Three-dimensional integrated thermal diffusion bonding structure and method of manufacture

Abstract

The application discloses a three-dimensional integrated thermal diffusion bonding structure and a preparation method. The bonding structure comprises a first bonding structure, a micro-nano protrusion array composed of a heat-conducting metal, protrusions in the micro-nano protrusion array are arranged in a direction away from the first bonding surface, and the extension height of the protrusions is greater than the maximum cross-sectional dimension of the protrusions in a direction parallel to the first bonding surface; a second bonding structure, a porous metal layer, the porosity of the porous metal layer decreases in a direction away from the second bonding surface; the maximum cross-sectional dimension of the protrusions matches the average pore diameter of the porous metal layer, so that in a bonded state, the micro-nano protrusion array can be partially embedded in the porous metal layer and form a metallurgical bond with the porous metal layer. The application can reduce the thermal resistance of the bonding interface, alleviate the local temperature rise caused by the heat flow concentration, and buffer the cyclic stress caused by the mismatch of the thermal expansion coefficient.

Description

Technical Field

[0001] This application belongs to the field of semiconductor packaging and integration technology, specifically relating to a three-dimensional integrated thermal diffusion bonding structure and its preparation method. Background Technology

[0002] Three-dimensional heterogeneous integration technology, by vertically stacking chips with different process nodes and functions, has become a core technological path for improving the computing power, bandwidth, and energy efficiency of computing systems in the post-Moore's Law era. In the heterogeneous integration scenario of high-power computing chips and heat sinks, the bonding interface not only needs to provide stable mechanical connections and electrical interconnections, but also needs to transfer the high heat flux density generated by the chip to the heat sink.

[0003] Currently, most mainstream hybrid bonding interfaces adopt a symmetrical design approach, where both the chip side and the heat sink side are fabricated as smooth planes or surfaces with similar roughness. Roughening or activation treatments are then used to promote atomic diffusion and reduce bonding voids. While this design can improve bonding yield and connection reliability, it does not address the structural optimization required for the high heat flux and thermal stress buffering needs of high-power chips.

[0004] Furthermore, in practical applications, the effective contact area of ​​the symmetrical planar bonding structure is limited, resulting in high thermal resistance at the bonding interface. The heat generated by the chip during operation cannot be effectively dissipated, which easily leads to heat accumulation and a continuous rise in the chip junction temperature, affecting computing performance and long-term operational reliability. At the same time, the chip generates continuous dynamic heat dissipation during operation, causing frequent temperature cycles and a mismatch in the thermal expansion coefficients between the chip and the heat sink. This results in continuous cyclic shear stress at the rigid bonding interface. Under long-term cumulative stress, the bonding interface is prone to fatigue cracking or even delamination failure. Summary of the Invention

[0005] This application provides a three-dimensional integrated thermally diffused bonding structure and its preparation method, which can reduce the thermal resistance of the bonding interface, alleviate the local temperature rise caused by heat flow concentration, and buffer the cyclic stress caused by the mismatch of thermal expansion coefficients.

[0006] To address the aforementioned technical problems, this application provides a three-dimensional integrated thermally diffused bonding structure, comprising: A first bonding structure is disposed on a first bonding surface of a first substrate. The first bonding structure includes a micro / nano bump array made of thermally conductive metal. The bumps in the micro / nano bump array extend in a direction away from the first bonding surface, and the extension height of the bumps is greater than their maximum cross-sectional size in a direction parallel to the first bonding surface. The second bonding structure is disposed on the second bonding surface of the second substrate. The second bonding structure includes a porous metal layer. The porosity of the porous metal layer decreases in the direction away from the second bonding surface. The porous metal layer and the micro / nano protrusion array are made of the same or compatible metals. The maximum cross-sectional size of the protrusion is matched with the average pore size of the porous metal layer, so that the micro-nano protrusion array can be partially embedded in the porous metal layer in the bonded state and form a metallurgical bond with the porous metal layer.

[0007] As a further improvement of this application, the ratio of the maximum cross-sectional size of the protrusion to the average pore diameter of the porous metal layer is 0.3≤D / R≤0.9; where D is the maximum cross-sectional size of the protrusion and R is the average pore diameter of the porous metal layer.

[0008] As a further improvement of this application, the protrusion is columnar or conical, and the cross-section of the protrusion is circular, polygonal, or irregular. When the protrusion is conical, the radius of curvature at the top of the protrusion is less than 50 nm.

[0009] As a further improvement of this application, the extension height H of the protrusion is 100nm to 5μm, the maximum cross-sectional size D of the protrusion is 20nm to 500nm, and the ratio H / D of the extension height H to the maximum cross-sectional size D is greater than 3.

[0010] As a further improvement of this application, the porosity of the porous metal layer is greater than 60% on the side closer to the second bonding surface and less than 40% on the side farther from the second bonding surface.

[0011] As a further improvement of this application, the thickness T of the porous metal layer is 200 nm to 3 μm, and the depth δ of the protrusion embedded in the porous metal layer satisfies: 0.2T≤δ≤0.8T.

[0012] As a further improvement of this application, the residual pores of the porous metal layer are filled with a thermally conductive phase change fluid.

[0013] As a further improvement to this application, the first substrate is a semiconductor chip, and the second substrate is a silicon interposer, a packaging substrate, or an integrated heat sink.

[0014] As a further improvement to this application, this application also provides a method for preparing a three-dimensional integrated thermally diffusing bonded structure, comprising the following steps: A micro / nano bump array made of thermally conductive metal is formed on the first bonding surface of the first substrate. The bumps in the micro / nano bump array extend in a direction away from the first bonding surface, and the extension height of the bumps is greater than their maximum cross-sectional size in the direction parallel to the first bonding surface. A porous metal layer is formed on the second bonding surface of the second substrate. The porosity of the porous metal layer decreases in the direction away from the second bonding surface. The porous metal layer and the micro / nano protrusion array are made of the same or compatible metals. Surface activation treatment is performed on the first bonding surface and the second bonding surface; After aligning the first substrate and the second substrate, hot-press bonding is performed to embed the micro-nano protrusion array into the porous metal layer and form a metallurgical bond with the porous metal layer. The maximum cross-sectional size of the protrusion is matched with the average pore size of the porous metal layer, so that the protrusion can be partially embedded in the porous metal layer under bonding pressure and form a metallurgical bond with the porous metal layer.

[0015] As a further improvement to this application, after aligning the first substrate and the second substrate and performing thermoforming bonding, the method further includes: A thermally conductive phase change fluid is injected into the residual pores of the porous metal layer using capillary force.

[0016] This application provides a three-dimensional integrated thermal diffusion bonding structure and its preparation method. A micro-nano protrusion array composed of thermally conductive metal and extending in height greater than the cross-sectional size is formed on a first substrate. A porous metal layer with porosity decreasing in the direction away from the second bonding surface is formed on a second substrate, so that the maximum cross-sectional size of the protrusion matches the average pore size of the porous metal layer, so that the protrusion portion can be embedded into the pores and form a metallurgical bond during bonding.

[0017] When heat is generated from the first substrate, it is first conducted away from the first bonding surface by the micro-nano protrusion array. After entering the porous metal layer, it diffuses and homogenizes laterally in the high porosity region near the second bonding surface in a direction parallel to the second bonding surface. Then it continues to be transferred away from the second bonding surface. As the porosity gradually decreases, the thermal conductivity of the porous metal layer gradually increases, and the heat is efficiently introduced into the second substrate. This reduces the thermal resistance of the bonding interface and alleviates the local temperature rise caused by heat flow concentration.

[0018] Meanwhile, the pore structures in the porous metal layer that are not embedded by the protrusions can buffer the cyclic stress caused by the mismatch of the thermal expansion coefficients of the first and second substrates through their own deformation; the metallurgical bond formed between the protrusions and the pores also ensures the reliability of the connection between the first and second bonding structures. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only a part of the embodiments of this application, and not all of the embodiments. For those skilled in the art, other drawings obtained from these drawings without creative effort are all within the scope of protection of this application.

[0020] Figure 1 This is a schematic diagram of the first bonding structure in the three-dimensional integrated thermal diffusion bonding structure provided in the embodiments of this application.

[0021] Figure 2 This is a schematic diagram of the second bonding structure in the three-dimensional integrated thermal diffusion bonding structure provided in the embodiments of this application.

[0022] Figure 3 This is a schematic diagram of a three-dimensional integrated thermal diffusion bonding structure provided in related technologies.

[0023] Figure 4 A schematic diagram of a three-dimensional integrated thermal diffusion bonding structure provided in an embodiment of this application.

[0024] Figure 5 A flowchart illustrating the preparation method of the three-dimensional integrated thermally diffused bonding structure provided in the embodiments of this application.

[0025] Figure 6 The flowchart illustrates the injection of thermally conductive phase change fluid in the preparation method of the three-dimensional integrated thermally diffused bonding structure provided in the embodiments of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0027] To make the description of this disclosure more detailed and complete, illustrative descriptions of the implementation methods and specific embodiments of this application are provided below; however, this is not the only form of implementing or utilizing the specific embodiments of this application. The implementation methods cover the features of multiple specific embodiments and the method steps and their order for constructing and operating these specific embodiments. However, other specific embodiments can also be used to achieve the same or equivalent functions and step sequences. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0029] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The word "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more. Other quantifiers should be understood similarly. The preferred embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. Furthermore, the embodiments of this application and the features in the embodiments can be combined with each other without conflict.

[0030] Three-dimensional heterogeneous integration technology, by vertically stacking chips with different process nodes and functions, has become a core technological path for improving the computing power, bandwidth, and energy efficiency of computing systems in the post-Moore's Law era. In the heterogeneous integration scenario of high-power computing chips and heat sinks, the bonding interface not only needs to provide stable mechanical connections and electrical interconnections, but also needs to transfer the high heat flux density generated by the chip to the heat sink.

[0031] Currently, most mainstream hybrid bonding interfaces adopt a symmetrical design approach, where both the chip side and the heat sink side are fabricated as smooth planes or surfaces with similar roughness. Roughening or activation treatments are then used to promote atomic diffusion and reduce bonding voids. While this design can improve bonding yield and connection reliability, it does not address the structural optimization required for the high heat flux and thermal stress buffering needs of high-power chips.

[0032] Furthermore, in practical applications, the effective contact area of ​​the symmetrical planar bonding structure is limited, resulting in high thermal resistance at the bonding interface. The heat generated by the chip during operation cannot be effectively dissipated, which easily leads to heat accumulation and a continuous rise in the chip junction temperature, affecting computing performance and long-term operational reliability. At the same time, the chip generates continuous dynamic heat dissipation during operation, causing frequent temperature cycles and a mismatch in the thermal expansion coefficients between the chip and the heat sink. This results in continuous cyclic shear stress at the rigid bonding interface. Under long-term cumulative stress, the bonding interface is prone to fatigue cracking or even delamination failure.

[0033] In view of this, please refer to Figures 1-6This application proposes a three-dimensional integrated thermal diffusion bonding structure and its preparation method, which can reduce the thermal resistance of the bonding interface, alleviate the local temperature rise caused by heat flow concentration, and buffer the cyclic stress caused by thermal expansion coefficient mismatch.

[0034] Please refer to Figure 1 and Figure 2 ,in Figure 1 This is a schematic diagram of the first bonding structure in the three-dimensional integrated thermally diffused bonding structure provided in the embodiments of this application. Figure 2 This is a schematic diagram of the second bonding structure in the three-dimensional integrated thermal diffusion bonding structure provided in this application embodiment. The three-dimensional integrated thermal diffusion bonding structure provided in this application includes a first bonding structure and a second bonding structure.

[0035] In the embodiments of this application, a first bonding structure is disposed on a first bonding surface of a first substrate, the first substrate being typically a chip that generates high heat flux density, and the first bonding structure comprising a micro-nano bump array made of thermally conductive metal.

[0036] Furthermore, a micro-nano protrusion array refers to an array structure composed of multiple micro-nano-sized protrusions arranged in a certain manner, where each protrusion in the array extends from the first bonding surface in a direction away from the first bonding surface.

[0037] Furthermore, the extension height of each protrusion is greater than its maximum cross-sectional dimension in the direction parallel to the first bonding surface. This application's high aspect ratio protrusion design effectively increases the contact area of ​​the bonding interface, while simultaneously forming a longitudinal heat conduction channel along the protrusion's extension direction, allowing heat to be vertically conducted from the chip to the heat dissipation carrier, reducing localized temperature rise caused by concentrated heat flow.

[0038] It should be noted that the maximum cross-sectional dimension of the aforementioned protrusion refers to the maximum cross-sectional dimension measured on any cross-section of the protrusion in its extension direction. When the cross-section of the protrusion is circular, the maximum cross-sectional dimension is the diameter; when the cross-section of the protrusion is polygonal or other irregularly shaped, the maximum cross-sectional dimension is the straight-line distance between the two farthest points on the cross-sectional profile. This application does not strictly limit the cross-sectional shape of the protrusion to accommodate deviations that may occur due to different manufacturing processes.

[0039] In one specific embodiment, the thermally conductive metal constituting the micro / nano bump array can be a metal with high thermal conductivity, such as copper, silver, or copper-silver alloy, to ensure that heat can be discharged from the chip through a low thermal resistance path. This application does not limit this.

[0040] Furthermore, the second bonding structure is disposed on the second bonding surface of the second substrate, which is typically a carrier that performs heat dissipation functions, such as a silicon interposer, a packaging substrate, or an integrated heat sink.

[0041] In this embodiment, the second bonding structure includes a porous metal layer with a three-dimensional interconnected framework structure and internal pores, which can provide an embedding space for the micro-nano protrusion array. At the same time, heat conduction is achieved through the framework structure. Moreover, the internal porosity of the porous metal layer is not uniformly distributed, but decreases along the direction away from the second bonding surface.

[0042] In other words, the porous metal layer has higher porosity on the side near the bonding interface, where the first bonding surface and the second bonding surface are in contact and connected. Higher porosity facilitates the smooth embedding of the micro / nano protrusion array during the bonding process. Conversely, the side of the porous metal layer closer to the second substrate is relatively dense, ensuring efficient heat conduction from the porous metal layer to the second substrate. Through this gradient change in porosity, the porous metal layer simultaneously possesses excellent embeddability and thermal conductivity.

[0043] Building upon this, this application sets the porous metal layer and the micro / nano protrusion array to be composed of the same or compatible metals. Using the same or compatible metals enables the formation of a strong bond through atomic diffusion during the bonding process, avoiding problems such as poor contact or delamination at the bonding interface.

[0044] For example, the porous metal layer and the micro / nano bump array can be made of the same metal. For instance, when the micro / nano bump array is made of copper, the porous metal layer can be made of copper; when the micro / nano bump array is made of silver, the porous metal layer can be made of silver.

[0045] For example, the porous metal layer and the micro / nano bump array can be made of compatible metals. For instance, when the micro / nano bump array is made of copper, the porous metal layer can also be made of silver. Copper and silver can diffuse into each other at the bonding temperature to form a solid solution, which can also achieve a reliable metallurgical bond.

[0046] This application does not specifically limit the materials of the micro-nano protrusion array and the porous metal layer, as long as the micro-nano protrusion array and the porous metal layer can form a metallurgical bond under bonding conditions, as should be known by those skilled in the art.

[0047] Understandably, since the maximum cross-sectional size of the protrusion matches the average pore size of the porous metal layer, the protrusions in the micro / nano protrusion array can be partially embedded in the pores of the porous metal layer in the bonded state. This application sets the protrusions to be partially embedded in the pores of the porous metal layer rather than completely embedded. This ensures mechanical connection strength while retaining the residual thickness in the porous metal layer to buffer thermal stress caused by CTE (Coefficient of Thermal Expansion) mismatch, and ensures sufficient contact between the protrusion surface and the framework of the porous metal layer.

[0048] Please refer toFigure 3 This is a schematic diagram of a three-dimensional integrated thermal diffusion bonding structure provided in the related technology. It can be observed that the three-dimensional integrated thermal diffusion bonding structure provided in the related technology usually has both the chip (first substrate) side and the heat dissipation carrier (second substrate) side made into smooth planes. However, the effective contact area of ​​this symmetrical planar bonding structure is limited, which will lead to high thermal resistance at the bonding interface, and the heat generated by the chip operation cannot be effectively dissipated.

[0049] In the embodiments of this application, please refer to Figure 4 The diagram shows a three-dimensional integrated thermal diffusion bonding structure provided in the embodiments of this application. It can be observed that the first bonding structure and the second bonding structure are no longer simply planar bonding, but rather the raised surface and the inner wall of the pore undergo atomic diffusion during the bonding process and form a metallurgical bond.

[0050] Specifically, metallurgical bonding refers to a bonding method in which two metal structures undergo atomic interpenetration and diffusion under hot-press bonding conditions to achieve atomic-level fusion. This bonding method has no obvious interface gaps, high bonding strength, and low interface contact thermal resistance. It is a solid-state connection achieved through the mutual diffusion of interface atoms at temperatures below their respective melting points. This application will not elaborate on the specific working principle of metallurgical bonding here.

[0051] In this way, after heat enters the porous metal layer from the chip through the micro-nano bump array of the first bonding structure, it will first spread laterally along the skeleton in the surface area with higher porosity to achieve uniform heat flow distribution, and then be vertically introduced into the second substrate through the gradient layer with gradually decreasing porosity, thereby achieving synergistic optimization of heat diffusion and heat conduction.

[0052] In an optional embodiment, the ratio of the maximum cross-sectional dimension D of the protrusion to the average pore diameter R of the porous metal layer is set to be between 0.3 and 0.9, i.e., 0.3 ≤ D / R ≤ 0.9. Here, D is the maximum cross-sectional dimension of the protrusion measured at any cross-section along its extension direction, and R is the average pore diameter of the porous metal layer.

[0053] In this embodiment, the engagement between the protrusion and the porous metal layer is not a simple contact, but rather requires the protrusion to be embedded inside the pores of the porous metal layer. This application sets a minimum D / R ratio of 0.3. When the maximum cross-sectional size of the protrusion is too small relative to the average pore size of the porous metal layer (i.e., the D / R ratio is below 0.3), although the protrusion can easily enter the pores, the contact area between its outer surface and the inner wall of the pores is limited, making it difficult to form a sufficient metallurgical bonding area. This results in a negligible decrease in interfacial thermal resistance, and insufficient mechanical interlocking strength, failing to effectively transfer the shear load between the chip and the heat sink.

[0054] On the other hand, the maximum value of the D / R ratio is set to 0.9. When the D / R ratio exceeds 0.9, under the action of bonding pressure, the protrusion is difficult to slide smoothly into the pore and tends to compact the pore, causing the porous metal layer to become dense in the area near the bonding interface. This causes the porous metal layer to lose its original stress buffering structural function and limits the effective embedding depth of the protrusion.

[0055] It is understood that this application limits the D / R ratio to the range of 0.3 to 0.9, so that the protrusion can reliably enter the pores of the porous metal layer, preserving the integrity of the porous metal layer's pore structure. Within the above-mentioned ratio range, the specific D / R value can be selected based on the chip's heat flux density level, the material of the heat sink, and the expected temperature cycling conditions; this application does not impose further limitations on this.

[0056] As an alternative implementation, the protrusion can be columnar or conical. Here, columnar means that the protrusion has a substantially uniform cross-sectional size along the direction away from the first bonding surface, while conical means that the cross-sectional size of the protrusion gradually decreases along the direction away from the first bonding surface.

[0057] This application specifies that the protrusions can be columnar or conical in shape, taking into account the variability and diversity of actual manufacturing processes. Under different electrodeposition conditions, or when using template-assisted growth, the formed metal protrusions may be nanopillars with relatively uniform thickness, or nanocones that naturally taper from the root to the tip. Regardless of whether the protrusion is columnar or conical, it should extend in a direction away from the first bonding surface, and the extension height should be greater than its maximum cross-sectional size in the direction parallel to the first bonding surface, so that it can penetrate deep into the pores of the porous metal layer during bonding.

[0058] For example, the cross-sectional shape of the protrusion can be circular, polygonal, or irregular. When the protrusion cross-section is circular, its maximum cross-sectional size is the diameter of the circle; when the protrusion cross-section is polygonal, its maximum cross-sectional size is the straight-line distance between the two farthest vertices on the cross-section; irregular cross-sections cover other irregular contour shapes, which are not strictly limited in this application.

[0059] Preferably, the conical protrusion has a smaller top size, resulting in better guidance and lower penetration resistance when embedded in the pores of the porous metal layer. When the protrusion is conical, the top radius of curvature is limited to less than 50 nm. Here, the top radius of curvature refers to the radius of curvature at the tip of the conical protrusion; the smaller the value, the sharper the tip.

[0060] During the bonding process, such sharp tips typically have a high surface chemical potential, thus enabling sufficient atomic diffusion with the pore walls of porous metal layers, promoting the formation of metallurgical bonds, and reducing the requirements for bonding temperature and bonding pressure.

[0061] In an optional embodiment, the extension height H of the protrusion is set between 100 nm and 5 μm, and the maximum cross-sectional size D of the protrusion is set between 20 nm and 500 nm.

[0062] In actual fabrication, the extension height H of the protrusion is usually directly related to process parameters such as the via etching depth, template thickness, and electrodeposition time. The lower limit of 100nm ensures that the protrusion has sufficient extension height to penetrate the surface of the porous metal layer and partially embed itself, while the upper limit of 5μm avoids the risk of buckling instability that the protrusion may face during hot-press bonding.

[0063] Meanwhile, the maximum cross-sectional size D of the protrusion is set between 20nm and 500nm. The lower limit of 20nm is limited by the technology of through-hole photolithography and electrodeposition process. If D is less than 20nm, the thermal conductivity cross-sectional area of ​​a single protrusion is too small, which is not conducive to efficient longitudinal heat conduction. The upper limit of 500nm matches the average pore size of the porous metal layer, ensuring that the protrusion can be smoothly embedded in the pores rather than compacting the pore structure.

[0064] Based on this, this application limits the ratio AR (Aspect Ratio) of the extension height H to the maximum cross-sectional dimension D to be greater than 3, that is, AR=H / D is greater than 3, to ensure that the protrusion has a high aspect ratio morphological feature, so that the protrusion can enter the pores of the porous metal layer in a suitable posture during the bonding process, rather than contacting the porous metal layer in a squeezed manner.

[0065] It is understandable that when the aspect ratio AR is too small, it means that the cross-sectional size of the protrusion is large and the extension height is insufficient, which will make the protrusion lack sufficient longitudinal depth. The side of the protrusion will also have difficulty forming effective contact with the inner wall of the pore, resulting in a decrease in thermal conductivity.

[0066] When the aspect ratio (AR) is greater than 3, the bumps typically possess a high aspect ratio morphology, providing numerous longitudinal heat conduction channels within a limited bonding interface area. Each bump forms a continuous metal heat conduction path from its root to its embedding depth, pointing from the chip end to the heat sink end. Furthermore, although the maximum cross-sectional size of the bumps is in the submicron range, and the thermal conductivity cross-sectional area of ​​a single bump is relatively small, the total effective contact area after arraying is significantly larger than that of traditional planar bonding, thereby effectively reducing the thermal resistance of the bonding interface.

[0067] Regarding the porosity distribution, this application provides that the porosity of the porous metal layer is greater than 60% on the side closer to the second bonding surface and less than 40% on the side farther from the second bonding surface.

[0068] It can be understood that the side near the second bonding surface mentioned here is the surface area where the porous metal layer contacts the first bonding structure in the bonded state. The porosity of this surface area is greater than 60%, which can provide sufficient space for the embedding of the micro-nano protrusion array, ensuring that the protrusion can be successfully embedded into the porous metal layer and form sufficient contact.

[0069] The side away from the second bonding surface is the bottom layer region where the porous metal layer is connected to the second substrate body. This application limits the porosity of the bottom layer region to less than 40%, which can reduce the thermal resistance of the bottom layer region and introduce the heat transferred through the surface region into the second substrate body with a lower diffusion thermal resistance.

[0070] Furthermore, this application sets the porosity of the porous metal layer to decrease gradually from the surface layer near the bonding interface to the bottom layer near the second substrate along a direction perpendicular to the second bonding surface. When heat is injected into the porous metal layer from the micro / nano protrusion array, it first enters the high-porosity surface region near the bonding interface. In this surface region, the heat preferentially spreads laterally along a direction parallel to the bonding interface, achieving uniform heat flow and eliminating local hot spots. As the heat continues to be transferred to the second substrate along a direction perpendicular to the second bonding surface, the porosity gradually decreases. The heat that has been laterally uniformly distributed can be introduced into the second substrate in the vertical direction with lower thermal resistance, thereby forming a heat dissipation path that first uniformly heats laterally and then discharges heat in the vertical direction.

[0071] In an optional embodiment, the thickness T of the porous metal layer is preferably set between 200 nm and 3 μm to ensure that the porous metal layer has sufficient thickness to prevent protrusions from penetrating the porous metal layer and directly contacting the second substrate, while also preventing the porous metal layer from being too thick and increasing the thermal resistance of heat diffusion within the porous metal layer.

[0072] Furthermore, the relationship between the depth δ of the protrusion embedded in the porous metal layer and the thickness T of the porous metal layer is defined as 0.2T≤δ≤0.8T. When the embedding depth δ is less than 0.2T, the protrusion only enters the surface region of the porous metal layer, and the contact area between the side of the protrusion and the inner wall of the pores is limited, resulting in insufficient metallurgical bonding. Under the shear stress caused by temperature cycling, the bonding interface may slip or separate.

[0073] When the embedding depth δ is greater than 0.8T, the protrusion almost penetrates the entire porous metal layer. The remaining porous layer below the embedding depth is too thin, and the pore structure cannot effectively play the stress buffering function. The cyclic strain caused by CTE mismatch will be concentrated near the interface between the porous metal layer and the second substrate, increasing the risk of delamination or cracking at this point.

[0074] Thus, this application controls the embedding depth to between 20% and 80% of the thickness of the porous metal layer, which can form a sufficient metallurgical bond between the protrusion and the porous metal layer, while leaving a sufficiently thick porous metal layer outside the embedding position, ensuring the connection reliability of the bonding interface while giving full play to the stress buffering capacity of the porous metal layer.

[0075] In an optional embodiment, after the porous metal layer and the micro / nano protrusion array complete the bonding and form a metallurgical bond, there are still some residual pores in the porous metal layer that are not occupied by the protrusions.

[0076] To further enhance the heat dissipation capacity of the bonding interface, this application proposes filling the residual pores of the porous metal layer with a thermally conductive phase change fluid. This thermally conductive phase change fluid can be a low-viscosity, high-thermal-conductivity liquid medium. Specifically, it can be filled into the residual pores of the porous metal layer through heat dissipation holes on the back of the heat dissipation carrier combined with a capillary filling process, without the need for additional pressurization, relying solely on capillary force.

[0077] After filling, the thermally conductive phase change fluid replaces the air that was originally present in the remaining pores. When the chip generates instantaneous high heat flux density under high power consumption conditions, the thermally conductive phase change fluid can absorb a large amount of heat through its own phase change process and quickly dissipate the excess heat that has accumulated locally. Based on the original structure of longitudinal heat conduction of the protrusion and transverse uniform heat dissipation of the metal porous layer, the overall heat dissipation capacity of the bonding interface is further improved.

[0078] In one specific implementation, the first substrate can be a semiconductor chip. This semiconductor chip can be a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or other high-power computing chips. A common characteristic of these chips is that they generate high heat flux density during operation, requiring efficient heat transfer to the heat dissipation side via a bonding interface.

[0079] Furthermore, the second substrate can be any one of a silicon interposer, a packaging substrate, or an integrated heat sink to adapt to different chip integration scenarios, and this application does not impose too many restrictions on this.

[0080] It is understandable that this application, through the setting of asymmetric micro / nano protrusions and porous metal layers, can effectively improve... Figure 3 The inherent defects of traditional planar bonding structures are shown.

[0081] In terms of interfacial thermal conductivity, the high aspect ratio metal protrusions extend longitudinally, forming continuous and complete heat conduction channels that can stably and directionally conduct the heat generated by the semiconductor chip to the interior of the porous metal layer. Combined with the gradient structure of the porous metal layer—high porosity on the surface and low porosity on the bottom—the concentrated heat transferred from the protrusions can be fully diffused on the surface of the porous layer and then uniformly transferred to the second substrate via the dense bottom layer, effectively improving the problem of heat concentration at the bonding interface and optimizing overall thermal conductivity.

[0082] Regarding mechanical reliability, this application employs a bonding method where the protruding portion is embedded in a porous metal layer. Compared to traditional planar bonding, this method enhances the overall connection strength at the bonding interface. Simultaneously, the highly porosity surface of the porous metal layer possesses excellent deformability. When the first and second substrates experience cyclic shear stress due to differences in their thermal expansion coefficients under temperature cycling conditions, the microscopic deformation of the porous structure buffers and absorbs thermal strain, alleviating interface stress concentration and improving the stability of the integrated structure. Furthermore, the residual pores remaining within the porous metal layer after bonding can be filled with a highly thermally conductive phase-change fluid through capillary action, further enhancing heat dissipation.

[0083] Based on the above-described three-dimensional integrated thermally diffusing bonded structure, this application also provides a method for preparing a three-dimensional integrated thermally diffusing bonded structure. Please refer to... Figure 5 This is a flowchart of a method for preparing a three-dimensional integrated thermally diffused bonding structure according to an embodiment of this application. The preparation method specifically includes the following steps: S1: A micro-nano bump array made of thermally conductive metal is formed on the first bonding surface of the first substrate. The bumps in the micro-nano bump array extend in a direction away from the first bonding surface, and the extension height of the bumps is greater than their maximum cross-sectional size in the direction parallel to the first bonding surface. S2: A porous metal layer is formed on the second bonding surface of the second substrate. The porosity of the porous metal layer decreases in the direction away from the second bonding surface. The porous metal layer and the micro / nano protrusion array are made of the same or compatible metals. S3: Perform surface activation treatment on the first bonding surface and the second bonding surface; S4: After aligning the first substrate and the second substrate, perform hot-press bonding to embed the micro-nano protrusion array into the porous metal layer and form a metallurgical bond with the porous metal layer. The maximum cross-sectional size of the protrusion is matched with the average pore size of the porous metal layer, so that the protrusion can be partially embedded in the porous metal layer under bonding pressure and form a metallurgical bond with the porous metal layer.

[0084] As an optional implementation method, please refer to Figure 6This is a flowchart illustrating the injection of thermally conductive phase change fluid in the fabrication method of the three-dimensional integrated thermally diffused bonded structure provided in this application embodiment. After aligning the first substrate and the second substrate and performing thermo-press bonding, the method further includes: S5: Inject thermally conductive phase change fluid into the residual pores of the porous metal layer using capillary force.

[0085] The following will provide a detailed explanation of the three-dimensional integrated thermally diffused bonding structure and its preparation method based on a specific embodiment.

[0086] In this specific embodiment, the first substrate is a semiconductor chip that generates high heat flux density, with an operating heat flux density of approximately 100 W / cm² (unit of heat flux density); the second substrate is a silicon interposer that performs heat dissipation function.

[0087] In the design of the first bonding structure, copper was chosen as the thermally conductive metal for the micro / nano bump array. The height H of the bumps was designed to be 500 nm, the maximum cross-sectional size D was designed to be 100 nm, and the aspect ratio AR = H / D = 5. The bumps were arranged in a square pattern with a center-to-center distance of 250 nm. The bumps were conical with a top radius of curvature of less than 20 nm to utilize high surface energy to promote atomic diffusion in the subsequent bonding process.

[0088] In the design of the second bonding structure, the porous metal layer uses the same copper as the micro / nano protrusion array as its material. The thickness T of the porous metal layer is designed to be 800 nm, and its porosity decreases along the direction away from the second bonding surface.

[0089] Specifically, the surface region of the porous metal layer near the second bonding surface has a depth of about 200 nm. The porosity of this region is about 75%, and the average pore size R is about 150 nm, satisfying D / R≈0.67, which falls within the ratio range of 0.3 to 0.9, ensuring that the protrusion can effectively embed into the pores of the porous metal layer rather than compacting it.

[0090] The bottom layer region on the side of the porous metal layer away from the second bonding surface has a thickness of about 200 nm and a porosity of about 30%, which is close to that of dense copper, to ensure that heat can be efficiently transferred from the porous metal layer to the second substrate. The porosity decreases linearly from the surface layer to the bottom layer along the thickness direction.

[0091] In the bonded state, the depth δ of the protrusion embedded in the porous metal layer is designed to be 300nm, satisfying δ / T=0.375, which falls within the ratio range of 0.2 to 0.8. While ensuring sufficient mechanical interlock strength, a residual porous metal layer of about 500nm thickness is retained for stress buffering.

[0092] The specific preparation process is as follows: First, a first bonding structure is formed on the first bonding surface of the first substrate.

[0093] In this specific embodiment, the present application deposits a silicon dioxide dielectric layer on a chip wafer after front-end manufacturing is completed, and forms a via array in the dielectric layer by photolithography and dry etching. The via diameter is about 100nm and the depth is about 600nm.

[0094] Furthermore, an ALD (Atomic Layer Deposition) method is used to sequentially deposit a TaN / Ta (tantalum nitride / metallic tantalum) diffusion barrier layer and a copper seed layer on the inner wall of the via.

[0095] Subsequently, AAO (Anodic Aluminum Oxide) template-assisted electrodeposition was used, in which an AAO template with regular nanopores and a pore size of about 120 nm was temporarily bonded to the wafer surface and aligned. Pulse electroplating was then performed in the electrolyte to selectively grow copper within the pores, forming copper protrusions extending away from the first bonding surface, with a growth height of about 600 nm.

[0096] After removing the AAO template, a light CMP (Chemical Mechanical Polishing) was performed to obtain a micro-nano protrusion array with an extension height of about 500 nm and a maximum cross-sectional size of about 100 nm.

[0097] Secondly, a second bonding structure is formed on the second bonding surface of the second substrate.

[0098] Specifically, a copper film with a thickness of approximately 1 μm is deposited on a silicon substrate using PVD (Physical Vapor Deposition), and then a uniformly composed Cu is electroplated onto the copper film. 30 Zn 70 The alloy layer is approximately 1.2 μm thick.

[0099] Furthermore, a gradient electrochemical dealloying process is adopted, using dilute hydrochloric acid as the electrolyte, and anodic corrosion is performed by linear scanning voltammetry. The voltage scan is controlled to make the zinc in the surface region of the alloy layer dissolve preferentially and rapidly, while the zinc in the bottom region dissolves more slowly, thereby forming a porous copper structure in situ with porosity decreasing along the direction away from the second bonding surface.

[0100] After cleaning and drying, a porous metal layer with a thickness of about 800 nm is obtained. The porosity on the side close to the second bonding surface is about 75%, and the porosity on the side away from the second bonding surface is about 30%. The bottom porosity of the porous metal layer is set to 30% to approach dense copper, which can prevent heat from being retained in the bottom area of ​​the porous metal layer and improve the heat dissipation effect.

[0101] Then, surface activation and bonding are performed.

[0102] Specifically, the first and second bonding surfaces are activated by nitrogen-hydrogen mixed plasma to clean the surfaces. The first and second substrates are aligned in a vacuum environment, and a pressure of 10 MPa (megapascal) is applied for thermo-press bonding at 300°C for 60 minutes.

[0103] After bonding is completed, the protrusions in the micro-nano protrusion array are embedded in the pores of the porous metal layer to a depth of about 300 nm. Metallurgical bonding is formed between the protrusion surface and the inner wall of the pore through atomic diffusion.

[0104] As an alternative implementation, after bonding is completed, a low-viscosity, high-thermal-conductivity thermally conductive phase change fluid can be injected into the residual pores of the porous metal layer through the microchannels on the back side of the second substrate using capillary force, thereby further improving the heat dissipation capacity.

[0105] It should be noted that the photolithography, dry etching, ALD, electrodeposition, PVD, CMP, and other processes used in the above embodiments are all mature processes in the semiconductor field. Those skilled in the art can select and adjust them according to actual process conditions. The reference to these processes in this embodiment is only for illustrative purposes to illustrate the fabrication process of the three-dimensional integrated thermally diffused bonding structure described in this application, and does not constitute a limitation on the scope of protection of this application, nor will it elaborate on the specific details of these processes in this document.

[0106] For further details regarding the preparation method of the above-mentioned three-dimensional integrated thermally diffusing bonded structure to achieve the above technical solution, please refer to the description of the three-dimensional integrated thermally diffusing bonded structure provided in the above-mentioned application embodiments, which will not be repeated here.

[0107] It should be noted that, in the several embodiments provided in this application, it should be understood that the disclosed devices, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed between each other can be through some interfaces, or indirect coupling or communication connection between devices or units, and can be electrical, mechanical, or other forms.

[0108] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0109] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A three-dimensional integrated thermally diffusing bonding structure, characterized in that, include: A first bonding structure is disposed on a first bonding surface of a first substrate. The first bonding structure includes a micro / nano bump array made of thermally conductive metal. The bumps in the micro / nano bump array extend in a direction away from the first bonding surface, and the extension height of the bumps is greater than their maximum cross-sectional size in a direction parallel to the first bonding surface. The second bonding structure is disposed on the second bonding surface of the second substrate. The second bonding structure includes a porous metal layer. The porosity of the porous metal layer decreases in the direction away from the second bonding surface. The porous metal layer and the micro / nano protrusion array are made of the same or compatible metals. The maximum cross-sectional size of the protrusion is matched with the average pore size of the porous metal layer, so that the micro-nano protrusion array can be partially embedded in the porous metal layer in the bonded state and form a metallurgical bond with the porous metal layer.

2. The three-dimensional integrated thermally diffused bonding structure as described in claim 1, characterized in that, The ratio of the maximum cross-sectional size of the protrusion to the average pore diameter of the porous metal layer is 0.3 ≤ D / R ≤ 0.9; where D is the maximum cross-sectional size of the protrusion and R is the average pore diameter of the porous metal layer.

3. The three-dimensional integrated thermally diffused bonding structure as described in claim 1, characterized in that, The protrusion is columnar or conical, and the cross-section of the protrusion is circular, polygonal, or irregular. When the protrusion is conical, the radius of curvature at the top of the protrusion is less than 50 nm.

4. The three-dimensional integrated thermally diffused bonding structure as described in claim 1, characterized in that, The extension height H of the protrusion is 100nm to 5μm, the maximum cross-sectional size D of the protrusion is 20nm to 500nm, and the ratio H / D of the extension height H to the maximum cross-sectional size D is greater than 3.

5. The three-dimensional integrated thermally diffused bonding structure according to claim 1, characterized in that, The porosity of the porous metal layer is greater than 60% on the side closer to the second bonding surface and less than 40% on the side farther from the second bonding surface.

6. The three-dimensional integrated thermally diffused bonding structure according to claim 1, characterized in that, The thickness T of the porous metal layer is 200 nm to 3 μm, and the depth δ of the protrusion embedded in the porous metal layer satisfies: 0.2T≤δ≤0.8T.

7. The three-dimensional integrated thermally diffused bonding structure according to any one of claims 1-6, characterized in that, The residual pores of the porous metal layer are filled with a thermally conductive phase change fluid.

8. The three-dimensional integrated thermally diffused bonding structure according to any one of claims 1-6, characterized in that, The first substrate is a semiconductor chip, and the second substrate is a silicon interposer, a packaging substrate, or an integrated heat sink.

9. A method for preparing a three-dimensional integrated thermally diffusing bonded structure, characterized in that, Includes the following steps: A micro / nano bump array made of thermally conductive metal is formed on the first bonding surface of the first substrate. The bumps in the micro / nano bump array extend in a direction away from the first bonding surface, and the extension height of the bumps is greater than their maximum cross-sectional size in the direction parallel to the first bonding surface. A porous metal layer is formed on the second bonding surface of the second substrate. The porosity of the porous metal layer decreases in the direction away from the second bonding surface. The porous metal layer and the micro / nano protrusion array are made of the same or compatible metals. Surface activation treatment is performed on the first bonding surface and the second bonding surface; After aligning the first substrate and the second substrate, hot-press bonding is performed to embed the micro-nano protrusion array into the porous metal layer and form a metallurgical bond with the porous metal layer. The maximum cross-sectional size of the protrusion is matched with the average pore size of the porous metal layer, so that the protrusion can be partially embedded in the porous metal layer under bonding pressure and form a metallurgical bond with the porous metal layer.

10. The method for preparing a three-dimensional integrated thermally diffusing bonded structure according to claim 9, characterized in that, After aligning the first substrate and the second substrate and performing thermo-press bonding, the process further includes: A thermally conductive phase change fluid is injected into the residual pores of the porous metal layer using capillary force.

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