Preparation method of composite copper layer

Abstract

A composite copper layer and its preparation method are disclosed. The composite copper layer comprises bicrystalline copper grains and nanocrystalline copper grains. The bicrystalline copper grains and nanocrystalline copper grains are interspersed, which gives the composite copper layer an initial temperature. The composite copper layer is in a stable state with no substantial grain growth change at temperatures below the initial temperature. The initial temperature of the composite copper layer is determined by the volume percentage of the bicrystalline copper grains in the composite copper layer.

Description

Composite Copper Layer and Its Preparation Method The present invention relates to a composite copper layer and a method for preparing the same, and more particularly to a composite copper layer and a method for preparing the same, which determine the starting temperature of grain growth change of the composite copper layer according to the volume ratio of twin copper grains in the composite copper layer. Copper is often used in the fields of electricity, chemical industry, aerospace, etc. because of its good thermal conductivity, electrical conductivity, corrosion resistance and plasticity, which plays a crucial role in human life and work. Since coarse-grained pure copper has a high deformation ability but low strength. To improve the properties of copper, alloys are usually made by adding trace elements to increase its hardness and strength, but this will cause a significant decrease in the electrical conductivity of copper, thereby reducing the application of copper in the field of electricity. Moreover, the doping of a small amount of iron and nickel elements will affect the magnetism of copper, which is not conducive to the application in the manufacture of magnetic-sensitive devices such as compasses. In addition, the grain growth starting temperature of the copper film significantly affects the application of the copper film in various fields (such as the copper-copper metal bonding process). In particular, when the grain growth starting temperature of the copper film is lower than the process temperature, the copper film may exhibit an unstable state of grain growth before the process starts, making it difficult to control the process conditions, and thus resulting in a process effect that is not as expected. Therefore, how to effectively control the grain growth starting temperature of the copper film is one of the important issues for the application of the copper film in various fields. One object of the present invention is to provide a composite copper layer and a method for preparing the same, which can effectively control the grain growth starting temperature of the composite copper layer according to the process requirements, so that the composite copper layer has a relatively stable state before the process, and thus can achieve effective process condition control and the expected process effect. Another object of the present invention is to provide a composite copper layer and a method for preparing the same, which determine the starting temperature of grain growth by adjusting the volume percentage of twin copper grains in the composite copper layer, so that the composite copper layer is in a stable state with substantially no grain growth change at a temperature lower than the starting temperature, which is helpful for the application of the copper-copper metal bonding process. In one embodiment, the present invention provides a composite copper layer, which includes twin copper grains and nano copper grains. The twin copper grains and the nano copper grains are arranged in an interspersed manner, so that the composite copper layer has a starting temperature. The composite copper layer is in a stable state with substantially no grain growth change at a temperature lower than the starting temperature, wherein the starting temperature of the composite copper layer is determined according to the volume percentage of the twin copper grains in the composite copper layer. In one embodiment, the volume percentage of the twin copper grains in the composite copper layer is less than 1%, and the starting temperature is less than 50 degrees Celsius. In one embodiment, in the range where the volume percentage of the twin copper grains in the composite copper layer is 1% to 60%, the starting temperature increases with the increase of the volume percentage. In one embodiment, the volume percentage of twin copper grains in the composite copper layer is 10-20%, and the starting temperature is less than 100 degrees Celsius. In one embodiment, the volume percentage of twin copper grains in the composite copper layer is 30-45%, and the starting temperature is less than 200 degrees Celsius. In one embodiment, the composite copper layer is applied to a copper-copper metal bonding process. In another embodiment, the present invention provides a method for preparing a composite copper layer, comprising: using an electrolyte containing a copper chloride, an acid, and a water-soluble or alcohol-soluble organic additive, and depositing a composite copper layer containing twin copper grains and nano copper grains on the surface of a cathode by electrolytic deposition technology, with the twin copper grains and nano copper grains being interspersed, so that the composite copper layer has a starting temperature, and the composite copper layer is in a stable state with substantially no grain growth change at a temperature lower than the starting temperature, wherein the starting temperature of the composite copper layer is changed by adjusting the volume percentage of twin copper grains in the composite copper layer. In one embodiment, the volume percentage of twin copper grains in the composite copper layer is adjusted by adjusting the content of the water-soluble or alcohol-soluble organic additive. In one embodiment, the volume percentage of twin copper grains in the composite copper layer is adjusted to less than 1%, so that the starting temperature is less than 50 degrees Celsius. In one embodiment, the volume percentage of twin copper grains in the composite copper layer is adjusted to the range of 1% to 60%, so that the starting temperature increases with the increase of the volume percentage. In one embodiment, the volume percentage of twin copper grains in the composite copper layer is adjusted to 10-20%, so that the starting temperature is less than 100 degrees Celsius. In one embodiment, the volume percentage of twin copper grains in the composite copper layer is adjusted to 30-45%, so that the starting temperature is less than 200 degrees Celsius. In one embodiment, the electrolysis conditions include a current density of 20-100 mA / cm 2 , a cell voltage of 0.2-3 V, and a distance between the cathode and the anode of 10-300 mm. Compared with the prior art, the composite copper layer and its preparation method of the present invention determine (change) the starting temperature of grain growth by adjusting the volume percentage of twin copper grains in the composite copper layer, so that the composite copper layer is in a stable state with substantially no grain growth change at a temperature lower than the starting temperature, and thus the starting temperature of grain growth of the composite copper layer can be effectively controlled according to the process requirements, so that the composite copper layer has a more stable state before the process, in order to achieve effective process control and expected process effects. In the accompanying drawings, for clarity, the thicknesses of layers, films, panels, regions, etc. are exaggerated. Throughout the specification, like reference numerals denote like elements. It should be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" or "connected to" another element, it can be directly on or connected to the other element, or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element, no intervening elements are present. As used herein, "connected" can refer to physical and / or electrical connection. Further, "electrically connected" or "coupled" can mean that other elements exist between two elements. In addition, relative terms such as "lower" or "bottom" and "upper" or "top" may be used herein to describe the relationship of one element to another element, as shown in the figures. It should be understood that the relative terms are intended to encompass different orientations of the device in addition to the orientation shown in the figures. For example, if the device in one figure is flipped, an element described as being on the "lower" side of another element will be oriented on the "upper" side of the other element. Thus, the exemplary term "lower" can include both the "lower" and "upper" orientations, depending on the specific orientation of the figure. Similarly, if the device in one figure is flipped, an element described as being "beneath" or "below" another element will be oriented as being "above" the other element. Thus, the exemplary terms "beneath" or "below" can include both above and below orientations. As used herein, "about", "approximately", or "substantially" includes the stated value and an average within an acceptable deviation range of a particular value determined by one of ordinary skill in the art, taking into account the particular quantities of the measurements discussed and the errors associated with the measurements (i.e., the limitations of the measurement system). For example, "about" can mean within one or more standard deviations of the stated value, or within ±30%, ±20%, ±10%, ±5%. Further, "about", "approximately", or "substantially" as used herein can be selected with a more acceptable deviation range or standard deviation depending on optical, chemical, physical, or other properties, rather than using one standard deviation for all properties. FIG. 1 is a schematic diagram showing the relationship between the annealing temperature and the resistance change of the composite copper layer according to various embodiments of the present invention, where the horizontal axis represents the temperature (°C) and the vertical axis represents the resistance change (R / R0). R0 represents the reference resistance of the composite copper layer obtained at room temperature, and R represents the measured resistance of the composite copper layer obtained at different temperatures. Furthermore, the change in grains affects the change in resistance. For example, when the resistance value starts to decrease, it means that the grains start to grow and become larger. Therefore, by observing the resistance change, the starting temperature of the grain growth corresponding to the composite copper layer of each embodiment can be obtained. Furthermore, in the embodiment, "the resistance value starts to decrease" can be expressed as the resistance change (R / R0) reaching a preset value and starting to decline. The preset value is preferably in the range of, for example, 1 to 0.95. Before the resistance change reaches the preset value, it means that the composite copper layer is in a stable state with substantially no grain growth change. Even if there may be some slight grain growth changes, the growth changes are due to negligible or measurement errors. Therefore, the starting temperature of the grain growth corresponding to the composite copper layer is the temperature corresponding to the resistance change (such as R / R0) reaching the preset value. That is, the composite copper layer at a temperature lower than the starting temperature can be regarded as a stable state with substantially no grain growth change. As shown in FIG. 1, in the composite copper layer of Example 1, the volume percentage of twin copper grains in the composite copper layer is less than 1%, and the starting temperature of the grain growth of the composite copper layer is less than 50 degrees Celsius, for example, about 30 degrees Celsius. In other words, the composite copper layer of Example 1 has a very large volume fraction of nano-copper grains (such as a volume percentage greater than 99%), so it is relatively unstable at high temperatures, and the temperature effect must be considered in the high-temperature process. In the composite copper layer of Example 2, the volume percentage of twin copper grains in the composite copper layer is 10-20%, and the starting temperature of the grain growth of the composite copper layer is less than 100 degrees Celsius. In Example 2, as the volume percentage of twin copper grains in the composite copper layer increases, the starting temperature of the grain growth of the composite copper layer of Example 2 is greater than or equal to the starting temperature of the grain growth of the composite copper layer of Example 1 (such as greater than or equal to 50 degrees Celsius). In the composite copper layer of Example 3, the volume percentage of twin copper grains in the composite copper layer is 30-45%, and the starting temperature of the grain growth of the composite copper layer is less than 200 degrees Celsius. Due to the increase in the volume percentage of twin copper grains in the composite copper layer, the starting temperature of the grain growth of the composite copper layer of Example 3 is greater than or equal to the starting temperature of the grain growth of the composite copper layer of Example 2 (such as greater than or equal to 100 degrees Celsius). In the composite copper layer of Example 4, the volume percentage of twin copper grains in the composite copper layer is greater than 60%, and the starting temperature of the grain growth of the composite copper layer is greater than (or equal to) 400 degrees Celsius. As can be seen from FIG. 1, by adjusting the volume percentage of twin copper grains in the composite copper layer, the starting temperature of grain growth in the composite copper layer can be adjusted, which is beneficial for the application of the composite copper layer in the copper-copper metal bonding process. Specifically, in the range where the volume percentage of twin copper grains in the composite copper layer is 1% to 60%, the starting temperature increases with the increase in the volume percentage of twin copper grains. Thereby, according to the process requirements, a composite copper layer with an appropriate volume percentage of twin copper grains in the composite copper layer can be applied, so that the composite copper layer has a better starting temperature to meet the process requirements, which helps to achieve process control and the expected process effects. Furthermore, as shown in Example 4, when the volume percentage of twin copper grains in the composite copper layer is greater than 60%, the resistance change of the composite copper layer is not significant with the increase in temperature, which means that the composite copper layer is quite stable even at a high temperature of 400 °C and is suitable for high-temperature processes. FIGS. 2 to 4 show schematic diagrams of the structural changes of the composite copper layer of different embodiments of the present invention at different annealing temperatures. Among them, in FIG. 2, since the volume percentage of twin copper grains in the composite copper layer 501 is less than 1%, twin copper grains are not marked in FIG. 2, and only nano copper grains 200 are marked. As shown in FIG. 2, corresponding to Example 1 in FIG. 1, the composite copper layer 501 represents a structure with a volume percentage of twin copper grains in the composite copper layer 501 less than 1%, and its starting temperature is less than 50 °C. Specifically, since the starting temperature of the composite copper layer 501 is less than 50 °C (for example, about 30 °C), the composite copper layer 501 can perform self-annealing within several hours, and the grains grow into grown grains 300. As shown in FIG. 3, corresponding to Example 3 in FIG. 1, the composite copper layer 502 represents a structure with a volume percentage of twin copper grains 100 in the composite copper layer 502 of 30-45%, and its starting temperature is less than 200 °C. Specifically, since the starting temperature of the composite copper layer 502 is less than 200 °C and greater than 100 °C, the composite copper layer 502 is in a stable state with substantially no grain growth change when annealed at 100 °C. However, when annealed at 200 °C, the grains of the composite copper layer 502 grow (i.e., the twin copper grains 100 and / or nano copper grains 200 are joined to each other) into grown grains 300. As shown in FIG. 4, corresponding to Example 4 in FIG. 1, the composite copper layer 503 represents a structure with a volume percentage of twin copper grains 100 in the composite copper layer 503 greater than 60%, and its starting temperature is greater than 400 °C. Specifically, since the starting temperature of the composite copper layer 503 is greater than 400 °C, the composite copper layer 503 is in a stable state with substantially no grain growth change when annealed at 200 °C, and is still in a stable state with substantially no grain growth change when annealed at 400 °C. In the above embodiments, the composite copper layer provided by the present invention (such as the composite copper layers 501, 502, or 503 in FIGS. 2 to 4) includes twin copper grains 100 and nano copper grains 200. The twin copper grains 100 and the nano copper grains 200 are arranged in an interspersed manner, such that the composite copper layers 501, 502, or 503 have corresponding starting temperatures, and the composite copper layers 501, 502, or 503 are in a stable state with substantially no grain growth change at temperatures lower than the starting temperature. The starting temperature of the composite copper layers 501, 502, or 503 can be determined (changed) according to the volume percentage of the twin copper grains 100 occupying the composite copper layers 501, 502, or 503. In one embodiment, a method for preparing a composite copper layer of the present invention includes: using an electrolytic solution containing a copper chloride, an acid, and a water-soluble or alcohol-soluble organic additive, and depositing a composite copper layer containing twin copper grains and nano copper grains on the surface of a cathode by electrolytic deposition technology. The twin copper grains and the nano copper grains are arranged in an interspersed manner, such that the composite copper layer has a starting temperature, and the composite copper layer is in a stable state with substantially no grain growth change at temperatures lower than the starting temperature, wherein the starting temperature of the composite copper layer is changed by adjusting the volume percentage of the twin copper grains occupying the composite copper layer. FIG. 5 is a schematic diagram of an electrolytic deposition apparatus used in a method for preparing a composite copper layer according to an embodiment of the present invention. As shown in FIG. 5, the electrolytic deposition apparatus 1 includes an electrolytic cell 10, a cathode 20, an anode 30, and a current supply source 40. The cathode 20 and the anode 30 are spaced apart and disposed in the electrolytic cell 10, and the current supply source 40 is electrically connected to the cathode 20 and the anode 30 to supply the electric power required for the reaction. In one embodiment, the anode 30 is preferably, for example, a copper plate with a purity higher than 99.99%, but is not limited thereto. In other embodiments, the anode 30 can be other metal materials, such as phosphor bronze, and other insoluble anodes, such as a titanium metal plate and a titanium metal plate coated with iridium dioxide. The surface 22 of the cathode 20 is preferably a suitable surface on which a copper film is to be deposited, such as the surface of a semiconductor in a semiconductor process (such as the surface of a silicon wafer), the surface of a metal material (such as the surface of a titanium sheet, an iron sheet, a nickel sheet, or a pure copper sheet), or the surface of a metal layer or a seed layer on a non-metal substrate (such as a glass substrate, a quartz substrate, a plastic substrate, or a printed circuit board), or the surface of a substrate having a crystal orientation. The electrolytic solution 50 used in the present invention is injected into the electrolytic cell 10 to contact the cathode 20 and the anode 30. In one embodiment, the acid in the electrolyte 50 can be sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, sulfonic acid, or a mixture thereof. The copper chloride contained in the electrolyte 50 is preferably copper sulfate, and the concentration of copper sulfate in the electrolyte 50 is about 0.3 mol / L or more. The water-soluble or alcohol-soluble organic additive in the electrolyte 50 can be a cellulose-based organic additive, and its molecular weight is preferably between 500 and 100,000 and can include cellulose, hemicellulose, carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, ethyl cellulose, propyl cellulose. The content of the cellulose-based organic additive is preferably 0.01 grams per liter (g / L) or more, more preferably 0.01 g / L to 1 g / L, but not limited thereto. According to actual needs, the preparation method of the present invention can adjust the volume percentage of twin copper grains in the composite copper layer by adjusting the content of the water-soluble or alcohol-soluble organic additive, so that the composite copper layer has a corresponding grain growth starting temperature. For example, the content of the cellulose-based organic additive can also be 1 g / L or more. Furthermore, the conditions of electrolytic deposition can be, for example, a current density of 20 to 100 mA / cm 2 , a cell voltage of 0.2 to 3 V, and an electrolyte temperature of 15 to 30 °C under the condition that the distance between the cathode and the anode is 10 to 300 mm. For example, when using an insoluble anode, a higher cell voltage can be used. A composite copper layer containing twin copper grains and nano copper grains is deposited on the surface of the cathode by electrolytic deposition technology, and the volume percentage of twin copper grains in the composite copper layer is preferably adjusted to the range of 1% to 60%, so that the starting temperature increases with the increase of the volume percentage of twin copper grains. Preparation of Examples 1 to 4 In the preparation of Example 1, the copper sulfate content in the electrolyte 50 is, for example, 60 to 80 grams of copper sulfate per liter (i.e., 60~80g CuSO 4 / L). The electrolyte 50 may further contain an inhibitor and an accelerator. For example, the content of the inhibitor is 30 ml / L, and the content of the accelerator is 6 ml / L. The inhibitor contains a water-soluble or alcohol-soluble organic additive, which is a cellulose organic additive, and its content is 0.3 g / L. Thereby, the volume percentage of twin copper grains in the formed composite copper layer is less than 1%, and the grain growth initiation temperature of the composite copper layer is less than 50 degrees Celsius. In addition, in this embodiment, on the surface of the composite copper layer, the surface percentage of twin copper grains in the composite copper layer is, for example, less than 1%. It should be noted here that the inhibitor inhibits the growth of copper grains during the electroplating process to achieve a suitable crystal growth rate and a specific crystal structure. For example, when there is a need for filling holes, an inhibitor is required; while the accelerator accelerates the growth of copper grains, which can significantly increase the nano copper grains. For example, an accelerator can be used to increase the flatness of the copper surface. The entire system can be adjusted with both the inhibitor and the accelerator. In the preparation of Example 2, the copper sulfate content of the electrolyte 50 is, for example, 60 to 80 grams of copper sulfate per liter (i.e., 60~80g Cu SO 4 / L). The electrolyte 50 may further contain an inhibitor and an accelerator. For example, the content of the inhibitor is 30 ml / L, and the content of the accelerator is 3 ml / L. The inhibitor contains a water-soluble or alcohol-soluble organic additive, which is a cellulose organic additive, and its content is 0.5 g / L. Thereby, the volume percentage of twin copper grains in the formed composite copper layer is 10~20%, and the grain growth initiation temperature of the composite copper layer is less than 100 degrees Celsius and greater than or equal to 50 degrees Celsius. In addition, in this embodiment, on the surface of the composite copper layer, the surface percentage of twin copper grains in the composite copper layer is, for example, 5~10%. In the preparation of Example 3, the copper sulfate content of the electrolyte 50 is, for example, 60 to 80 grams of copper sulfate per liter (i.e., 60~80g Cu SO 4 / L). The electrolyte 50 may further contain an inhibitor. For example, the content of the inhibitor is 30 ml / L, and the inhibitor contains a water-soluble or alcohol-soluble organic additive, which is a cellulose organic additive, and its content is 0.5 g / L. Thereby, the volume percentage of twin copper grains in the formed composite copper layer is 30-45% of the volume of the composite copper layer, so that the initial grain growth temperature of the composite copper layer is less than 200 °C and greater than or equal to 100 °C. In addition, in this embodiment, on the surface of the composite copper layer, the surface percentage of twin copper grains occupying the composite copper layer is, for example, 20-30%. It should be noted here that the accelerator essentially affects the growth of twin copper. To grow a certain proportion or a high proportion of twin copper, there is no need to add an accelerator, and obvious twin copper grains begin to appear inside the copper structure. Therefore, in this Example 3, although the usage amount of the inhibitor and the content of its water-soluble or alcohol-soluble organic additive are the same as those in Example 2, since no accelerator is used, the volume percentage of twin copper grains in the formed composite copper layer relative to the volume of the composite copper layer increases. In the preparation of Example 4, the copper sulfate content of the electrolyte 50 is, for example, 60 grams of copper sulfate per liter (i.e., 60 g Cu SO 4 / L). The electrolyte 50 may further contain an inhibitor. For example, the content of the inhibitor is 30 ml / L, and the inhibitor contains a water-soluble or alcohol-soluble organic additive, which is a cellulose organic additive, and its content is 0.6 g / L. Thereby, the volume percentage of twin copper grains in the formed composite copper layer is greater than 60% of the volume of the composite copper layer, so that the initial grain growth temperature of the composite copper layer is greater than (or equal to) 400 °C. In addition, in this embodiment, on the surface of the composite copper layer, the surface percentage of twin copper grains 100 occupying the composite copper layer is, for example, 50-70%. It should be noted here that in the above embodiments, the "volume percentage of twin copper grains in the composite copper layer" can also be expressed by the cross-sectional ratio of twin copper grains in the cross-section of the composite copper layer. For example, it is expressed as the volume percentage of twin copper grains in the composite copper layer by the cross-sectional ratio or average cross-sectional ratio of twin copper grains in one or several cross-sections. Compared with the prior art, the composite copper layer and its preparation method of the present invention determine (change) the initial grain growth temperature by adjusting the volume percentage of twin copper grains in the composite copper layer, so that the composite copper layer is in a stable state with substantially no grain growth change at a temperature lower than the initial temperature. Furthermore, the initial grain growth temperature of the composite copper layer can be effectively controlled according to the process requirements, so that the composite copper layer has a more stable state before the process, in order to achieve effective process control and the expected process effect. The present invention has been described by the above embodiments. However, the above embodiments are for illustrative purposes only and not for limitation. Those skilled in the art will know that without departing from the spirit of the present invention, other modifications of the illustrative embodiments may be made to the embodiments specifically described herein. Therefore, the scope of the present invention also covers such modifications and is limited only by the appended patent claims. 1: Electrolytic deposition device 10: Electrolytic cell 20: Cathode 22: Surface 30: Anode 40: Current supply source 50: Electrolyte 100: Twin copper grains 200 nm copper grains 300 Growing grains 501, 502, 503: Composite copper layer FIG. 1 is a schematic diagram showing the relationship between the annealing temperature and the resistance change of the composite copper layer of various embodiments of the present invention. FIGS. 2 to 4 show schematic diagrams of the structural changes of the composite copper layer of different embodiments of the present invention at different annealing temperatures. FIG. 5 is a schematic diagram of an electrolytic deposition device used in the preparation method of a composite copper layer according to an embodiment of the present invention.

Claims

1. A method for preparing a composite copper layer, comprising: depositing a composite copper layer comprising bicrystalline copper grains and nano-copper grains on the surface of a cathode using an electrolyte containing a copper salt, an acid, and a water-soluble or alcohol-soluble organic additive, wherein the bicrystalline copper grains and the nano-copper grains are interspersed, such that the composite copper layer has an initial temperature, and the composite copper layer is in a stable state with substantially no grain growth change at temperatures below the initial temperature, wherein the initial temperature of the composite copper layer is changed by adjusting the volume percentage of the bicrystalline copper grains in the composite copper layer, wherein the volume percentage of the bicrystalline copper grains in the composite copper layer is adjusted to be between 1% and 60%. When the volume percentage of the bicrystalline copper grains in the composite copper layer is less than 1%, the initial temperature is less than 50 degrees Celsius; when the volume percentage is 10-20%, the initial temperature is less than 100 degrees Celsius; when the volume percentage is 30-45%, the initial temperature is less than 200 degrees Celsius; and when the volume percentage is greater than 60%, the initial temperature is greater than or equal to 400 degrees Celsius. The electrolysis conditions include a current density of 20~100 mA / cm2, a cell voltage of 0.2~3 V, and a cathode-anode distance of 10~300 mm. The acid in the electrolyte is sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, sulfonic acid, or a mixture thereof. The copper salt in the electrolyte is copper sulfate, and the concentration of copper sulfate in the electrolyte is above 0.3 mol / L. The water-soluble or alcohol-soluble organic additives in the electrolyte are cellulose-based organic additives with a molecular weight between 500 and 100,000, including cellulose, hemicellulose, carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose, methylcellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, ethyl cellulose, and propyl cellulose.

2. The method for preparing the composite copper layer as described in claim 1, wherein the volume percentage of the bicrystalline copper grains occupying the composite copper layer is adjusted by adjusting the content of the water-soluble or alcohol-soluble organic additive.

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