Low temperature direct bonding

Abstract

The invention discloses a method for forming a bonding structure. The method may include providing a first element having a first non-conductive region and a first conductive feature, providing a second element having a second non-conductive region and a second conductive feature, bonding the first non-conductive region to the second non-conductive region, and applying a mechanical stress to at least one of the first conductive feature and the second conductive feature. The first conductive feature and the second conductive feature are separated by a gap when the first non-conductive region is bonded to the second non-conductive region. Applying a mechanical stress to at least one of the first conductive feature and the second conductive feature reduces a gap between the first conductive feature and the second conductive feature. The method may include annealing the first element and the second element while applying a mechanical stress to at least one of the first conductive feature and the second conductive feature.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 338,692, filed on May 5, 2022, the entire contents of which are incorporated herein by reference in their entirety and for all purposes. Technical Field

[0003] The field relates to structures and methods for direct bonding, and in particular to methods for hybrid direct bonding of components (eg, semiconductor components) at low temperatures. Background Art

[0004] Semiconductor elements such as integrated device dies or chips can be mounted or stacked on other elements. For example, the semiconductor element can be mounted on a carrier, such as an integrated device die, an interposer, a reconstituted wafer or element, etc. As another example, a semiconductor element can be stacked on top of another semiconductor element, for example, a first integrated device die can be stacked on a second integrated device die. Each of the semiconductor elements can have a conductive pad for mechanically and electrically bonding the semiconductor elements to each other.

[0005] There are many advantages to directly bonding components together without an intervening adhesive, such as solder. However, direct hybrid bonding of conductive features and non-conductive field regions can be challenging. Therefore, there is a continuing need for improved hybrid direct bonding methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1A is a schematic cross-sectional side view of a structure including a first element and a second element in a step of a method of forming a bonded structure according to one embodiment.

[0007] Figure 1B-1E Shows the formation Figure 1A steps of the structure.

[0008] Figure 2A is a schematic cross-sectional side view of a structure at a step in a method of forming a bonded structure according to another embodiment.

[0009] Figure 2B Shows Figure 2A Another view of the structure.

[0010] Figure 2C-2F Shows the formation Figure 2A steps of the structure.

[0011] Figure 3 The wafer is shown positioned on the mold surface of the mold structure.

[0012] Figure 4A method of deforming a bonding element over a curved surface by applying a distributed pressure over the bonding element is illustrated.

[0013] Figure 5A is a schematic cross-sectional side view of a bonding element coupled to a tensile layer.

[0014] Figure 5B is a schematic cross-sectional side view of a bonding element and a tensile layer positioned above a concave surface.

[0015] Figure 6 is a schematic cross-sectional side view of an assembly of a first element and a second element disposed over a convex support surface according to one embodiment.

[0016] Fig. 7A is a cross-sectional side view of a bonded first element and second element coupled to a compression layer or a tension layer according to one embodiment.

[0017] Figure 7B is a flow chart of a method of bonding a first component and a second component according to one embodiment.

[0018] Fig. 8A and Figure 8B A schematic cross-sectional side view of a bonded first element and a second element is shown during a bonding process.

[0019] Figure 8C is a flow chart of a method of bonding a first component and a second component according to one embodiment.

[0020] Fig.9A and Fig. 9B An example of a stress applying method is shown.

[0021] Fig.10 Shown are a first element and a second element coupled to a curved support structure.

[0022] Fig.11A and Fig. 11B A first support structure and a second support structure attached to a first element and a second element are shown. DETAILED DESCRIPTION

[0023] The present disclosure describes a method for directly bonding components (e.g., semiconductor components) to each other at a relatively low temperature (e.g., hybrid direct bonding). The resulting bonding structure may include a bonding conductive feature with an irregular grain size, the irregular grain size including a relatively small grain size and a relatively large grain size, the relatively large grain size being at least three times larger than the small grain size. For example, the large grain size may be at least three times, four times, or five times the small grain size. The bonding conductive feature of the resulting bonding structure may include a curved bonding interface. Two or more semiconductor components (such as integrated device dies, wafers, etc.) may be stacked or bonded to each other to form a bonding structure. The conductive contact pad of one component may be electrically connected to the corresponding conductive contact pad of another component. Any suitable number of components may be stacked in the bonding structure. The methods and bonding pad structures described herein may also be used in other contexts.

[0024] In some embodiments, the elements are directly bonded to each other without an adhesive (e.g., hybrid bonding). In various embodiments, the non-conductive (e.g., semiconductor or inorganic dielectric) material of the first element can be directly bonded to the corresponding non-conductive (e.g., semiconductor or inorganic dielectric) field region of the second element without an adhesive. In various embodiments, the conductive region (e.g., metal pad) of the first element can be directly bonded to the corresponding conductive region (e.g., metal pad, trench or via, such as through-substrate via (TSV)) of the second element without an adhesive. The non-conductive material can be referred to as a non-conductive bonding region or bonding layer of the first element. In some embodiments, the non-conductive material of the first element can be directly bonded to the corresponding non-conductive material of the second element using a bonding technique that uses at least the direct bonding techniques disclosed in U.S. Patents Nos. 9,564,414, 9,391,143, and 10,434,749, the entire contents of each of which are incorporated herein by reference in their entirety and for all purposes. In other applications, in a bonded structure, the non-conductive material of a first element may be directly bonded to the conductive material of a second element so that the conductive material of the first element is closely matched with the non-conductive material of the second element. Suitable dielectric materials for direct bonding include, but are not limited to, inorganic dielectrics such as silicon oxide, silicon nitride, or silicon oxynitride, or may include carbon, such as silicon carbide, silicon oxynitride, silicon carbonitride, or diamond-like carbon. Although including carbon, such carbon-containing ceramic materials may be considered inorganic. Other examples of hybrid direct bonding may be found in U.S. Patent No. 11,056,390, the entire contents of which are incorporated herein by reference in their entirety.

[0025] In various embodiments, direct bonding can be formed without an intermediate adhesive. For example, the semiconductor or dielectric bonding surface can be polished to a high degree of smoothness. The bonding surface can be cleaned and exposed to plasma and / or etchant to activate the surface. In some embodiments, the surface can be terminated with a substance after activation or during activation (e.g., during a plasma and / or etching process). Without being limited by theory, in some embodiments, an activation process can be performed to break the chemical bonds at the bonding surface, and the termination process can provide additional chemicals at the bonding surface, which improves the bonding energy during direct bonding. In some embodiments, activation and termination are provided in the same step, for example, plasma or wet etchant is used to activate and terminate the surface. In other embodiments, the bonding surface can be terminated in a separate process to provide additional substances for direct bonding. In various embodiments, the termination substance can include nitrogen. In addition, in some embodiments, the bonding surface can be exposed to fluorine. For example, one or more fluorine peaks can be present near the layer and / or bonding interface. Thus, in a directly bonded structure, the bonding interface between the two non-conductive materials may include a very smooth interface with a high nitrogen content and / or fluorine peak at the bonding interface. Other examples of activation and / or termination processes may be found in U.S. Patent Nos. 9,564,414, 9,391,143, and 10,434,749, each of which is incorporated herein by reference in its entirety and for all purposes.

[0026] In various embodiments, the conductive contact pad of the first element may also be directly bonded to the corresponding conductive contact of the second element. For example, direct hybrid bonding techniques may be used to provide a conductor-conductor direct bond along a bonding interface comprising a covalently directly bonded dielectric-dielectric surface prepared as described above. In various embodiments, direct bonding techniques disclosed at least in U.S. Patents Nos. 9,716,033 and 9,852,988 may be used to form direct bonds of conductors to conductors (e.g., contact pads to contact pads) and hybrid bonds of dielectrics to dielectrics, each of which is incorporated herein by reference in its entirety and for all purposes. The bonding structures described herein may also be used for direct metal bonding without the need for non-conductive region bonding, or may be used for other bonding techniques.

[0027] In some embodiments, inorganic dielectric bonding surfaces may be prepared without an intermediate adhesive as described above and bonded directly to each other. Conductive contact pads may also be bonded directly to each other without intervening adhesive (which may be surrounded by a non-conductive dielectric field region). In some embodiments, the corresponding contact pads may be recessed below the outer (e.g., upper) surface of the dielectric field or non-conductive bonding region, for example, the recess is less than 30nm, less than 20nm, less than 15nm, or less than 10nm, for example, the recess is in the range of 2nm to 20nm, or in the range of 2nm to 10nm. In some embodiments, the non-conductive bonding regions may be directly bonded to each other at room temperature without an adhesive, and subsequently, the bonding structure may be annealed. During annealing, the contact pads may expand relative to the non-conductive bonding regions and contact each other to form a metal-to-metal direct bond. The bonding structure may be annealed at an annealing temperature exceeding 250°C. For example, the annealing temperature may exceed 300°C or 350°C. The annealing temperature may be determined at least in part based on the material of the conductive contact pads, the coefficient of thermal expansion (CTE) mismatch between the conductive contact pads and the non-conductive bonding region, and the gap between the conductive contact pads. Advantageously, adhesive-free surface-to-surface direct bonding techniques, such as and / or use hybrid bonding techniques such as direct bonding interconnects or Commercially available from Adeia of San Jose, Calif., it enables high density pads (eg, regular arrays of small or fine pitch) connected across a direct bonding interface. In various embodiments, the contact pads may include copper, although other metals may be suitable.

[0028] Thus, in a direct bonding (e.g., hybrid bonding) process, the first element can be directly bonded to the second element without the intervening adhesive. In some arrangements, the first element can include a single element, such as a single integrated device die. In other arrangements, the first element can include a carrier or substrate (e.g., a wafer) that includes multiple (e.g., tens, hundreds, or more) device regions that form multiple integrated device dies when segmented. Similarly, the second element can include a single element, such as a single integrated device die. In other arrangements, the second element can include a carrier or substrate (e.g., a wafer).

[0029] As described herein, the first element and the second element can be directly bonded to each other without an adhesive, which is different from a deposition process. Therefore, the first element and the second element can include a non-deposited element. In addition, unlike a deposited layer, a directly bonded structure can include a defective region along a bonding interface, wherein there is a nanovoid. Nanovoids can be formed due to activation (e.g., exposure to plasma) of a bonding surface. As described above, a bonding interface can include material concentrations from activation and / or a final chemical treatment process. For example, in an embodiment activated using nitrogen plasma, a nitrogen peak can be formed at a bonding interface. In some embodiments, a bonding interface can include nitrogen-terminated inorganic non-conductive materials, such as nitrogen-terminated silicon, silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, silicon oxycarbon, carbon nitride silicon oxynitride, etc. Therefore, the surface of the bonding layer can include silicon nitride, silicon oxynitride, silicon oxynitride or silicon carbonitride, and there is a higher level of nitrogen at the bonding interface compared to the bulk material below the interface, which indicates that the nitrogen termination of at least one element before direct bonding. In addition to nitrogen-containing dielectrics, the nitrogen content of non-conductive materials typically has a gradient peak at or near the surface. In some embodiments, nitrogen and nitrogen related moieties may not be present at the bonding interface. As explained herein, direct bonds may include covalent bonds, which are stronger than van der Waals bonds. The bonding layer may also include a polished surface that is planarized to a high degree of smoothness.

[0030] As described above, the bonding structure can be annealed to expand the contact pad relative to the non-conductive bonding area and form a metal-to-metal direct bond. Various embodiments disclosed herein relate to methods for forming metal-to-metal direct bonds with relatively low annealing temperatures. In some embodiments, the methods disclosed herein can achieve sufficient metal-to-metal direct bonds at annealing temperatures below 250°C, below 200°C, or below 150°C. For example, the annealing temperature can be in the range of 100°C to 250°C, 100°C to 200°C, 100°C to 150°C, 125°C to 250°C, or 125°C to 200°C. In various embodiments, low temperature annealing can be performed while inducing stress in the contact pad to increase the amount of expansion of the pad, thereby assisting or accelerating bonding. It should be understood that, as used herein, a contact pad may include any suitable type of conductive feature configured to be electrically bonded or connected to an element of another element. For example, a contact pad may include conductive features such as discrete metal terminals connected to an underlying circuit device by means of traces and / or vias. Contact pads may also refer to conductive features exposed at the end(s) of through substrate vias (TSVs), for example, in embodiments where the exposed TSV ends of one component may be directly bonded to conductive features of another component.

[0031] According to various embodiments, a method for forming a bonding structure may include providing a first element having a first non-conductive region and a first conductive feature, and providing a second element having a second non-conductive region and a second conductive feature.

[0032] The method may also include bonding the first non-conductive region to the second non-conductive region without an intervening adhesive. The first non-conductive region may be directly bonded to the second non-conductive region. The bonding surface of the first non-conductive region and the bonding surface of the second non-conductive region may be prepared for direct bonding. For example, the surfaces may be polished to a root mean square (rms) surface roughness of less than 2 nm. For example, the roughness of the bonding surface may be about to to or to After the activation process, the roughness of the polished bonding surface can be slightly rougher (e.g., about to to Or maybe even cruder).

[0033] The method may also include bonding the first conductive feature to the second conductive feature without intervening adhesive. The first conductive feature may be directly bonded to the second conductive feature. In some embodiments, after the first non-conductive region is bonded to the second non-conductive region and before the first conductive feature is bonded to the second conductive feature, the first conductive feature and the second conductive feature are not in contact with each other and are separated by a gap.

[0034] Bonding the first conductive feature to the second conductive feature may include applying, applying or inducing mechanical stress in the first conductive feature, the second conductive feature, the first non-conductive region and / or the second non-conductive region. Bonding the first conductive feature to the second conductive feature may include annealing the first conductive feature and the second conductive feature under stress. Applying stress to the first conductive feature and / or the second conductive feature, and annealing the first conductive feature and the second conductive feature may occur simultaneously. The stress applied to the first conductive feature and / or the second conductive feature may be in the range of 20MPa to 1GPa, 350MPa to 1GPa, 20MPa to 500MPa, 50MPa to 400MPa, 50MPa to 100MPa, 100MPa to 250MPa, 100MPa to 350MPa, 150MPa to 300MPa or 175MPa to 275MPa. The applied stress should be sufficient to enhance the bonding of the first conductive feature and the second conductive feature without introducing undesirable defects in the bonding element. Undesirable defects may include cracks, delamination, crushing or fragmentation of components of the element. In some embodiments, applying stress to the first conductive feature and / or the second conductive feature may make the distance between the first conductive feature and the second conductive feature closer than before the stress was applied. In some embodiments, applying stress to the first conductive feature and / or the second conductive feature may enhance the surface mobility of the first conductive feature and / or the second conductive feature, thereby increasing the diffusion rate. The stress may be a tensile stress or a compressive stress or a hydrostatic force. The bonding process may occur at the wafer level or at the die level (before or after segmentation).

[0035] In some embodiments, after bonding the first element to the second element and annealing the bonded element under stress, the bonded conductive feature can have an abnormal grain size. The grain size distribution can be relatively wide. For example, the large grain size can be at least three, four, or five times the small grain size.

[0036] In some embodiments, the tensile stress and / or compressive stress induced on the first conductive feature and / or the second conductive feature can move the free surface of the first conductive feature and / or the second conductive feature (reduce the gap or depression between the relative conductive features of the corresponding elements), which can reduce the temperature to cause sufficient thermal expansion for bonding. The stress can increase the potential energy of the first conductive feature and / or the second conductive feature. The stress can increase the creep rate of the first conductive feature and / or the second conductive feature. A higher creep rate contributes to a higher bonding tendency compared to a lower creep rate.

[0037] According to various embodiments, a bonding structure may include a first element having a first non-conductive region and a first conductive feature, and a second element having a second non-conductive region and a second conductive feature. The first non-conductive region and the second non-conductive region may be bonded to each other, and the first conductive feature and the second conductive feature may be bonded to each other. The first non-conductive region and the second non-conductive region may be directly bonded to each other without an intermediate adhesive, and the first conductive feature and the second conductive feature may be directly bonded to each other without an intermediate adhesive. In some embodiments, the bonding interface between the first conductive feature and the second conductive feature may be deformed over a concave or convex mold or structure. Thus, during the bonding process of bonding the first conductive feature and the second conductive feature, the bonding interface may have a curved shape. Depending on the thickness of the bonding element, the curved shape of the bonding interface may have an intermediate ordinate, a sagitta, or a maximum deformation of about 10 μm to 5000 μm. For example, an element of a bonding element having a thickness of about 800 μm may be deformed over a mold so that the sagitta of the bonding interface is about 30 μm to 100 μm. For another example, an element of a bonding element having a thickness of about 100 μm to 200 μm may be deformed over a mold such that the sagitta of the bonding interface may be between 1000 μm and 2000 μm.

[0038] In some embodiments, the grains of the first conductive feature and / or the second conductive feature may have irregular grain sizes. For example, the grain size of the first conductive feature at the bonding interface may be greater than the grain size of the first conductive feature at a position away from the bonding interface. For example, the grain size of the second conductive feature at the bonding interface may be greater than the grain size of the second conductive feature at a position away from the bonding interface. The bonded first conductive feature and the second conductive feature may include a first average grain size in a first region of the bonded first conductive feature and the second conductive feature and a second average grain size greater than the first average grain size in a second region of the bonded first conductive feature and the second conductive feature. For example, the first average size may be at least three times larger than the second average size. The second region may be a region at or near the bonding interface, and the first region may be a region at or near a position away from the bonding interface. The first element may also include a third conductive feature below the first conductive feature. The third conductive feature may have a third average grain size. The third grain size may be smaller than the average grain size of the first conductive feature.

[0039] Figures 1A-2F Schematic cross-sectional side views of a first element 1 and / or a second element 2 in different steps of a method of forming a bonded structure according to different embodiments are illustrated. Figure 1A is a schematic cross-sectional side view of a structure comprising a first element 1 and a second element 2 in one step of a method of forming a bonded structure. Figure 1AIn the embodiment, stress (eg, mechanically induced biaxial tensile stress) may be applied to the bonding surfaces of the first element 1 and the second element 2. The structure may be stressed in an oven to simultaneously heat anneal. Figure 1B-1E Shows the formation Figure 1A The method may include providing a first element 1 having a first non-conductive region 10 and a first conductive feature 12. A bonding surface 12a of the first conductive feature 12 may be recessed relative to the bonding surface 10a of the first non-conductive region 10. The bonding surface 12a of the first conductive feature 12 may have a free surface. The first element 1 may also include an intermediate layer 14 between the first non-conductive region 10 and the first conductive feature 12. In some embodiments, the intermediate layer 14 may include a diffusion barrier layer. Figure 1B and Figure 2C No external pressure was applied.

[0040] like Figure 1C As shown, the method may include providing a second element 2 having a second non-conductive region 20 and a second conductive feature 22. The bonding surface 22a of the second conductive feature 22 may be recessed relative to the bonding surface 20a of the second non-conductive region 20. The second element 2 may also include an intermediate layer 24 between the second non-conductive region 20 and the second conductive feature 22. In some embodiments, the intermediate layer 24 may include a diffusion barrier layer. The first non-conductive region 10 and the second non-conductive region 20 may be disposed above a larger bulk portion (e.g., a carrier substrate, a handle substrate, or a semiconductor device portion, not shown) of the first element 1 and the second element 2.

[0041] The first non-conductive region 10 and the second non-conductive region 20 may be bonded to each other. The first non-conductive region 10 and the second non-conductive region 20 may be directly bonded to each other without intervening an adhesive and without applying external stress. For example, when the first element 1 and the second element 2 are in contact with each other, the first non-conductive region 10 and the second non-conductive region 20 may be directly bonded to each other without an intermediate adhesive. The first non-conductive region 10 and the second non-conductive region 20 may be bonded without applying external stress or pressure. Figure 1C and Figure 2D As shown, there may be a gap 26 between the bonding surface 12a of the first conductive feature 12 and the bonding surface 22a of the second conductive feature 22. Figure 1E and Figure 2FAs shown, the stress applied to the bonding surfaces of the first element 1 and the second element 2 can reduce the gap. In some embodiments, the stress applied to the bonding surfaces of the first element 1 and the second element 2 can reduce the gap 26, thereby contacting the bonding surface 12a of the first conductive feature 12 and the bonding surface 22a of the second conductive feature 22. In some embodiments, under such stress, the bonding surface 12a of the first conductive feature 12 and the bonding surface 22a of the second conductive feature 22 can enhance the bonding to each other. In some embodiments, applying stress to the first non-conductive region 10 and / or the second non-conductive region 20 alone or in addition to applying stress to the first conductive feature 12 and / or the second conductive feature 22 can increase the bonding strength between the first conductive feature 12 and the second conductive feature 22.

[0042] As shown in the figure, for example, Figure 1A , Figure 2A and Figure 2B , a force may be applied to the location of the first element 1 and the second element 2. Depending on the location where the force is applied, a tensile stress or a compressive stress may be applied to the first conductive feature 12 and the second conductive feature 22. For example, in Figure 1A In the embodiment, the downward force or the distributed downward force is applied to a plurality of positions (a first position L1 and a second position L2), and the upward force or the distributed upward force is applied to one or more positions (a third position L3) between the first position L1 and the second position L2. Figure 1A In the embodiment, depending on their relative sizes, the applied force can provide tensile (or compressive in another embodiment) stress to the bonding surface 12a of the first conductive feature 12 and the bonding surface 22a of the second conductive feature 22 (see Figure 1D and Figure 1E ). In some embodiments, the neutral plane NP of the force may be located in the first element 1, at least in part depending on the relative thickness of the first element 1 and the second element 2 and the relative magnitude of the force, for example when the first element 1 is thicker than the second element 2. The bonding surface 12a of the first conductive feature 12 and the bonding surface 22a of the second conductive feature 22 may define a bonding interface 28 after bonding. The tensile stress may significantly increase the vacancies in the conductive features 12, 22, so that the diffusion between the conductive features 12, 22 may be accelerated at a given temperature. The accelerated diffusion between the conductive features 12, 22 may enable the conductive features 12, 22 to bond to each other at a lower temperature than the conductive features 12, 22 without applying stress.

[0043] For another example, in Figure 2A and Figure 2BUpward forces are applied at two locations (a first location L1 and a second location L2), while a downward force is applied at another location (a third location L3) between the first location L1 and the second location L2. In some embodiments, the upward and downward forces may be distributed on the back sides of the first element 1 and the second element 2. The distributed forces may be uniform or non-uniform. For example, a known first distributed force may be applied at a portion or region from the center to the middle part of the back surface of an element (e.g., the first element 1), while a second known distributed force may be applied at a portion or region between the middle part and the periphery of the element. The second force may be higher than the first force to compensate for edge effects in the element. In some embodiments, forces may be applied at more than two regions. In Figure 2A and Figure 2B the applied forces may provide a compressive stress to the bonding surface 12a of the first conductive feature 12 and the bonding surface 22a of the second conductive feature 22 (see Figure 2E and Figure 2F ). The compressive stress may bring the bonding surface 12a of the first conductive feature 12 and the bonding surface 22a of the second conductive feature 22 closer to each other. The compressive stress applied to the conductive features 12, 22 enables the conductive features 12, 22 to bond to each other at a lower temperature than the conductive features 12, 22 without the applied stress. As described herein, in some embodiments, the applied compressive force may be distributed on the first element 1 and the second element 2. The distributed forces may be uniform or non-uniform. For example, a known first distributed force may be applied at a portion or region from the center to the middle part of the back surface of an element, while a second known distributed force may be applied at a portion or region between the middle part and the periphery of the element. The second force may be higher than the first force to compensate for edge effects in the element. In some embodiments, forces may be applied at more than two regions.

[0044] Figure 3 and Figure 4 describe the theoretical relationship between the acting force and the displacement caused by the acting force. Figure 3 shows a wafer 30 located on the die surface 32a of a die structure 32. The circle theory provides the following formula, where R represents the radius of curvature of the die surface 32a, and h represents the saggita of the curvature of the die surface 32a.

[0045] R = D 2 / 8h + h / 2; when h << D, this simplifies to R ≈ D 2 / 8h.

[0046] For example, for reversible deformation of wafer 30 over a mold structure (eg, a curved mold), based on circle theory, with a sagittal angle (h) of 200 μm, the radius of curvature of the mold surface can be approximated as D 2 / 8h. For a sagitta of 200μm for 200mm and 300mm wafers, the radius of curvature of the mold surface 32a can be approximately 25m and 56.25m, respectively. The bending stiffness of a 200mm or 300mm wafer with a sagitta of 200μm can be very small. In practice, since the geometric aspect ratio of the wafer is very large (e.g., wafer diameter / wafer thickness>80), the bonding element can be regarded as a film rather than a thin plate. The film (bonding element) can have very small bending stiffness and therefore can hardly withstand bending loads. Similarly, the bonding element may not be able to withstand compressive loads without wrinkling. In such cases, the bonding element can be supported on a convex or concave surface of a known radius of curvature, so that the bonding element can withstand tension and pressure. The radius of curvature R of the mold structure 32 or the mold support surface can be scaled to any specific value.

[0047] Figure 4 A method for deforming bonding elements 1, 2 over a curved surface (e.g., a chip-to-wafer (D2W) bonding structure) is illustrated by applying, for example, a distributed pressure or load P on the bonding elements 1, 2. For elastic deformation of a thin plate, such as when the plate deformation f divided by the plate thickness h (f / h) is less than 0.2, the relationship between the plate thickness h, bending stiffness or bending stiffness D, pressure P, mold radius a, Young's modulus E, and Poisson's ratio ν can be expressed by the following equation:

[0048] D=Eh 3 / 12(1-ν 2 ); f = Pa 4 / 64D.

[0049] The bending stiffness D approaches zero as the thickness of the plate h becomes thinner and approaches negligible thickness, for example, when a thin plate transforms into a thin film.

[0050] like Figure 5A and Figure 5B As shown, in some embodiments, the bonding elements 1, 2 can be coupled to the tensile layer 40. A known tensile force can be applied to the bonding elements 1, 2, for example, biaxially through the tensile layer 40. In some embodiments, the tensile layer 40 and the bonding elements 1, 2 can be annealed at a first temperature to enhance the conductive characteristics of the bonding elements 1, 2. In some embodiments, the bonding elements 1, 2 can be stretched over a concave surface of a known radius of curvature, and an additional compressive force or hydrostatic force P is applied to press the tensile layer 40 and the bonding elements 1, 2 against the concave surface (see Figure 5B). In this application, the bonding elements 1, 2 are stretched and compressed during an annealing process having a second temperature lower than the first temperature. In some embodiments, for example, instead of through an air bag, the applied hydrostatic force may include gas pressure applied through a forming plate having a plurality of holes. In some embodiments, the forming plate may have a plurality of zones having independently controlled pressures applied to the bonding elements 1, 2.

[0051] Figure 6 is a schematic cross-sectional side view of an assembly of a first element 1 and a second element 2 disposed above a convex support surface 44 according to one embodiment. A conformable loading element, such as a bladder 46, can expand to deform the first element 1 and the second element 2, bridge the sagittal body f to conform to the curvature of the support surface 44, and apply stress to the conductive features of the first element 1 and the second element 2. The pressure P applied by the bladder 46 during the annealing step can range from 0.1 MPa to 100 MPa, 20 MPa to 1 GPa, 350 MPa to 1 GPa, 20 MPa to 500 MPa, 50 MPa to 400 MPa, 50 MPa to 100 MPa, 100 MPa to 250 MPa, 100 MPa to 350 MPa, 150 MPa to 300 MPa, or 175 MPa to 275 MPa. The pressure P applied from the capsule 46 should be sufficient to enhance the bonding of the first conductive feature and the second conductive feature of the first element 1 and the second element 2 without introducing undesirable defects in the bonding elements 1 and 2. Undesirable defects may include cracks, delamination, crushing or fragmentation of the element, or the fracture of any one of the elements 1 and 2. In addition, the applied pressure P can be applied periodically. In some embodiments, the applied pressure P can be applied for 60 seconds, and the pressure is released for 3 seconds. In other embodiments, for example, the pressure can be cycled between the upper pressure limit Pmax and the lower pressure limit Pmin, such as 0.5P MPa. The applied pressure P is transmitted to the first conductive feature and the second conductive feature of the bonding element 1 and 2 to reduce or bridge the depression between the conductive features. Compared with the element with unbridged grooves, the bridge groove can allow bonding to occur at a lower temperature. In addition, the creep induced on the conductive features of the first element 1 and the second element 2 and the generated crystal defects, such as vacancies or dislocations created by the elastic or plastic deformation of the applied pressure P, enhance the diffusion of atoms of the conductive features of the bonding elements 1 and 2.

[0052] Fig. 7A is a schematic cross-sectional side view of a bonding element 1, 2 coupled to a compression layer or a tension layer 50 according to one embodiment. Fig. 7AAs shown, a compression layer or tension layer 50 may be disposed on the back side opposite to the bonding surface of the first element 1 (or the second element 2 in some other embodiments). In some embodiments, the compression layer or tension layer 50 may be coated on the back side of the first element 1 (or the second element 2 in some other embodiments). The tension layer 50 induces compressive pressure or force between the bonding elements 1, 2 during the bonding operation at high temperatures, such as temperatures below 220°C or even below 180°C. In some embodiments, the compression layer or tension layer 50 may be removed after the bonding step is completed.

[0053] Figure 7B 6 is a flow chart of a method for bonding a first element 1 and a second element 2 according to one embodiment. In step 60, the bonding surface 10a of the first non-conductive region 10 of the first element 1 and / or the bonding surface 20a of the second non-conductive region 20 of the second element 2 can be prepared for direct bonding. For example, the bonding surfaces 10a, 20a can be cleaned and activated. In step 62, the bonding surfaces 10a and 10b can be bonded to each other by means of dielectric-dielectric direct bonding. In step 64, a compression layer or a tension layer 50 can be provided to the bonding elements 1, 2. In step 66, the bonding elements 1, 2 can be annealed to form a bonded structure (e.g., a direct hybrid bonded structure). In step 68, the compression layer or the tension layer 50 can be removed from the bonded structure.

[0054] Fig. 8A and Figure 8B A schematic cross-sectional side view of a bonding element 1 , 2 is shown. Figure 8C is a flow chart of a method for bonding a first element 1 and a second element 2 according to one embodiment. In step 70, the bonding surface 10a of the first non-conductive region 10 of the first element 1 and / or the bonding surface 20a of the second non-conductive region 20 of the second element 2 may be prepared for direct bonding. For example, the bonding surfaces 10a, 20a may be cleaned and activated. In step 72, as shown in FIG. Fig. 8A As shown, the bonding surfaces 10a and 10b can be bonded to each other. In step 74, the bonding elements 1, 2 can be heated at a low temperature (first temperature), such as a temperature below 100°C. The bonding surfaces 10a and 10b can be bonded to each other at the first temperature. Figure 8BAs shown, in step 76, a hydrostatic stress may be applied to the first element 1 and the second element 2. In such embodiments, the first element 1 and the second element 2 may not be deformed or bent. The hydrostatic stress may reduce the gap between the relative first conductive feature and the second conductive feature before bonding, thereby reducing the distance between the first conductive feature and the second conductive feature compared to the distance when the hydrostatic stress is not applied. The hydrostatic stress may enhance the surface mobility of the first conductive feature and the second conductive feature at the bonding surface compared to when the hydrostatic stress is not applied. The bonding elements 1, 2 may be heated (e.g., annealed) at a second temperature higher than the first temperature. For example, the second temperature may be in the range of from 100°C to 250°C. The bonding elements 1, 2 may form a bonding structure (e.g., a direct hybrid bonding structure).

[0055] Fig.9A and Fig. 9B An example of a stress application method is shown. In some embodiments, Fig.9A and Fig. 9B As shown, stress can be applied by bending the bonding elements 1, 2. For example, Fig.9A As shown, the bonding elements 1, 2 can be bent by applying stress to three locations L1, L2, L3. In some embodiments, the bonding elements 1, 2 can be bent by applying stress to one location while moving the bonding elements 1, 2 along their length.

[0056] Fig.10 A first element 1 and a second element 2 are shown coupled to a curved support structure 82. In some embodiments, the curved support structure 82 may include a metal support structure. For example, the curved support structure 82 may be attached to the first element 1 and the second element 2 by means of a clamp 84. The support structure 82 may initially be straight, and the support structure 82 may be curved to allow the first element 1 and the second element 2 to bend. The support structure 82 may be bent by mechanically bending the support structure 82. The support structure 82 may be bent by heating the support structure 82 and the first element 1 and the second element 2. For example, a difference between the coefficient of thermal expansion of the support structure 82 and the coefficient of thermal expansion of the first element 1 and / or the second element 2 may cause the support structure 82 to bend when heated. Fig.10 Flexing the elements 1 , 2 in the manner shown may apply stress to first and second conductive features (eg, contact pads) of the first and second elements 1 , 2 , as described herein.

[0057] Fig.11A and Fig. 11BA first support structure 86 (e.g., a bottom plate) and a second support structure 88 (e.g., a top plate) are shown, which can be attached to the first element 1 and the second element 2. The first element 1 and the second element 2 can be located between the first support structure 86 and the second support structure 88. The first support structure 86 and the second support structure 88 can be clamped to apply stress to the first element 1 and the second element 2 by one or more clamps 90. For example, in Fig.11A In the embodiment, before clamping the first support structure 86 and the second support structure 88, the first element 1 and the second element 2 can be heated and expanded, and then, Fig. 11B In the embodiment, after clamping the first support structure 86 and the second support structure 88, the first support structure 86 and the second support structure 88 can be cooled. In some embodiments, the first support structure 86 and / or the second support structure 88 can include a metal plate.

[0058] In one aspect, a method of forming a bonding structure is disclosed. The method may include providing a first component having a first non-conductive region and a first conductive feature, providing a second component having a second non-conductive region and a second conductive feature, bonding the first non-conductive region to the second non-conductive region, and applying a mechanical stress to at least one of the first conductive feature and the second conductive feature. When the first non-conductive region is bonded to the second non-conductive region, the first conductive feature and the second conductive feature are separated by a gap, and applying a mechanical stress to at least one of the first conductive feature and the second conductive feature reduces the gap between the first conductive feature and the second conductive feature.

[0059] In one embodiment, the method further includes annealing the first element and the second element while applying mechanical stress to at least one of the first conductive feature and the second conductive feature so that the first conductive feature contacts the second conductive feature. Prior to applying and annealing, the bonding surface of the first conductive feature may be recessed by less than 30 nm relative to the bonding surface of the first non-conductive region. The annealing temperature for annealing the first conductive feature and the second conductive feature may be less than 250°C. The annealing temperature may be in the range of 100°C to 250°C. The annealing temperature may be in the range of 100°C to 200°C. The annealing temperature may be in the range of 100°C to 150°C. The method may include applying a compressive layer on the back side of the first element opposite to the bonding surface of the first element before annealing.

[0060] In one embodiment, the method further comprises directly bonding the first non-conductive region to the second non-conductive region without an adhesive.The method may also comprise directly bonding the first conductive feature to the second conductive feature without an intervening adhesive.

[0061] In one embodiment, the root mean square (rms) surface roughness of the bonding surface of the first non-conductive region is less than 2 nm.

[0062] In one embodiment, applying mechanical stress to at least one of the first conductive feature and the second conductive feature increases metal surface mobility of the first conductive feature and / or the second conductive feature at a bonding interface.

[0063] In one embodiment, applying mechanical stress to at least one of the first conductive feature and the second conductive feature may substantially close a gap between the first conductive feature and the second conductive feature.

[0064] In one embodiment, applying the mechanical stress includes applying a tensile stress or a compressive stress to the first conductive feature and / or the second conductive feature.

[0065] In one embodiment, applying the mechanical stress includes applying a hydrostatic stress to the first element and the second element.

[0066] In one embodiment, applying the mechanical stress includes applying a stress in a range of 0.1 MPa to 100 MPa.

[0067] In one embodiment, applying the mechanical stress comprises attaching a curved support structure to the first element and the second element.

[0068] In one embodiment, applying the mechanical stress comprises attaching a first support structure to the first element and attaching a second support structure to the second element such that the first element and the second element are disposed between the first support structure and the second support structure, and clamping the first support structure to the second support structure.

[0069] In one embodiment, applying mechanical stress includes deforming the first element and the second element. Deforming the first element and the second element may include applying a force to a first position of the first element in a first direction, and applying a force to a second position of the second element in a second direction opposite to the first direction. The method may also include applying a force to a third position of the first element in the first direction to bend the first element and the second element. The second position may be located laterally between the first position and the third position. The method may also include moving the first position, the second position, and the third position along the length of the first element and the second element while maintaining the relative position between the first position, the second position, and the third position.

[0070] In one embodiment, the first component further comprises a substrate portion that is thicker than a substrate portion of the second component.

[0071] In one aspect, a method of forming a bonding structure is disclosed. The method may include providing a first element having a first non-conductive region and a first conductive feature, providing a second element having a second non-conductive region and a second conductive feature, bonding the first non-conductive region to the second non-conductive region, applying stress to at least one of the first conductive feature and the second conductive feature, and annealing the first element and the second element while applying mechanical stress to at least one of the first conductive feature and the second conductive feature. When the first non-conductive region is bonded to the second non-conductive region, the first conductive feature and the second conductive feature are separated by a gap. Annealing the first element and the second element while applying mechanical stress causes the first conductive feature to contact the second conductive feature.

[0072] In one embodiment, the method further comprises directly bonding the first non-conductive region to the second non-conductive region without an intervening adhesive, and directly bonding the first conductive feature to the second conductive feature without an intervening adhesive.

[0073] In one embodiment, prior to applying and annealing, the bonding surface of the first conductive feature is recessed by less than 30 nm relative to the bonding surface of the first non-conductive region.

[0074] In one embodiment, the bonding surface of the first non-conductive region has a root mean square (rms) surface roughness of less than 2 nm.

[0075] In one embodiment, applying mechanical stress to at least one of the first conductive feature and the second conductive feature increases metal surface mobility of the first conductive feature and / or the second conductive feature at a bonding interface.

[0076] In one embodiment, applying mechanical stress to at least one of the first conductive feature and the second conductive feature substantially closes a gap between the first conductive feature and the second conductive feature.

[0077] In one embodiment, applying the mechanical stress includes applying a tensile stress or a compressive stress to the first conductive feature and / or the second conductive feature.

[0078] In one embodiment, applying the mechanical stress includes applying a hydrostatic stress to the first element and the second element.

[0079] In one embodiment, applying the mechanical stress includes applying a stress in a range of 0.1 MPa to 100 MPa.

[0080] In one embodiment, applying the mechanical stress comprises attaching a curved support structure to the first element and the second element.

[0081] In one embodiment, applying the mechanical stress comprises attaching a first support structure to the first element and attaching a second support structure to the second element such that the first element and the second element are disposed between the first support structure and the second support structure, and clamping the first support structure to the second support structure.

[0082] In one embodiment, applying mechanical stress includes deforming the first element and the second element. Deforming the first element and the second element may include applying a force to a first position of the first element in a first direction, and applying a force to a second position of the second element in a second direction opposite to the first direction. The method may also include applying a force to a third position of the first element in the first direction to bend the first element and the second element. The second position may be located laterally between the first position and the third position. The method may also include moving the first position, the second position, and the third position along the length of the first element and the second element while maintaining the relative position between the first position, the second position, and the third position.

[0083] In one embodiment, the annealing temperature for annealing the first conductive feature and the second conductive feature is less than 250° C. The annealing temperature may be in the range of 100° C. to 250° C. The annealing temperature may be in the range of 100° C. to 200° C. The annealing temperature may be in the range of 100° C. to 150° C.

[0084] In one embodiment, the method further comprises, prior to annealing, applying a compressive layer on a back side of the first component opposite the bonding surface of the first component.

[0085] In one embodiment, the first component further comprises a substrate portion that is thicker than a substrate portion of the second component.

[0086] Unless the context clearly requires otherwise, throughout the specification and claims, the words "comprise / comprising", "include / including", etc. should be interpreted as inclusive, rather than exclusive or exhaustive; that is, in the sense of "including, but not limited to". The word "coupled" as generally used herein refers to two or more elements that can be directly connected or connected by means of one or more intermediate elements. Similarly, the word "connected" as generally used herein refers to two or more elements that can be directly connected or connected by means of one or more intermediate elements. In addition, when used in this application, the words "herein", "above", "below" and words of similar meaning should refer to the entirety of this application, rather than to any particular part of this application. In addition, as used herein, when a first element is described as being "on" or "above" a second element, the first element can be directly on or above the second element, so that the first element and the second element are in direct contact, or the first element can be indirectly on or above the second element, so that one or more elements are between the first element and the second element. Where the context permits, words in the above detailed description that use the singular or plural may also include the plural or singular, respectively. The word "or" when referring to a list of two or more items, includes all of the following interpretations of the word: any item in the list, all items in the list, and any combination of items in the list.

[0087] Furthermore, conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “eg,” “for example,” “such as,” and the like, unless expressly stated otherwise or understood otherwise in the context of use, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and / or states. Thus, such conditional language is generally not intended to imply that one or more embodiments require a feature, element, and / or state in any way.

[0088] Although certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. In fact, the novel devices, methods, and systems described herein may be embodied in various other forms; in addition, various omissions, substitutions, and changes may be made to the forms of the methods and systems described herein without departing from the spirit of the present disclosure. For example, although the blocks are presented in a given arrangement, alternative embodiments may perform similar functionality with different components and / or circuit topologies, and some blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these blocks may be implemented in various different ways. Any suitable combination of the elements and actions of the various embodiments described above may be combined to provide additional embodiments. The attached claims and their equivalents are intended to cover these forms or modifications that fall within the scope and spirit of the present disclosure.

Claims

1. A method for forming a bonding structure, the method comprising: providing a first element having a first non-conductive region and a first conductive feature; providing a second element having a second non-conductive region and a second conductive feature; bonding the first non-conductive region to the second non-conductive region, the first conductive feature and the second conductive feature being separated by a gap; and A mechanical stress is applied to at least one of the first conductive feature and the second conductive feature to reduce the gap between the first conductive feature and the second conductive feature.

2. The method according to claim 1, further comprising: The first element and the second element are annealed while applying the mechanical stress to the at least one of the first conductive feature and the second conductive feature so that the first conductive feature contacts the second conductive feature. 3 . The method of claim 2 , wherein prior to said applying and said annealing, a bonding surface of said first conductive feature is recessed by less than 30 nm relative to a bonding surface of said first non-conductive region.

4. The method of claim 2, wherein an annealing temperature for annealing the first conductive feature and the second conductive feature is in a range of 100°C to 250°C. The method according to claim 4 , wherein the annealing temperature is in the range of 100° C. to 150° C.

6. The method of claim 2, further comprising, prior to the annealing, coating a compressive layer on a back side of the first component opposite to a bonding surface of the first component.

7. The method according to claim 1, further comprising: The first non-conductive region is directly bonded to the second non-conductive region without intervening adhesive, and the first conductive feature is directly bonded to the second conductive feature without intervening adhesive.

8. The method of claim 1, wherein applying the mechanical stress to at least one of the first conductive feature and the second conductive feature increases the metal surface mobility of the first conductive feature and / or the second conductive feature at a bonding interface and substantially closes the gap between the first conductive feature and the second conductive feature.

9. The method of claim 1, wherein applying the mechanical stress comprises: Applying a tensile stress or a compressive stress to the first conductive feature and / or the second conductive feature, or applying a hydrostatic stress to the first element and the second element, wherein applying the mechanical stress comprises applying a stress in a range of 0.1 MPa to 100 MPa.

10. The method of claim 1, wherein applying the mechanical stress comprises: A curved support structure is attached to the first element and the second element, and the first element and the second element are deformed.

11. The method of claim 10, wherein deforming the first element and the second element comprises: A force is applied to a first position of the first element in a first direction, a force is applied to a second position of the second element in a second direction opposite to the first direction, and a force is applied to a third position of the first element in the first direction to bend the first element and the second element, wherein the second position is laterally located between the first position and the third position. 12 . The method of claim 11 , wherein a median ordinate of the bent first element and the second element is greater than 10 μm.

13. The method of claim 12, wherein a median ordinate of the bent first element and the second element is greater than 1000 μm.

14. A method for forming a bonding structure, the method comprising: providing a first element having a first non-conductive region and a first conductive feature; providing a second element having a second non-conductive region and a second conductive feature; bonding the first non-conductive region to the second non-conductive region, the first conductive feature and the second conductive feature being separated by a gap; applying a mechanical stress to at least one of the first conductive feature and the second conductive feature; and The first element and the second element are annealed while applying the mechanical stress to the at least one of the first conductive feature and the second conductive feature so that the first conductive feature contacts the second conductive feature.

15. The method according to claim 14, further comprising: Directly bonding the first non-conductive region to the second non-conductive region without intervening adhesive, and directly bonding the first conductive feature to the second conductive feature without intervening adhesive, wherein prior to the applying and the annealing, the bonding surface of the first conductive feature is recessed by less than 30 nm relative to the bonding surface of the first non-conductive region.

16. The method of claim 14, wherein applying the mechanical stress to the at least one of the first conductive feature and the second conductive feature increases metal surface mobility of the first conductive feature and / or the second conductive feature at a bonding interface.

17. The method of claim 14, wherein applying the mechanical stress comprises: A tensile stress or a compressive stress is applied to the first conductive feature and / or the second conductive feature, or a hydrostatic stress is applied to the first element and the second element.

18. The method of claim 14, wherein applying the mechanical stress comprises: A first support structure is attached to the first element and a second support structure is attached to the second element such that the first element and the second element are disposed between the first support structure and the second support structure, and the first support structure is clamped to the second support structure.

19. The method of claim 14, wherein applying the mechanical stress comprises: The first element and the second element are deformed, and the deforming the first element and the second element includes applying a force to a first location of the first element in a first direction and applying a force to a second location of the second element in a second direction opposite to the first direction.

20. The method of claim 14, wherein an annealing temperature for annealing the first conductive feature and the second conductive feature is in a range of 100°C to 250°C, wherein the first element further comprises a substrate portion that is thicker than a substrate portion of the second element.

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