Method of metal bonding and applications thereof

Abstract

The application relates to a metal bonding method and application thereof, and belongs to the technical field of microelectronic interconnection. The metal bonding method comprises the following steps: step 1, cleaning a bonding surface; step 2, depositing a metal nanometer film on the cleaned bonding surface; and step 3, aligning and adhering two bonding surfaces completed in the step 2, and then bonding, wherein the bonding temperature is 300-600 DEG C, and the bonding pressure is 3-10 MPa. The metal bonding method can be used for bonding at a lower temperature.

Description

Technical Field

[0001] This application relates to the field of microelectronic interconnect technology, and in particular to a metal bonding method and its application. Background Technology

[0002] As chip manufacturing processes advance to 5nm and even 3nm, Moore's Law is approaching its limits due to the constraints of physical laws. Continuing to shrink transistor feature sizes in a two-dimensional plane to improve chip performance is becoming increasingly difficult. Therefore, the development of new three-dimensional integrated structures from two-dimensional planes has become a crucial direction for transcending Moore's Law and driving the semiconductor industry's development. Wafer bonding is one of the core technologies of three-dimensional integration. Semiconductor wafer bonding technology uses chemical and physical interactions to tightly bond two mirror-polished wafers together, thereby improving device performance and functionality while reducing system power consumption, size, and manufacturing costs. Common wafer bonding methods currently include: adhesive bonding, anodic bonding, direct wafer bonding, and metal eutectic bonding.

[0003] Adhesive bonding uses organic materials such as epoxy resin as the bonding layer for wafer bonding. During bonding, the surface morphology of the sample can be compensated, avoiding some surface treatment steps. However, because the thickness of the adhesive used is usually on the micrometer scale and the adhesive itself has poor thermal conductivity, it can severely affect the heat dissipation of the device. Anodic bonding is a technique that achieves bonding by applying a strong electrostatic field to the materials to be bonded at a certain temperature. This technique has lower requirements for wafer surface roughness than direct bonding and relatively less stringent requirements for the bonding environment. However, this technique is generally used for bonding alkali-containing glass materials. After bonding, the structure can... Significant residual thermal stress may occur. Direct wafer bonding is a wafer bonding method that has been developed in recent years and does not require an intermediate layer. Avoiding the intermediate layer can indeed effectively reduce the thermal resistance of the bonding interface. However, this bonding technology has very high requirements for the surface roughness and cleanliness of the wafer. Obtaining a bonding surface that meets the requirements is undoubtedly very expensive and complex, which poses a significant challenge to the cost and efficiency of wafer bonding. In addition, the method modifies the surface of the wafer through immersion or dry treatment, making the wafer surface exhibit extreme hydrophilicity or hydrophobicity, thus limiting its applicability. Metal eutectic bonding achieves bonding by fusing two metals into an alloy and then solidifying it. Compared to the bonding methods mentioned above, metal eutectic bonding is more attractive, primarily because the metal forms a fluid state, easily expanding within the bonding region. Therefore, it can adapt to higher surface morphologies and non-planarity than other bonding methods. However, the molten metal must be thick enough to wet the irregularly shaped region (typically 3-5 µm) and form a high-melting-point intermetallic compound at the interface. The eutectic bonding temperature must reach the eutectic temperature of the alloy, which typically requires thousands of degrees Celsius. With the development of optoelectronic technology and 3D heterogeneous integration technology, new requirements have been placed on wafer bonding processes, making the development of low-temperature wafer bonding technology inevitable. Summary of the Invention

[0004] Therefore, this application aims to provide a metal bonding method and its application, which can be performed at lower temperatures.

[0005] This application provides a metal bonding method, comprising the following steps: Step 1, cleaning the surfaces to be bonded; Step 2, depositing a metal nanofilm on the cleaned surfaces to be bonded; Step 3, aligning and bonding the two surfaces to be bonded after Step 2, with a bonding temperature of 300~600℃ and a bonding pressure of 3~10MPa.

[0006] This application grows an ultrathin metal nanofilm on the surfaces to be bonded, bringing the two surfaces with the metal nanofilm into contact. Bonding is then performed at temperatures and pressures sufficient to cause nanoscale islanding and nanobridge formation in the metal nanofilm, thereby forming a three-dimensional interpenetrating metallurgical network. Since nanomaterials have lower melting points than bulk materials, bonding at lower temperatures can be achieved by depositing the metal nanofilm, avoiding the impact of high-temperature bonding on device reliability. Furthermore, the deposited ultrathin metal nanofilm enables metal bonding of an ultrathin metal interlayer, reducing thermal resistance. The reduced thickness of the metal interlayer also reduces the amount of metal material used, and low-temperature bonding reduces the required heat, thus lowering costs. The metal bonding method provided in this application is a low-temperature, low-cost, and low-thermal-resistance bonding method with high application value. Attached Figure Description

[0007] To more clearly illustrate the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0008] Figure 1 This is a schematic flowchart of the metal bonding method for the wafer in Example 1; Figure 2 This is a schematic diagram of the thermally induced network shrinkage structure formed after annealing of the metal nanofilm in Example 1. Figure 3 This is a schematic diagram of the hot-press bonding process in Example 1; Figure 4 This is an SEM image of the surface to be bonded after step (2) in Example 1; Figure 5 This is an SEM image of the surface to be bonded after step (3) in Example 1; Figure 6 The image shown is an ultrasonic scanning microscope image of the bonded wafer after step (4) in Example 1. Figure 7 The image shown is a transmission electron microscope image of the bonding wafer after step (4) in Example 1. Figure 8 This is an SEM image of the surface to be bonded after step (3) in Example 7; Figure 9 The image shown is an ultrasonic scanning microscope image of the bonded wafer after step (4) in Example 7. Figure 10 This is an SEM image of the surface to be bonded after step (3) in Example 8; Figure 11The image shown is an ultrasonic scanning microscope image of the bonded wafer after step (4) in Example 8. Figure 12 This is an ultrasonic scanning microscope image of the bonding wafer after step (4) in Example 9. Detailed Implementation

[0009] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this application.

[0010] It should be noted that, in the description of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. The terms "first," "second," etc., in this application are used to distinguish similar objects and are not used to describe a specific order or sequence.

[0011] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0012] Existing metal bonding methods involve high bonding temperatures. To address the problems in the aforementioned related technologies, this application provides a metal bonding method comprising the following steps: Step 1: Clean the surfaces to be bonded; Step 2: Deposit a metal nanofilm on the cleaned bonding surface; Step 3: Align and bond the two surfaces to be bonded after completing step 2. The bonding temperature is 300~600℃ and the bonding pressure is 3~10MPa.

[0013] For example, the bonding temperature can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, or 600°C. For example, the bonding pressure can be 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, or 10 MPa.

[0014] This application grows an ultrathin metal nanofilm on the surfaces to be bonded, bringing the two surfaces with the metal nanofilm into contact. Bonding is then performed at temperatures and pressures sufficient to cause nanoscale islanding and nanobridge formation in the metal nanofilm, thereby forming a three-dimensional interpenetrating metallurgical network. Since nanomaterials have lower melting points than bulk materials, bonding at lower temperatures can be achieved by depositing the metal nanofilm, avoiding the impact of high-temperature bonding on device reliability. Furthermore, the deposited ultrathin metal nanofilm enables metal bonding of an ultrathin metal interlayer, reducing thermal resistance. The reduced thickness of the metal interlayer also reduces the amount of metal material used, and low-temperature bonding reduces the required heat, thus lowering costs. The metal bonding method provided in this application is a low-temperature, low-cost, and low-thermal-resistance bonding method with high application value.

[0015] In some embodiments, the material of the metal nanofilm includes one or more of Au, Cu, and Al; In some embodiments, the thickness of the metal nanofilm is 5 to 30 nm; for example, the thickness of the metal nanofilm can be 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 25 nm or 30 nm.

[0016] In some implementations, the bonding time is set to 10-30 minutes. For example, the bonding time can be 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

[0017] In some embodiments, an adhesive layer is provided between the surface to be bonded and the metal nanofilm; the adhesive layer can increase the adhesion between the metal nanofilm and the surface to be bonded, and prevent the metal nanofilm from falling off.

[0018] Optionally, the material of the adhesive layer includes one or more of Ti, Ni, Pt, Cr, and TiO2; Optionally, the thickness of the adhesive layer is 5~50 nm. For example, the thickness of the adhesive layer can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm.

[0019] In some embodiments, the adhesive layer is prepared by magnetron sputtering, electron beam evaporation, or electroplating. Preferably, the adhesive layer is prepared by DC magnetron sputtering with a sputtering power of 100~300W. For example, the sputtering power can be 100 W, 150 W, 200 W, 250 W or 300 W.

[0020] In some embodiments, after the adhesion layer is prepared on the surface to be bonded, pre-annealing is performed before depositing the metal nanofilm; In some embodiments, the pre-annealing temperature is 200~500℃ and the pre-annealing time is 20~60min; for example, the pre-annealing temperature can be 200℃, 300℃, 400℃, or 500℃, and the pre-annealing time can be 20min, 30min, 40min, 50min, or 60min.

[0021] In some embodiments, the pre-annealing is performed in an atmospheric atmosphere.

[0022] In some embodiments, the method for depositing the metal nanofilm is magnetron sputtering, electron beam evaporation, or electroplating; Preferably, the method for depositing the metal nanofilm is radio frequency magnetron sputtering, with a sputtering power of 100~300W. For example, the sputtering power can be 100 W, 150 W, 200 W, 250 W or 300 W.

[0023] In some implementations, annealing is also included after the metal nanofilm deposition is completed; In some embodiments, the annealing temperature is 200~500℃ and the time is 5~20min; for example, the annealing temperature can be 200℃, 250℃, 300℃, 350℃ or 500℃, and the annealing time can be 5 min, 7 min, 10 min, 15 min or 20 min.

[0024] This application involves growing an ultrathin metal nanofilm on the bonding surfaces, followed by annealing to form a relatively uniform thermotropic network pore structure on the bonding surfaces. The two bonding surfaces are then aligned and bonded, and the resulting metal nanoparticles are heated and pressurized. Since nanomaterials have lower melting points than bulk materials, the thermotropic network pore structure obtained by depositing a metal nanofilm followed by annealing enables bonding at lower temperatures, avoiding the impact of high-temperature bonding on device reliability.

[0025] In some embodiments, the annealing is performed in a protective atmosphere; Optionally, the protective atmosphere includes one or more of nitrogen and argon; Optionally, the protective atmosphere is at atmospheric pressure.

[0026] Metal nanofilms on wafer surfaces form thermally induced network cavities due to nanoscale effects. By controlling the thickness of the metal nanofilm and the annealing process parameters, network cavities of different sizes and shapes can be obtained. During the annealing process, high-purity protective gases, such as nitrogen or argon, must be introduced at atmospheric pressure to ensure that the metal nanoparticles are not oxidized during formation.

[0027] In some embodiments, step 1 includes: ultrasonically cleaning the bonding surfaces with acetone, ethanol, and deionized water for 10-60 min respectively, rinsing with deionized water, then ultrasonically cleaning the bonding surfaces with a solution of HCl:H2O = 1:(1-10) for 5-30 min, rinsing with deionized water again, and finally drying with a nitrogen gun. For example, the HCl:H2O ratio is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10.

[0028] In some embodiments, the methods for preparing the adhesive layer and the metal nanofilm are independently selected from magnetron sputtering, electron beam evaporation, or electroplating.

[0029] In some implementations, magnetron sputtering equipment is used to perform DC sputtering and RF sputtering of Ti and Au metal targets on the wafer, respectively.

[0030] In some implementations, the metal bonding method includes the following steps: Step 1: Clean the surfaces to be bonded; Step 2: Deposit an adhesion layer on the surface to be bonded using DC magnetron sputtering. The material of the adhesion layer includes one or more of Ti, Ni, Pt and Cr. The thickness of the adhesion layer is 5~50nm. The sputtering power of the DC magnetron sputtering is 100~300W. A metal nanofilm is deposited on the surface of the adhesive layer by radio frequency magnetron sputtering, the metal nanofilm comprising one or more of Au, Cu and Al, the thickness of the metal nanofilm being 5-30 nm, and the radio frequency magnetron sputtering power being 100-300 W; Anneal at 200~500℃ for 5~20min; Step 3: Align and bond the two surfaces to be bonded after completing step 2, and perform bonding in a vacuum hot press bonding machine; The bonding pressure is 3~10MPa, the bonding temperature is 300~600℃, and the bonding time is set to 10~30min.

[0031] In some implementations, the surface to be bonded refers to the surface of a chip and / or a wafer.

[0032] In some implementations, the metal bonding method includes the following steps: (1) Clean the wafer to be bonded to remove impurities from the wafer surface: First, ultrasonically clean the wafer to be bonded with acetone, ethanol, and deionized water for 10-60 minutes respectively, then rinse with deionized water. Next, ultrasonically clean the wafer to be bonded with a solution of HCl:H2O=1:(1-10) for 5-30 minutes, then rinse with deionized water, and finally dry with a nitrogen gun.

[0033] (2) Deposit an adhesion layer on the cleaned wafer surface to be bonded. The sputtering power of magnetron sputtering is 100~300W; the thickness of the adhesion layer is 5~50nm; and the material of the adhesion layer includes one or more of Ti, Ni and Cr.

[0034] A metal nanofilm is deposited on the surface of the adhesive layer using a magnetron sputtering power of 100-300W; the thickness of the metal nanofilm is 5-30nm, and the material of the metal nanofilm is one or more of Au, Cu and Al.

[0035] Anneal at 200~500℃ for 5~20 minutes.

[0036] (3) Place the sample after depositing the metal nanofilm into an annealing furnace for annealing. The heating temperature is 200~500℃ and the heating time is set to 5~20min. Then cool to room temperature.

[0037] (4) Align and bond the two annealed wafers separately, place them in a vacuum hot press bonding machine, set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 3~10MPa, the bonding temperature is 300~600℃, and the bonding time is 10~30min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafer to complete the metal bonding of the wafer.

[0038] High-quality metal nanofilms are first obtained using magnetron sputtering. Then, the material is heated during annealing due to the relatively low melting point of the nanomaterials. The surface tension of the molten metal then causes the surface to automatically shrink, forming a thermally induced network of shrinkage cavities. This method yields thermally induced network shrinkage cavities with high microstructure density and good dispersibility. Furthermore, this method for preparing metal nanoparticles is simple and easy to implement.

[0039] Figure 3This diagram illustrates how, during the heating and pressurization process, metal atoms in the upper and lower layers of a thermo-induced network cavity structure formed after annealing a metal nanofilm approach each other, forming metallic bonds when the distance is sufficiently close, thus achieving bonding between the upper and lower metal layers. At the nanoscale, the melting point of gold is reduced to below 400 degrees Celsius. By heating and pressurizing the wafer after growing the thermo-induced network cavity structure, wafer bonding of an ultrathin metal interlayer can be achieved, while avoiding the impact of high temperatures on material and device performance. Therefore, this invention minimizes the thickness of the metal interlayer, helping to reduce interfacial thermal resistance. Furthermore, this invention lowers the requirements for wafer surface condition, eliminating the need for additional polishing and modification of the material surface, simplifying the process, significantly reducing costs, and improving bonding efficiency.

[0040] In some possible implementations, in (4), the two annealed wafers are aligned and bonded together, placed in a vacuum hot press bonding machine, pre-pressurized at room temperature, and then heated to the bonding temperature while maintaining the pressure. Optionally, the pre-pressurization pressure is 3~10MPa, and the pre-pressurization time is 1~3min.

[0041] In some possible implementations, after preparing an adhesion layer on the surfaces to be bonded, a metal nanofilm is directly deposited, and then the two surfaces to be bonded are directly aligned and bonded. No plasma or wet chemical surface activation or annealing treatment is required for the metal bonding layer throughout the process; the nanoscale islanding step is completed simultaneously with the bonding step.

[0042] This application can be used not only for metal bonding of wafers to reduce bonding temperature and metal interlayer thickness, but also for temporary bonding during wafer stripping (temporary bonding refers to the bonding between a temporary support substrate and the wafer to be stripped, which plays a supporting role during the stripping process), heterogeneous integration of three-dimensional integrated circuits, advanced packaging and other fields.

[0043] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0044] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0045] Example 1 This embodiment provides a metal bonding method for wafers, such as... Figures 1-3 As shown, it includes the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0046] (2) A Ti / Au bimetallic layer was deposited on the cleaned wafer surface, wherein metallic Ti served as the adhesive layer and Au served as the metal nanofilm. The thickness of metallic Ti was 10 nm, and the adhesive layer was deposited by DC magnetron sputtering at a sputtering power of 100 W; the thickness of the metal nanofilm Au was deposited by RF magnetron sputtering at a sputtering power of 100 W. The SEM image of the bonding surface after step (2) is shown below. Figure 4 .

[0047] (3) The sample after step (2) is placed in an annealing furnace and annealed under a nitrogen atmosphere. The gas pressure is atmospheric pressure, the heating temperature is 300℃, and the heating time is set to 10 min. Then, it is cooled to room temperature. The SEM image of the bonding surface after annealing (i.e., after step (3)) is shown in the figure. Figure 5 .

[0048] (4) Align and bond the surfaces of the two wafers that have completed steps (1)-(3) respectively, place them in a vacuum hot press bonding machine, set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 5MPa, the bonding temperature is 320℃, and the bonding time is set to 15min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafers to complete the metal bonding of the wafers.

[0049] The ultrasonic scanning microscope image after bonding in this embodiment is as follows: Figure 6 As shown, the surface spot areas are delamination defects (i.e., unbonded areas). The transmission electron microscope image after bonding in this embodiment is shown below. Figure 7 As shown, by Figure 7 It can be seen that the bonding interface is uniform and free of voids, and the original gold / gold interface has disappeared. This is due to the mutual diffusion of gold atoms at the interface and the recrystallization of the grains during the bonding process.

[0050] Example 2 This embodiment provides a metal bonding method for wafers, including the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0051] (2) A Ti / Au bimetallic layer is deposited on the cleaned wafer surface, wherein the metallic Ti is used as the adhesive layer and the Au is a metal nanofilm. The thickness of the metallic Ti is 10 nm, and the adhesive layer is deposited by DC magnetron sputtering with a sputtering power of 100 W; the metal nanofilm Au is deposited by RF magnetron sputtering with a thickness of 20 nm and a sputtering power of 100 W.

[0052] (3) Place the completed sample in an annealing furnace and anneal it under a nitrogen atmosphere. The gas pressure is normal pressure, the heating temperature is 300℃, the heating time is 10min, and then cool it to room temperature.

[0053] (4) Align and bond the surfaces of the two wafers that have completed (1)-(3) respectively, place them in a vacuum hot press bonding machine, set the bonding pressure to 5MPa, and pressurize the wafers to be bonded.

[0054] (5) After applying pressure for 1 minute, heat the wafer to be bonded while maintaining pressure. Set the bonding temperature and bonding time respectively. The bonding temperature is 320℃ and the bonding time is 15 minutes. After bonding is completed, wait for the sample to cool to below 60℃, then depressurize and take out the bonded wafer to complete the metal bonding of the wafer.

[0055] Example 3 This embodiment provides a metal bonding method for wafers, including the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0056] (2) A Ti / Au bimetallic layer is deposited on the cleaned wafer surface, wherein the metallic Ti is used as the adhesive layer and the Au is a metal nanofilm. The thickness of the metallic Ti is 10 nm, and the adhesive layer is deposited by DC magnetron sputtering with a sputtering power of 100 W; the metal nanofilm Au is deposited by RF magnetron sputtering with a thickness of 20 nm and a sputtering power of 100 W.

[0057] (3) Place the completed sample in an annealing furnace and anneal it under a nitrogen atmosphere. The gas pressure is normal pressure, the heating temperature is 250℃, the heating time is 20min, and then cool it to room temperature.

[0058] (4) Align and bond the surfaces of the two wafers that have completed (1)-(3) respectively, and place them in a vacuum hot press bonding machine. Set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 5 MPa, the bonding temperature is 320℃, and the bonding time is set to 15 min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafers to complete the metal bonding of the wafers.

[0059] Example 4 This embodiment provides a metal bonding method for wafers, including the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0060] (2) A Ti / Au bimetallic layer is deposited on the cleaned wafer surface, wherein the metallic Ti serves as the adhesive layer and the Au is a metal nanofilm. The thickness of the metallic Ti is 10 nm, and the adhesive layer is deposited by DC magnetron sputtering with a sputtering power of 100 W; the metal nanofilm Au is deposited by RF magnetron sputtering with a thickness of 30 nm and a sputtering power of 100 W.

[0061] (3) Place the completed sample in an annealing furnace and anneal it under a nitrogen atmosphere. The gas pressure is normal pressure, the heating temperature is 300℃, the heating time is 20min, and then cool it to room temperature.

[0062] (4) Align and bond the surfaces of the two wafers that have completed (1)-(3) respectively, and place them in a vacuum hot press bonding machine. Set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 10MPa, the bonding temperature is 300℃ and the bonding time is 20min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafer to complete the metal bonding of the wafer.

[0063] Example 5 This embodiment provides a metal bonding method for wafers, including the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0064] (2) A Ni / Cu bimetallic layer is deposited on the cleaned wafer surface, wherein metallic Ni serves as the adhesive layer and Cu serves as the metal nanofilm. The adhesive layer is 10 nm thick and is deposited by DC magnetron sputtering with a sputtering power of 100 W. The metal nanofilm is deposited by RF magnetron sputtering with a thickness of 20 nm and a sputtering power of 100 W.

[0065] (3) Place the completed sample in an annealing furnace and anneal it under a nitrogen atmosphere. The gas pressure is normal pressure, the heating temperature is 300℃, the heating time is 20min, and then cool it to room temperature.

[0066] (4) Align and bond the surfaces of the two wafers that have completed (1)-(3) respectively, place them in a vacuum hot press bonding machine, set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 5MPa, the bonding temperature is 320℃, and the bonding time is set to 15min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafers to complete the metal bonding of the wafers.

[0067] Example 6 This embodiment provides a metal bonding method for wafers, including the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0068] (2) A Cr / Cu bimetallic layer is deposited on the cleaned wafer surface, wherein Cr is used as the adhesive layer and Cu is used as the metal nanofilm. The adhesive layer is 5 nm thick and is deposited by DC magnetron sputtering with a sputtering power of 100 W. The metal nanofilm is deposited by RF magnetron sputtering with a thickness of 20 nm and a sputtering power of 100 W.

[0069] (3) Place the completed sample in an annealing furnace and anneal it under a nitrogen atmosphere. The gas pressure is normal pressure, the heating temperature is 300℃, the heating time is 20min, and then cool it to room temperature.

[0070] (4) Align and bond the surfaces of the two wafers that have completed (1)-(3) respectively, place them in a vacuum hot press bonding machine, set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 5MPa, the bonding temperature is 400℃ and the bonding time is 15min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafer to complete the metal bonding of the wafer.

[0071] Example 7 This embodiment provides a metal bonding method for wafers, including the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0072] (2) A Ti / Au bimetallic layer was deposited on the cleaned wafer surface, wherein the metallic Ti was used as the adhesive layer and the Au was used as the metal nanofilm. The thickness of the metallic Ti was 10 nm. The adhesive layer was deposited by DC magnetron sputtering with a sputtering power of 100 W. After the growth was completed, the Ti metal layer was placed in an annealing furnace and pre-annealed in an atmospheric atmosphere. The pre-annealing temperature was set to 350 °C and the pre-annealing time was 40 min. Then, the metal nanofilm Au was deposited by radio frequency magnetron sputtering with a thickness of 20 nm and a sputtering power of 100 W.

[0073] (3) The sample completed in (2) was placed in an annealing furnace and annealed under a nitrogen atmosphere. The gas pressure was atmospheric pressure, the heating temperature was 300℃, and the heating time was set to 10 min. The sample was then cooled to room temperature. The SEM image of the bonding surface after annealing (i.e., after completing step (3)) is shown in the figure. Figure 8 .

[0074] (4) Align and bond the surfaces of the two wafers that have completed (1)-(3) respectively, place them in a vacuum hot press bonding machine, set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 5MPa, the bonding temperature is 320℃, and the bonding time is set to 15min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafers to complete the metal bonding of the wafers.

[0075] The ultrasonic scanning microscope image of the bonded wafer after step (4) in this embodiment is as follows: Figure 9 As shown, the surface spot area is a layered defect.

[0076] Example 8 This embodiment provides a metal bonding method for wafers, including the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0077] (2) A Ti / Au bimetallic layer was deposited on the cleaned wafer surface, wherein the metallic Ti was used as the adhesive layer and the Au was used as the metal nanofilm. The thickness of the metallic Ti was 10 nm. The adhesive layer was deposited by DC magnetron sputtering with a sputtering power of 100 W. After the growth was completed, the Ti metal layer was placed in an annealing furnace and pre-annealed in an atmospheric atmosphere. The pre-annealing temperature was set to 350 °C and the annealing time was 40 min. Then, the metal nanofilm Au was deposited by radio frequency magnetron sputtering with a thickness of 20 nm and a sputtering power of 100 W.

[0078] (3) The sample completed in (2) was placed in an annealing furnace and annealed under a nitrogen atmosphere. The gas pressure was atmospheric pressure, the heating temperature was 250℃, and the heating time was set to 20 min. The sample was then cooled to room temperature. The SEM image of the bonding surface after annealing (i.e., after completing step (3)) is shown in the figure. Figure 10 .

[0079] (4) Align and bond the surfaces of the two wafers that have completed (1)-(3) respectively, place them in a vacuum hot press bonding machine, set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 5MPa, the bonding temperature is 320℃, and the bonding time is set to 15min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafers to complete the metal bonding of the wafers.

[0080] The ultrasonic scanning microscope image after bonding in this embodiment is as follows: Figure 11 As shown, the surface spot area is a layered defect.

[0081] Example 9 This embodiment provides a metal bonding method for wafers, including the following steps: (1) Clean the wafer to be bonded and remove impurities on the wafer surface: First, use acetone, ethanol and deionized water to ultrasonically clean the wafer to be bonded for 10 min each, then rinse with deionized water, then use HCl:H2O=1:10 solution to ultrasonically clean the wafer to be bonded for 10 min, then rinse with deionized water, and finally blow dry with nitrogen gun.

[0082] (2) A Ti / Au bimetallic layer is deposited on the cleaned wafer surface, wherein the metallic Ti is used as the adhesive layer and the Au is a metal nanofilm. The thickness of the metallic Ti is 10 nm, and the adhesive layer is deposited by DC magnetron sputtering with a sputtering power of 100 W; the metal nanofilm Au is deposited by RF magnetron sputtering with a thickness of 20 nm and a sputtering power of 100 W.

[0083] (3) Align and bond the surfaces of the two wafers that have completed (1)-(2) respectively, place them in a vacuum hot press bonding machine, set the bonding pressure, bonding temperature and bonding time, and bond the wafers to be bonded. The bonding pressure is 5MPa, the bonding temperature is 320℃, and the bonding time is set to 15min. After the bonding is completed, wait for the sample to cool to below 60℃, then release the pressure and take out the bonded wafers to complete the metal bonding of the wafers.

[0084] Figure 12 This is an ultrasonic scanning microscope image of the bonding wafer after step (4) in Example 9.

[0085] As can be seen from Examples 1-9, this application can achieve wafer bonding at a lower temperature.

[0086] Furthermore, a comparison of Example 1 with Examples 7 and 8 shows that the bonding effect of Example 1 is better than that of Examples 7 and 8, and there are fewer delamination defects at the bonding interface after bonding. The main reasons are as follows: Ultra-high driving force: The island structure has a huge specific surface area, storing extremely high surface energy. During the bonding process, once these two high-energy surfaces come close, they have an incredibly strong tendency to combine with each other to significantly reduce the total energy of the system. This driving force is far greater than the force between two flat surfaces.

[0087] An effective bonding mechanism: When two islanded gold surfaces come into contact, a process similar to nanopowder sintering occurs. At temperatures far below the melting point of bulk gold, the gold nanoislands rapidly form strong "nanobridges" with the opposite islands through extremely high surface diffusivity. This process is fast and efficient, creating a dense network of connection points across the entire interface.

[0088] Tolerance and Penetration: Island structures are more prone to plastic deformation under pressure, enabling them to better adapt to microscopic irregularities at the bonding interface. Simultaneously, the tips of the islands may more easily pierce interfacial barriers (such as trace adsorption layers), promoting direct metal-metal contact.

[0089] The poor bonding results in Examples 7 and 8 are due to loss of adhesion and uncontrolled islanding. Pre-annealing causes the Ti metal layer surface to oxidize into TiO2. When Au is deposited on the inert TiO2 surface, due to extremely poor adhesion, the gold film grows from the outset in a high-density nano-island pattern, rather than a continuous film. During subsequent annealing, without strong anchoring forces to "pin" the gold atoms to the substrate, the gold atoms migrate and aggregate violently under surface diffusion, causing small islands to merge into larger islands to reduce the total surface energy. This leads to severe, uncontrolled islanding, with exposed, isolated TiO2 substrates between the islands. During bonding, due to the poor adhesion between gold nanoparticles and smooth TiO2, these gold islands may indeed form some connections with the gold layer on the mat (nanosintering) when pressure and temperature are applied. However, because their bonding with their own substrate is weak, these connections may detach entirely from the substrate or slide between interfaces under bonding stress or subsequent thermal stress. Ultimately, a large number of voids were formed at the bonding interface. These voids are the areas where the gold islands could not effectively and uniformly bridge the two wafers.

[0090] A comparison between Example 1 and Example 9 shows that Example 9 exhibits the best bonding effect, with fewer delamination defects at the bonding interface after bonding. The main reasons are as follows: Compared to the surface oxidation, contamination, or structural relaxation that may occur during the waiting and transfer process of pre-formed nano-islands in the annealing path, the continuous film of the unannealed sample undergoes thermal instability, islanding, and bridging processes simultaneously during bonding. This coupled dynamic path avoids the energy decay of metastable islands after pretreatment, allowing the metal layer to be directly transformed into the bonding interface at the highest energy state. At the same time, it reduces the risk of interface contamination introduced by additional process steps, thereby obtaining a bonding interface with a more uniform structure and more thorough metallurgical bonding.

[0091] The metal bonding method and its application provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only intended to help understand the method and its core ideas. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A metal bonding method, characterized in that, Includes the following steps: Step 1: Clean the surfaces to be bonded; Step 2: Deposit a metal nanofilm on the cleaned bonding surface; Step 3: Align and bond the two surfaces to be bonded after completing step 2. The bonding temperature is 300~600℃ and the bonding pressure is 3~10MPa.

2. The metal bonding method according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The material of the metal nanofilm includes one or more of Au, Cu and Al; (2) The thickness of the metal nanofilm is 5~30nm; (3) The bonding time is set to 10~30 min; (4) The surface to be bonded refers to the surface of the chip and / or wafer.

3. The metal bonding method according to claim 1, characterized in that, An adhesion layer is provided between the surface to be bonded and the metal nanofilm; Optionally, the material of the adhesive layer includes one or more of Ti, Ni, Pt, Cr, and TiO2; Optionally, the thickness of the adhesive layer is 5~50nm.

4. The metal bonding method according to claim 3, characterized in that, The adhesive layer is prepared by magnetron sputtering, electron beam evaporation, or electroplating. and / or After the adhesion layer is prepared on the surface to be bonded, pre-annealing is performed, and then the metal nanofilm is deposited. Optionally, the pre-annealing temperature is 200~500℃, and the pre-annealing time is 20~60min; Optionally, the pre-annealing is performed in an atmospheric atmosphere.

5. The metal bonding method according to any one of claims 1-4, characterized in that, The method for depositing the metal nanofilm is magnetron sputtering, electron beam evaporation, or electroplating; Preferably, the method for depositing the metal nanofilm is radio frequency magnetron sputtering with a sputtering power of 100~300W.

6. The metal bonding method according to any one of claims 1-4, characterized in that, After the deposition of the metal nanofilm is completed, annealing is also included; Optionally, the annealing temperature is 200~500℃ and the time is 5~20min; Optionally, the annealing is performed in a protective atmosphere; Optionally, the protective atmosphere includes one or more of nitrogen and argon; Optionally, the protective atmosphere is at atmospheric pressure.

7. The metal bonding method according to any one of claims 1-4, characterized in that, Step 1 includes: ultrasonically cleaning the bonding surface with acetone, ethanol, and deionized water for 10-60 min respectively, rinsing with deionized water, ultrasonically cleaning the bonding surface with a solution of HCl:H2O=1:(1-10) for 5-30 min, rinsing with deionized water, and finally drying with a nitrogen gun.

8. The metal bonding method according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Clean the surfaces to be bonded; Step 2: Deposit an adhesion layer on the surface to be bonded using DC magnetron sputtering. The material of the adhesion layer includes one or more of Ti, Ni, Pt and Cr. The thickness of the adhesion layer is 5~50nm. The sputtering power of the DC magnetron sputtering is 100~300W. A metal nanofilm is deposited on the surface of the adhesive layer by radio frequency magnetron sputtering. The metal nanofilm includes one or more of Au, Cu and Al, and the thickness of the metal nanofilm is 5~30 nm. The radio frequency magnetron sputtering power is 100~300 W. Anneal at 200~500℃ for 5~20min; Step 3: Align and bond the two surfaces to be bonded after completing step 2, and perform bonding in a vacuum hot press bonding machine; The bonding pressure is 3~10MPa, the bonding temperature is 300~600℃, and the bonding time is set to 10~30min.

9. The metal bonding method according to any one of claims 1-4, characterized in that, After preparing an adhesion layer on the surfaces to be bonded, a metal nanofilm is directly deposited, and then the two surfaces to be bonded are directly aligned and bonded.

10. The application of the metal bonding method according to any one of claims 1-9 in wafer stripping processes, heterogeneous integration or packaging of three-dimensional integrated circuits.

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