). The addition amount of CUSO₄.5H₂O powders was 196.61 g. The addition amount of H₂SO₄(96%) was 100 g. The addition amount of AgNO₃aqueous solution (0.1 M) was 10 ml. The addition amount of the additive may be ranged from 10 ml to 20 ml. The deionized water was added until the total volume of the plating solution was 1 L, and the plating solution was stirred with a stir bar until the plating solution was mixed well. After mixing, the obtained plating solution was placed into an electrodeposition tank, and the rotation speed was 1200 rpm per minute to maintain the flow of the plating solution. The electrodeposition was performed at room temperature, 1 atm. The power supply (Keithley 2400) was controlled by the computer, and the electrodeposition was performed with the direct current electrodeposition. After the electrodeposition was performed under the current density of 1.5 ASD (A/dm²) for 1 hr, a twinned copper layer with flake twinned grains was obtained, and the thickness of the twinned copper layer was 20 μm. Then, the obtained specimen was polished by electropolishing, wherein the solution for the electropolishing comprised 100 ml of H₃PO₄, 1 ml of acetic acid and 1 ml of glycerol. The specimen to be polished was placed onto the anode, and the electropolishing was performed under 1.75 V for 10 min. The specimen after the electropolishing has a thickness of about 19 μm. The surface preferred direction and the micro-structure of the specimen after the electropolishing was analyzed with electron backscatter diffraction (EBSD) and focus ion beam (FIB), and the hardness of the specimen after the electropolishing was measured with Vickers hardness tester.
FIG. 1 is an EBSD photo of the twinned copper layer of the present embodiment, and FIG. 2 is a FIB photo of the twinned copper layer of the present embodiment.
As shown in FIG. 1, the result obtained by the EBSD measurement indicates that 32.7% of the surface of the twinned copper layer is the (111) surface, and 19.3% of the surface of the twinned copper layer is the (211) surface.
As shown in FIG. 2, the result obtained by the FIB measurement indicates that most of the grains in the twinned copper layer 12 are twinned with high density. 50% or more in volume of the twinned copper layer comprises twinned grains. The included angles between the twin boundaries (indicated by the arrow) of 50% or more of the twinned grains and the thickness direction of the twinned copper layer 12 are ranged from 0 degree to 30 degrees. The included angles between the twin boundaries (indicated by the arrow) of 50% or more of the twinned grains and the surface of the substrate 11 are ranged from 60 degrees to 90 degrees. 50% or more of the twinned grains in the twinned copper layer 12 have the thickness ranging from about 1 μm to about 10 μm, and 50% or more of the twinned grains in the twinned copper layer 12 have the thickness ranging from about 0.2 μm to about 5 μm. The included angle between the twin directions of two adjacent twinned grains may be ranged from 5 degrees to 60 degrees.
As shown in FIG. 1 and FIG. 2, 50% or more of the twinned grains are flake twinned grains. In addition, the flake twinned grain indicated in FIG. 1 has a maximum length (L) of about 10 μm measured at the extension direction of the twin boundary, and a maximum thickness (T) of about 3.5 μm measured at the lamination direction of the twins or the twin boundaries. Thus, the ratio of the length to the thickness (L/T) is greater than 2. Furthermore, the flake twinned grain indicated in FIG. 2 has a maximum length (L) of about 10 μm measured at the extension direction of the twin boundary, and a maximum thickness (T) of about 2 μm measured at the lamination direction of the twins or the twin boundaries. Thus, the ratio of the length to the thickness (L/T) is greater than 2.
In addition, after measuring with the Vickers hardness tester, the twinned copper layer containing 0.1 at % of Ag has the hardness of about 262.8±17.9 Hv (n=5). This result indicates that the twinned copper layer containing 0.1 at % of Ag have excellent hardness.

Embodiment 2—Twinned Copper Layer Comprising 0.1 at % of Ag

The twinned copper layer of the present embodiment was prepared by the similar process illustrated in Embodiment 1. The obtained specimen was placed into the furnace to perform the annealing process. The vacuum pressure was 10⁻³torr, the annealing temperature was 200° C., and the annealing period was 1 hr. The surface preferred direction and the micro-structure of the specimen after the annealing was analyzed with EBSD and FIB, and the hardness of the specimen after the annealing was measured with Vickers hardness tester.
FIG. 3 is an EBSD photo of the twinned copper layer after annealing of the present embodiment, and FIG. 4 is a FIB photo of the twinned copper layer after annealing of the present embodiment.
As shown in FIG. 3 and FIG. 4, after annealing, the structure of the twinned grains of the twinned copper layer is still maintained and similar to that of Embodiment 1. In addition, after measuring with the Vickers hardness tester, the twinned copper layer after annealing has the hardness of about 237.2±14 Hv (n=5). This result indicates that the twinned copper layer containing 0.1 at % of Ag have excellent hardness as well as good thermal stability.

Embodiment 3—Twinned Copper Layers Comprising 0.3 at % and 0.6 at % of Ag

The twinned copper layers of the present embodiment were prepared by the similar process illustrated in Embodiment 1, except that the concentration of AgNO₃comprised in the plating solution was adjusted to 20 ml and 30 ml.
The surface preferred direction and the micro-structure of the specimen was analyzed with EBSD and FIB. The structure of the twinned grains of the twinned copper layer comprising 0.3 at % or 0.6 at % of Ag of the present embodiment is similar to that of Embodiment 1. In addition, after measuring with the Vickers hardness tester, the twinned copper layers comprising 0.3 at % and 0.6 at % of Ag of the present embodiment respectively have the hardness of about 305.6±32.9 Hv (n=5) and 266.4±23.9 Hv (n=5).

Embodiment 4—Twinned Copper Layers without Ag

The twinned copper layer of the present embodiment was prepared by the similar process illustrated in Embodiment 1, except that the plating solution does not comprise AgNO₃and the thickness of the twinned copper layer was 5 μm. In addition, the specimen was placed into the furnace to perform the annealing process. The vacuum pressure was 10⁻³torr, the annealing temperature was 250° C. and 300° C., and the annealing period was 1 hr.
FIG. 5 is an EBSD photo of the twinned copper layer before annealing of the present embodiment, and FIG. 6 is a FIB photo of the twinned copper layer before annealing of the present embodiment.
The surface preferred direction and the micro-structure of the specimen was analyzed with EBSD and FIB. The structures of the twinned grains of the twinned copper layer without Ag of the present embodiment before annealing or after annealing at 250° C. and 300° C. are similar to that of Embodiment 1.

Embodiment 5—Twinned Copper Layers without Ag

The twinned copper layer of the present embodiment was prepared by the similar process illustrated in Embodiment 1, except that the plating solution does not comprise AgNO₃. After measuring with the Vickers hardness tester, the twinned copper layer without Ag of the present embodiment has the hardness of about 255.8±10.55 Hv (n=5).

Comparative Embodiment

The plating solution used in the present comparative embodiment was formulated by CUSO₄.5H₂O, H₂SO₄, HCl and an additive provided by Chemleader Corporation (DP-101L). The addition amount of CUSO₄.5H₂O powders was 196.61 g. The addition amount of H₂SO₄(96%) was 100 g. The addition amount of HCl (38.5%) was 0.1 ml. The addition amount of the additive was 4.5 ml. The deionized water was added until the total volume of the plating solution was 1 L, and the plating solution was stirred with a stir bar until the plating solution was mixed well. After mixing, the obtained plating solution was placed into an electrodeposition tank, and the rotation speed was 1200 rpm per minute to maintain the flow of the plating solution. The electrodeposition was performed at room temperature, 1 atm. The power supply (Keithley 2400) was controlled by the computer, and the electrodeposition was performed with the direct current electrodeposition. After the electrodeposition was performed under the current density of 6 ASD (A/dm²) for 20 minutes, a nano-twinned copper layer with columnar nano-twinned grains having high <111> preferred direction can be obtained, and the thickness of the nano-twinned copper layer was 20 μm. Then, the obtained specimen was polished by electropolishing, wherein the solution for the electropolishing comprises 100 ml of H₃PO₄, 1 ml of acetic acid and 1 ml of glycerol. The specimen to be polished was placed onto the anode, and the electropolishing was performed under 1.75 V for 10 min. The specimen after the electropolishing has a thickness of about 19 μm. The surface preferred direction and the micro-structure of the specimen after the electropolishing was analyzed with EBSD and FIB, and the hardness of the specimen after the electropolishing was measured with Vickers hardness tester. After measuring with the Vickers hardness tester, the nano-twinned copper layer without Ag of the present comparative embodiment has the hardness of about 195 Hv.
From the aforesaid results, the twinned copper layers comprising Ag of Embodiments 1 to 3 have the hardness up to 305 Hv. Compared with the nano-twinned copper layer of Comparative embodiment having the hardness of 195 Hv, the hardness of the twinned copper layers comprising Ag can be greatly improved by 60% or more. In addition, even though the twinned copper layers of Embodiments 4 and 5 do not comprise Ag, the hardness thereof is still higher than that of the nano-twined copper layer of Comparative embodiment. The aforesaid results indicate that the twinned copper layers with specific structures of Embodiments 1 to 5 have improved strength.
In conclusion, the present disclosure provides a twinned copper layer with a specific structure, which comprises flake twinned grains with specific length to thickness ratio, and the twin direction of the flake twinned grains are intersected. Thus, the hardness of the twinned copper layer can be improved. In addition, the twinned copper layer of the present disclosure is prepared by co-electrodeposition to form the twinned copper layer comprising different metal elements. Thus, the strength of the twinned grains in the twinned copper layer can be improved. In addition, the effect of the precipitation hardening or solid solution strengthening can be achieved, so the hardness of the twinned copper layer can further be improved. Meanwhile, the electrical conductivity and the thermal conductivity of silver are better than those of copper, and silver does not react with copper. Thus, the strength of the twinned Cu/Ag alloy layer can be greatly improved by 60% or more without losing the electrical conductivity and the thermal conductivity of the twinned copper layer. In addition, the twinned copper layers with or without Ag of the present disclosure have high thermal stability. After annealing at 300° C. for 1 hr, most of the twinned grains are maintained and the strength of the twinned copper layer is not significantly decreased. Thus, the twinned copper layer provided by the present disclosure has high strength, high electrical conductivity, high thermal conductivity and/or excellent thermal stability, and can be applied to various electronic elements.
Although the present disclosure has been explained in relation to its embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the disclosure as hereinafter claimed.

Claims

What is claimed is:

1. A twinned copper layer, wherein 35% or more in volume of the twinned copper layer comprises plural twinned grains, 30% or more of the plural twinned grains are flake twinned grains, and a ratio of a length to a thickness of at least a part of the flake twinned grains is greater than or equal to 2.

2. The twinned copper layer of claim 1, wherein a thickness direction of the flake twinned grains is a twin direction of the flake twinned grains.

3. The twinned copper layer of claim 1, wherein an included angle between a twin boundary of at least a part of the plural twinned grains and a thickness direction of the twinned copper layer is ranged from 0 degree to 30 degrees.

4. The twinned copper layer of claim 1, including:

0.05 at % to 20 at % of at least one element selected from the group consisting of Ag, Ni, Zn, Pb, Al, Au, Pt, Mg and Cd; and

rest of Cu.

5. The twinned copper layer of claim 4, wherein the at least one element is Ag.

6. The twinned copper layer of claim 1, wherein a length of the at least a part of the flake twinned grains is ranged from 0.5 μm to 20 μm.

7. The twinned copper layer of claim 1, wherein two adjacent twinned grains of the plural twinned grains are intersected.

8. The twinned copper layer of claim 1, wherein the plural twinned grains are formed by staking plural twins along a [111] crystal axis.

9. A substrate having a twinned copper layer, comprising:

a substrate; and

a twinned copper layer disposed on the substrate or embedded into the substrate, wherein 35% or more in volume of the twinned copper layer comprises plural twinned grains, 30% or more of the plural twinned grains are flake twinned grains, and a ratio of a length to a thickness of at least a part of the flake twinned grains is greater than or equal to 2.

10. The substrate of claim 9, wherein an included angle between a twin boundary of at least a part of the plural twinned grains and a surface of the substrate is ranged from 60 degrees to 90 degrees.

11. A method for preparing a twinned copper layer, comprising the following steps:

providing an electrodeposition device, comprising an anode, a cathode, a plating solution and a power supply, wherein the power supply is respectively connected to the cathode and the anode, and the cathode and the anode are immersed into the plating solution; and

performing an electrodeposition process with the electrodeposition device to grow a twinned copper layer on a surface of the cathode,

wherein 35% or more in volume of the twinned copper layer comprises plural twinned grains, 30% or more of the plural twinned grains are flake twinned grains, and a ratio of a length to a thickness of at least a part of the flake twinned grains is greater than or equal to 2; and

wherein the plating solution comprises a copper salt and an acid, and the plating solution does not comprise a chloride ion.

12. The method of claim 11, wherein a thickness direction of the flake twinned grains is a twin direction of the flake twinned grains.

13. The method of claim 11, wherein an included angle between a twin boundary of at least a part of the plural twinned grains and a thickness direction of the twinned copper layer is ranged from 0 degree to 30 degrees.

14. The method of claim 11, wherein the twinned copper layer includes:

rest of Cu.

15. The method of claim 14, wherein plating solution further comprises a salt of the at least one element.

16. The method of claim 14, wherein the at least one element is Ag.

17. The method of claim 16, wherein the plating solution comprises a silver salt.

18. The method of claim 11, wherein a length of the at least a part of the flake twinned grains is ranged from 0.5 μm to 20 μm.

19. The method of claim 11, wherein two adjacent twinned grains of the plural twinned grains are intersected.

20. The method of claim 11, wherein the plural twinned grains are formed by staking plural twins along a [111] crystal axis.