TWI850951B - Nano-twinned copper foil, electronic element and methods for manufacturing the same - Google Patents

Abstract

A nano-twinned copper foil is provided, which comprises: plural twinned grains, wherein at least part of the plural twinned grains are formed by plural nano-twins stacking along a [111] crystal axis. The nano-twinned copper foil has a first surface and a second surface opposite to the first surface, and 80% or more of the areas of the first surface and the second surface respectively are the (111) surface of the nano-twins. In addition, the present invention further provides a method for manufacturing the aforesaid nano-twinned copper foil, an electronic element comprising the same, and a method for manufacturing the electronic element.

Description

Nano-twin-crystal copper foil, electronic component containing the same and preparation method thereof

The present invention relates to a nano-twin copper foil, an electronic component containing the same and a preparation method thereof, and in particular to a nano-twin copper foil having a (111) preferred direction on both sides, an electronic component containing the same and a preparation method thereof.

High-power components generate a lot of heat during operation, and the temperature can even exceed 300 degrees Celsius. If the heat cannot be dissipated in time, it is easy to cause component failure or reliability-related problems. Therefore, various bonding layers and thermal interface materials are currently developed to solve this problem. However, the bonding layers and thermal interface materials currently developed still have their own shortcomings.

For example, the traditional chip bonding layer uses solder, but with the need to remove lead from solder, solder that can withstand 300-degree high temperatures has become a challenge, and the reliability problem caused by intermetallic compounds is also a major problem. In addition, the porous structure of sintered copper or silver as bonding layer and thermal interface material will lead to increased thermal resistance, and the high temperature and long-term sintering and high material prices will increase the cost. Furthermore, using high molecular polymer as bonding layer and thermal interface material, although the bonding can be completed at a low temperature and is cheaper, its thermal conductivity is about two orders of magnitude lower than that of metal, and it needs to overcome the problems of high temperature resistance and large difference in thermal expansion coefficient, and the heat dissipation coefficient is also lower.

Therefore, there is an urgent need to develop a novel bonding layer and thermal interface material in order to solve the above problems.

The main purpose of the present invention is to provide a nano-bicrystalline copper foil, both sides of which have a (111) preferred direction, which can be applied to the bonding of electronic components.

The nano-twin copper foil of the present invention comprises: a plurality of twin crystal grains, wherein at least part of the twin crystal grains are formed by stacking a plurality of nano-twin crystals along the [111] crystal axis direction; wherein the nano-twin copper foil has a first surface and a second surface opposite to the first surface; and more than 80% of the area of the first surface and the second surface respectively expose the (111) plane of the nano-twin crystals. In addition, the first surface and the second surface of the nano-twin copper foil of the present invention have low roughness.

In addition to retaining the good mechanical strength and electrical performance of nano-twin-crystal copper, the nano-twin-crystal copper foil of the present invention has surfaces with a highly (111) preferred direction on both sides, and even has low roughness on both sides. By utilizing the high diffusion rate characteristics of the (111) surface, the nano-twin-crystal copper foil of the present invention can be similar to the concept of a double-sided tape, and can be bonded to two substrates at low temperature and/or in a short time. Compared with the sintering bonding of copper or silver, the use of the nano-twin-crystal copper foil of the present invention for bonding can produce fewer holes on the bonding surface, and the resulting electronic components can have lower electrical resistance or thermal resistance. Therefore, the nano-bicrystalline copper foil of the present invention can be applied to the bonding between the backside metallization and direct copper bond (DCB) substrate of high-power components, the DCB substrate and the heat sink fin, and can also be applied to the bonding of thermal interface materials and heat sink copper tubes.

In one embodiment, the roughness of the first surface and the second surface of the nanobicrystalline copper foil may be less than or equal to 20 nm, for example, may be between 0.1 nm and 20 nm, 0.5 nm and 20 nm, 1 nm and 20 nm, 2 nm and 20 nm, 3 nm and 20 nm, 4 nm and 20 nm, or 5 nm and 20 nm, respectively.

In one embodiment, more than 80% of the volume of the nano-twin copper foil may include a plurality of twin crystal grains. In one embodiment, for example, 80% to 99%, 80% to 95%, 85 to 95%, or 90% to 95% of the volume of the nano-twin copper foil may include a plurality of twin crystal grains; however, the present invention is not limited thereto.

In one embodiment, at least part of the plurality of twinned grains of the nano-twinned copper foil may be columnar twinned grains, wherein the columnar twinned grains may be formed by stacking a plurality of nano-twinned grains along a direction within a range of ±15 degrees along the [111] crystal axis direction, and the angle between the stacking direction of at least part of the nano-twinned grains and the thickness direction of the nano-twinned copper foil is between 0 degrees and 20 degrees. In one embodiment, more than 80% of the plurality of twinned grains, such as 80% to 99%, 80% to 95%, 85 to 95% or 90% to 95%, are columnar twinned grains. When the columnar twin crystal grains grow to the surface of the nano-twin copper foil, more than 80% of the surface area of the nano-twin copper foil can reveal the (111) plane of the nano-twin; at this time, the surface of the nano-twin copper foil can have a preferred direction of (111).

In one embodiment, more than 80% of the area of the first surface and the second surface of the nano-twin copper foil respectively expose the (111) plane of the nano-twin. In other words, the first surface and the second surface of the nano-twin copper foil may both have a preferred direction of (111). In one embodiment, the (111) plane of the nano-twin exposed on the first surface and the second surface of the nano-twin copper foil may account for, for example, 80% to 100%, 85% to 100%, 90% to 100%, 90% to 99.5%, 90% to 99%, 95% to 99% or 97% to 99% of the total area of the first surface and the second surface of the nano-twin copper foil; but the present invention is not limited thereto. Here, the preferred directions of the first surface and the second surface of the nano-twin copper foil can be measured by an Electron Backscatter Diffraction (EBSD) instrument.

In one embodiment, when the bicrystalline grain of the nano bicrystalline copper foil has a significant bicrystalline grain thickness to diameter ratio, for example, when the thickness is significantly greater than the diameter, the bicrystalline grain is a columnar bicrystalline grain.

In one embodiment, at least a portion of the bicrystalline dies may be connected to each other, for example, more than 50%, 60%, 70%, 80%, 90% or 95% of the bicrystalline dies may be connected to each other.

In one embodiment, the thickness of the nano-twin-crystal copper foil can be adjusted as required. In one embodiment, the thickness of the nano-twin-crystal copper foil can be, for example, between 10 μm to 500 μm, 10 μm to 400 μm, 10 μm to 300 μm, 10 μm to 200 μm, or 10 μm to 100 μm; but the present invention is not limited thereto.

In one embodiment, the diameter of the bicrystalline grains (e.g., columnar bicrystalline grains) may be between 0.1 μm and 50 μm. In one embodiment of the present disclosure, the diameter of the bicrystalline grains (e.g., columnar bicrystalline grains) may be between 0.1 μm and 45 μm, 0.1 μm and 40 μm, 0.1 μm and 35 μm, 0.5 μm and 35 μm, 0.5 μm and 30 μm, 1 μm and 30 μm, 1 μm and 25 μm, 1 μm and 20 μm, 1 μm and 15 μm, or 1 μm and 10 μm, but the present invention is not limited thereto. In one embodiment, the diameter of a bicrystalline grain (e.g., a columnar bicrystalline grain) may be a length measured in a direction substantially perpendicular to the bicrystalline direction of the bicrystalline grain; in more detail, the diameter of a bicrystalline grain (e.g., a columnar bicrystalline grain) may be a length (e.g., a maximum length) measured in a direction substantially perpendicular to the stacking direction of the bicrystalline planes of the bicrystalline grain (i.e., the direction in which the bicrystalline planes extend).

In one embodiment, the thickness of the bicrystalline grains (e.g., columnar bicrystalline grains) may be between 0.1 μm and 500 μm, respectively. In one embodiment, the thickness of the bicrystalline grains (e.g., columnar bicrystalline grains) may be, for example, between 0.1 μm and 500 μm, 0.1 μm and 400 μm, 0.1 μm and 300 μm, 0.1 μm and 200 μm, 0.1 μm and 100 μm, 0.1 μm and 80 μm, 0.1 μm and 50 μm, 1 μm and 50 μm, 2 μm and 50 μm, 3 μm and 50 μm, 4 μm and 50 μm, 5 μm and 50 μm, 5 μm and 40 μm, 5 μm and 35 μm, 5 μm and 30 μm, or 5 μm and 25 μm. In one embodiment, the thickness of a bicrystalline grain (e.g., a columnar bicrystalline grain) may be a thickness measured in the bicrystalline direction of the bicrystalline grain; more specifically, the thickness of a bicrystalline grain (e.g., a columnar bicrystalline grain) may be a thickness (e.g., a maximum thickness) measured in the stacking direction of the bicrystalline planes of the bicrystalline grain.

In the present invention, the so-called "twin direction of a twin grain" refers to the stacking direction of twin planes in the twin grain. The twin planes of the twin grain may be substantially perpendicular to the stacking direction of the twin planes.

In the present invention, a cross section of a nano-twin copper foil can be used to measure the angle between the twin crystal direction of the twin crystal grains and the thickness direction of the nano-twin copper foil. Similarly, a cross section of a nano-twin copper foil can be used to measure the thickness of the nano-twin copper foil, the diameter and thickness of the twin crystal grains, and other characteristics. Alternatively, the diameter and thickness of the twin crystal grains can also be measured on the surface (e.g., the first surface or the second surface) of the nano-twin copper foil. In the present invention, there is no special limitation on the measurement method, and the measurement can be performed using a scanning electron microscope (SEM), a transmission electron microscope (TEM), a focused ion beam system (FIB), or other suitable means.

In addition to the aforementioned nano twin-crystal copper foil, the present invention further provides a method for preparing the aforementioned nano twin-crystal copper foil, comprising the following steps: providing an electroplating device, comprising an anode, a cathode, an electroplating solution, and an electric power source, wherein the electric power source is connected to the anode and the cathode respectively, and the anode and the cathode are immersed in the electroplating solution. in a plating solution; using a power supply source to provide power for electroplating to form a nano-twin-crystal copper layer on a cathode; and removing the cathode and polishing a surface (lower surface) of the nano-twin-crystal copper layer to obtain the aforementioned nano-twin-crystal copper foil, wherein the surface is the surface of the nano-twin-crystal copper layer in contact with the cathode before removing the cathode.

In one embodiment, the cathode may include: a substrate; and a titanium-tungsten bonding layer disposed on the substrate, wherein the nano-bicrystalline copper layer is formed on the titanium-tungsten bonding layer. The substrate may be a silicon substrate, a glass substrate, a quartz substrate, a metal substrate, a plastic substrate, a printed circuit board, a III-V material substrate or a laminated substrate thereof; and the substrate may have a single-layer or multi-layer structure.

In one embodiment, the titanium-tungsten bonding layer may include a titanium-tungsten alloy as shown in the following formula (I): Ti _x W _100-x (I) wherein x is between 5 and 20. In one embodiment, the titanium-tungsten alloy is Ti ₁₀ W ₉₀ . When the titanium-tungsten alloy as shown in formula (I) is used as the titanium-tungsten bonding layer, the nano-tungsten twin-crystal copper layer and the cathode (including the substrate and the titanium-tungsten bonding layer) can be effectively separated; on the other hand, when the titanium bonding layer is used, the nano-tungsten twin-crystal copper layer and the cathode (including the substrate and the titanium-tungsten bonding layer) cannot be effectively separated. In one embodiment, the nano-twin-crystal copper layer can be separated from the cathode (including the substrate and the titanium-tungsten bonding layer) by tearing off the cathode to obtain the nano-twin-crystal copper foil.

In one embodiment, the thickness of the TiT bonding layer may be between 100 nm and 200 nm. When the thickness of the TiT bonding layer is less than 100 nm, it is difficult to grow twin crystal grains with a (111) preferred orientation. When the thickness of the TiT bonding layer exceeds 200 nm, it is difficult to separate the nano twin crystal copper layer from the cathode (including the substrate and the TiT bonding layer).

In one embodiment, before removing the cathode, a further step may be included: polishing the other surface (upper surface) of the nano-twin crystal copper layer away from the cathode.

In one embodiment, before removing the cathode, or after removing the cathode and before polishing the surface (lower surface) of the nano-twin-crystal copper layer, a step may be further included: forming a protective layer on the other surface (upper surface) of the nano-twin-crystal copper layer away from the cathode. After polishing the surface (lower surface) of the nano-twin-crystal copper layer, the protective layer is removed.

In one embodiment, polishing of both surfaces (ie, upper and lower surfaces) of the nano bi-crystalline copper layer can also be performed in the same polishing process.

In one embodiment, the plating solution may include a copper salt and an acid. Examples of the copper salt in the plating solution may include, but are not limited to, copper sulfate, copper methanesulfonate, or a combination thereof; examples of the acid in the plating solution may include, but are not limited to, hydrochloric acid, sulfuric acid, methanesulfonic acid, or a combination thereof. In addition, the plating solution may further include an additive, such as gelatin, a surfactant, a lattice modifier, or a combination thereof.

In one embodiment, direct current plating, pulse plating, or a combination of direct current plating and pulse plating can be used to form the nano-bicrystalline copper layer.

In one embodiment, direct current plating may be used to form the nano bicrystalline copper layer, wherein the current density of the direct current plating may be, for example, 0.5 ASD to 30 ASD, 1 ASD to 30 ASD, 2 ASD to 30 ASD, 2 ASD to 25 ASD, 2 ASD to 20 ASD, 2 ASD to 15 ASD, or 2 ASD to 10 ASD; however, the present invention is not limited thereto.

In addition to the aforementioned nano twin-crystal copper foil, the present invention further provides the application of the aforementioned nano twin-crystal copper foil in electronic components and a preparation method thereof.

The electronic element of the present invention comprises: a first substrate; a second substrate; and a bonding unit disposed between the first substrate and the second substrate, wherein the bonding unit is the aforementioned nano-twin crystal copper foil.

The method for preparing an electronic component of the present invention comprises the following steps: providing a first substrate and a second substrate; arranging a bonding unit between the first substrate and the second substrate, and bonding the first substrate and the second substrate by the bonding unit to form an electronic component, wherein the bonding unit is the aforementioned nano-twin-crystal copper foil.

In the electronic component of the present invention, when the nano-twin copper foil provided by the present invention is used to bond the first substrate and the second substrate, since the two surfaces of the nano-twin copper foil of the present invention have a highly (111) preferred direction and low roughness, excellent bonding quality with almost no gaps can be achieved under low temperature and short bonding time.

In one embodiment, the first substrate and the second substrate may be a metal substrate, respectively, and the material thereof may include at least one selected from the group consisting of copper, silver, gold, palladium, nickel, and platinum.

In one embodiment, the first substrate and the second substrate may be a substrate having a metal layer formed thereon, wherein the substrate may be a silicon substrate, a glass substrate, a quartz substrate, a plastic substrate, a ceramic substrate or a circuit board, and the material of the metal layer may include at least one selected from the group consisting of copper, silver, gold, palladium, nickel and platinum.

In one embodiment, there is no particular limitation on the device for bonding, for example, a clamp can be used for bonding. In addition, if necessary, bonding can be selectively performed by pressurization. The pressure of pressurization is not particularly limited, and preferably low pressure, such as bonding at a pressure of about 5 MPa to 50 MPa.

In one embodiment, the bonding can be performed at an elevated temperature, wherein the bonding temperature is not particularly limited, as long as the bonding purpose can be achieved without affecting the structures of the first substrate and the second substrate, for example, the bonding can be performed at a low temperature of 150°C to 400°C, 150°C to 350°C, or 200°C to 350°C. In addition, the bonding time is not particularly limited, as long as the first substrate and the second substrate can be bonded, for example, about 0.5 hours to 5 hours, 0.5 hours to 4 hours, 0.5 hours to 3 hours, 0.5 hours to 2 hours, or 0.5 hours to 1 hour.

The following will be accompanied by drawings and detailed descriptions to make the features of the present disclosure more obvious.

The following provides different embodiments of the present disclosure. These embodiments are used to illustrate the technical content of the present disclosure, but are not used to limit the scope of the present disclosure. A feature of an embodiment can be applied to other embodiments through appropriate modification, replacement, combination, and separation.

It should be noted that, in this document, unless otherwise specified, “a” element is not limited to a single element but may include one or more elements.

In this document, unless otherwise specified, the so-called feature A "or" or "and/or" feature B means that A exists alone, B exists alone, or A and B exist at the same time; the so-called feature A "and" or "and" or "and" feature B means that A and B exist at the same time; the so-called "include", "comprise", "have" and "contain" mean including but not limited to these.

Furthermore, herein, unless specifically stated otherwise, “an element is on another element” or similar descriptions do not necessarily mean that the element contacts the other element.

In addition, in this document, unless otherwise specified, a numerical value may include a range of ±10% of the numerical value, in particular, a range of ±5% of the numerical value. Unless otherwise specified, a numerical range is composed of multiple sub-ranges defined by a lower endpoint, a lower quartile, a median, an upper quartile, and a higher endpoint.

Example 1 - Preparation of Nano-twin Crystal Copper Foil

Figures 1A and 1B are schematic cross-sectional views of the preparation of nano bicrystalline copper foil in this embodiment. As shown in Figure 1A, in this embodiment, a silicon substrate 11 with a titanium tungsten bonding layer 12 formed thereon is used as a cathode, wherein the titanium tungsten bonding layer 12 includes Ti ₁₀ W ₉₀ and has a thickness of 100 nm.

The electroplating solution used in this embodiment is prepared from copper sulfate pentahydrate crystals. A total of 196.54 g of copper sulfate pentahydrate (containing 50 g/L of copper ions) is used, and 1.5 ml of additives, 100 g of sulfuric acid (96%) are added, and finally 0.1 ml of hydrochloric acid (12N) is added to the electroplating solution, and a magnet is used to stir until the copper sulfate pentahydrate is evenly mixed in 1 liter of the solution. The magnet at the bottom of the electroplating tank rotates at 1200 revolutions per minute to maintain the uniformity of the ion concentration, and the electroplating is performed at room temperature under atmospheric pressure. The hydrochloric acid added to the electroplating solution can make the copper target (as the anode) in the electroplating tank dissolve normally to balance the copper ion concentration in the electroplating solution. Here, a power supply (Keithley 2400) is controlled by a computer, and direct current electroplating is used. The forward current density is set to 6 ASD (A/dm ² ). After electroplating for about 20 minutes, a nano-twin copper metal layer 13 with a thickness of about 20 µm can be formed on the titanium-tungsten bonding layer 12.

Then, the upper surface 13a of the nano-twin copper metal layer 13 is polished, wherein the composition of the electrolytic polishing liquid is 100 ml of phosphoric acid plus 1 ml of acetic acid and 1 ml of glycerol. At this time, the sample to be electrolytically polished is clamped to the anode and a voltage of 1.75 V is applied for 10 minutes to achieve the effect of electrolytic polishing. The thickness of the sample after electrolytic polishing is about 17 µm, and the roughness of the upper surface 13a of the nano-twin copper metal layer 13 can be reduced to less than 20 nm.

After the upper surface 13a of the nano-twin copper metal layer 13 is polished, a protective layer (not shown) is formed on the upper surface 13a of the nano-twin copper metal layer 13; here, the protective layer can be a polymer layer. Then, as shown in FIG. 1B, the silicon substrate 11 and the titanium tungsten connecting layer 12 are removed, and the lower surface 13b of the nano-twin copper metal layer 13 is polished to remove the copper seed layer and the transition layer. Here, the electrolytic polishing process of the upper surface 13a of the nano-twin copper metal layer 13 can be used to polish the lower surface 13b of the nano-twin copper metal layer 13. The thickness of the sample after electrolytic polishing is about 10 µm, and the roughness of the lower surface 13b of the nano-twin-crystal copper metal layer 13 can be reduced to less than 20 nm.

Through the above process, the nano-twin copper foil of this embodiment can be obtained. The nano-twin copper foil of this embodiment is subjected to backscattered electron diffraction (EBSD), focused ion beam (FIB) and atomic force microscope (AFM) to analyze the surface preferred direction and microstructure respectively.

FIG2 is a focused ion beam image of the nano-twin copper foil of the present embodiment. FIG3A and FIG3B are diffraction images of the upper and lower surfaces of the nano-twin copper foil of the present embodiment respectively by a backscattered electron diffraction instrument. FIG4A and FIG4B are atomic force microscope images of the upper and lower surfaces of the nano-twin copper foil of the present embodiment respectively.

As shown in Figure 2, the measurement results of the focused ion beam show that most of the grains in the nano-twin copper foil have very dense twin crystals. More than 95% of the volume of the nano-twin copper foil includes columnar twin crystal grains. The twin crystal direction of more than 95% of the twin crystal grains is about 0 degrees to 10 degrees with the thickness direction of the nano-twin copper foil, and the twin crystal direction of more than 95% of the twin crystal grains is about 80 degrees to 90 degrees with the surface of the substrate, which means that the twin crystal plane of the twin crystal grain is substantially parallel to the surface of the substrate. In addition, the thickness of more than 95% of the twin crystal grains in the nano-twin copper foil is about 1 μm to 10 μm. Furthermore, no transition layer was observed at the bottom of the nanotwin copper foil, confirming that the transition layer had been removed, leaving behind a nanotwin structure with a high (111) preferred orientation.

As shown in FIG. 3A and FIG. 3B , the measurement results of the backscattered electron diffraction instrument show that the nano-twin copper foil prepared in this embodiment has almost all volume (more than 95% of the volume) of columnar twin crystal grains connected to each other, and the diameter of the columnar twin crystal grains is in the range of about 0.5 μm to 3 μm. In addition, the twin crystal grains are stacked along the [111] crystal axis direction of the nano-twin crystals, and the twin crystal planes of the nano-twin crystals are substantially parallel to the cathode surface (i.e., the stacking direction of the nano-twin crystals is substantially parallel to the thickness direction of the nano-twin copper foil). In addition, after calculation, the proportions of the (111) planes of the nanotwins on the upper and lower surfaces of the nanotwin copper foil are 100% and 99.6%, respectively, indicating that the upper and lower surfaces of the nanotwin copper foil of this embodiment both have a preferred direction of (111).

As shown in FIG. 4A and FIG. 4B , the measurement results of the atomic force microscope show that the roughness of the upper and lower surfaces of the nano-twin-crystal copper foil prepared in this embodiment is 18.9 nm and 7.7 nm, respectively, indicating that the nano-twin-crystal copper foil of this embodiment has an extremely low roughness.

The above experimental results show that the upper and lower surfaces of the nano-twin copper foil of this embodiment have a preferred direction of (111) and a roughness of less than 20 nm, which means that the nano-twin copper foil of this embodiment is beneficial to the subsequent bonding of electronic components.

Example 2 - Preparation of electronic components

5A and 5B are cross-sectional schematic diagrams of the preparation of the electronic component of this embodiment. As shown in FIG5A, a first substrate 21 and a second substrate 22 are provided; a bonding unit 23 is disposed between the first substrate 21 and the second substrate 22, and the first substrate 21 and the second substrate 22 are bonded by the bonding unit 23 to form the electronic component of this embodiment, as shown in FIG5B.

In this embodiment, the first substrate 21 and the second substrate 22 are respectively silicon substrates with copper seed layers disposed thereon, and the surfaces thereof have a roughness of 3.1 nm and a (111) ratio close to 100%; and the bonding unit 23 is the nano-twin copper foil prepared in Embodiment 1. Here, the bonding is performed with the copper seed layer side to the bonding unit 23. In addition, in this embodiment, the bonding is performed at 250 degrees and 35 MPa for 1 hour. The ion and electron images of the focused ion beam of the electronic component obtained after bonding are shown in FIG6A and FIG6B , respectively.

As shown in FIG. 6A and FIG. 6B , the bonding unit 23 is well bonded to the copper seed layer 211 on the first substrate and the copper seed layer 221 on the second substrate, and there is almost no gap between the upper and lower bonding surfaces (as indicated by arrows) of the bonding unit 23 .

Example 3 - Preparation of electronic components

The preparation method of the electronic component of this embodiment is the same as that of embodiment 2, except that the first substrate 21 and the second substrate 22 used in this embodiment are copper substrates, respectively, with a surface roughness of 48 nm and an extremely low (111) ratio of 2.7%; and the bonding is performed at 300 degrees and 30 MPa for 30 minutes. The ion and electron images of the focused ion beam of the electronic component obtained after bonding are shown in Figures 7A and 7B, respectively.

As shown in FIG. 7A and FIG. 7B , since the copper substrates used for the first substrate 21 and the second substrate 22 have a relatively large roughness and an extremely low (111) ratio, under low temperature and short-time bonding conditions, some small cracks are unavoidable on the upper and lower bonding surfaces of the bonding unit 23 (as indicated by the arrows), but most of the bonding still maintains a seamless and excellent bonding quality.

The results of Examples 2 and 3 show that when the nano-bicrystalline copper foil prepared in Example 1 is used for bonding, good bonding quality can be obtained regardless of whether the bonding surface of the bonded substrates has a low roughness or a high (111) ratio.

In summary, the nano-twin copper foil provided by the present invention can be applied to the bonding of high-power components and the bonding of thermal interface materials and heat sinks, and can reduce the thermal budget of the process, because more than 80% of the area of both sides respectively expose the (111) surface of the nano-twin, and even have a roughness of less than 20 nm.

11                 Silicon substrate 12                 Titanium tungsten bonding layer 13                 Nano bicrystalline copper metal layer 13a               Upper surface 13b               Lower surface 21                 First substrate 211, 221       Copper seed layer 22                 Second substrate 23                 Bonding unit

Figures 1A and 1B are schematic cross-sectional views of the nano-twin copper foil prepared in Example 1 of the present invention. Figure 2 is a focused ion beam image of the nano-twin copper foil in Example 1 of the present invention. Figures 3A and 3B are diffraction images of the upper and lower surfaces of the nano-twin copper foil in Example 1 of the present invention, respectively, by a backscattered electron diffraction device. Figures 4A and 4B are atomic force microscope images of the upper and lower surfaces of the nano-twin copper foil in Example 1 of the present invention, respectively. Figures 5A and 5B are schematic cross-sectional views of the electronic component prepared in Example 2 of the present invention. Figures 6A and 6B are ion and electron images of the electronic component in Example 2 of the present invention, respectively. Figures 7A and 7B are respectively the ion and electron images of the focused ion beam of the electronic component of Example 3 of the present invention.

without.

13                 Nanocrystalline copper metal layer 13a               Upper surface 13b               Lower surface

Claims (17)

A nano-twin copper foil comprises: a plurality of twin crystal grains, wherein at least a portion of the plurality of twin crystal grains are formed by stacking a plurality of nano-twin crystals along the [111] crystal axis direction; wherein the nano-twin copper foil has a first surface and a second surface opposite to the first surface; and more than 80% of the area of the first surface and the second surface respectively expose the (111) surface of the nano-twin crystal; wherein the roughness of the first surface and the second surface is less than or equal to 20nm respectively. The nano-twin copper foil as described in claim 1, wherein more than 80% of the volume of the nano-twin copper foil comprises the plurality of twin crystal grains. The nano-twin copper foil as described in claim 2, wherein at least part of the plurality of twin crystal grains are columnar twin crystal grains. The nano-twin copper foil as described in claim 2, wherein the diameters of the plurality of twin crystal grains are respectively between 0.1 μm and 50 μm. The nano-twin copper foil as described in claim 2, wherein the thickness of the plurality of twin crystal grains is between 0.1 μm and 500 μm. The nano-twin copper foil as described in claim 2, wherein at least a portion of the plurality of twin crystal grains are interconnected. The nano-twin copper foil as described in claim 1, wherein the angle between the stacking direction of the plurality of nano-twins and the thickness direction of the nano-twin copper foil is between 0 degrees and 20 degrees. The nano-twin copper foil as described in claim 1, wherein the thickness of the nano-twin copper foil is between 10μm and 500μm. A method for preparing nano-twin copper foil comprises the following steps: Providing an electroplating device, comprising an anode, a cathode, an electroplating solution, and a power supply source, wherein the power supply source is connected to the anode and the cathode respectively, and the anode and the cathode are immersed in the electroplating solution; wherein the cathode comprises: a substrate; and a titanium tungsten contact layer disposed on the substrate, wherein the nano-twin copper A layer is formed on the titanium-tungsten contact layer; the power supply source is used to provide power for electroplating to form a nano-twin-crystal copper layer on the titanium-tungsten contact layer of the cathode; and the cathode is removed and a surface of the nano-twin-crystal copper layer is polished to obtain a nano-twin-crystal copper foil as described in any one of claims 1 to 8, wherein the surface is the surface of the nano-twin-crystal copper layer in contact with the cathode before the cathode is removed. The preparation method as described in claim 9, wherein the titanium-tungsten bonding layer comprises a titanium-tungsten alloy represented by the following formula (I): Ti _x W _100-x (I) wherein x is between 5 and 20. The preparation method as described in claim 9, wherein the thickness of the titanium tungsten bonding layer is between 100nm and 200nm. The preparation method as described in claim 9, wherein the substrate is a silicon substrate. The preparation method as described in claim 9 further includes a step of polishing the other surface of the nano-twin-crystal copper layer away from the cathode before removing the cathode. An electronic component comprises: a first substrate; a second substrate; and a bonding unit disposed between the first substrate and the second substrate, wherein the bonding unit is a nano-twin copper foil as described in any one of claims 1 to 8. The electronic component as described in claim 14, wherein the first substrate and the second substrate are respectively a metal substrate or a substrate with a metal layer formed thereon, wherein the material of the metal substrate or the metal layer includes at least one selected from the group consisting of copper, silver, gold, palladium, nickel and platinum. A method for preparing an electronic component includes the following steps: providing a first substrate and a second substrate; placing a bonding unit between the first substrate and the second substrate, and bonding the first substrate and the second substrate with the bonding unit to form an electronic component, wherein the bonding unit is a nano-twin copper foil as described in any one of claims 1 to 8. A preparation method as described in claim 16, wherein the first substrate and the second substrate are respectively a metal substrate or a substrate with a metal layer formed thereon, wherein the material of the metal substrate or the metal layer includes at least one selected from the group consisting of copper, silver, gold, palladium, nickel and platinum.