TWM668127U - A bonding structure - Google Patents

Abstract

A bonding structure is provided. The bonding structure includes a first substrate; a first nano-twinned layer on the first substrate; and a second substrate on the first nano-twinned layer. In a cross-sectional view of the bonding structure, a first region of at least 1 μm proximate an upper surface of the first nano-twinned layer includes a first parallel-arranged twin boundary, and the first parallel-arranged twin boundary includes 50% or more [111] crystal orientation.

Description

Joint structure

The present disclosure relates to a bonding structure, and in particular to a bonding structure having a nanocrystalline layer.

Copper has high thermal and electrical conductivity, while stainless steel has excellent corrosion resistance. The cost of 304 Austenitic stainless steel is much lower than that of 316 stainless steel. Heterogeneous welding of copper and stainless steel can produce structural parts that require both thermal conductivity and corrosion resistance, which can give full play to the advantages of the above two materials. In the past, it has been widely used in high-calorie accelerator cooling systems and liquid-cooled heat exchangers. In recent years, it has also been widely used in solar thermal absorbers.

However, the traditional method of welding copper and stainless steel requires high temperatures above 600℃ or even up to 950℃. Due to the large difference in the expansion coefficients of copper and stainless steel, the workpiece will produce high thermal stress after the welding, causing deformation and even damage to the entire module. For example: arc welding of copper and stainless steel is prone to thermal cracking; sub arc welding will cause cracks and pores; TIG (tungsten inert gas) welding will also cause copper penetration cracks. In other words, it is very difficult to use traditional fusion welding technology for heterogeneous welding of copper and stainless steel. When using traditional silver (Ag)-copper (Cu) or gold (Au)-copper (Cu) alloy fillers to vacuum braze copper and stainless steel, the welding temperature is as high as 900℃ or above. Due to the large difference in thermal expansion coefficients between copper and stainless steel, the joint interface position and gap of the workpiece will move during and after the brazing process, resulting in poor welding yield. In recent years, attempts have been made to use solid diffusion bonding methods to heterogeneously weld copper and stainless steel. The bonding temperature is about 850℃ to 950℃, which is close to the melting point of copper at 1100℃, causing copper to penetrate into the grain boundaries of stainless steel, causing brittle fracture of the grain boundaries. Patents US4194672 and CN1197682C respectively add nickel (Ni) and chromium (Cr) alloy barrier layers between copper and stainless steel to perform solid diffusion bonding to reduce the grain boundary penetration of copper into stainless steel. The bonding temperature is also higher than 800°C. When the bonding is completed and the temperature drops to room temperature, the difference in thermal expansion coefficients between copper and stainless steel can easily cause cracks in the bonding interface.

Considering the above problems, existing heterogeneous bonding technology still faces many challenges.

In order to overcome the material damage phenomenon of the various high-temperature welding technologies known above applied to the heterogeneous bonding of copper and stainless steel. The disclosed embodiment can form a heterogeneous bonding structure of copper and stainless steel at a low temperature by utilizing the high diffusion rate characteristics of the nanocrystalline layer.

The joint structure provided by the disclosed embodiment can be applied to, for example, electric vehicle energy storage systems or liquid cooling heat dissipation elements of AI servers.

In some embodiments, the present disclosure provides a bonding structure. The bonding structure includes: a first substrate; a first nanocrystalline layer on the first substrate; and a second substrate on the first nanocrystalline layer. In a cross-sectional view of the bonding structure, a first region of at least 1 micron close to the upper surface of the first nanocrystalline layer includes a first parallel twin grain boundary, and the first parallel twin grain boundary has a [111] crystal orientation of more than 50%.

In some embodiments, a distance between the first parallel twin grain boundaries is 1 nm to 100 nm.

In some embodiments, a first transition grain layer is further included between the first substrate and the first nano-twin crystal layer, wherein the first transition grain layer includes more than 10% annealed twin crystals, and the annealed twin crystal spacing of the first transition grain layer is greater than 100 nanometers.

In some embodiments, the first parallel twin grain boundaries in the first region on the first transition grain layer are a continuous structure or include multiple separated parts.

In some embodiments, a second nanocrystalline layer is further included between the first nanocrystalline layer and the second substrate, and the second nanocrystalline layer includes silver, copper, or a silver-copper alloy.

In some embodiments, a second region of at least 1 micron close to the upper surface of the second nanocrystalline twin layer includes second parallel twin grain boundaries, the second parallel twin grain boundaries have more than 50% [111] crystal orientation, and the spacing between the second parallel twin grain boundaries is 1 nanometer to 100 nanometers.

In some embodiments, a second transition grain layer is further included between the second substrate and the second nano-twin crystal layer, wherein the second transition grain layer includes more than 10% annealed twin crystals, and the annealed twin crystal spacing of the second transition grain layer is greater than 100 nanometers.

In some embodiments, an adhesive layer is further included between the second substrate and the second nanocrystalline layer, and the adhesive layer includes titanium, chromium, tungsten, titanium-tungsten or a combination thereof.

In some embodiments, the first substrate includes copper or a copper-based alloy.

In some embodiments, the second substrate includes SAE430 (Fe-18Cr) stainless steel, SAE304 (Fe-18Cr-8Ni) stainless steel, SAE316 (Fe-18Cr-8Ni-3Mo) stainless steel, or other suitable iron-based stainless steel.

In some embodiments, the first nanocrystalline layer includes silver, copper, or a silver-copper alloy.

In some embodiments, an adhesive layer is further included between the first substrate and the first nanocrystalline layer, and the adhesive layer includes titanium, chromium, tungsten, titanium-tungsten or a combination thereof.

In other embodiments, the present disclosure provides a bonding structure. The bonding structure includes: a first substrate; an equiaxed grain layer on the first substrate; and a second substrate on the equiaxed grain layer. The equiaxed grain layer includes more than 10% annealed twin crystals, and the annealed twin crystal spacing of the equiaxed grain layer is greater than 100 nanometers.

In other embodiments, the first substrate includes copper or a copper-based alloy.

In other embodiments, the second substrate includes SAE430 (Fe-18Cr) stainless steel, SAE304 (Fe-18Cr-8Ni) stainless steel, SAE316 (Fe-18Cr-8Ni-3Mo) stainless steel or other suitable iron-based stainless steel.

10: Substrate

10’: Substrate

12: Adhesive layer

12’: Adhesive layer

14: Nanocrystalline layer

14’: Nanocrystalline layer

16: Nanocrystalline columns

16’: Nanocrystalline columns

22: Transition grain layer

22’: Transition grain layer

24: Annealing twin crystals

24’: Annealing twin crystals

26: Equiaxed grain layer

R: Region

R’: Region

The following will be described in detail with the attached drawings in various aspects of the present disclosure. It should be noted that, in accordance with standard practices in the industry, various features are not drawn to scale and are only used for illustration. In fact, the size of the components can be arbitrarily enlarged or reduced to clearly show the features of the embodiments of the present disclosure. It should also be noted that the attached drawings only illustrate typical embodiments of the present disclosure and should not be considered as limiting its scope. The present disclosure can also be applied to other embodiments.

According to some embodiments, FIG. 1 shows a schematic cross-sectional view of a substrate.

According to some embodiments, FIG. 2 shows a schematic cross-sectional view of a substrate having a nanocrystalline layer.

According to some embodiments, FIG. 3 shows a schematic cross-sectional view of a substrate having an adhesive layer and a nanocrystalline layer.

According to some embodiments, FIG. 4 shows a schematic cross-sectional view of the substrate.

According to some embodiments, FIG. 5 shows a schematic cross-sectional view of a substrate having a nanocrystalline layer.

According to some embodiments, FIG. 6 shows a schematic cross-sectional view of a substrate having an adhesive layer and a nanocrystalline layer.

According to some embodiments, FIGS. 7A to 7C illustrate schematic cross-sectional views of forming a bonding structure at different stages, wherein an adhesive layer is not formed during the bonding process.

According to some embodiments, FIGS. 8A to 8C show schematic cross-sectional views of forming a bonding structure at different stages, wherein an adhesive layer is additionally formed during the bonding process.

According to some embodiments, FIGS. 9A to 9C show schematic cross-sectional views of forming a bonding structure at different stages, wherein an adhesive layer is not formed during the bonding process.

According to some embodiments, FIGS. 10A to 10C show schematic cross-sectional views of forming a bonding structure at different stages, wherein an adhesive layer is additionally formed during the bonding process.

According to some embodiments, FIGS. 11A to 11C show schematic cross-sectional views of forming a bonding structure at different stages, wherein an adhesive layer is not formed during the bonding process.

According to some embodiments, FIGS. 12A to 12C show schematic cross-sectional views of forming a bonding structure at different stages, wherein an adhesive layer is additionally formed during the bonding process.

According to some embodiments, FIGS. 13A to 13C show schematic cross-sectional views of forming a bonding structure at different stages, wherein an adhesive layer is additionally formed during the bonding process.

According to some embodiments, FIGS. 14A to 14C show schematic cross-sectional views of forming a bonding structure at different stages, wherein an adhesive layer is additionally formed during the bonding process.

According to some embodiments, FIG. 15 is a photograph of a bonding structure of copper and stainless steel having a titanium adhesive layer and a silver nanocrystalline layer.

According to some embodiments, FIG. 16 is a photograph of a bonding structure of copper and stainless steel having a titanium adhesive layer and a copper nanocrystal layer.

Some embodiments or examples of the present disclosure are provided below for implementing different elements of the subject matter provided. Specific examples of each element and its configuration are described below to simply and clearly describe the disclosed embodiments. Of course, these are only examples and are not intended to limit the disclosed embodiments. For example, if the description refers to a first element formed on a second element, it may include an embodiment in which the first and second elements are directly in contact, and it may also include an embodiment in which an additional element is formed between the first and second elements so that they are not directly in contact. In addition, the disclosed embodiments may repeat reference numbers and/or letters in various examples. Such repetition is for the purpose of simplicity and clarity, and is not used to indicate the relationship between the different embodiments and/or configurations discussed.

In addition, spatially relative terms such as "under", "below", "lower", "above", "higher" and the like may be used to facilitate the description of the relationship between one (or more) parts or features and another (or more) parts or features in the diagram. Spatially relative terms are used to include different orientations of the device in use or operation, as well as the orientations described in the diagram. When the device is turned to a different orientation (rotated 90 degrees or other orientations), the spatially relative adjectives used will also be interpreted according to the orientation after the rotation.

The ordinal numbers used in this disclosure, such as "first", "second", "third", etc., are used to modify the components. They do not represent any previous ordinal numbers of the component (or components), nor do they represent the order of one component to another component, or the order of the manufacturing method. The use of these ordinal numbers is only used to make a component with a name clearly distinguishable from another component with the same name. Different terms may be used in the claim and the specification. For example, the first component in the specification may be the second component in the claim.

In this disclosure, the terms "about" and "substantially" generally mean within 10%, within 5%, within 3%, within 2%, within 1%, or within 0.5% of a given value or range. The term "ranging from a first value to a second value" means that the range includes the first value, the second value, and other values between them. For example, the term "about 5 nm (nanometer)" can cover a size range from 4.5 nm to 5.5 nm.

Some embodiments of the present disclosure are described below. Additional steps or operations may be provided before, during and/or after the steps or operations described in these embodiments. Some of the steps or operations may be replaced or deleted in different embodiments. In addition, it should be understood that the following embodiments may replace, combine, or reorganize the features of several different embodiments to complete other embodiments without departing from the spirit of the present disclosure. The features of the embodiments may be arbitrarily recombined and used as long as they do not violate the spirit of the present disclosure or conflict with each other.

Some embodiments of the present disclosure provide a bonding structure and a method for forming the same, including a bonding process using a nano-twin crystal layer. Due to the characteristics of the twin crystal structure, atoms have a higher diffusion ability, so that the present disclosure can perform a bonding process at a temperature of 100°C to 400°C to avoid degradation of the bonding structure caused by high temperature. In addition, some other embodiments of the present disclosure can additionally form an adhesive layer on the substrate. The adhesive layer can provide a better bonding force between the substrate and the nano-twin crystal layer to avoid peeling, and the adhesive layer can reduce the influence of the crystal orientation of the substrate on the nano-twin crystal layer.

Referring to FIG. 1 , a first substrate 10 is provided. In some embodiments, the first substrate 10 may include copper, a copper-based alloy, or a combination thereof.

Referring to FIG. 2 , a first nano-twin crystal layer 14 is formed on a first substrate 10. In some embodiments, the first nano-twin crystal layer 14 includes silver, copper, or a silver-copper alloy. In some embodiments, the first nano-twin crystal layer 14 includes first parallel twin grain boundaries (Σ3+Σ9) at the nanoscale. In the cross-sectional view, using electron backscatter diffraction (EBSD) analysis, the first parallel twin grain boundaries of at least 1 micron in the first region R close to the upper surface of the first nano-twin crystal layer 14 have a [111] crystal orientation of more than 50%. In some embodiments, the nano-twin crystal spacing of the first parallel twin grain boundaries can be 1 nm to 100 nm, for example, 2 nm to 50 nm. In some embodiments, the first nanocrystalline layer 14 includes parallel stacked first nanocrystalline columns 16. The diameter of the first nanocrystalline columns 16 may be 0.1 micrometers to 10 micrometers, for example, 0.3 micrometers to 1.0 micrometers.

Continuing with reference to FIG. 2, in some embodiments, a first transition grain layer 22 is further included between the first substrate 10 and the first nano-twin crystal layer 14. When the first nano-twin crystal layer 14 is initially formed on the first substrate 10, the first nano-twin crystal layer 14 having the first parallel twin grain boundary is not immediately formed, but a first transition grain layer 22 without the first parallel twin grain boundary is formed. In some embodiments, the first transition grain layer 22 includes more than 10% of annealed twin crystals 24, and the annealed twin crystal spacing of the first transition grain layer 22 is greater than 100 nanometers. In some embodiments, the first parallel twin grain boundary of the first region R on the first transition grain layer 22 is a continuous structure or includes a plurality of separated parts. For example, in FIG. 2, the first parallel twin grain boundary may cover the entire top surface of the structure shown (i.e., the first parallel twin grain boundary is a continuous structure) and has a [111] crystal orientation of more than 50%. Alternatively, in FIG. 2, the first parallel twin grain boundary may include a plurality of separated island-like portions at the top surface of the structure shown (i.e., the first parallel twin grain boundary includes a plurality of separated portions) and has a [111] crystal orientation of more than 50%.

In some embodiments, the first nanocrystalline layer 14 can be formed on the first substrate 10 by electroplating, sputtering or evaporation.

In some embodiments, sputter plating adopts single-gun sputter plating or multi-gun co-plating. The sputter plating power source can use, for example, DC, DC plus, RF, high-power impulse magnetron sputtering (HIPIMS), etc. The sputtering power of the first nanocrystalline layer 14 can be, for example, about 100W to about 500W. The temperature of the sputtering process is room temperature. The temperature of the sputtering process will rise by about 50°C to about 200°C. The background pressure of the sputtering process is less than 1× ^10-5 torr, and the working pressure can be, for example, about 1× ^10-3 torr to 1× ^10-2 torr. The argon flow rate is about 10sccm to about 20sccm. The rotation speed of the carrier can be, for example, about 5 rpm to about 20 rpm. During the sputtering process, the substrate is biased at about -100 V to about -200 V. The deposition rate of the first nanocrystalline layer 14 can be, for example, 0.5 nm/s to about 3 nm/s. It should be understood that the above-mentioned sputtering process parameters can be appropriately adjusted according to actual applications, and the present disclosure is not limited thereto.

In some embodiments, the background pressure of the evaporation process is less than 1×10 ^-5 torr, and the working pressure can be, for example, about 1×10 ^-4 torr to about 5×10 ^-4 torr. The argon flow rate is about 2 sccm to about 10 sccm. The carrier rotation speed can be, for example, about 5 rpm to about 20 rpm. The deposition rate of the first nanocrystalline layer 14 can be, for example, about 1 nm/s to about 5.0 nm/s. Additionally, during the evaporation process, ion impact can be applied to the first nanocrystalline layer 14, with a voltage of about 10 V to about 300 V and a current of about 0.1 A to about 1.0 A. It should be understood that the above-mentioned evaporation process parameters can be appropriately adjusted according to the actual application, and the present disclosure is not limited thereto.

The formation of twin crystal structure is due to the accumulated strain energy inside the material driving the atoms in some areas to uniformly shear to form a lattice position that is mirror-symmetrical with the unsheared atoms in the grain where they are located. The mutually symmetrical interface is the twin boundary.

Twin crystals mainly occur in face centered cubic (FCC) or hexagonal closed-packed (HCP) crystal materials with the most compact lattice arrangement. In addition to the most compact lattice arrangement crystal structure conditions, the smaller the stacking fault energy, the easier it is to produce twin crystals. For example, although aluminum is a face centered cubic crystal structure material, its stacking fault energy is relatively large, so twin crystals rarely appear. The stacking fault energy of silver is about 25mJ/ ^m2 , and the stacking fault energy of copper is about 70 mJ/ ^m2 . Therefore, compared with aluminum, silver and copper are more likely to form twin crystals.

Twin grain boundaries are coherent crystal structures and belong to the low-energy Σ3 and Σ9 special grain boundaries. The crystal orientation is the {111} plane. Compared with the high-angle grain boundaries formed by general annealing and recrystallization, the interface energy of twin grain boundaries is about 5% of that of general high-angle grain boundaries (please refer to: George E. Dieter, Mechanical Metallurgy, McGraw-HILL Book Company, 1976, P.135-141).

Due to the low interfacial energy of the twin grain boundary, it can avoid becoming a path for oxidation, sulfidation and chlorine ion corrosion, so it exhibits better oxidation resistance and corrosion resistance. In addition, the symmetrical lattice arrangement of this twin crystal has less resistance to electron transmission, so it exhibits better conductivity and thermal conductivity. Because the twin grain boundary blocks the movement of dislocations, the material can still maintain high strength. This characteristic of both high strength and high conductivity has been confirmed in copper thin films (please refer to: L. Lu, Y. Shen, X. Chen, L. Qian, and K. Lu, Ultrahigh Strength and High Electrical Conductivity in Copper, Science, vol. 304, 2004, p. 422-426).

In terms of high temperature stability, due to the lower interface energy of twin grain boundaries, the twin grain boundaries are more stable than general high-angle grain boundaries. Twin grain boundaries themselves are not easy to move at high temperatures, and they will also have a locking effect on the high-angle grain boundaries around the grains where they are located, making these high-angle grain boundaries unable to move. Therefore, the overall grain will not have obvious grain growth at high temperatures to maintain the high-temperature strength of the material.

In terms of reliability of current flow, the diffusion rate of atoms passing through low-energy twin grain boundaries or crossing twin grain boundaries is low. When using electronic products, it is difficult for atoms inside the wire to move with high-density current. This solves the problem of electromigration that often occurs when current flows through the wire. It has been reported in copper thin films that twin grains can inhibit the electromigration phenomenon of materials (please refer to: K.C.Chen, W.W.Wu, C.N.Liao, L.J.Chen, and K.N.Tu, Observation of Atomic Diffusion at Twin-Modified Grain Boundaries in Copper, Science, vol.321, 2008, p.1066-1069.).

The nanocrystal structure is mainly composed of symmetrical fine flat grains with nanometer-level spacing. These symmetrical fine flat nanocrystals have a (111) preferred crystal orientation. It is known that the atomic diffusion rate of the (111) crystal plane is 3 to 5 orders of magnitude faster than that of the (100) and (110) crystal planes (see Table 1 below (Agrawal, P.M., Rice, B.M., & Thompson, D.L. (2002). Predicting trends in rate parameters for self-diffusion on FCC metal surfaces. Surface Science, 515 (1), 21-35.)).

Referring to FIG. 3, the difference from the embodiment shown in FIG. 2 is that before forming the first nanocrystalline layer 14, an adhesive layer 12 may be additionally formed on the first substrate 10. In some embodiments, the adhesive layer 12 includes titanium, chromium, tungsten, titanium-tungsten or a combination thereof. The adhesive layer 12 may improve the bonding force between the first nanocrystalline layer 14 and the first substrate 10, and reduce the influence of the crystal orientation of the first substrate 10 on the first nanocrystalline layer 14.

In some embodiments, the adhesion layer 12 can be formed on the first substrate 10 by sputtering. Sputtering adopts single-gun sputtering or multi-gun co-plating. The sputtering power source can use, for example, DC, DC plus, RF, high-power pulsed magnetron sputtering (HIPIMS), etc. The sputtering power of the adhesion layer 12 can be, for example, about 100W to about 500W. The temperature of the sputtering process is room temperature, but the temperature of the sputtering process will rise by about 50°C to about 200°C. The background pressure of the sputtering process is less than 1× ^10-5 torr, and the working pressure can be, for example, about 1× ^10-3 torr to 1× ^10-2 torr. The argon flow rate is about 10sccm to about 20sccm. The rotation speed of the stage can be, for example, about 5 rpm to about 20 rpm. During the sputtering process, the substrate is biased at about -100 V to about -200 V. The deposition rate of the adhesive layer 12 can be, for example, 0.5 nm/s to about 3 nm/s. It should be understood that the above-mentioned sputtering process parameters can be appropriately adjusted according to actual applications, and the present disclosure is not limited thereto.

In some embodiments, the adhesive layer 12 can be formed on the first substrate 10 by evaporation. The background pressure of the evaporation process is less than 1×10 ^-5 torr, and the working pressure can be, for example, about 1×10 ^-4 torr to about 5×10 ^-4 torr. The argon flow rate is about 2 sccm to about 10 sccm. The stage rotation speed can be, for example, about 5 rpm to about 20 rpm. The deposition rate of the adhesive layer 12 can be, for example, about 1 nm/s to about 5.0 nm/s. It should be understood that the above evaporation process parameters can be appropriately adjusted according to actual applications, and the present disclosure is not limited thereto.

In practice, when the thickness of the nano-twin crystal layer is greater than 2 microns, the bonding force between the nano-twin crystal layer and the metal substrate has been significantly deteriorated and is very easy to peel off. When the thickness of the nano-twin crystal layer is less than 2 microns, the nano-twin crystal layer will quickly react with the bonding material in the subsequent bonding process, which is meaningless in application. The present disclosed embodiment forms an adhesive layer on the metal substrate before forming the nano-twin crystal layer, which can ensure that the nano-twin crystal layer has a thickness greater than 10 microns and the nano-twin crystal layer and the metal substrate are still well bonded and not peeled off. In addition, the adhesive layer has the effect of lattice buffering for forming twin crystal structures on metal substrates in different orientations. In detail, regardless of the crystal orientation of the metal substrate, the formed nanocrystals have a [111] crystal orientation.

Referring to FIG. 4 , a second substrate 10 'is provided. In some embodiments, the second substrate 10 'may include SAE430 (Fe-18Cr) stainless steel, SAE304 (Fe-18Cr-8Ni) stainless steel, SAE316 (Fe-18Cr-8Ni-3Mo) stainless steel or other suitable iron-based stainless steel. Taking SAE316 stainless steel as an example, its material composition is based on iron (Fe) and contains about 18% chromium (Cr), about 8% nickel (Ni) and about 3% molybdenum (Mo).

Referring to Figures 5 and 6, the difference between them and Figures 2 and 3 is that the first nanocrystalline layer 14 and the adhesive layer 12 (if present) are formed on the second substrate 10', not on the first substrate 10. The materials and formation methods of the adhesive layer 12 and the first nanocrystalline layer 14 can refer to the embodiments described in Figures 2 and 3, so they will not be described here.

Referring to FIGS. 7A and 7B , after forming the first nanocrystalline layer 14 on the first substrate 10, it is bonded to the second substrate 10'. In some embodiments, the first nanocrystalline layer 14 and the second substrate 10' are bonded at a temperature of 100° C. to 400° C. and a pressure of 1 kg/mm ² to 30 kg/mm ² to form a bonded structure. In some embodiments, the bonding time is 10 minutes to 60 minutes.

Since the [111] crystal orientation of the nano-twin crystal has a higher diffusion rate, the present disclosure can perform a heterogeneous bonding process of copper and stainless steel at a temperature of 100°C to 400°C (lower than the conventional bonding temperature) to avoid material degradation caused by high temperature. In addition, the present disclosure uses a pressure of 1kg/ ^mm2 to 30kg/ ^mm2 , and both the metal and the nano-twin crystal can remain intact. Although the conventional technology can perform a bonding process at low pressure, the nano-twin crystal film must be subjected to chemical mechanical polishing (CMP) to reduce the surface roughness before bonding, which is not only complicated but also will damage the nano-twin crystal. The present disclosure applies a pressure of 1kg/ ^mm2 to 30kg/ ^mm2 to plastically deform the protruding structures on the surface of the nanocrystalline so as to achieve the effect of close contact. It not only solves the problem of surface roughness of the nanocrystalline, but also eliminates the need for additional complicated chemical mechanical polishing or other surface treatment steps in the conventional technology, thereby improving production capacity and yield.

Referring to FIG. 7C , in some embodiments, after forming the bonding structure (as shown in FIG. 7B ), the bonding structure can be heated at a temperature above 400° C. to recrystallize the first nanocrystalline twin layer 14 and transform it into an equiaxed grain layer 26. In some embodiments, the equiaxed grain layer 26 includes more than 10% of annealed twin crystals 24, and the annealed twin crystal spacing of the equiaxed grain layer 26 is greater than 100 nanometers.

Referring to Figures 8A to 8C, the difference between them and Figures 7A to 7C is that an adhesive layer 12 is additionally formed on the first substrate 10. The temperature, pressure and time of the bonding between the first substrate 10 and the second substrate 10' can refer to the embodiment described in Figures 7A to 7C, so it will not be repeated here.

Referring to Figures 9A to 9C, the difference between them and Figures 7A to 7C is that the first nanocrystalline layer 14 is formed on the second substrate 10' instead of on the first substrate 10. The temperature, pressure and time of the bonding between the first substrate 10 and the second substrate 10' can refer to the embodiment described in Figures 7A to 7C, so it will not be repeated here.

Referring to Figures 10A to 10C, the difference between them and Figures 9A to 9C is that an adhesive layer 12 is additionally formed on the second substrate 10'. The temperature, pressure and time of the bonding between the first substrate 10 and the second substrate 10' can refer to the embodiment described in Figures 7A to 7C, so it will not be repeated here.

Referring to FIG. 11A , the difference from FIG. 7A is that a second nano-twin crystal layer 14 ′ is additionally formed on the second substrate 10 ′. In some embodiments, the second nano-twin crystal layer 14 ′ includes silver, copper, or a silver-copper alloy. In some embodiments, the second nano-twin crystal layer 14 ′ includes a second parallel twin grain boundary (Σ3+Σ9) at the nanoscale. In the cross-sectional view, using electron backscatter diffraction (EBSD) analysis, the second parallel twin grain boundary of at least 1 micron in the second region R ′ close to the upper surface of the second nano-twin crystal layer 14 ′ has a [111] crystal orientation of more than 50%. In some embodiments, the nano-twin crystal spacing of the second parallel twin grain boundary can be 1 nm to 100 nm, for example, 2 nm to 50 nm. In some embodiments, the second nanocrystalline layer 14' includes parallel stacked second nanocrystalline columns 16'. The diameter of the second nanocrystalline columns 16' can be 0.1 microns to 10 microns, for example, 0.3 microns to 1.0 microns.

In some embodiments, a second transition grain layer 22' is further included between the second substrate 10' and the second nano-twin crystal layer 14'. When the second nano-twin crystal layer 14' is initially formed on the second substrate 10', a second nano-twin crystal layer 14' having a second parallel twin grain boundary is not immediately formed, but a second transition grain layer 22' without a second parallel twin grain boundary is formed. In some embodiments, the second transition grain layer 22' includes more than 10% of annealed twin crystals 24', and the annealed twin crystal spacing of the second transition grain layer 22' is greater than 100 nanometers. The method for forming the second nano-twin crystal layer 14' can refer to the method for forming the first nano-twin crystal layer 14 in the embodiment of Figure 2, so it is not repeated here.

Referring to FIG. 11B, the difference between FIG. 11B and FIG. 7B is that FIG. 11B is bonded by the first nanocrystalline layer 14 and the second nanocrystalline layer 14'. The temperature, pressure and time of the first substrate 10 and the second substrate 10' can refer to the embodiments described in FIGS. 7A and 7B, so they will not be described here.

Referring to FIG. 11C, similar to FIG. 7C, after the bonding structure is formed (as shown in FIG. 11B), the bonding structure can be heated at a temperature above 400°C to allow the first nanocrystalline twin layer 14 and the second nanocrystalline twin layer 14' to recrystallize and transform into an equiaxed grain layer 26. In some embodiments, the equiaxed grain layer 26 includes more than 10% of annealed twin crystals 24, 24', and the annealed twin crystal spacing of the equiaxed grain layer 26 is greater than 100 nanometers.

Referring to Figures 12A to 12C, the difference between them and Figures 11A to 11C is that an adhesive layer 12 is additionally formed on the first substrate 10. The temperature, pressure and time of the bonding between the first substrate 10 and the second substrate 10' can refer to the embodiment described in Figures 7A to 7C, so it will not be repeated here.

Referring to FIGS. 13A to 13C, the difference between them and FIGS. 11A to 11C is that an adhesive layer 12' is additionally formed on the second substrate 10'. The material and formation method of the adhesive layer 12' can refer to the material and formation method of the adhesive layer 12 described in the embodiment of FIG. 3, so it is not repeated here. The temperature, pressure and time of the bonding between the first substrate 10 and the second substrate 10' can refer to the embodiment described in FIGS. 7A to 7C, so it is not repeated here.

Referring to FIGS. 14A to 14C, the difference between them and FIGS. 11A to 11C is that an adhesive layer 12 is additionally formed on the first substrate 10, and an adhesive layer 12' is additionally formed on the second substrate 10'. The temperature, pressure and time of the bonding between the first substrate 10 and the second substrate 10' can refer to the embodiment described in FIGS. 7A to 7C, so it will not be repeated here.

Refer to Figure 15, which is a photo of the bonding structure of the copper substrate and the stainless steel substrate. In Figure 15, the copper substrate is located on the top and the stainless steel substrate is located on the bottom. After forming the titanium adhesive layer and the silver nanocrystalline layer, the two substrates are heterogeneously bonded. After forming the bonding structure, the silver nanocrystalline layer has a thickness of about 7.81 microns, as shown in Figure 15.

Refer to Figure 16, which is a photo of the bonding structure of the copper substrate and the stainless steel substrate. In Figure 16, the stainless steel substrate is located on the top and the copper substrate is located on the bottom. After forming the titanium adhesive layer and the copper nanocrystalline layer, the two substrates are heterogeneously bonded. After forming the bonding structure, the copper nanocrystalline layer has a thickness of about 7.20 microns, as shown in Figure 16.

The disclosed embodiments have some advantageous features, including using the nano-twin crystal layer to perform a heterogeneous bonding process (e.g., heterogeneous bonding of copper and stainless steel). Due to the characteristics of the twin crystal structure, atoms have a higher diffusion ability, so that the disclosed embodiments can perform a heterogeneous bonding process at low temperature and low pressure (e.g., a temperature of 100° C. to 400° C. and a pressure of 1 kg/mm ² to 30 kg/mm ² ) to avoid material degradation, thereby improving the reliability of the bonding structure. In addition, the adhesive layer can provide a better bonding force between the substrate and the nano-twin crystal layer to avoid peeling, and the adhesive layer can reduce the influence of the crystal orientation of the substrate on the nano-twin crystal layer.

Although the embodiments and benefits of the present disclosure have been disclosed as above, it should be understood that those with ordinary knowledge in the relevant technical field can make changes, substitutions and modifications to the present disclosure without departing from the spirit and scope of the present disclosure. The features between the embodiments can be mixed and matched as needed as long as they do not violate the spirit of the present disclosure or conflict with each other. In addition, the scope of protection of the present disclosure is not limited to the processes, machines, manufactures, material compositions, devices, methods and steps in the specific embodiments described in the specification. Those with ordinary knowledge in the relevant technical field can understand from the content of the present disclosure that the processes, machines, manufactures, material compositions, devices, methods and steps currently or in the future can be used according to the present disclosure as long as they can implement substantially the same functions or obtain substantially the same results in the embodiments described herein. Therefore, the protection scope of this disclosure includes the above-mentioned processes, machines, manufacturing, material compositions, devices, methods and steps. The protection scope of this disclosure shall be determined by the scope of the claims attached hereto. Any embodiment or claim of this disclosure does not need to achieve all the purposes, benefits and features disclosed in this disclosure.

10: Substrate

10’: Substrate

14: Nanocrystalline layer

16: Nanocrystalline columns

22: Transition grain layer

24: Annealing twin crystals

Claims (15)

A bonding structure comprises: a first substrate; a first nanocrystalline layer on the first substrate; and a second substrate on the first nanocrystalline layer, wherein in a cross-sectional view of the bonding structure, a first region of at least 1 micron close to an upper surface of the first nanocrystalline layer comprises a first parallel twin grain boundary, and the first parallel twin grain boundary has a [111] crystal orientation of more than 50%. The bonding structure as described in claim 1, wherein a distance between the first parallel twin grain boundaries is 1 nm to 100 nm. The bonding structure as described in claim 1 further includes a first transition grain layer between the first substrate and the first nano-twin crystal layer, wherein the first transition grain layer includes more than 10% annealed twin crystals, and an annealed twin crystal spacing of the first transition grain layer is greater than 100 nanometers. The bonding structure as described in claim 3, wherein the first parallel twin grain boundaries in the first region on the first transition grain layer are a continuous structure or include a plurality of separated parts. The bonding structure as described in claim 1 further includes a second nanocrystalline layer between the first nanocrystalline layer and the second substrate, and the second nanocrystalline layer includes silver, copper or silver-copper alloy. A bonding structure as described in claim 5, wherein a second region of at least 1 micron close to an upper surface of the second nano-twin crystal layer includes a second parallel twin grain boundary, the second parallel twin grain boundary has a [111] crystal orientation of more than 50%, and a spacing between the second parallel twin grain boundaries is 1 nanometer to 100 nanometers. The bonding structure as described in claim 5 further includes a second transition grain layer between the second substrate and the second nano-twin crystal layer, wherein the second transition grain layer includes more than 10% annealed twin crystals, and an annealed twin crystal spacing of the second transition grain layer is greater than 100 nanometers. The bonding structure as described in claim 5 further includes an adhesive layer between the second substrate and the second nanocrystalline layer, and the adhesive layer includes titanium, chromium, tungsten, titanium-tungsten or a combination thereof. A bonding structure as described in claim 1, wherein the first substrate comprises copper or a copper-based alloy. The bonding structure as described in claim 1, wherein the second substrate comprises SAE430 (Fe-18Cr) stainless steel, SAE304 (Fe-18Cr-8Ni) stainless steel or SAE316 (Fe-18Cr-8Ni-3Mo) stainless steel. The bonding structure as described in claim 1, wherein the first nanocrystalline layer comprises silver, copper or a silver-copper alloy. The bonding structure as described in claim 1 further includes an adhesive layer between the first substrate and the first nanocrystalline layer, and the adhesive layer includes titanium, chromium, tungsten, titanium-tungsten or a combination thereof. A bonding structure includes: a first substrate; an equiaxial grain layer on the first substrate; and a second substrate on the equiaxial grain layer, wherein the equiaxial grain layer includes more than 10% annealed twin crystals, and an annealed twin crystal spacing of the equiaxial grain layer is greater than 100 nanometers. A bonding structure as described in claim 13, wherein the first substrate comprises copper or a copper-based alloy. A bonding structure as described in claim 13, wherein the second substrate comprises SAE430 (Fe-18Cr) stainless steel, SAE304 (Fe-18Cr-8Ni) stainless steel or SAE316 (Fe-18Cr-8Ni-3Mo) stainless steel.