Direct bonded metal structure with aluminum features and method of making same

Abstract

Disclosed are devices, bonding structures including the devices, and methods of forming them. The bonding structure can include a first device having a first non-conductive field region and a first conductive feature. The surface of the first non-conductive field region and the surface of the first conductive feature at least partially define a bonding surface of the first device. The first conductive feature includes a first portion and a second portion over the first portion that at least partially defines the surface of the first conductive feature. The first portion includes aluminum. The first conductive feature has continuous sidewalls along the first and second portions. The second portion includes a different metal composition than the first portion or includes fluorine at the surface of the first conductive feature. The bonding structure can include a second device having a second non-conductive field region and a second conductive feature. The surface of the second non-conductive field region is bonded directly to the first non-conductive field region without any intervening adhesive along the bonding interface, and the surface of the second conductive feature is bonded directly to the second conductive feature without any intervening adhesive along the bonding interface.

Description

[Technical Field]

[0001] The field of the invention relates to bonding structures containing aluminum features and methods of forming direct metallurgical bonds. [Background technology]

[0002] Microelectronic elements, such as integrated device dies or chips, can be mounted or stacked on another element, thereby forming a bonding structure. Direct metal bonding can be performed at low temperatures and without external pressure. For example, direct hybrid bonding involves directly bonding non-conductive features (e.g., inorganic dielectrics) of different elements together with simultaneously directly bonding conductive features (e.g., metal pads or lines) of the elements without an intervening adhesive. For example, microelectronic elements can be mounted on a carrier such as an interposer, a reconstituted wafer, or an element. As another example, microelectronic elements can be stacked on top of other microelectronic elements, e.g., a first integrated device die can be stacked on top of a second integrated device die. Each of the microelectronic elements can have conductive pads for mechanically and electrically bonding the elements to each other. There is a continuing need for improved methods for forming bonding structures. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 9,564,414 [Patent Document 2] U.S. Patent No. 9,391,143 [Patent Document 3] U.S. Patent No. 10,434,749 [Patent Document 4] U.S. Patent No. 9,716,033 [Patent Document 5] U.S. Patent No. 9,852,988 [Patent Document 6] U.S. Patent No. 11,195,748

[0004] Specific embodiments will now be described with reference to the following figures, which are offered by way of example and not by way of limitation: [Brief explanation of the drawings]

[0005] [Figure 1A] FIG. 1 is a schematic cross-sectional side view of two elements prior to direct hybrid bonding. [Figure 1B] FIG. 1B is a schematic cross-sectional side view of the two elements shown in FIG. 1A after direct hybrid bonding. [Figure 2] 1 is a schematic cross-sectional side view of a bonding structure including elements bonded via solder balls. [Figure 3A] 1A-1C are schematic cross-sectional views illustrating a method of forming copper pads on aluminum interconnects formed in a back-end-of-line (BEOL) layer of a device. [Figure 3B] 1A-1C are schematic cross-sectional views illustrating a method of forming copper pads on aluminum interconnects formed in a back-end-of-line (BEOL) layer of a device. [Figure 3C] 1A-1C are schematic cross-sectional views illustrating a method of forming copper pads on aluminum interconnects formed in a back-end-of-line (BEOL) layer of a device. [Figure 3D] 1A-1C are schematic cross-sectional views illustrating a method of forming copper pads on aluminum interconnects formed in a back-end-of-line (BEOL) layer of a device. [Figure 3E] 1A-1C are schematic cross-sectional views illustrating a method of forming copper pads on aluminum interconnects formed in a back-end-of-line (BEOL) layer of a device. [Figure 4A] 1A-1C are schematic cross-sectional views illustrating a method of forming aluminum pads on aluminum interconnects formed in the BEOL layers of a device. [Figure 4B]1A-1C are schematic cross-sectional views illustrating a method of forming aluminum pads on aluminum interconnects formed in the BEOL layers of a device. [Figure 4C] 1A-1C are schematic cross-sectional views illustrating a method of forming aluminum pads on aluminum interconnects formed in the BEOL layers of a device. [Figure 4D] 1A-1C are schematic cross-sectional views illustrating a method of forming aluminum pads on aluminum interconnects formed in the BEOL layers of a device. [Figure 4E] 1A-1C are schematic cross-sectional views illustrating a method of forming aluminum pads on aluminum interconnects formed in the BEOL layers of a device. [Figure 5A] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features, according to one embodiment. [Figure 5B] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features, according to one embodiment. [Figure 5C] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features, according to one embodiment. [Figure 5D] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features, according to one embodiment. [Figure 5E] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features, according to one embodiment. [Figure 5F] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features, according to one embodiment. [Figure 5G] 5F is a schematic cross-sectional side view of a bonding structure including the element formed in FIG. 5F and a second element (such as a wafer). [Figure 5H] 5F is a schematic cross-sectional side view of a bonding structure including the element formed in FIG. 5F and a plurality of second elements (such as dies). [Figure 6A] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained aluminum, according to one embodiment. [Figure 6B]1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained aluminum, according to one embodiment. [Figure 6C] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained aluminum, according to one embodiment. [Figure 6D] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained aluminum, according to one embodiment. [Figure 6E] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained aluminum, according to one embodiment. [Figure 6F] FIG. 6F is a schematic cross-sectional side view of a bonding structure including the element formed in FIG. 6E before annealing. [Figure 6G] FIG. 6C is a schematic cross-sectional side view of a bonding structure including the element formed in FIG. 6F after annealing. [Figure 6H] 6F or 6G after singulation. FIG. 6C is a schematic cross-sectional side view of a bonding structure including the element formed in FIG. 6F or 6G after singulation. [Figure 6I] FIG. 6C is a schematic cross-sectional side view of the device of FIG. 6D or FIG. 6E after formation of a protective layer and singulation. [Figure 6J] FIG. 6J is a schematic cross-sectional side view of the singulated device of FIG. 6I after removal of the protective layer. [Figure 6K] FIG. 6E shows the device of FIG. 6D after singulation and during the termination process.

[0006] [Figure 6L] FIG. 6K is a schematic cross-sectional side view of a bonding structure including the singulated element of FIG. 6K. [Figure 7A] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained copper, according to one embodiment. [Figure 7B] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained copper, according to one embodiment. [Figure 7C] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained copper, according to one embodiment. [Figure 7D] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained copper, according to one embodiment. [Figure 7E] 1A-1C are schematic cross-sectional views illustrating a method of forming a bonding surface of a device including conductive features with fine-grained copper, according to one embodiment. [Figure 7F] 7F is a schematic cross-sectional side view of a bonding structure including the element formed in FIG. 7E. DETAILED DESCRIPTION OF THE INVENTION

[0007] Various embodiments disclosed herein relate to direct bonding structures in which two or more elements can be directly bonded without an intervening adhesive. FIGS. 1A and 1B schematically illustrate a process for forming a direct hybrid bonding structure without an intervening adhesive, according to some embodiments. In FIGS. 1A and 1B, a bonding structure 100 includes first and second elements 102 and 104 that can be directly bonded to each other at a bonding interface 118 without an intervening adhesive. Two or more microelectronic elements 102 and 104 (e.g., semiconductor elements including integrated device dies, wafers, passive devices, individual active devices such as power switches, etc.) can be stacked or bonded to each other to form the bonding structure 100. A conductive feature 106 a (e.g., a contact pad, an exposed end of a via or through-substrate via (TSV), an elongated trace, etc.) of the first element 102 can be mechanically and electrically connected to a corresponding conductive feature 106 b of the second element 104. Any suitable number of elements can be stacked on the bonding structure 100. For example, a third element (not shown) can be stacked on the second element 104, a fourth element (not shown) can be stacked on the third element, etc. Additionally or alternatively, one or more additional elements (not shown) can be stacked laterally adjacent to one another along the first element 102. In some embodiments, the laterally adjacent additional stacked elements can be smaller than the second element. In some embodiments, the laterally adjacent additional stacked elements can be less than half the size of the second element in a lateral dimension.

[0008] In some embodiments, the elements 102 and 104 are bonded directly to one another without adhesive. In various embodiments, a non-conductive field region comprising a non-conductive or dielectric material can serve as the first bonding layer 108a of the first element 102. The first bonding layer 108a can be bonded directly, without adhesive, to a corresponding non-conductive field region comprising a non-conductive or dielectric material that serves as the second bonding layer 108b of the second element 104. The non-conductive bonding layers 108a and 108b can be disposed on the front sides 114a and 114b of device portions 110a and 110b, such as semiconductor (e.g., silicon) portions, of the elements 102 and 104, respectively. Active devices and / or circuitry can be patterned and / or otherwise disposed within or on the device portions 110a and 110b. Active devices and / or circuitry may be located on or near the front sides 114a, 114b of the device portions 110a, 110b and / or on or near the opposite back sides 116a, 116b of the device portions 110a, 110b. Bonding layers may be provided on the front and / or back sides of the elements. The non-conductive material may be referred to as a non-conductive bonding region or bonding layer 108a of the first element 102. In some embodiments, the non-conductive bonding layer 108a of the first element 102 may be directly bonded to a corresponding non-conductive bonding layer 108b of the second element 104 using dielectric-to-dielectric bonding techniques. For example, non-conductive or dielectric-dielectric bonds can be formed without adhesives using direct bonding techniques as disclosed in at least U.S. Patent 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 for all purposes. It should be understood that in various embodiments, bonding layers 108a and / or 108b can include a non-conductive material, such as a dielectric material, e.g., silicon oxide, or an undoped semiconductor material, e.g., undoped silicon.Dielectric bonding surfaces or materials suitable for direct bonding include, but are not limited to, inorganic dielectrics such as silicon oxide, silicon nitride, or silicon oxynitride, and may contain carbon, such as silicon carbide, silicon oxynitride, low-K dielectric materials, SiCOH dielectrics, silicon carbonitride, glass, ceramic, glass-ceramic, or materials containing diamond-like carbon or diamond surfaces. Such carbon-containing materials may be considered inorganic, despite containing carbon. In some embodiments, the dielectric material does not include adhesives or polymeric materials such as epoxies, resins, or molding compounds. In some embodiments, including those described below, the dielectric bonding surface is defined by wafer-level processing of the underlying device, such as an upper interlevel dielectric layer or passivation layer formed in back-end-of-line (BEOL) processing of an integrated circuit, and a separate bonding layer is not deposited after the formation of the underlying device.

[0009] In some embodiments, device portions 110a and 110b can have significantly different coefficients of thermal expansion (CTE), defining dissimilar structures. The CTE difference between device portions 110a, 110b, and particularly between the bulk semiconductor, typically single-crystal portions of device portions 110a, 110b, can be greater than 5 ppm or greater than 10 ppm. For example, the CTE difference between device portions 110a, 110b can be in the range of 5 ppm to 100 ppm, 5 ppm to 40 ppm, 10 ppm to 100 ppm, or 10 ppm to 40 ppm. In some embodiments, one of device portions 110a, 110b can comprise an optoelectronic single-crystal material, including perovskite materials useful for optoelectronic or pyroelectric applications, while the other of device portions 110a, 110b can comprise a conventional substrate material (e.g., Si, Ge, SiGe, III-V materials, etc.). For example, one of the device portions 110a, 110b may include lithium tantalate (LiTaO) or lithium niobate (LiNbO), and the other of the device portions 110a, 110b may include silicon (Si), quartz, fused silica, sapphire, or glass. In other embodiments, one of the device portions 110a, 110b may include a single III-V semiconductor material such as gallium arsenide (GaAs) or gallium nitride (GaN), and the other of the device portions 110a, 110b may include a non-III-V semiconductor material such as silicon (Si) and / or germanium (Ge), or may include other materials with similar CTEs, such as quartz, fused silica, sapphire, or glass.

[0010] In various embodiments, the direct hybrid bond can be formed without an intervening adhesive. For example, the non-conductive bonding surfaces 112a and 112b can be polished to a high degree of smoothness. The non-conductive bonding surfaces 112a and 112b can be polished using, for example, chemical mechanical polishing (CMP). The roughness of the polished bonding surfaces 112a and 112b can be less than 30 Å rms. For example, the roughness of the bonding surfaces 112a and 112b can be in the range of approximately 0.1 Å rms to 15 Å rms, 0.5 Å rms to 10 Å rms, or 1 Å rms to 5 Å rms. The bonding surfaces 112a and 112b can be cleaned and exposed to a plasma and / or an etchant to activate the surfaces 112a and 112b. In some embodiments, the surfaces 112a and 112b can be terminated with chemical species after or during activation (e.g., during a plasma and / or etching process). Without being limited by theory, in some embodiments, the activation process can be performed to break chemical bonds at the bonding surfaces 112a and 112b, and the termination process can provide the bonding surfaces 112a and 112b with additional chemical species that improve the bond energy during direct bonding. In some embodiments, activation and termination are provided in the same step, e.g., a plasma to activate and terminate the surfaces 112a and 112b. In other embodiments, the bonding surfaces 112a and 112b can be terminated in a separate process to provide additional chemical species for direct bonding. In various embodiments, the termination species can include nitrogen. For example, in some embodiments, the bonding surfaces 112a, 112b can be exposed to a nitrogen-containing plasma. Furthermore, in some embodiments, including those described in more detail below, the bonding surfaces 112a, 112b can be exposed to fluorine. For example, one or more fluorine peaks may be present at or near the bonding interface 118 between the first and second elements 102,104.Thus, in the direct bonding structure 100, the bonding interface 118 between the two non-conductive materials (e.g., bonding layers 108a and 108b) can include a very smooth interface with a higher nitrogen content and / or fluorine peak at the bonding interface 118. In the embodiments described below, fluorine can be found at or near the bonding interface 118 of both the non-conductive regions 108a / 108b and the conductive regions 106a / 106b of the bonding structure 100. Additional examples of activation and / or termination processes can be found throughout U.S. Patent Nos. 9,564,414; 9,391,143; and 10,434,749, the entire contents of each of which are incorporated herein by reference for all purposes. The roughness of the polished bonding surfaces 112a and 112b may be slightly rougher (eg, about 1 Å rms to 30 Å rms, 3 Å rms to 20 Å rms, or possibly even rougher) after the activation process.

[0011] In various embodiments, the conductive feature 106 a of the first element 102 can also be directly bonded to the corresponding conductive feature 106 b of the second element 104. For example, direct hybrid bonding techniques can be used to provide conductor-conductor direct bonding along the bonding interface 118, which includes the covalently directly bonded non-conductive-non-conductive (e.g., dielectric-dielectric) surfaces prepared as described above. In various embodiments, the conductor-conductor (e.g., conductive feature 106 a - conductive feature 106 b) direct bonding and dielectric-dielectric hybrid bonding can be formed using direct bonding techniques similar to those disclosed in at least U.S. Patent Nos. 9,716,033 and 9,852,988, which are incorporated herein by reference in their entireties for all purposes. In the embodiments described below, aluminum can be used instead of copper at the bonding surfaces, and fluorine termination can be used instead of the nitrogen termination described in the incorporated disclosures. In the direct hybrid bonding embodiments described herein, conductive features are provided within a non-conductive bonding layer, and both conductive and non-conductive features are prepared for direct bonding, such as by planarization, activation, and / or termination processes described above. In this manner, the bonding surface prepared for direct bonding includes both conductive and non-conductive features. Specific additional preparation options for direct bonding of aluminum conductive features are described below.

[0012] For example, non-conductive (e.g., dielectric) bonding surfaces 112a, 112b (e.g., inorganic dielectric surfaces) can be prepared and bonded directly to one another without an intervening adhesive, as described above. Conductive contact features (e.g., conductive features 106a, 106b, which can be partially or completely surrounded by non-conductive dielectric field regions within bonding layers 108a, 108b) can also be bonded directly to one another without an intervening adhesive. In various embodiments, conductive features 106a, 106b can include discrete pads or traces at least partially embedded in non-conductive field regions. In some embodiments, the conductive contact features can include exposed contact surfaces of through-substrate vias (e.g., through-silicon vias (TSVs)). In some embodiments, each conductive feature 106a and 106b is recessed below the dielectric field region or outer (e.g., upper) surface (non-conductive bonding surface 112a and 112b) of the non-conductive bonding layer 108a and 108b, e.g., recessed by less than 30 nm, less than 20 nm, less than 15 nm, or less than 10 nm, e.g., recessed in a range of 2 nm to 20 nm, or in a range of 4 nm to 10 nm. In various embodiments, prior to direct bonding, the recesses of the opposing elements can be sized such that the total gap between the opposing contact pads is less than 15 nm, or less than 10 nm. The non-conductive bonding layers 108a and 108b can be directly bonded to each other at room temperature without adhesive, in some embodiments, after which the bonding structure 100 can be annealed. Upon annealing, the conductive features 106a and 106b can expand and contact each other, forming a metal-metal direct bond. Advantageously, Direct Bond Interconnect or DBI® technology, commercially available from Adeia, Inc. of San Jose, California, can be used to connect a high density of conductive features 106a and 106b across the direct bond interface 118 (e.g., small or fine pitch for a regular array).In various embodiments, the conductive features 106a and 106b and / or traces can include copper or a copper alloy, although other metals may be suitable. For example, the conductive features disclosed herein, such as the conductive features 106a and 106b, can include a fine-grained metal (e.g., fine-grained copper). In specific embodiments described below, at least one of the conductive features 106a and 106b is primarily aluminum or includes a predominantly aluminum portion.

[0013] Thus, in a direct bonding process, the first element 102 can be bonded directly to the second element 104 without an intervening adhesive. In some arrangements, the first element 102 can comprise a singulated or singulated element, such as a singulated or singulated integrated device die. In other arrangements, the first element 102 can comprise a carrier or substrate (e.g., a wafer) including a plurality (e.g., tens, hundreds, or more) of device regions that, when singulated, form a plurality of integrated device dies. Similarly, the second element 104 can comprise a singulated element, such as a singulated integrated device die. In other arrangements, the second element 104 can comprise a carrier or substrate (e.g., a wafer). The embodiments disclosed herein can be applied to wafer-to-wafer (W2W), die-to-die (D2D), or die-to-wafer (D2W) bonding processes, as appropriate. In a wafer-to-wafer (W2W) process, two or more wafers can be directly bonded together (e.g., direct hybrid bonded) and then singulated using an appropriate singulation process. After singulation, the side edges of the singulated structure (e.g., the side edges of the two bonded elements) can be substantially flush and can include markings indicative of a common singulation process for the bonded structures (e.g., sawtooth markings if a sawtooth singulation process is used).

[0014] As described herein, the first element 102 and the second element 104 can be directly bonded to each other without adhesive, which, unlike a deposition process, results in a structurally different interface compared to deposition. In some applications, the width of the first element 102 in the bonding structure is similar to the width of the second element 104. In some other embodiments, the width of the first element 102 in the bonding structure 100 is different from the width of the second element 104. Similarly, the width or area of ​​the larger element in the bonding structure may be at least 10% larger than the width or area of ​​the smaller element. The first and second elements 102 and 104 may accordingly include non-deposited elements. Furthermore, unlike deposited layers, the direct bonding structure 100 may include defect regions along the bonding interface 118 where nanometer-scale voids (nanovoids) exist. The nanovoids may form due to activation (e.g., exposure to plasma) of the bonding surfaces 112a and 112b. As discussed above, the bonding interface 118 may include a concentration of material from the activation and / or final chemical treatment process. For example, in embodiments utilizing nitrogen plasma for activation, a nitrogen peak may form at the bonding interface 118. The nitrogen peak may be detectable using secondary ion mass spectrometry (SIMS) techniques. In various embodiments, for example, nitrogen termination (e.g., exposing the bonding surface to a nitrogen-containing plasma) may replace OH groups on a hydrolyzed (OH-terminated) surface with NH molecules, resulting in a nitrogen-terminated surface. In embodiments utilizing oxygen plasma for activation, an oxygen peak may form at the bonding interface 118. In exemplary embodiments described herein below that employ fluorine treatment for termination, a fluorine peak may form at the bonding interface 118. In some embodiments, the bonding interface 118 may include silicon oxynitride, silicon oxycarbonitride, or silicon carbonitride. As discussed herein, direct bonding may involve covalent bonds stronger than van der Waals bonds.The bonding layers 108a and 108b may also have polished surfaces that are planarized to a high degree of smoothness.

[0015] In various embodiments, the metal-metal bond between the conductive features 106a and 106b can be bonded such that the metal grains grow together across the bonding interface 118. In some examples of direct hybrid bonding, the metal can be or include copper and have grains oriented along crystal planes 111 to improve copper diffusion across the bonding interface 118. In some examples of direct hybrid bonding, the conductive features 106a and 106b can include a nanotwin copper grain structure, which can help fuse the conductive features together during annealing. In exemplary embodiments described below, one or both of the conductive features 106a and 106b include fluorine-treated aluminum. The bonding interface 118 can extend substantially entirely to at least a portion of the bonded conductive features 106a and 106b, such that there is substantially no gap between the non-conductive bonding layers 108a and 108b at or near the bonded conductive features 106a and 106b. In some embodiments, a barrier layer may be provided underneath and / or laterally surrounding the conductive features 106a and 106b (which may comprise, for example, copper). However, in other embodiments, there may not be a barrier layer underneath the conductive features 106a and 106b, as described, for example, in U.S. Pat. No. 11,195,748.

[0016] Advantageously, use of the direct hybrid bonding techniques described herein can enable extremely fine pitches and / or small pad sizes between adjacent conductive features 106a and 106b. For example, in various embodiments, the pitch p (edge-to-edge or center-to-center distance, as shown in FIG. 1A ) between adjacent conductive features 106a (or 106b) can be in the range of 0.5 microns to 100 microns, 0.5 microns to 50 microns, 0.75 microns to 25 microns, 1 micron to 25 microns, 1 micron to 10 microns, or 1 micron to 5 microns. Furthermore, the major lateral dimensions (e.g., pad diameter) can be similarly small, for example, in the range of 0.25 microns to 30 microns, 0.25 microns to 5 microns, or 0.5 microns to 5 microns.

[0017] As described above, the non-conductive bonding layers 108 a, 108 b can be directly bonded to one another without adhesive, after which the bonding structure 100 can be annealed. Upon annealing, the conductive features 106 a, 106 b can expand and contact one another, forming a metal-to-metal direct bond. In some embodiments, the materials of the conductive features 106 a, 106 b can interdiffuse during the annealing process.

[0018] 2 is a schematic cross-sectional side view of a bonding structure 1. The bonding structure 1 includes a first component 10 and a second component 12 bonded together by solder balls 14. The first component 10 includes a first back-end-of-line (BEOL) layer 16 and an aluminum pad 18. A polymer layer 20 may be disposed on a surface of the BEOL layer 16 to support the solder balls 14. The second component 12 includes a second BEOL layer 26 and an aluminum pad 28. The solder balls 14 are provided on the first component 10 and bonded to the aluminum pads 28 of the second component 12.

[0019] The use of solder balls 14 may not be feasible for relatively fine-pitch interconnects, such as interconnect pitches of less than 20 microns or even less than 2 microns. Furthermore, because the mechanical connection between the devices 10 and 12 is limited to solder joints, the mechanical connection is weak and susceptible to separation due to physical stress or impact due to the brittleness of the intermetallic compounds (IMCs) typically formed in the solder balls. After bonding, the gap between the top surfaces of the BEOL layers 16, 26 is cleaned and filled with a dielectric underfill material (not shown) to encapsulate the solder balls 14 and corresponding contacts. The resistivity of the alloy formed with solder is typically at least three times that of aluminum pads or copper posts, causing electrical losses. Furthermore, the dielectric underfill that mechanically connects the top surfaces of the BEOL layers 16, 26 inhibits heat transfer between the first device 10 and the second device 12. Therefore, it may be beneficial to provide a bonding surface that allows for direct hybrid bonding of the devices 10, 12.

[0020] 3A-3E illustrate a method of forming a copper pad 32 on an aluminum pad or interconnect 34 formed in a BEOL layer 16 of a device 30. In FIG. 3A, a BEOL layer 16 can be provided. The BEOL layer 16 can include a planar dielectric surface and an aluminum pad or interconnect 34 at least partially embedded in the dielectric. As shown in FIG. 3B, the method includes forming a planarized dielectric layer 36 on the BEOL layer 16. In FIG. 3C, a cavity 38 is formed in the dielectric layer 36. The aluminum pad or interconnect 34 can be exposed through the cavity 38.

[0021] In FIG. 3D, a barrier layer 40 and / or a seed layer can be formed on the surface of the dielectric layer 36 and the cavity 38. Copper 42 is provided in the cavity on at least the barrier layer 40. In FIG. 3D, the copper 42 is overfilled, with excess copper 42 present on the surface of the dielectric layer 36. The device 30 can be annealed, for example, at a temperature less than 200° C., if necessary, to at least partially stabilize the microstructure of the copper 42. To form the copper pad 32, the excess copper 42 can be removed in FIG. 3E. The excess copper 42 can be removed by polishing, for example, chemical mechanical planarization (CMP). The polishing process can also remove a portion of the barrier layer 40 from the surface of the dielectric layer 36, forming a direct bonded surface for the device 30 after activation and / or termination, as described above.

[0022] As shown in Figures 4A-4E, aluminum pads 44 can be formed in a manner similar to the formation of copper pads 32 shown in Figures 3A-3E. Instead of copper 42 provided in Figure 3D, aluminum 46 can be provided in Figure 4D, and the excess aluminum 46 can be removed to form aluminum pads 44. Alternatively, a blanket layer of aluminum can be deposited over the structure of Figure 4A, patterned with an appropriate masking process, and then etched away the unwanted portions of the aluminum (e.g., reactive ion etching). In an alternative process, a dielectric bonding layer 36 can be deposited over the patterned aluminum layer and polished down to the aluminum pads 4 to form a smooth dielectric bonding surface.

[0023] One drawback of the process of Figures 3A-4E is the separate deposition of the bonding layer 36, which often exposes the device to high-temperature processing and involves expensive masking processes to define the cavity 38. Furthermore, with the process of Figures 4A-4E, the aluminum pad 44 is susceptible to oxidation, and surface oxides may form on the aluminum pad 44. Furthermore, when the bonding layer 36 is deposited on the pre-patterned aluminum pad 44, the aluminum pad 44 is exposed to high temperatures, typically exceeding 250°C, usually between 300°C and 350°C. Higher temperature dielectric processes induce large grain formation in the aluminum pad 44. A subsequent dielectric planarization step produces a smooth dielectric bonding surface, including the surface of the aluminum pad 44 with large grains. Metal pads with large grains (0.5-3 microns or larger) have fewer grain boundaries than metal pads with finer grains (e.g., less than 0.3 microns). In fact, pads using finer metals tend to bond at lower temperatures than pads with larger grains. Aluminum's tendency to form a thin surface aluminum oxide during the planarization process and upon exposure to ambient air can present a problem during the direct bonding operation. The bonding surface on the aluminum pad 44 or 34 prevents direct bonding of the aluminum pad 44 or 34 to a corresponding aluminum pad on another device. Therefore, prior to bonding, processes such as argon sputtering are sometimes employed to remove the oxide from the bonding surface. However, such steps can be time-consuming and costly. Such processes can also redeposit aluminum particles on portions of the dielectric bonding surface. One solution to avoid surface oxidation is to activate the surface of the aluminum pad 44 or 34 with nitrogen plasma. Exposing the aluminum pad 44 or 34 to nitrogen plasma results in the formation of aluminum nitride on the surface of the aluminum pad 44.Although aluminum nitride on the surface is easier to process for direct bonding than aluminum oxide, such processes may require high-temperature (e.g., 300°C-400°C) bonding processes to decompose the aluminum nitride on the surface or for the aluminum to diffuse through the nitride on the surface and form a metallurgical bond between the pads 34, 44 of the opposing elements. High-temperature bonding processes increase the thermal budget for forming the bonding structure. Various embodiments disclosed herein may provide a simplified, cost-effective method and structure for forming the bonding structure.

[0024] 5A-5F illustrate a method of forming a bonding surface 76a of a device 76 according to one embodiment. FIG. 5A is a schematic cross-sectional side view illustrating an aluminum layer 60 on a back-end-of-line (BEOL) layer 62, which is formed over a device (not shown), such as in or on a semiconductor material. A barrier layer 68 and / or a seed layer, such as TiN, TiN / Ti, TiW, or TiW / Ti, may be disposed between the BEOL layer 62 and the aluminum layer 60. The BEOL layer 62 may include a dielectric region 64 and an interconnect structure 66. The interconnect structure 66 may comprise an aluminum interconnect. The barrier layer 68 may be deposited on a surface of the BEOL layer 62, and the aluminum layer 60 may be deposited on the barrier layer 68. For example, the aluminum layer 60 may be provided by sputtering. For example, the aluminum layer 60 may be sputter-deposited at about 150° C. or less. The aluminum layer 60 may be relatively thin. For example, the thickness of aluminum layer 60 can range from 0.5 μm to 7 μm, 0.5 μm to 5 μm, 0.5 μm to 4 μm, 1 μm to 5 μm, 1 μm to 3 μm, or 1 μm to 2 μm, depending at least in part on the circuit requirements.

[0025] 5B, a selected or desired masking layer, such as a resist layer 70, may be lithographically applied over the aluminum layer 60. The resist layer 70 may be patterned over the aluminum layer 60 such that a portion of the resist layer 70 overlies the interconnect structure 66.

[0026] 5C , portions of aluminum layer 60 can be selectively removed, for example, by reactive ion etching (RIE) or wet etching, to form conductive feature 72. For example, portions of aluminum layer 60 not covered by or including resist layer 70 can be etched using any suitable etching process, such as plasma etching, including reactive ion etching, to define conductive feature 72. Conductive feature 72 is one example of a conductive feature. Conductive feature 72 can be a conductive metal pad, via, or line containing greater than 50% aluminum by volume. For example, conductive feature 72 can contain greater than 80%, greater than 90%, or greater than 95% aluminum by volume. In the illustrated embodiment, conductive feature 72 is patterned from aluminum layer 60 and thus can be considered an aluminum feature; however, in other embodiments, conductive feature 72 can include one or more other metal layers while still constituting a unique feature defined by a single mask and containing greater than 50% aluminum by volume. In this manner, each of the conductive features 72 can have continuous sidewalls with defined features by a single mask process.

[0027] In FIG. 5D , a dielectric layer 74 may be provided over the conductive feature 72 and over a portion of the BEOL layer 62. In some embodiments, the dielectric layer 74 may include an oxide layer. For example, the oxide layer may be deposited at about 350° C. or other desired temperature by known methods. In some embodiments, multiple dielectric coating steps with other intermediate processes may be applied to form the dielectric layer 74. The dielectric coating may include a conformal coating (as shown) or a non-conformal coating. In some embodiments, the dielectric layer 74 may include a combination of a conformal dielectric coating and a non-conformal dielectric coating. The dielectric layer 74 may be referred to as a non-conductive field region. In some embodiments, the dielectric layer 74 is formed by sputtering, spin-on deposition, or other low-temperature processes.

[0028] As shown in FIG. 5E, a portion of the dielectric layer 74 can be removed (e.g., polished) to expose the surface of the conductive feature 72. The surface of the conductive feature 72 and the surface of the remaining dielectric layer 74 can define a bonding surface 76a of the element 76. The bonding surface 76a of the element 76 can be polished, for example, using chemical mechanical polishing (CMP), as disclosed herein. The surface of the conductive feature 72 can be recessed below the dielectric layer 74 either by CMP chemistry or by subsequent selective etching. The roughness of the polished bonding surface 76a can be less than 30 Å rms. For example, the roughness of the bonding surface 76a can be in the range of approximately 0.1 Å rms to 15 Å rms, 0.5 Å rms to 10 Å rms, or 1 Å rms to 5 Å rms. Furthermore, the conductive feature 72 and the surrounding dielectric layer 74 can be formed during back-end-of-line processing, and the element 76 can be formed before or after singulation, as supplied by an integrated circuit manufacturer. The thickness of the conductive features 72 may range from approximately 0.5 μm to 7 μm or 1 μm to 5 μm.

[0029] In FIG. 5F, the bonding surface 76a of the element 76 can be terminated. Although not shown, it will be understood that a protective layer can be provided and removed between the polishing of FIG. 5E and the termination of FIG. 5F, similar to the process described below with respect to FIG. 6I. The bonding surface 76a of the element 76 can be terminated, for example, with fluorine to define a continuous or discontinuous surface of an ultrathin layer of aluminum fluoride (Al-F) complex, fluorinated aluminum oxide (Al-FO) complex, or fluorinated boron aluminum oxide (Al-FBO) complex. In some embodiments, the bonding surface 76a can be rinsed with a rinse solution that provides a surface termination. For example, the rinse solution can include 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, tetramethylammonium tetrafluoroborate, tetramethylammonium tetrafluoroborate, hydrogen fluoride (HF), or any suitable combination thereof. After termination, the bonding surface 76a can be spin-dried, with or without a prior deionized water rinse. In some embodiments, fluorine termination can be achieved by a plasma process. For example, the surface of the conductive feature can be exposed to a mild fluoride plasma or placed in a chamber with a fluorine-bearing gas such as carbon tetrafluoride (CF4). Residual fluorine on the chamber walls can adsorb to the bonding surface 76a. The fluorine can reduce some of the native aluminum oxide. In some embodiments, the bonding surface 76a of the element 76 is not exposed to a nitrogen plasma and / or an ammonium dip before or after the fluorine treatment.

[0030] After the bonding surface 76a of the element 76 is terminated, there may be a gradient of fluorine concentration from the bonding surface 76a into the element 76. Thus, the element 76 may have a higher fluorine content at the bonding surface 76a than portions of the element 76 further from the surface. For example, one or more fluorine peaks may be present at or near the bonding surface 76a. In some embodiments, the conductive feature 72 may have a gradient of fluorine concentration such that the surface of the conductive feature 72 has a higher fluorine content than the depth of the conductive feature. For example, the conductive feature 72 may have the highest fluorine concentration at the surface, and the fluorine concentration gradually decreases from the surface of the conductive feature 72 to portions of the conductive feature 72 further from the surface. In some embodiments, fluorine may be present approximately 4 nm to 6 nm (e.g., 5 nm) below the surface. In some embodiments, the level of oxygen present on the surface of the conductive feature 72 may be extremely low or undetectable. For example, the oxygen present on the surface of the conductive feature 72 may be less than 20 ppm. In some embodiments, bonding surface 76a may include portions that are free of aluminum oxide. In some embodiments, conductive feature 72 and / or dielectric layer 74 may have very little or no carbon and / or nitrogen. For example, the surface of conductive feature 72 or dielectric layer 74 may have less than 50 ppm, less than 40 ppm, or less than 20 ppm of carbon or nitrogen.

[0031] Without such termination, exposure to room temperature air, including clean room air, can result in the formation of aluminum oxide (Al2O3) on the surface of conductive feature 72. Fluoride termination of bonding surface 76a can reduce or prevent the formation of aluminum oxide (Al2O3) on the surface of conductive feature 72. Table 1 below shows the melting points and thermal expansion coefficients of aluminum (Al), aluminum oxide (Al2O3), aluminum nitride (AlN), and aluminum fluoride (AlF3). TIFF2025542482000002.tif39153

[0032] Among the four materials in Table 1, aluminum has the lowest melting point and a relatively high coefficient of thermal expansion, but it is prone to forming aluminum oxide on its surface when exposed to air. Aluminum oxide has a significantly higher melting point (approximately 4.5 times that of aluminum) and a significantly lower coefficient of thermal expansion than the other three materials. Aluminum nitride has a lower melting point and a slightly higher coefficient of thermal expansion than aluminum oxide. However, aluminum nitride has a significantly higher melting point and a significantly lower coefficient of thermal expansion than aluminum. Aluminum fluoride has a relatively low melting point and a significantly higher coefficient of thermal expansion. Therefore, terminating the surface of the conductive feature 72 with fluorine can provide a reliable bonding surface (bonding surface 76a) for the element 76 and facilitate lower annealing temperatures for forming metallurgical bonds during direct hybrid bonding. Depending on the conditions, the fluorine-terminated surface can mitigate or prevent oxide formation on the surface of the conductive feature 72 for, for example, three days, four days, one week, or even up to ten days.

[0033] The element 76 can be a wafer or a die, and the element 76 can be bonded to a second element (e.g., a wafer or a die). FIG. 5G is a schematic cross-sectional side view of a bonding structure 2 including an element 76 in the form of a wafer and a second element 80 (another wafer) bonded to the element 76 along a bonding interface 82. In some embodiments, the second element 80 can be bonded to another substrate of interest. FIG. 5H is a schematic cross-sectional side view of a bonding structure 2′ including an element 76 in the form of a wafer and a plurality of second elements 84 (dies) bonded to the element 76 along a bonding interface 86. The second element 80 or 84 can include conductive features 92 and non-conductive field regions 94 and can have a similar structure to the first element 76 (including the aluminum-based conductive features 92).

[0034] The bonding surface 76a of the element 76 can be directly bonded to the bonding surfaces 80a, 84a of the second elements 80, 84 by any suitable method disclosed herein. The bonding surface 76a of the element 76 can be directly bonded to the bonding surfaces 80a, 84a of the second elements 80, 84 such that the non-conductive field regions 94 of the second elements 80, 84 are directly bonded to the dielectric layer 74 of the element 76 (which can be considered the first element in the embodiments of Figures 5H and 5G). This initial direct bonding of the dielectric material can form a strong covalent bond between the non-conductive field regions 94 of the opposing elements 76, 80, 84 at room temperature. In some embodiments, the second element 84 can be bonded to another substrate of interest.

[0035] The bonded elements 76 and 80, or 76 and 84, can then be heated (e.g., annealed) so that the conductive features 72, 92 expand across the gaps left by the recessed aluminum to contact each other and form a direct metal bond. In some embodiments, the bonded elements 76 and 80, or 76 and 84, can be annealed at a temperature below 350°C, such as below about 300°C or below about 250°C, for about 4 hours or less, such as between about 2.5 hours and 4 hours. For example, the annealing temperature can range between about 150°C and 300°C, between about 200°C and 300°C, or between about 200°C and 250°C. The annealing process can strengthen the bond between the conductive features 72 and 92.

[0036] The fluorine content may be higher at the bonding surface 76a compared to deeper within the elements 76 and 80, 76 and 84. A gradient of fluorine concentration at or near the bonding surface 76a may exist in the bonding structure 2, 2′. For example, one or more fluorine peaks may exist at or near the bonding interface 82, 86 between the first and second elements 76 and 80, 76 and 84 in the bonding structure 2, 2′. In some embodiments, very low or undetectable levels of oxygen are present between the conductive features 72 and 92 after metallurgical bonding. For example, less than 1000 ppm, less than 500 ppm, or less than 100 ppm of oxygen may be present between the bonded conductive features 72 and 92. Similarly, there may be very little or no terminating molecules or molecule-associated carbon and / or nitrogen between the bonded conductive features 72 and 92 and / or between the dielectric layer 74 and the non-conductive field region 94. For example, there may be less than 100 ppm or less than 80 ppm of nitrogen and / or carbon between conductive feature 72 and conductive feature 92 after bonding.

[0037] 6A-6E illustrate a method for forming bonding surface 150a of device 150 according to one embodiment. FIG. 6A is a schematic cross-sectional side view illustrating an aluminum layer 73, including large aluminum metal grains or fine aluminum grains, and a dielectric layer 74 formed on back-end-of-line (BEOL) layers 62, including interconnect structures 66. Aluminum layer 73 and / or dielectric layer 74 may be planarized. The structure of FIG. 6A may be the same as or substantially similar to the structure of FIG. 5E. As mentioned above, aluminum layer 73 and dielectric layer 74 may also be part of a BEOL or redistribution layer (RDL) structure of an integrated device.

[0038] 6B, at least a portion of aluminum layer 73 may be selectively removed to form recesses 152 on aluminum layer 73, such as by RIE, wet etching, or other known methods. The depth of the recesses may range from 0.1 μm to 0.5 μm, 0.1 μm to 0.25 μm, or 0.15 μm to 0.2 μm. The portion of aluminum layer 73 may be removed by, for example, dry etching (e.g., steam or plasma etching) or wet etching methods.

[0039] 6C , a barrier layer 153 and a fine-grained aluminum layer 154 can be provided within the recesses 152 and on the surface 74a of the dielectric layer 74. For example, aluminum having a fine-grained microstructure can be formed on the recesses 152 by sputtering the BEOL layer 62 and cooling it, or by cooling a substrate (not shown) to which the BEOL layer 62 is bonded to, during sputtering, to less than 100° C., preferably less than 50° C., e.g., less than 20° C. In some embodiments, the barrier layer 153 can completely or partially separate the fine-grained aluminum layer 154 from the aluminum layer 73 and the dielectric layer 74. In some embodiments, the barrier layer 153 can be omitted, and the fine-grained aluminum layer 154 can be coated directly on the large-grained aluminum 73. Fine-grained aluminum can be defined as aluminum having an average grain size (e.g., width) of less than 15 nm, less than 20 nm, less than 50 nm, less than 100 nm, less than 200 nm, less than 300 nm, or less than 500 nm. For example, the maximum width of the crystal grains in the fine-grained aluminum layer 154 can be in the range of about 10 nm to about 500 nm, about 10 nm to about 300 nm, about 15 nm to about 500 nm, about 15 nm to about 300 nm, about 15 nm to about 100 nm, about 15 nm to about 50 nm, about 50 nm to about 500 nm, about 50 nm to about 300 nm, or about 100 nm to about 300 nm. In some embodiments, the majority of the crystal grains in the fine-grained aluminum layer 154 can have a width in the range of about 10 nm to about 500 nm, about 10 nm to about 300 nm, about 15 nm to about 500 nm, about 15 nm to about 300 nm, about 15 nm to about 100 nm, about 15 nm to about 50 nm, about 50 nm to about 500 nm, about 50 nm to about 300 nm, or about 100 nm to about 300 nm.

[0040] In some embodiments, the fine-grained aluminum layer 154 can be provided by low-temperature deposition. For example, the fine-grained aluminum layer 154 can be deposited at a temperature of less than about 100° C., less than about 65° C., or less than about 20° C. For example, the deposition temperature for depositing the fine-grained aluminum layer 154 can range between about 10° C. and 100° C., between about 10° C. and 65° C., between about 10° C. and 50° C., or between about 10° C. and 20° C. The thickness of the fine-grained aluminum layer 154 can be the same as or greater than the depth of the recesses 152.

[0041] 6D , portions of the barrier layer 153 and the fine-grained aluminum layer 154 above the surface 74a of the dielectric layer 74 can be removed. For example, portions of the barrier layer 153 and the fine-grained aluminum layer 154 can be removed by polishing (e.g., chemical-mechanical polishing (CMP)) to a degree sufficient to define a bonding surface 150a of the device 150, including the surface 74a of the dielectric layer 74 and the surface 154a of the fine-grained aluminum layer 154. Either the CMP chemistry or a subsequent etching process can recess the aluminum surface 154a below the dielectric surface 74a. The CMP process can be performed at a temperature lower than the deposition temperature for depositing the fine-grained aluminum layer 154. The aluminum layer 73, the barrier layer 153, and the fine-grained aluminum layer 154 can together define a conductive feature 155. As with the previous embodiment, the conductive feature 155 can include more than 50% aluminum by volume, for example, more than 80% aluminum by volume, and can have continuous sidewalls characterized by definition by a single mask process. When aluminum is predominant, as in the illustrated embodiment, the conductive feature 155 can be referred to as an aluminum feature in some embodiments. The conductive feature 155 can have a first portion (e.g., aluminum layer 73) and a second portion (e.g., fine-grained aluminum layer 154). The second portion can have a different microstructure than the first portion. The thickness of the conductive feature 155 can range from approximately 0.5 μm to 7 μm, or 1 μm to 5 μm.

[0042] In FIG. 6E, the bonding surface 150a of the element 150 can be terminated in the same or similar manner as disclosed above with respect to FIG. 5F. The bonding surface 150a of the element 150 can be terminated, for example, with fluorine to define a surface aluminum fluoride complex, aluminum fluoride oxide complex, or aluminum fluoride boron oxide complex. In some embodiments, the bonding surface 150a can be rinsed with a rinsing solution. For example, the rinsing solution can include 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, tetramethylammonium tetrafluoroborate, hydrogen fluoride (HF), buffered hydrogen fluoride (BHF), or any suitable combination thereof. The bonding surface 150a can be spin-dried with deionized (DI) water without rinsing. In some embodiments, the treated surface can be rinsed with DI water or another suitable solvent and dried by known methods, such as spin-drying. In some embodiments, fluorine termination can be achieved by a plasma process as described above.

[0043] The bonding surface 150a of the element 150 can be formed without high temperature processes, thus maintaining a relatively small grain size of the fine-grained aluminum layer 154, which can be advantageous for subsequent metal bonding.

[0044] FIG. 6F is a schematic cross-sectional side view of a bonding structure 3 including an element 150 and a second element 160 bonded to the element 150. In some embodiments, the second element 160 can have the same or substantially similar structure as the element 150. The second element 160 can include a back-end-of-liquid (BEOL) layer 162 including interconnect features, a dielectric layer 164, and a conductive feature 165 including an aluminum layer 166 and a fine-grained aluminum layer 168, which together can function as pads. The bonding surface 150a of the element 150 can be directly bonded to the bonding surface 160a of the second element 160 along a bonding interface 170, such that the dielectric layer 74 is directly bonded to the dielectric layer 164. This initial direct bonding of the dielectric materials can form a strong covalent bond between the dielectric layers 74, 164 of the opposing elements 150, 160 at room temperature. In some embodiments, the second element 160 can be bonded to another substrate of interest.

[0045] In FIG. 6G, the bonding structure 3 formed in FIG. 6F can be heated (e.g., annealed). In some embodiments, the structure formed in FIG. 6F can be annealed at a temperature below about 350°C, below about 300°C, or below about 250°C for about two hours or less. For example, the annealing temperature can range between about 150°C and 300°C, between about 200°C and 300°C, or between about 200°C and 250°C. The annealing process can cause the fine-grained aluminum layers 154, 168 to expand across the gaps left by the recessed aluminum surfaces, potentially causing metallurgical bonding between the fine-grained aluminum layers 154, 168. The annealing can also strengthen the bond between the dielectric layers 74, 164. The grains of the fine-grained aluminum layer 154 can grow due to the heating process. In some embodiments, the grains of the fine-grained layer 154 can remain smaller than the grains of the aluminum layer 73. For example, the average grain size (e.g., width) of the grains in the annealed fine-grained aluminum layer 154 can be less than 1000 nm, less than 750 nm, or less than 500 nm. For example, the maximum width of the largest grain in the annealed fine-grained aluminum layer 154 can be in the range of approximately 20 nm to 500 nm. In some embodiments, the majority of the grains in the annealed fine-grained aluminum layer 154 can have a width in the range of approximately 200 nm to 500 nm. In some embodiments, the fine-grained aluminum layer 154 can be deposited on only one of the bonded substrates. In some embodiments, the fine-grained aluminum layer 154 can include aluminum nanoparticles formed by physical vapor deposition (PVD) or atomic layer deposition (ALD), or other known methods.

[0046] Like device 76, device 150 can be a die or a wafer, and second device 160 can be a die or a wafer. Accordingly, the process for bonding device 150 and second device 160 can include wafer-to-wafer (W2W), die-to-die (D2D), or die-to-wafer (D2W) bonding processes. In some embodiments, bonding structure 3 can include an additional wafer, substrate, or die stacked and bonded on top of second device 160. The stacked devices can be electrically connected, for example, via various TSVs.

[0047] 6H is a side cross-sectional view of singulated bonding structures 3a, 3b, and 3c. In some embodiments, the singulated bonding structures 3a, 3b, and 3c can be formed by a singulation process after W2W bonding the device 150 and the second device 160 of FIG. 6F. For example, the singulation process can include attaching the bonded W2W structure to a dicing film or tape 172, forming a protective layer 174 on the bonded W2W structure, and singulating the bonded W2W structure into multiple singulated structures, such as the singulated bonding structures 3a, 3b, and 3c. Each of the singulated bonding structures 3a, 3b, and 3c can include a die from the device 150 and a die from the second device 160.

[0048] FIG. 6I is a cross-sectional side view of singulated elements 151 a, 151 b, and 151 c after at least partial preparation for direct hybrid bonding but before actual bonding. In some embodiments, element 150 shown in FIG. 6D can comprise a wafer from which singulated elements 151 a, 151 b, and 151 c can be formed. For example, element 150 in wafer form can be disposed on dicing film or tape 172. A protective layer 174 can be formed over element 150. Elements 150 can be singulated into singulated elements 151 a, 151 b, and 151 c. After singulation, protective layer 174 can be removed, as shown in FIG. 6J.

[0049] As shown in Figure 6K, after removing the protective layer 174, the bonding sides of the singulated elements 151a, 151b, and 151c can be terminated as described with respect to Figure 6F. After terminating the sides of the singulated elements 151a, 151b, and 151c, the singulated elements 151a, 151b, and 151c can be bonded to a second element 160, thereby forming a D2W bonding structure 4, as shown in Figure 6L. In the D2W bonding structure 4, the singulated elements 151a, 151b, and 151c can be bonded to a second element 160 as described with respect to Figure 6G.

[0050] 7A-7E illustrate a method of forming bonding surface 200a of device 200 according to one embodiment. Figure 7A is a schematic cross-sectional side view showing aluminum layer 202 and dielectric layer 74 formed over back-end-of-line (BEOL) or RDL layer 62, which includes interconnect structure 66. The structure of Figure 7A can be the same as or substantially similar to the structures of Figures 5E and 6A.

[0051] 7B, at least a portion of the aluminum layer 202 can be removed to form recesses 152 on each aluminum layer 202. The depth of the recesses can range from 0.1 μm to 0.5 μm, 0.1 μm to 0.35 μm, or 0.15 μm to 0.25 μm. The portions of the aluminum layer 202 can be removed by, for example, dry etching (e.g., steam or plasma etching) or wet etching.

[0052] 7C, different types of conductive materials, such as barrier layer 153 and illustrated copper layer 204, can be provided within recess 152 and on surface 74a of dielectric layer 74. Copper layer 204 is one example of a different type of conductive material; another example may include a silver layer. Copper layer 204 can include fine-grained copper having an average grain width of less than about 15 nm, less than about 20 nm, less than about 50 nm, less than about 100 nm, less than about 200 nm, less than about 300 nm, or less than about 500 nm. For example, the maximum grain width of copper layer 204 can be in the range of about 10 nm to about 500 nm, about 10 nm to about 300 nm, about 15 nm to about 500 nm, about 15 nm to about 300 nm, about 15 nm to about 100 nm, about 15 nm to about 50 nm, about 50 nm to about 500 nm, about 50 nm to about 300 nm, or about 100 nm to about 300 nm. In some embodiments, the majority of the grains in the fine-grained copper layer 204 can have widths ranging from about 10 nm to about 500 nm, about 10 nm to about 300 nm, about 15 nm to about 500 nm, about 15 nm to about 300 nm, about 15 nm to about 100 nm, about 15 nm to about 50 nm, about 50 nm to about 500 nm, about 50 nm to about 300 nm, or about 100 nm to about 300 nm. In some embodiments, the different conductive layers can be coated by electroless plating or electroplating. Alternatively, the different conductive layers can be coated by printing or physical vapor deposition (PVD) methods such as evaporation or sputtering. In some embodiments, the different conductive layers can comprise nanoparticle copper, nanoparticle silver, or other nanoparticle metals. The nanoparticle metals can be coated by electroless, electrolytic, or low-temperature sputtering, among other methods.

[0053] In some embodiments, the copper layer 204 can be provided by low-temperature deposition. For example, the copper layer 204 can be deposited at a temperature below 100°C, below 65°C, or below 20°C. For example, the deposition temperature for depositing the copper layer 204 can range between 1°C and 10°C, 10°C and 100°C, 10°C and 65°C, 10°C and 50°C, or 10°C and 35°C. The thickness of the copper layer 204 can be the same as or approximately similar to the depth of the recesses 152. The copper layer 204 can be deposited by physical vapor deposition (e.g., sputtering) rather than by plating. Due to the nature of the deposition process, the copper layer 204 can have a predominantly 111 texture and a randomly oriented grain structure.

[0054] 7D , portions of the barrier layer 153 and copper layer 204 on the surface 74a of the dielectric layer 74 can be removed. For example, portions of the barrier layer 153 and copper layer 204 on the dielectric layer 74 can be removed by polishing (e.g., chemical-mechanical polishing (CMP)) to define a bonding surface 200a of the device 200, including the surface 74a of the dielectric layer 74 and the surface 204a of the copper layer 204. In practice, the CMP process for forming the dielectric bonding surface 200a can polish away a very small portion of the dielectric material 74 during the barrier layer 153 removal step. The CMP process can be performed at a lower temperature than the deposition temperature for depositing the copper layer 204. Either the CMP chemistry or a subsequent etching process can recess the copper surface 204a below the dielectric surface 74a. The aluminum layer 202 and the copper layer 204 can together form the conductive feature 206. Because the upper copper layer 204 and the lower aluminum layer 202 have their sidewalls or lateral extents defined by the same mask (e.g., a mask for etching aluminum to form the aluminum layer 202 or for etching the dielectric layer 74 to fill with aluminum), the sidewalls of the upper and lower portions are continuous and lack misalignment discontinuities (e.g., corners or angles) that are typical when the upper and lower portions are defined by separate masks. At least the lower aluminum layer 202 comprises aluminum. In the illustrated embodiment, the copper layer 204 comprises copper or another conductive material (e.g., silver), although in other embodiments, the upper portion may also comprise fine-grained aluminum. The conductive feature 206 may have a first portion (e.g., the aluminum layer 73) and a second portion (e.g., the upper copper layer 204). The second portion may have a different microstructure than the first portion. The thickness of the conductive feature 206 may range from approximately 0.5 μm to 7 μm or 1 μm to 5 μm.

[0055] In FIG. 7E , the bonding surface 200 a of the element 200 can be cleaned and exposed to a plasma and / or an etchant to activate the bonding surface 200 a. In some embodiments, the bonding surface 200 a of the element 200 can be terminated with chemical species after or during activation (e.g., during a plasma and / or etch process). Without being limited by theory, in some embodiments, the activation process can be performed to break chemical bonds at the bonding surface 200 a of the element 200, and the termination process can provide the bonding surface 200 a with additional chemical species that improve the bond energy during direct bonding. In some embodiments, activation and termination are provided in the same step, e.g., a plasma to activate and terminate the bonding surface 200 a of the element 200. In other embodiments, the bonding surface 200 a of the element 200 can be terminated in a separate process to provide additional chemical species for direct bonding.

[0056] As explained above, the bonding surface 200a may contain concentrations of materials from the activation process and / or the final chemical treatment process. For example, in embodiments utilizing nitrogen plasma for activation, nitrogen peaks may form at the bonding surface 200a. The nitrogen peaks may be detectable using secondary ion mass spectrometry (SIMS) techniques.

[0057] In various embodiments, for example, nitrogen termination (e.g., exposing the bonding surface to a nitrogen-containing plasma) can replace OH groups on a hydrolyzed (OH-terminated) surface with NH molecules, resulting in a nitrogen-terminated surface. In embodiments utilizing an oxygen plasma for activation, oxygen peaks can form on the bonding surface 200a. In some embodiments, the bonding surface 200a can include silicon oxynitride, silicon oxycarbonitride, or silicon carbonitride.

[0058] Similar to the elements 76, 150 of the previous embodiments, the element 200 can be a die or a wafer, and the element 200 can be bonded to another element (e.g., a wafer or a die). FIG. 7F is a schematic cross-sectional side view of a bonding structure 5 including the element 200 in the form of a wafer and a second element 220 (another wafer) bonded to the element 200 along a bonding interface 221. The second element 220 can include a BEOL layer 222, a dielectric layer 224, and a conductive feature 232, which can also include a lower portion 228 (e.g., aluminum) and an upper portion 230 (e.g., copper), as shown. The dielectric layer 74 and the dielectric layer 224 can be bonded directly to each other without an intervening adhesive, and the copper layer 204 and the upper layer 230 (e.g., copper layer) can be bonded directly to each other without an intervening adhesive. In other embodiments, additional wafers or substrates (e.g., 1 to 8 wafers) can be mechanically and electrically bonded onto the second element 220. The bonded wafer or substrate stack can be singulated for subsequent processing. Similarly, additional dies (e.g., 1 to 40 dies) can be bonded or stacked onto the second element 220. The wafer or substrate with the bonded dies can be singulated for subsequent processing. One of the subsequent processes can include encapsulating the sides of the singulated stack with a dielectric layer. In some embodiments, the encapsulating dielectric layer comprises a molding compound.

[0059] 6I and 6J, in some embodiments, device 200 can be singulated into a singulated device prior to bonding. The singulated device can be bonded to another device (e.g., a wafer or a die) as described herein.

[0060] Various embodiments or features thereof disclosed herein can be combined to provide further embodiments. For example, any two or more of the elements disclosed herein can be bonded together to define various bonding structures. For example, any two or more of the elements 76, 150, 200 can be bonded together to define a bonding structure.

[0061] In the above-described embodiments, aluminum-based features, such as contact pads, can be prepared for efficient direct metal bonding, including direct hybrid bonding. In the illustrated embodiments, aluminum features can be defined and processed for direct bonding without additional high-temperature deposition or masking processes. For example, unlike the processes of FIGS. 3A-3D, no masking steps or insulating layer depositions are shown after the aluminum features are defined (e.g., at the stage of FIG. 5E). As a result, in all of the illustrated embodiments, metal contact features prepared for direct hybrid bonding can have continuous sidewalls characterized by definition through a single masking process, with a lower aluminum portion and either a fluorinated upper aluminum portion or an upper copper portion. In the embodiments of FIGS. 5A-5H, no deposition or masking processes are shown after the definition of the aluminum feature at the surface, and fluorination facilitates low-temperature direct metal bonding of the aluminum feature. 6A-6L and 7A-7F may use metal recess and redeposition to form a different upper portion of a contact feature compared to the lower portion (e.g., a different aluminum grain structure or copper on top and aluminum on the bottom), but these embodiments also do not rely on additional insulator deposition or mask steps, such that contact features having a lower aluminum portion and a different metal upper portion still have continuous sidewalls characterized by definition by a single masking process. Furthermore, the recess, metal redeposition, and CMP steps of FIGS. 6A-7F can all be performed at lower temperatures compared to oxide deposition.

[0062] In one aspect, a method for forming a bonding surface for direct hybrid bonding is disclosed. The method can include providing a device having a non-conductive field region and an aluminum feature, and exposing a surface of the aluminum feature to fluorine. The surface of the aluminum feature and the surface of the non-conductive field region define a direct bonding surface.

[0063] In one embodiment, exposing the surface of the aluminum feature to fluorine inhibits the formation of aluminum oxide.

[0064] In one embodiment, the method further includes defining an aluminum layer on a backing layer (BEOL), removing at least a terminal portion of the aluminum layer to define an aluminum feature, and providing a dielectric layer adjacent the aluminum feature to define a non-conductive field region.

[0065] In one embodiment, the aluminum feature includes a first portion and a second portion overlying the first portion and at least partially defining a surface of the aluminum feature. The second portion may have an average grain size smaller than that of the first portion. The method may further include removing metal from the initial aluminum feature to leave the first portion recessed about 0.1 μm to 0.3 μm relative to the surface of the non-conductive field region, and depositing the second portion in the recess on the first portion. The second portion may have a different microstructure than the first portion. The second portion may be deposited at a deposition temperature less than about 100°C. A majority of the grains in the second portion may have widths in the range of 10 nm to 500 nm. The aluminum feature may have a continuous sidewall along the sidewall of the first portion and the sidewall of the second portion.

[0066] In one embodiment, the thickness of the aluminum feature is in the range of about 0.5 μm to 7 μm. The thickness of the aluminum feature can be in the range of about 1 μm to 5 μm.

[0067] In one embodiment, the device includes an aluminum interconnect structure electrically connected to the aluminum feature.

[0068] In one embodiment, exposing the surface of the aluminum feature to fluorine includes forming aluminum fluoride, aluminum fluoride oxide, or boron fluoride aluminum oxide. Exposing the surface of the aluminum feature to fluorine can include forming at least a portion that is free of aluminum oxide.

[0069] In one embodiment, exposing the surface of the aluminum feature to fluorine comprises exposing the surface to a rinse comprising 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, tetramethylammonium tetrafluoroborate, tetramethylammonium tetrafluoroborate, or hydrogen fluoride (HF).

[0070] In one embodiment, the surface of the aluminum feature is exposed to fluorine without exposing the aluminum feature to a nitrogen plasma or an ammonium dip.

[0071] In one embodiment, a method of forming a bonding structure is disclosed that includes providing an element formed using the method, providing a second element having a second non-conductive field region and a conductive feature, directly bonding the non-conductive field region to the second non-conductive field region without an intervening adhesive, and directly bonding the aluminum feature to the conductive feature without an intervening adhesive.

[0072] In one aspect, a direct hybrid bonding structure is disclosed. The bonding structure can include a first element having a first non-conductive field region and a first aluminum feature. A surface of the first non-conductive field region and a surface of the first aluminum feature at least partially define a bonding surface of the first element. The bonding structure can include a second element having a second non-conductive field region and a second aluminum feature. The surface of the second non-conductive field region is directly bonded to the first non-conductive field region without an intervening adhesive along the bonding interface, and the surface of the second aluminum feature is directly bonded to the second aluminum feature without an intervening adhesive along the bonding interface. The surface of the first aluminum feature includes a higher fluorine content than a portion of the first aluminum feature further away from the surface.

[0073] In one embodiment, the bonding interface between the first aluminum feature and the second aluminum feature includes one or more fluorine peaks.

[0074] In one embodiment, the first aluminum feature includes a first gradient of fluorine concentration that decreases with distance from the bonding interface, and the second aluminum feature can include a second gradient of fluorine concentration that decreases with distance from the bonding interface.

[0075] In one embodiment, the first aluminum feature includes a first portion and a second portion overlying the first portion and at least partially defining a surface of the first aluminum feature. The second portion can include an average grain size smaller than the average grain size of the first portion. A majority of the grains in the second portion can have a width in the range of 10 nm to 500 nm. The first aluminum feature can further include a barrier layer between the first and second portions.

[0076] In one embodiment, the bonding interface between the first aluminum feature and the second aluminum feature comprises less than 1000 ppm oxygen.

[0077] In one embodiment, the bonding interface between the first and second aluminum features comprises less than 100 ppm nitrogen.

[0078] In one embodiment, the first aluminum feature has a thickness in the range of 0.5 μm to 5 μm.

[0079] In one aspect, a device is disclosed having a bonding surface configured for direct hybrid bonding to another device. The device can include a non-conductive field region and an aluminum feature. The surface of the non-conductive field region and the surface of the aluminum feature together define the bonding surface of the device. The surface of the aluminum feature includes aluminum and fluorine.

[0080] In one embodiment, the aluminum feature has a thickness in the range of approximately 0.5 μm to 5 μm. The thickness of the aluminum feature can be in the range of approximately 1 μm to 3 μm.

[0081] In one embodiment, the aluminum feature includes a first portion and a second portion on the first portion. The second portion can define a surface of the aluminum feature. The second portion can include an average grain size smaller than the average grain size of the first portion. A majority of the grains in the second portion can have a width in the range of 10 nm to 500 nm. The thickness of the second portion can be in the range of 0.1 μm to 0.3 μm.

[0082] In one embodiment, the surface of the aluminum feature is recessed from the surface of the non-conductive field region by about 2 nm to 20 nm.

[0083] In one aspect, a bonding structure is disclosed. The bonding structure can include a first element having a first non-conductive field region and a first conductive feature. The surface of the first non-conductive field region and the surface of the first conductive feature at least partially define a bonding surface of the first element. The first conductive feature includes a first portion and a second portion covering the first portion, at least partially defining a surface of the first conductive feature. The first portion includes aluminum. The first conductive feature has continuous sidewalls along the first and second portions. The second portion includes a different metal composition than the first portion, or includes fluorine on the surface of the first conductive feature. The bonding structure can include a second element having a second non-conductive field region and a second conductive feature. The second non-conductive field region has a surface directly bonded to the first non-conductive field region without an intervening adhesive along the bonding interface, and the second conductive feature has a surface directly bonded to the second conductive feature without an intervening adhesive along the bonding interface.

[0084] In one embodiment, the second portion has an average grain size smaller than the average grain size of the second portion. Most of the grains in the second portion may have a width in the range of 10 nm to 500 nm.

[0085] In one embodiment, the aluminum feature has a thickness in the range of 0.5 μm to 5 μm, and the second portion has a thickness in the range of 0.1 μm to 0.3 μm. The first portion and the second portion can have different metal structures. The second portion can include aluminum. The surface of the conductive feature can include aluminum fluoride. The second portion can include copper.

[0086] In one aspect, a device is disclosed having a bonding surface configured to be directly bonded to another device. The device can include a non-conductive field region and a conductive feature including a first portion and a second portion above the first portion, at least partially defining a surface of the conductive feature. The first portion includes aluminum. The conductive feature has continuous sidewalls along the first and second portions. The second portion includes a different metal composition than the first portion, or includes fluorine on the surface of the first conductive feature. The surface of the non-conductive field region and the surface of the aluminum feature together define the bonding surface of the device.

[0087] In one embodiment, the second portion has an average grain size smaller than the average grain size of the second portion. Most of the grains in the second portion may have a width in the range of 10 nm to 500 nm.

[0088] In one embodiment, the aluminum feature has a thickness in the range of about 0.5 μm to 5 μm, and the second portion has a thickness in the range of about 0.1 μm to 0.3 μm. The second portion can include aluminum. The surface of the conductive feature can include aluminum fluoride. The second portion can include copper.

[0089] A method for forming a device having a bonding surface configured to be directly bonded to another device is disclosed. The method can include forming a non-conductive field region and a first portion of a conductive feature. The first portion includes aluminum. The method can include forming a second portion of the conductive feature over the first portion. The second portion at least partially defines a surface of the conductive feature. The first and second portions are defined by a single masking process. The second portion includes a different metal composition than the first portion, or includes fluorine on the surface of the first conductive feature. The surface of the non-conductive field region and the surface of the conductive feature together define the bonding surface of the device.

[0090] In an embodiment, the second portion comprises fine grain aluminum.

[0091] In an embodiment, the second portion comprises copper.

[0092] In one embodiment, the second portion comprises aluminum and fluorine.

[0093] In embodiments, the method further includes exposing the surface of the conductive feature to fluorine. Exposing the surface of the conductive feature to fluorine can inhibit the formation of aluminum oxide. Exposing the surface of the aluminum feature to fluorine can be performed without exposing the aluminum feature to a nitrogen plasma or an ammonium dip.

[0094] Unless the context clearly requires otherwise, throughout this specification and claims, the terms "comprises," "comprising," "includes," "including," and the like are to be construed in an inclusive sense, i.e., meaning "including, but not limited to," as opposed to an exclusive or exhaustive sense. The term "coupled," as generally used herein, refers to two or more elements that may be either directly connected or connected via one or more intermediate elements. Similarly, the term "connected," as generally used herein, refers to two or more elements that may be either directly connected or connected via one or more intermediate elements. Furthermore, the terms "herein," "above," "below," and similar terms, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words using the singular or plural number in the above detailed description can also include the plural or singular number, respectively. The term "or" in reference to a list of two or more items covers all of the following interpretations of that term: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0095] Additionally, conditional language used herein, such as, among others, "can," "could," "might," "for example," "such as," and the like, is generally intended to convey that certain embodiments include certain features, elements, and / or conditions, and other embodiments do not, unless otherwise specified or understood within the context in which it is used. Thus, such conditional language is generally not intended to imply that a feature, element, and / or condition is in any way required in one or more embodiments.

[0096] While specific embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the present disclosure. For example, while the illustrated embodiments include preparations for direct hybrid bonding, those skilled in the art will understand that the techniques taught herein are useful for direct metallurgical bonding even in the absence of direct dielectric bonding. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms, and various omissions, substitutions, and modifications of the forms of the methods and systems described herein may be made without departing from the spirit of the present disclosure. For example, while blocks are shown in a given arrangement, similar functions may be performed by different components and / or circuit topologies in alternative embodiments, and some blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these blocks may be implemented in a variety of different ways. In the various embodiments described above, any appropriate combination of elements and acts may be combined to provide further embodiments. It is also contemplated that various combinations or subcombinations of specific features and aspects of the embodiments may be made and still fall within the scope of an embodiment. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the present disclosure. [Explanation of symbols]

[0097] 62 Back-End-of-Line (BEOL) Layer 66 Interconnect Structures 68 Barrier Layer 72 Conductive Features 74 Dielectric Layer 76 elements 80 Second element 82 Bonding Interface 92 Conductive Features 94 Non-conductive field areas

Claims

1. 1. A method of preparing a bonding surface for direct hybrid bonding, comprising: providing an element having a non-conductive field region and an aluminum feature; exposing a surface of the aluminum feature to fluorine, the surface of the aluminum feature and a surface of the non-conductive field region defining a direct bonding surface; A method comprising:

2. The method of claim 1 , wherein exposing the surface of the aluminum feature to fluorine inhibits the formation of aluminum oxide.

3. providing an aluminum layer on a back end of line (BEOL) layer; removing at least a portion of the aluminum layer to define the aluminum feature; providing a dielectric material adjacent the aluminum feature to define the non-conductive field region; The method of claim 1 further comprising:

4. 10. The method of claim 1, wherein the aluminum feature comprises a first portion and a second portion overlying the first portion and at least partially defining a surface of the aluminum feature, the second portion having an average grain size smaller than the average grain size of the first portion.

5. removing metal from the initial aluminum feature to leave the first portion recessed about 0.1 μm to 0.3 μm below the surface of the non-conductive field region; depositing the second portion in the recess over the first portion, the second portion having a different microstructure than the first portion; The method of claim 4 further comprising:

6. The method of claim 5 , wherein the second portion is deposited at a deposition temperature of less than about 100° C.

7. The method of claim 5, wherein a majority of the grains of the second portion have widths in the range of 10 nm to 500 nm.

8. The method of claim 4 , wherein the aluminum feature has a sidewall that is continuous along a sidewall of the first portion and a sidewall of the second portion.

9. The method of claim 1 , wherein the aluminum feature has a thickness in the range of about 0.5 μm to 7 μm.

10. The method of claim 9, wherein the aluminum feature has a thickness in the range of about 1 μm to 5 μm.

11. The method of claim 1 , wherein the device includes an aluminum interconnect structure electrically connected to the aluminum feature.

12. The method of claim 1 , wherein exposing the surface of the aluminum feature to fluorine comprises forming aluminum fluoride, aluminum fluoride oxide, or boron fluoride aluminum oxide.

13. The method of claim 12 , wherein exposing the surface of the aluminum feature to fluorine comprises forming at least a portion that is free of aluminum oxide.

14. 10. The method of claim 1, wherein exposing the surface of the aluminum feature to fluorine comprises exposing the surface to a rinse comprising 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, tetramethylammonium tetrafluoroborate, tetramethylammonium tetrafluoroborate, or hydrogen fluoride (HF).

15. 10. The method of claim 1, wherein exposing the surface of the aluminum feature to fluorine is performed without exposing the aluminum feature to a nitrogen plasma or an ammonium dip.

16. 1. A method of forming a bonding structure, comprising: providing a device formed using the method of claim 1; providing a second element having a second non-conductive field region and a conductive feature; directly bonding the non-conductive field region and the second non-conductive field region without an intervening adhesive; directly bonding the aluminum feature and the conductive feature without an intervening adhesive; A method comprising:

17. 1. A direct hybrid bonding structure comprising: a first element having a first non-conductive field region and a first aluminum feature, a surface of the first non-conductive field region and a surface of the first aluminum feature at least partially defining a bonding surface of the first element; a second element having a second non-conductive field region and a second aluminum feature, wherein a surface of the second non-conductive field region is directly bonded to the first non-conductive field region without an intervening adhesive along the bonding interface, and a surface of the second aluminum feature is directly bonded to the second aluminum feature without an intervening adhesive along the bonding interface; Equipped with A direct hybrid bonding structure, wherein a surface of the first aluminum feature has a higher fluorine content than a portion of the first aluminum feature remote from the surface.

18. 20. The bonding structure of claim 17, wherein the bonding interface between the first aluminum feature and the second aluminum feature includes one or more fluorine peaks.

19. 20. The bonding structure of claim 17, wherein the first aluminum feature has a first gradient of fluorine concentration that decreases with distance from the bonding interface.

20. 20. The bonding structure of claim 19, wherein the second aluminum feature has a second gradient of fluorine concentration that decreases with distance from the bonding interface.

21. 20. The bonding structure of claim 17, wherein the first aluminum feature comprises a first portion and a second portion overlying the first portion and at least partially defining a surface of the first aluminum feature, the second portion having an average grain size smaller than the average grain size of the first portion.

22. 22. The bonding structure of claim 21, wherein a majority of the grains of the second portion have widths in the range of 10 nm to 500 nm.

23. 22. The bonding structure of claim 21, wherein the first aluminum feature further comprises a barrier layer between the first portion and the second portion.

24. 20. The bonding structure of claim 17, wherein the bonding interface between the first aluminum feature and the second aluminum feature comprises less than 1000 ppm oxygen.

25. 20. The bonding structure of claim 17, wherein the bonding interface between the first aluminum feature and the second aluminum feature comprises less than 100 ppm nitrogen.

26. 18. The bonding structure of claim 17, wherein the first aluminum feature has a thickness in the range of 0.5 μm to 5 μm.

27. A device having a bonding surface configured for direct hybrid bonding to another device, a non-conductive field region; an aluminum feature, the surface of the non-conductive field region and the surface of the aluminum feature together defining a bonding surface of the element, the surface of the aluminum feature comprising aluminum and fluorine; An element comprising:

28. 28. The device of claim 27, wherein the aluminum feature has a thickness in the range of about 0.5 μm to 5 μm.

29. 29. The device of claim 28, wherein the aluminum feature has a thickness in the range of about 1 μm to 3 μm.

30. 28. The device of claim 27, wherein the aluminum feature comprises a first portion and a second portion on the first portion, the second portion defining a surface of the aluminum feature, the second portion having an average grain size smaller than the average grain size of the first portion, and a majority of the grains in the second portion having widths in a range of 10 nm to 500 nm.

31. 31. The device of claim 30, wherein the thickness of the second portion is in the range of 0.1 μm to 0.3 μm.

32. 28. The device of claim 27, wherein the surface of the aluminum feature is recessed from the surface of the non-conductive field region by about 2 nm to 20 nm.

33. 1. A bonding structure comprising: a first element having a first non-conductive field region and a first conductive feature, wherein a surface of the first non-conductive field region and a surface of the first conductive feature at least partially define a bonding surface of the first element, the first conductive feature including the first portion and a second portion overlying the first portion and at least partially defining a surface of the first conductive feature, the first portion including aluminum, the first conductive feature having continuous sidewalls along the first portion and the second portion, and the second portion including a metal composition different from the first portion or including fluorine at a surface of the first conductive feature; a second element having a second non-conductive field region and a second conductive feature, wherein a surface of the second non-conductive field region is bonded directly to the first non-conductive field region without an intervening adhesive along a bonding interface, and a surface of the second conductive feature is bonded directly to the second conductive feature without an intervening adhesive along the bonding interface; A bonding structure comprising:

34. 34. The bonding structure of claim 33, wherein the second portion has an average grain size smaller than the average grain size of the second portion, and a majority of the grains of the second portion have a width in the range of 10 nm to 500 nm.

35. 34. The bonding structure of claim 33, wherein the aluminum feature has a thickness in the range of 0.5 μm to 5 μm and the second portion has a thickness in the range of 0.1 μm to 0.3 μm.

36. 36. The bonding structure of claim 35, wherein the first portion and the second portion have different metallurgical structures.

37. 36. The bonding structure of claim 35, wherein the second portion comprises aluminum.

38. 38. The bonding structure of claim 37, wherein the surface of the conductive feature comprises aluminum fluoride.

39. 36. The bonding structure of claim 35, wherein the second portion comprises copper.

40. A device having a bonding surface configured for direct bonding to another device, a non-conductive field region; a conductive feature including a first portion and a second portion on the first portion, the second portion at least partially defining a surface of the conductive feature, the first portion comprising aluminum, the conductive feature having continuous sidewalls along the first portion and the second portion, the second portion comprising a different metal composition than the first portion or comprising fluorine at a surface of the first conductive feature, and a surface of the non-conductive field region and a surface of the aluminum feature together defining a bonding surface of the element; An element comprising:

41. 41. The device of claim 40, wherein the second portion has an average grain size smaller than the average grain size of the second portion, and a majority of the grains in the second portion have widths in the range of 10 nm to 500 nm.

42. 41. The device of claim 40, wherein the aluminum feature has a thickness in a range of approximately 0.5 μm to 5 μm and the second portion has a thickness in a range of approximately 0.1 μm to 0.3 μm.

43. 43. The element of claim 42, wherein the second portion comprises aluminum.

44. 44. The device of claim 43, wherein the surface of the conductive feature comprises aluminum fluoride.

45. 43. The device of claim 42, wherein the second portion comprises copper.

46. 1. A method of forming a device having a bonding surface configured for direct bonding to another device, comprising: forming a first portion of a non-conductive field region and a conductive feature, the first portion comprising aluminum; forming a second portion of the conductive feature on the first portion, the second portion at least partially defining a surface of the conductive feature; Including, the first portion and the second portion are defined by a single masking method; the second portion comprises a different metal composition than the first portion or comprises fluorine at the surface of the conductive feature; The method wherein a surface of the non-conductive field region and a surface of the conductive feature together define a bonding surface of the component.

47. 47. The method of claim 46, wherein the second portion comprises fine-grained aluminum.

48. 47. The method of claim 46, wherein the second portion comprises copper.

49. 47. The method of claim 46, wherein the second portion comprises aluminum and fluorine.

50. 47. The method of claim 46, further comprising exposing a surface of the conductive feature to fluorine.

51. 51. The method of claim 50, wherein exposing the surface of the conductive feature to fluorine inhibits the formation of aluminum oxide.

52. 51. The method of claim 50, wherein exposing the surface of the aluminum feature to fluorine is performed without exposing the aluminum feature to a nitrogen plasma or an ammonium dip.

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