Direct bond metal structures with aluminum features and methods of making same

Abstract

An element, a bonding structure including the element, and a method of forming the same are disclosed. The bonding structure may include a first element having a first non-conductive field region and a first conductive feature. 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 includes a first portion and a second portion over the first portion and 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 portion and the second portion. The second portion includes a different metal composition than the first portion or includes fluorine at a surface of the first conductive feature. The bonding structure may include a second element having a second non-conductive field region and a second conductive feature. A surface of the second non-conductive field region is directly bonded to the first non-conductive field region along a bonding interface without an intermediate adhesive; and the surface of the second conductive feature is directly bonded to the second conductive feature along the bonding interface without an intermediate adhesive.

Description

Technical Field

[0001] The present invention relates to bonded structures and methods of forming direct metal bonds including aluminum features. Background Art

[0002] Microelectronic components such as integrated device dies or chips can be mounted or stacked on other components to form a joint structure. Direct metal bonding can be performed at low temperatures and without the need for external pressure. For example, direct hybrid bonding involves directly bonding the non-conductive features (such as inorganic dielectrics) of different components together in the absence of an adhesive, while also directly bonding the conductive features (such as metal pads or lines) of the components together. For example, a microelectronic component can be mounted on a carrier such as an interposer, a reconstructed wafer or a component. For another example, a microelectronic component can be stacked on another microelectronic component, for example, a first integrated device die can be stacked on a second integrated device die. Each microelectronic component can have a conductive pad for mechanically and electrically bonding the components to each other. Currently, there is a continuing demand for improved methods for forming joint structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The detailed description will now be described with reference to the following figures, which are provided by way of example and not limitation.

[0004] Figure 1A is a schematic cross-sectional side view of two elements prior to direct hybrid joining.

[0005] Figure 1B yes Figure 1A Schematic cross-sectional side view of the two elements shown in after direct hybrid joining.

[0006] Figure 2 is a schematic cross-sectional side view of a joined structure including elements joined by solder balls.

[0007] Figure 3A-Figure 3E is a schematic cross-section illustrating a method of forming a copper pad over an aluminum interconnect formed in a back-end-of-line (BEOL) layer of a device.

[0008] Figures 4A-4E is a schematic cross-section illustrating a method of forming an aluminum pad over an aluminum interconnect formed in the BEOL layer of a component.

[0009] Figures 5A to 5F is a schematic cross-section illustrating a method of forming a bonding surface for an element including conductive features, according to an embodiment.

[0010] Figure 5G is included Figure 5FSchematic cross-sectional side view of a bonded structure of an element formed in and a second element (such as a wafer).

[0011] Figure 5H is included Figure 5F Schematic cross-sectional side view of a bonded structure of an element formed in FIG. 1 and a plurality of second elements, such as dies.

[0012] Figures 6A to 6E is a schematic cross-section illustrating a method of forming a bonding surface of an element including conductive features having fine grain aluminum, according to an embodiment.

[0013] Figure 6F is included Figure 6E Schematic cross-sectional side view of the joined structure of the elements formed in FIG. 1 prior to annealing.

[0014] Figure 6G is included Figure 6F Schematic cross-sectional side view of the joined structure of the elements formed in after annealing.

[0015] Figure 6H is included Figure 6F or Figure 6G Schematic cross-sectional side view of the joined structure of the elements formed in after cutting.

[0016] Figure 6I yes Figure 6D or Figure 6E Schematic cross-sectional side view of an element after forming a protective layer and cutting.

[0017] Figure 6J yes Figure 6I Schematic cross-sectional side view of a singulated element after removal of the protective layer.

[0018] Figure 6K Shows the results after cutting and during the termination process Figure 6D components.

[0019] Figure 6L is included Figure 6K Schematic cross-sectional side view of the joined structure of individualized elements.

[0020] 7A to 7E is a schematic cross-section illustrating a method of forming a bonding surface of an element including a conductive feature having fine grain copper, according to an embodiment.

[0021] Figure 7F is included Figure 7E Schematic cross-sectional side view of the joined structure of elements formed in. DETAILED DESCRIPTION

[0022] Various embodiments disclosed herein relate to direct-bonded structures, where two or more components may be directly bonded together without an intervening adhesive. Figure 1A and Figure 1B Schematically illustrates a process for forming a direct hybrid joint structure without an intermediate adhesive, according to some embodiments. Figure 1A and Figure 1B In the embodiment of the present invention, a bonding structure 100 includes a first element 102 and a second element 104, which can be directly bonded together at a bonding interface 118 without an intermediate adhesive. Two or more microelectronic elements 102 and 104 (such as semiconductor elements, including, for example, integrated device dies, wafers, passive devices, individual active devices (such as power switches), etc.) can be stacked or bonded together to form the bonding structure 100. The conductive features 106a of the first element 102 (such as contact pads, exposed ends of through-holes or through-substrate vias (TSVs), elongated traces, etc.) can be mechanically and electrically connected to corresponding conductive features 106b of the second element 104. Any suitable number of elements can be stacked in 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, and so on. Additionally or alternatively, one or more additional elements (not shown) can be stacked laterally adjacent to the first element 102. In some embodiments, the laterally adjacent additional stacked element(s) can be smaller than the second element. In some embodiments, the lateral dimension of the laterally adjacent additional stacked element(s) may be less than half that of the second element.

[0023] In some embodiments, elements 102 and 104 are directly bonded together without an adhesive. In various embodiments, a non-conductive field region comprising a non-conductive or dielectric material can be used as a first bonding layer 108a of the first element 102. In the absence of an adhesive, the first bonding layer 108a can be directly bonded to a corresponding non-conductive field region comprising a non-conductive or dielectric material, which serves as a second bonding layer 108b of the second element 104. Non-conductive bonding layers 108a and 108b can be provided on respective front sides 114a and 114b of device portions 110a and 110b (such as semiconductor (e.g., silicon) portions) of elements 102 and 104. Active devices and / or circuitry can be patterned and / or otherwise provided in or on device portions 110a and 110b. Active devices and / or circuit devices can be arranged at or near the front sides 114a and 114b of the device portions 110a and 110b, and / or at or near the relative back sides 116a and 116b of the device portions 110a and 110b. A bonding layer can be provided on the front side and / or back side of the element. The non-conductive material can be referred to as a non-conductive bonding area or bonding layer 108a of the first element 102. In some embodiments, the non-conductive bonding layer 108a of the first element 102 can be directly bonded to the corresponding non-conductive bonding layer 108b of the second element 104 using a dielectric to dielectric bonding technique. For example, non-conductive or dielectric-to-dielectric bonds can be formed without an adhesive using direct bonding techniques disclosed in at least U.S. Patent Nos. 9,564,414; 9,391,143; and 10,434,749, each of which is incorporated herein by reference in its entirety for all purposes. It should be understood that in various embodiments, bonding layers 108a and / or 108b may include a non-conductive material, such as a dielectric material (e.g., silicon oxide) or an undoped semiconductor material (e.g., undoped silicon). Suitable dielectric bonding surfaces or materials for direct bonding include, but are not limited to, inorganic dielectric materials (such as silicon oxide, silicon nitride, or silicon oxynitride), and may include carbon (such as silicon carbide, silicon oxynitride), low-K dielectric materials, SiCOH dielectric materials, silicon carbonitride, glass, ceramics, glass-ceramics, diamond-like carbon, or materials including a diamond surface. Such carbon-containing materials may still be considered inorganic materials despite including carbon. In some embodiments, the dielectric material does not include an adhesive or a polymeric material, such as an epoxy, resin, or molding material. 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 interlayer dielectric layer or passivation layer formed during back-end-of-line (BEOL) processing of an integrated circuit, and no separate bonding layer needs to be deposited after the underlying device is formed.

[0024] In some embodiments, device portions 110a and 110b can have significantly different coefficients of thermal expansion (CTE), thereby defining a heterostructure. The CTE difference between device portions 110a and 110b, and in particular the CTE difference between the bulk semiconductor (typically single crystal portions) of device portions 110a and 110b, can be greater than 5 ppm or greater than 10 ppm. For example, the CTE difference between device portions 110a and 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 and 110b can include optoelectronic single crystal materials (including perovskite materials), which can be used for optical piezoelectric or thermoelectric applications, while the other of device portions 110a and 110b can include more traditional substrate materials (e.g., Si, Ge, SiGe, III-V materials, etc.). For example, one of the device portions 110a and 110b may include lithium tantalate (LiTaO3) or lithium niobate (LiNbO3), while the other of the device portions 110a and 110b may include silicon (Si), quartz, fused silica glass, sapphire, or glass. In other embodiments, one of the device portions 110a and 110b may include a single III-V semiconductor material (such as gallium arsenide (GaAs) or gallium nitride (GaN)), while the other of the device portions 110a and 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 glass, sapphire, or glass.

[0025] In various embodiments, a direct hybrid bond can be formed without an intermediate adhesive. For example, the non-conductive bonding surfaces 112a and 112b can be polished to a high 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 For example, the roughness of the bonding surfaces 112a and 112b may be about to to or to within the range of . The bonding surfaces 112a and 112b can be cleaned and exposed to plasma and / or etchant to activate the surfaces 112a and 112b. In some embodiments, the surfaces 112a and 112b can be terminated with a substance after activation or during activation (e.g., during the plasma and / or etching process). Without being limited by theory, in some embodiments, the activation process can be performed to destroy the chemical bonds at the bonding surfaces 112a and 112b, and the termination process can provide additional chemicals at the bonding surfaces 112a and 112b, thereby improving the bonding energy during direct bonding. In some embodiments, activation and termination are provided in the same step, for example, using plasma to activate and terminate the surfaces 112a and 112b. In other embodiments, the bonding surfaces 112a and 112b can be terminated in separate processes to provide additional substances for direct bonding. In various embodiments, the termination substance can include nitrogen. For example, in some embodiments, (multiple) bonding surfaces 112a and 112b can be exposed to a nitrogen-containing plasma. In addition, in some embodiments (including embodiments described in more detail below), the bonding surfaces 112a and 112b can be exposed to fluorine. For example, there may be one or more fluorine peaks at or near the bonding interface 118 between the first element 102 and the second element 104. Therefore, in the direct bonding structure 100, the bonding interface 118 between the two non-conductive materials (e.g., bonding layers 108a and 108b) may include a very smooth interface that has a higher nitrogen content and / or there are fluorine peaks at the bonding interface 118. In the embodiments described below, fluorine can be found at or near the bonding interface 118 of the non-conductive region 108a / 108b and the conductive region 106a / 106b of the bonding structure 100. Additional examples of activation and / or termination processes can be found in 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 and for all purposes. After the activation process, the roughness of the polished bonding surfaces 112a and 112b may be slightly rough (e.g., about rms to to Or maybe even cruder).

[0026] In various embodiments, the conductive feature 106a of the first element 102 can also be directly bonded to the corresponding conductive feature 106b of the second element 104. For example, direct hybrid bonding techniques can be used to provide a direct conductor-to-conductor bond along a bonding interface 118 that includes a covalently directly bonded non-conductive to non-conductive (e.g., dielectric to dielectric) surface prepared as described above. In various embodiments, direct conductor-to-conductor (e.g., conductive feature 106a to conductive feature 106b) bonds and dielectric-to-dielectric hybrid bonds 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, the entire contents of which are incorporated herein by reference and for all purposes. In the embodiments described below, aluminum can be used in place of copper at the bonding surfaces, and a fluorine termination layer can be used in place of the nitrogen termination layer described in the incorporated disclosures. In the direct hybrid bonding embodiments described herein, conductive features are provided within the non-conductive bonding layer, and both the conductive features and the non-conductive features are prepared for direct bonding, such as by the planarization, activation, and / or termination processes described above. Thus, the bonding surface prepared for direct bonding includes both conductive and non-conductive features. Specific additional preparation options for direct bonding aluminum conductive features are described below.

[0027] For example, non-conductive (e.g., dielectric) bonding surfaces 112a, 112b (e.g., inorganic dielectric surfaces) can be prepared and directly bonded together without an intermediate adhesive, as explained above. Conductive contact features (e.g., conductive features 106a and 106b, which can be partially or fully surrounded by non-conductive dielectric field regions within bonding layers 108a and 108b) can also be directly bonded together without an intermediate adhesive. In various embodiments, conductive features 106a, 106b can include discrete pads or traces at least partially embedded in the 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, the respective conductive features 106a and 106b can be recessed below the dielectric field region or outer (e.g., upper) surface of the non-conductive bonding layer 108a and 108b (non-conductive bonding surfaces 112a and 112b), for example, by less than 30 nm, less than 20 nm, less than 15 nm, or less than 10 nm, for example, within a range of 2 nm to 20 nm, or within a range of 4 nm to 10 nm. In various embodiments, the recess size in the relative elements can be adjusted prior to direct bonding so that the total gap between the relative contact pads is less than 15 nm or less than 10 nm. In some embodiments, the non-conductive bonding layers 108a and 108b can be directly bonded together at room temperature without an adhesive, and the bonded structure 100 can then be annealed. After annealing, the conductive features 106a and 106b can expand and contact each other to form a metal-to-metal direct bond. Advantageously, direct bonding interconnects available from Adeia, Inc. of San Jose, California are used. The technology can enable a high density of conductive features 106a and 106b to be connected across a direct bonding interface 118 (e.g., for a small or fine pitch of a regular array). In various embodiments, the conductive features 106a and 106b and / or the traces can include copper or a copper alloy, but other metals may also be suitable. For example, the conductive features disclosed herein, such as conductive features 106a and 106b, can include 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 portion that is primarily aluminum.

[0028] Thus, in a direct bonding process, the first element 102 can be directly bonded to the second element 104 without an intermediate adhesive. In some arrangements, the first element 102 can include a singulated element, such as a singulated integrated device die. In other arrangements, the first element 102 can include a carrier or substrate (e.g., a wafer) that includes multiple (e.g., dozens, hundreds, or more) device regions that, after being singulated, form multiple integrated device dies. Similarly, the second element 104 can include a singulated element, such as a singulated integrated device die. In other arrangements, the second element 104 can include a carrier or substrate (e.g., a wafer). Thus, the embodiments disclosed herein can be applied to wafer-to-wafer (W2W), die-to-die (D2D), or die-to-wafer (D2W) bonding processes. In a wafer-to-wafer (W2W) process, two or more wafers can be directly bonded together (e.g., direct hybrid bonding) and then singulated using a suitable singulation process. After singulation, the sides of the singulated structure (eg, sides of two joined elements) can be substantially flush and can include markings indicating a common singulation process for the joined structure (eg, saw marks if a saw singulation process was used).

[0029] As described herein, the first element 102 and the second element 104 are directly bonded together without an adhesive, which is different from a deposition process and can produce an interface that is structurally different from a deposition process. In one application, the width of the first element 102 in the bonded structure is similar to the width of the second element 104. In some other embodiments, the width of the first element 102 in the bonded structure 100 is different from the width of the second element 104. Similarly, the width or area of ​​the larger element in the bonded structure can be at least 10% larger than the width or area of ​​the smaller element. Therefore, the first element 102 and the second element 104 can include non-deposition elements. In addition, unlike a deposited layer, the direct bonded structure 100 can include a defective area along the bonding interface 118, in which there are nanoscale voids (nano voids). Nano voids may be formed due to the activation (e.g., exposure to plasma) of the bonding surfaces 112a and 112b. As explained above, the bonding interface 118 can include the concentration of the material from the activation and / or final chemical treatment process. For example, in an embodiment in which nitrogen plasma is utilized for activation, a nitrogen peak can be formed at the bonding interface 118. The nitrogen peak can be detected using secondary ion mass spectrometry (SIMS) technology. For example, in various embodiments, nitrogen termination treatment (e.g., exposing the bonding surface to a nitrogen-containing plasma) can replace the OH groups of the hydrolysis (OH termination) surface with NH2 molecules, thereby producing a nitrogen-terminated surface. In an embodiment in which oxygen plasma is utilized for activation, an oxygen peak can be formed at the bonding interface 118. In the illustrative embodiments described below, termination is performed using fluorine treatment, and a fluorine peak can be formed at the bonding interface 118. In some embodiments, the bonding interface 118 can include silicon oxynitride, silicon oxycarbonitride, or silicon carbonitride. As explained herein, direct bonding can include covalent bonds, which are stronger than van der Waals bonds. The bonding layers 108a and 108b can also include polished surfaces that are planarized to a high degree of smoothness.

[0030] In various embodiments, the metal-to-metal bond between conductive features 106a and 106b can be combined such that metal grains grow relative to each other at the bonding interface 118. In some examples of direct hybrid bonding, the metal is or includes copper, which can have grains oriented along 111 crystal planes to improve copper diffusion at the bonding interface 118. In some examples of direct hybrid bonding, conductive features 106a and 106b can include a nano-twinned copper grain structure, which can facilitate merging of the conductive features during annealing. In the illustrative embodiments described below, one or both of conductive features 106a and 106b include fluorine-treated aluminum. The bonding interface 118 can extend substantially completely 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 layer 108a and 108b at or near the bonded conductive features 106a and 106b. In some embodiments, a barrier layer can be provided below and / or laterally around the conductive features 106a and 106b (e.g., which can include copper). However, in other embodiments, there may be no barrier layer beneath the conductive features 106a and 106b, for example, as described in US Pat. No. 11,195,748, which is incorporated herein by reference in its entirety for all purposes.

[0031] Advantageously, the direct hybrid bonding technique described herein can achieve very fine pitches between adjacent conductive features 106a and 106b, and / or smaller pad sizes. For example, in various embodiments, the pitch p between adjacent conductive features 106a (or 106b) (i.e., as shown in FIG. Figure 1A As shown in FIG, edge-to-edge or center-to-center distances) 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. In addition, the major lateral dimension (e.g., pad diameter) can also be smaller, such as in the range of 0.25 microns to 30 microns, 0.25 microns to 5 microns, or 0.5 microns to 5 microns.

[0032] As described above, the non-conductive bonding layers 108a, 108b can be directly bonded together without an adhesive, and the bonded structure 100 can then be annealed. After annealing, the conductive features 106a, 106b can expand and contact each other to form a metal-to-metal direct bond. In some embodiments, the materials of the conductive features 106a, 106b can diffuse into each other during the annealing process.

[0033] Figure 21 is a schematic cross-sectional side view of a bonded structure 1. Bonded structure 1 includes a first component 10 and a second component 12 bonded by solder balls 14. First component 10 includes a first back-end-of-line (BEOL) layer 16 and an aluminum pad 18. A polymer layer 20 may be provided on a surface of BEOL layer 16 to support solder balls 14. Second component 12 includes a second BEOL layer 26 and an aluminum pad 28. Solder balls 14 are provided with first component 10 and bonded to aluminum pads 28 of second component 12.

[0034] For relatively fine pitch interconnects (such as interconnect pitches less than 20 microns or less than 2 microns), the use of solder balls 14 may not be feasible. In addition, because the mechanical connection between the components 10 and 12 is limited to the solder joints, the mechanical connection may be weak and easily separated due to physical stress or impact because the solder balls typically form brittle intermetallic compounds (IMCs). After bonding, the gap between the top surfaces of the BEOL layers 16, 26 needs to be cleaned and filled with a dielectric underfill material (not shown) to encapsulate the solder balls 14 and the corresponding contacts. The resistivity of the alloy formed with solder is typically at least three times that of an aluminum pad or copper pillar, which may result in electrical losses. In addition, the dielectric underfill that mechanically connects the top surfaces of the BEOL layers 16, 26 hinders heat transfer between the first component 10 and the second component 12. Therefore, it may be beneficial to provide a bonding surface that can directly hybrid bond the components 10, 12 together.

[0035] Figure 3A-Figure 3E A method of forming a copper pad 32 over an aluminum pad or interconnect 34 formed in the BEOL layer 16 of a component 30 is shown. Figure 3A At this location, a BEOL layer 16 may be provided. The BEOL layer 16 may include a planar dielectric surface and aluminum pads or interconnects 34 at least partially embedded in the dielectric. Figure 3B As shown in , the method includes forming a planarized dielectric layer 36 over the BEOL layer 16. Figure 3C At , a cavity 38 is formed in dielectric layer 36. Aluminum pad or interconnect 34 may be exposed through cavity 38.

[0036] exist Figure 3D At , a barrier layer 40 and / or seed layer may be formed over the surface of the dielectric layer 36 and the cavity 38. Copper 42 is provided at least in the cavity above the barrier layer 40. Figure 3D At , copper 42 is overfilled, and excess copper 42 exists above the surface of dielectric layer 36. If desired, component 30 may be annealed, for example, at a temperature below 200° C., to at least partially stabilize the microstructure of copper 42. Figure 3EIn the process, excess copper 42 may be removed to form copper pad 32. For example, excess copper 42 may be removed by polishing, such as chemical mechanical planarization (CMP). The polishing process may also remove portions of barrier layer 40 above the surface of dielectric layer 36 and form a direct bonding surface for component 30 after activation and / or termination, as described above.

[0037] like Figures 4A-4E As shown in Figure 3A-Figure 3E The aluminum pad 44 is formed in a similar manner to the method of forming the copper pad 32 shown in FIG. Figure 3D The copper 42 provided in Figure 4D Aluminum 46 may be provided in the , and excess aluminum 46 may be removed to form aluminum pads 44. Alternatively, aluminum may be provided in the Figure 4A A layer of aluminum is deposited on the structure and patterned using an appropriate masking process, and then the undesired portions of the aluminum are etched away (e.g., by reactive ion etching). For an alternative process, a dielectric bonding layer 36 is deposited on top of the patterned aluminum layer and polished to the aluminum pad 4 to form a smooth dielectric bonding surface.

[0038] Figures 3A-4E A disadvantage of the process is that a separate deposition of the bonding layer 36 is required, which typically requires exposing the component to high temperature processing and also requires an expensive masking process to define the cavity 38. Figures 4A-4EDuring the process, the aluminum pad 44 is susceptible to oxidation and surface oxide may form on the aluminum pad 44. In addition, when the bonding layer 36 is deposited on the pre-patterned aluminum pad 44, the aluminum pad 44 is exposed to a higher temperature, typically above 250°C and typically 300°C to 350°C. The higher temperature dielectric process triggers the formation of large grains in the aluminum pad 44. The subsequent dielectric planarization step forms a smooth dielectric bonding surface, which includes the surface of the aluminum pad 44 with large grains. Metal pads with larger grains (0.5 to 3 microns or larger) have fewer grain boundaries than metal pads with finer grains (e.g., less than 0.3 microns). In fact, pads with finer grains tend to be bonded at lower temperatures than pads with larger grains. Aluminum tends to form a thin aluminum oxide on the surface during the planarization process and when exposed to ambient air, which may cause problems during the direct bonding operation step. The surface oxide on the aluminum pad 44 hinders the direct bonding of the aluminum pad 44 or 34 to the corresponding aluminum pad of the other component. Therefore, some treatment (such as argon sputtering) can be used to remove the surface oxide before bonding. However, this process can be time-consuming and costly. This process may also redeposit aluminum particles on some parts 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. Exposure of the aluminum pads 44, 34 to nitrogen plasma causes aluminum nitride to form on the surface of the aluminum pad 44. Although aluminum nitride on the surface is easier to bond directly than aluminum oxide, such a process may require a high temperature (e.g., 300°C to 400°C) bonding process to allow the surface aluminum nitride to decompose or allow aluminum to diffuse through the surface nitride and form a metallurgical joint between the pads 34, 44 of the opposing components. The high temperature bonding process increases the thermal budget for forming the bonding structure. The various embodiments disclosed herein can achieve a simpler, more cost-effective method and structure for forming a bonding structure.

[0039] Figures 5A to 5F A method of forming the engagement surface 76a of the element 76 according to an embodiment is shown. Figure 5Ais a schematic cross-sectional side view illustrating an aluminum layer 60 over a back-end-of-line (BEOL) layer 62, which is formed over a device (not shown) of a component, such as within or over a semiconductor material. A barrier layer 68 (such as TiN, TiN / Ti, TiW, or TiW / Ti) and / or a seed layer 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 include an aluminum interconnect. The barrier layer 68 may be deposited over a surface of the BEOL layer 62, and the aluminum layer 60 may be deposited over 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 a temperature of approximately 150° C. or less. The aluminum layer 60 may be relatively thin. For example, the thickness of aluminum layer 60 may be in a range of 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 circuit requirements.

[0040] exist Figure 5B In the embodiment of the present invention, a selected or desired mask layer, such as a resist layer 70, can be provided on the aluminum layer 60 by a photolithography method. The resist layer 70 can be patterned on the aluminum layer 60 so that some portions of the resist layer 70 are positioned on the interconnect structure 66.

[0041] exist Figure 5C In the embodiment, portions of the aluminum layer 60 can be selectively removed and conductive features 72 can be formed by, for example, a reactive ion etching (RIE) process or by wet etching. For example, portions of the aluminum layer 60 not covered or uncovered by the resist layer 70 can be etched using any suitable etching process (such as plasma etching, including reactive ion etching) to define the conductive features 72. The conductive features 72 are examples of conductive features. The conductive features 72 can be conductive metal pads, vias, or lines that include more than 50% aluminum (by volume). For example, the conductive features 72 can include more than 80%, more than 90%, or more than 95% aluminum (by volume). In the illustrated embodiment, the conductive features 72 are patterned from the aluminum layer 60 and can therefore be considered aluminum features. However, in other embodiments, the conductive features 72 can include one or more other metal layers while still constituting a single feature defined by a single mask and still including more than 50% aluminum (by volume). Thus, each conductive feature 72 can have a continuous sidewall defined by a single mask process.

[0042] exist Figure 5D, a dielectric layer 74 can be provided over the conductive features 72 and over portions of the BEOL layer 62. In some embodiments, the dielectric layer 74 can comprise an oxide layer. For example, the oxide layer can be deposited by known methods at about 350° C. or other desired temperature. In some embodiments, multiple dielectric coating steps and (multiple) other intermediate processes can be applied to form the dielectric layer 74. The dielectric coating can comprise a conformal coating (as shown) or a non-conformal coating. In some embodiments, the dielectric layer 74 can comprise a combination of conformal and non-conformal dielectric coatings. The dielectric layer 74 can 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.

[0043] like Figure 5E As shown in FIG, portions of dielectric layer 74 may be removed (e.g., polished) to expose the surface of conductive feature 72. The surface of conductive feature 72 and the surface of remaining dielectric layer 74 may define a bonding surface 76a of element 76. Bonding surface 76a of element 76 may be polished using, for example, chemical mechanical polishing (CMP) as disclosed herein. CMP chemistry or subsequent selective etching may recess the surface of conductive feature 72 below dielectric layer 74. The roughness of polished bonding surface 76a may be less than For example, the roughness of the engagement surface 76a may be about to to or to Furthermore, conductive feature 72 and the surrounding dielectric layer 74 can be formed during back-end-of-line processing, allowing device 76 to be supplied by an integrated circuit manufacturer before or after singulation. The thickness of conductive feature 72 can be in the range of approximately 0.5 μm to 7 μm or 1 μm to 5 μm.

[0044] exist Figure 5F In the embodiment, the engaging surface 76a of the element 76 may be terminated. Although not shown, it is understood that in Figure 5E Polishing and Figure 5F A protective layer may be provided and removed between terminations, similar to the following regarding Figure 6IAs described. The bonding surface 76a of the element 76 can be terminated with, for example, fluorine to define a very thin layer of continuous or discontinuous surface aluminum fluoride (Al-F) compound, aluminum fluoride oxide (Al-FO) compound, or aluminum fluoride boron oxide (Al-FBO) compound. In some embodiments, the bonding surface 76a can be rinsed with a rinse solution that provides 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 accomplished using a plasma process. For example, the surface of the conductive feature can be exposed to a mild fluoride plasma or placed in a chamber that uses a fluorine-containing gas (such as carbon tetrafluoride (CF4)). Residual fluorine on the walls of the chamber may be adsorbed on the bonding surface 76a. Fluoride may reduce some of the native aluminum oxide.In some embodiments, the bonding surface 76a of the component 76 is not exposed to a nitrogen plasma and / or an ammonia immersion solution both before and after the fluorine treatment.

[0045] After the bonding surface 76a of element 76 has been terminated, there may be a fluorine concentration gradient from the bonding surface 76a to the element 76. Therefore, the element 76 may have a higher fluorine content at the bonding surface 76a than the portion of the element 76 away 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 fluorine concentration gradient so that the surface of the conductive feature 72 has a higher fluorine content than the conductive feature deeper. 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 the portion of the conductive feature 72 away from the surface. In some embodiments, fluorine may be present at about 4nm to 6nm (e.g., 5nm) below the surface. In some embodiments, the oxygen content present on the surface of the conductive feature 72 may be very low or undetectable. For example, the oxygen content present on the surface of the conductive feature 72 may be lower than 20ppm. In some embodiments, the bonding surface 76a may include a portion that does not contain aluminum oxide. In some embodiments, very low carbon and / or nitrogen content or no carbon and / or nitrogen content may be present in the conductive feature 72 and / or dielectric layer 74. For example, the carbon or nitrogen content present on the surface of conductive feature 72 or dielectric layer 74 may be less than 50 ppm, 40 ppm, or 20 ppm.

[0046] Without such termination, aluminum oxide (Al2O3) may form on the surface of the conductive features 72 even when exposed to air (including clean room air) at room temperature. Terminating the bonding surface 76a with fluoride can inhibit or prevent the formation of aluminum oxide (Al2O3) on the surface of the conductive features 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).

[0047]

[0048]

[0049] Table 1

[0050] Although aluminum has the lowest melting point among the four materials in Table 1 and a relatively high thermal expansion rate, aluminum readily forms aluminum oxide on its surface under any air exposure. Aluminum oxide has a significantly higher melting point than the other three materials (approximately 4.5 times the melting point of aluminum) and has a significantly lower thermal expansion rate. Aluminum nitride has a lower melting point and a slightly higher thermal expansion rate than aluminum oxide. Nevertheless, the melting point of aluminum nitride is still significantly higher than that of aluminum, and the thermal expansion rate is also significantly lower than that of aluminum. Aluminum fluoride has a relatively low melting point and a significantly higher thermal expansion rate. 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 reducing the annealing temperature for forming the metal bond during direct hybrid bonding. In some cases, the fluorine-terminated surface can reduce or prevent the formation of oxides on the surface of the conductive feature 72 for up to, for example, three days, four days, a week, or ten days.

[0051] Component 76 may be a wafer or die, and component 76 may be bonded to a second component (eg, a wafer or die). Figure 5G is a schematic cross-sectional side view of a bonded structure 2 comprising an element 76 in wafer form and a second element 80 (another wafer) bonded to element 76 along a bonding interface 82. In some embodiments, second element 80 may be bonded to another substrate of interest. Figure 5H is a schematic cross-sectional side view of a bonded structure 2′ including a component 76 in wafer form and a plurality of second components 84 (die) bonded to the component 76 along bonding interfaces 86. The second components 80 or 84 may include conductive features 92 and non-conductive field regions 94 and may have a similar structure to the first component 76 (including the aluminum-based conductive features 92).

[0052] The bonding surface 76a of the element 76 can be directly bonded to the bonding surface(s) 80a, 84a of the second element 80, 84 in any suitable manner disclosed herein. The bonding surface 76a of the element 76 can be directly bonded to the bonding surface(s) 80a, 84a of the second element(s) 80, 84 such that the non-conductive field region(s) 94 of the second element(s) 80, 84 are directly bonded to the element 76 (at Figure 5H and Figure 5G In some embodiments, the second element 84 may be bonded to another substrate of interest.

[0053] The bonded elements 76 and 80, or 76 and 84, can then be heated (e.g., annealed) to expand the conductive features 72 and 92 across the gap left by the recessed aluminum, 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 less than 350° C., for example, less than or equal to about 300° C., or less than or equal to about 250° C., for a time less than or equal to about 4 hours, such as between about 2.5 hours and 4 hours. For example, the annealing temperature can be in the range of 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 enhance the bond between the conductive features 72 and the conductive features 92.

[0054] In some embodiments, the fluorine content of the conductive features 72 and the conductive features 92 is less than 1000ppm, less than 500ppm or less than 100ppm. Similarly, in some embodiments, the fluorine content of the conductive features 72 and the conductive features 92 is less than 1000ppm, less than 500ppm or less than 100ppm. Similarly, in some embodiments, the fluorine content of the conductive features 72 and the conductive features 92 is less than 1000ppm, less than 500ppm or less than 100ppm. Similarly, in some embodiments, the fluorine content of the conductive features 72 and the conductive features 92 is less than 1000ppm, less than 500ppm or less than 100ppm. For example, after bonding, the nitrogen and / or carbon content between conductive features 72 and conductive features 92 may be less than 100 ppm or less than 80 ppm.

[0055] Figures 6A to 6E A method of forming the bonding surface 150a of the element 150 according to an embodiment is shown. Figure 6A is a schematic cross-sectional side view showing an aluminum layer 73 including large aluminum metal particles or fine aluminum particles and a dielectric layer 74 formed over back-end-of-line (BEOL) layer 62 including interconnect structure 66. Aluminum layer 73 and / or dielectric layer 74 may be planar. Figure 6A The structure can be Figure 5E As mentioned above, the aluminum layer 73 and the dielectric layer 74 may also be part of the BEOL or redistribution layer (RDL) structure of the integrated device.

[0056] exist Figure 6B In the embodiment of the present invention, at least a portion of the aluminum layer 73 can be selectively removed, such as by RIE, wet etching, or other known methods, to form a groove 152 above the aluminum layer 73. The depth of the groove can be in the range of 0.1 μm to 0.5 μm, 0.1 μm to 0.25 μm, or 0.15 μm to 0.2 μm. For example, the portion of the aluminum layer 73 can be removed by dry etching (e.g., vapor or plasma etching) or wet etching.

[0057] exist Figure 6CIn the embodiment of the present invention, a barrier layer 153 and a fine-grained aluminum layer 154 can be provided in the grooves 152 and on the surface 74a of the dielectric layer 74. For example, the aluminum having a fine-grained microstructure can be formed above the grooves 152 by sputtering and cooling the BEOL layer 62, or by cooling the substrate (not shown) to which the BEOL layer 62 is bonded to below 100° C., preferably below 50° C. or lower, such as 20° C. during sputtering. In some embodiments, the barrier layer 153 can completely separate 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 directly coated on the larger-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 grains in the fine-grained aluminum layer 154 may be in the range of about 10 nm to 500 nm, about 10 nm to 300 nm, about 15 nm to 500 nm, about 15 nm to 300 nm, about 15 nm to 100 nm, about 15 nm to 50 nm, about 50 nm to 500 nm, about 50 nm to 300 nm, or about 100 nm to 300 nm. In some embodiments, a majority of the grains in the fine-grained aluminum layer 154 may have a width in the range of about 10 nm to 500 nm, about 10 nm to 300 nm, about 15 nm to 500 nm, about 15 nm to 300 nm, about 15 nm to 100 nm, about 15 nm to 50 nm, about 50 nm to 500 nm, about 50 nm to 300 nm, or about 100 nm to 300 nm.

[0058] In some embodiments, the fine-grained aluminum layer 154 may be provided by low-temperature deposition. For example, the fine-grained aluminum layer 154 may be deposited at a temperature below about 100° C., below about 65° C., or below about 20° C. For example, the deposition temperature for depositing the fine-grained aluminum layer 154 may be in the range of about 10° C. to 100° C., about 10° C. to 65° C., about 10° C. to 50° C., or about 10° C. to 20° C. The thickness of the fine-grained aluminum layer 154 may be equal to or greater than the depth of the recess 152.

[0059] exist Figure 6DIn the embodiment of the present invention, portions of the fine-grained aluminum layer 154 and the barrier layer 153 above the surface 74a of the dielectric layer 74 can be removed. For example, portions of the fine-grained aluminum layer 154 and the barrier layer 153 can be removed by polishing, such as chemical mechanical polishing (CMP), to a degree sufficient to define a bonding surface 150a of the component 150, which includes the surface 74a of the dielectric layer 74 and the surface 154a of the fine-grained aluminum layer 154. The CMP chemistry or a subsequent etching process can recess the aluminum surface 154a below the dielectric surface 74a. The CMP process can occur at a temperature lower than that at which the fine-grained aluminum layer 154 was deposited. 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), such as more than 80% aluminum (by volume), and can have continuous sidewall characteristics defined by a single mask process. In some embodiments, when the primary component is aluminum (as in the illustrated embodiment), conductive feature 155 may be referred to as an aluminum feature. Conductive feature 155 may have a first portion (e.g., aluminum layer 73) and a second portion (e.g., fine-grained aluminum layer 154). The second portion may have a different microstructure than the first portion. The thickness of conductive feature 155 may be in the range of approximately 0.5 μm to 7 μm or 1 μm to 5 μm.

[0060] exist Figure 6E In the embodiment, the bonding surface 150a of the element 150 can be similar to the above-mentioned Figure 5F The bonding surface 150a of element 150 can be terminated in the same or similar manner as disclosed. The bonding surface 150a of element 150 can be terminated with, for example, fluorine, to limit surface fluoride aluminum compound, fluoride aluminum oxide compound or fluoride aluminum boron oxide compound. In certain embodiments, the bonding surface 150a can be rinsed by a rinsing solution. For example, the rinsing solution can include 1-ethyl-3-methylimidazole tetrafluoroborate, 1-butyl-3-methylimidazole tetrafluoroborate, tetramethylammonium tetrafluoroborate, tetramethylammonium tetrafluoroborate, hydrogen fluoride (HF), buffered hydrogen fluoride (BHF) or any suitable combination thereof. The bonding surface 150a can be spin-dried without rinsing with deionized (DI) water. In certain embodiments, the treated surface can be rinsed with DI water or other suitable solvents and dried by known methods (for example, by spin-drying). In certain embodiments, fluorine termination can be completed by a plasma process, as described above.

[0061] The bonding surface 150a of the element 150 can be formed without a high temperature process. Therefore, the relatively small grain size of the fine-grained aluminum layer 154 can be maintained, which can facilitate subsequent metal bonding.

[0062] Figure 6FFIG3 is a schematic cross-sectional side view of a bonded structure 3, comprising element 150 and a second element 160 bonded to element 150. In some embodiments, second element 160 can have the same or substantially similar structure as element 150. Second element 160 can include a BEOL layer 162 including interconnect features, a dielectric layer 164, and conductive features 165, including an aluminum layer 166 and a fine-grained aluminum layer 168, which together can function as bonding pads. Bonding surface 150a of element 150 can be directly bonded to bonding surface 160a of second element 160 along bonding interface 170, such that dielectric layer 74 is directly bonded to dielectric layer 164. This initial direct bonding of dielectric materials can form strong covalent bonds between dielectric layers 74 and 164 of opposing elements 150 and 160 at room temperature. In some embodiments, second element 160 can be bonded to another substrate of interest.

[0063] exist Figure 6G In Figure 6F In some embodiments, the bonding structure 3 formed in the embodiment of the present invention may be heated (e.g., annealed) at a temperature below about 350°C, below about 300°C, or below about 250°C. Figure 6F The structure formed in the step of heating is annealed for a time period of less than or equal to about 2 hours. For example, the annealing temperature may be in a range of 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 may cause the fine-grained aluminum layers 154 and 168 to expand, spanning the gap left by the recessed aluminum surface and forming a metallic bond between the fine-grained aluminum layers 154 and 168. Annealing may also enhance the bond between the dielectric layers 74 and 164. Due to the heating process, the grains of the fine-grained aluminum layer 154 may grow. In some embodiments, the grains of the fine-grained aluminum layer 154 may still be smaller than the grains of the aluminum layer 73. For example, the average grain size (e.g., width) of the grains in the fine-grained aluminum layer 154 after annealing may be less than 1000 nm, 750 nm, or 500 nm. For example, the maximum width of the largest grains in the fine-grained aluminum layer 154 after annealing may be in a range of about 20 nm to 500 nm. In some embodiments, a majority of the grains in the fine-grained aluminum layer 154 after annealing may have a width in the range of approximately 200 nm to 500 nm. In some embodiments, the fine-grained aluminum layer 154 may be deposited on only one of the bonded substrates. In some embodiments, the fine-grained aluminum layer 154 may include aluminum nanoparticles formed by physical vapor deposition (PVD) or atomic layer deposition (ALD), or other known methods.

[0064] Similar to element 76, element 150 can be a tube die or wafer, and second element 160 can be a tube die or wafer. Therefore, the process of bonding element 150 and second element 160 can include wafer to wafer (W2W), tube die to tube die (D2D) or tube die to wafer (D2W) bonding process. In some embodiments, bonding structure 3 can include additional wafers, substrates or tube die stacked and bonded on second element 160. Stacked elements can be electrically connected via, for example, various TSVs.

[0065] Figure 6H is a cross-sectional side view of the individualized joining structures 3a, 3b, 3c. In some embodiments, the individualized joining structures 3a, 3b, 3c can be formed by Figure 6F Element 150 and second element 160 are bonded together by W2W bonding, followed by a singulation process. For example, the singulation process may 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 a plurality of singulated structures, such as singulated bonded structures 3a, 3b, and 3c. Each of the singulated bonded structures 3a, 3b, and 3c may include a die from element 150 and a die from second element 160.

[0066] Figure 6I is a cross-sectional side view of individualized elements 151a, 151b, 151c after being at least partially prepared for direct hybrid joining but before actual joining. Figure 6D The element 150 shown in FIG. 1 may include a wafer from which individualized elements 151a, 151b, 151c may be formed. For example, the element 150 in wafer form may be positioned on a dicing film or tape 172. A protective layer 174 may be formed over the element 150. The element 150 may be individualized into individualized elements 151a, 151b, 151c. After individualization, the individualized elements 151a, 151b, 151c may be formed as shown in FIG. Figure 6J The protective layer 174 is removed as shown in FIG.

[0067] After removing the protective layer 174, as shown in FIG. Figure 6K As shown in Figure 6F After terminating the surfaces of the singulated elements 151a, 151b, 151c, the singulated elements 151a, 151b, 151c may be bonded to the second element 160, thereby forming a D2W bonded structure 4, as shown. Figure 6L In the D2W bonding structure 4, the individualized elements 151a, 151b, 151c can be bonded to the second element 160, as shown in FIG. Figure 6G As shown in .

[0068] 7A to 7E A method of forming the joining surface 200 a of the element 200 according to an embodiment is shown. Figure 7A is a schematic cross-sectional side view illustrating aluminum layer 202 and dielectric layer 74 formed over back-end-of-line (BEOL) or RDL layer 62 including interconnect structure 66 . Figure 7A The structure can be Figure 5E and Figure 6A The structures are the same or roughly similar.

[0069] exist Figure 7B In the embodiment of the present invention, at least a portion of the aluminum layer 202 can be removed to form a groove 152 above each aluminum layer 202. The depth of the groove can be in the range of 0.1 μm to 0.5 μm, 0.1 μm to 0.35 μm, or 0.15 μm to 0.25 μm. The portion of the aluminum layer 202 can be removed by, for example, dry etching (e.g., vapor or plasma etching) or wet etching.

[0070] exist Figure 7C In the embodiment of the present invention, a barrier layer 153 and a different type of conductive material (such as copper layer 204 as shown) can be provided in the groove 152 and on the surface 74a of the dielectric layer 74. The copper layer 204 is an example of a different type of conductive material, and another example can include a silver layer. The 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 width of the grains in the copper layer 204 can be in the range of about 10 nm to 500 nm, about 10 nm to 300 nm, about 15 nm to 500 nm, about 15 nm to 300 nm, about 15 nm to 100 nm, about 15 nm to 50 nm, about 50 nm to 500 nm, about 50 nm to 300 nm, or about 100 nm to 300 nm. In some embodiments, the majority of the grains in the fine grain copper layer 204 may have a width in the range of about 10 nm to 500 nm, about 10 nm to 300 nm, about 15 nm to 500 nm, about 15 nm to 300 nm, about 15 nm to 100 nm, about 15 nm to 50 nm, about 50 nm to 500 nm, about 50 nm to 300 nm, or about 100 nm to 300 nm. In some embodiments, the different conductive layers may be applied by chemical plating or electroplating. In addition, the different conductive layers may be applied by printing or physical vapor deposition (PVD) methods such as evaporation or sputtering. In some embodiments, the different conductive layers may include nanoparticle copper, nanoparticle silver, or other nanoparticle metals. The nanoparticle metals may be applied by methods such as chemical plating, electroplating, or low temperature sputtering.

[0071] 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 be in the range of 1° C. to 10° C., 10° C. to 100° C., 10° C. to 65° C., 10° C. to 50° C., or 10° C. to 35° C. The thickness of the copper layer 204 can be the same as or substantially similar to the depth of the recess 152. The copper layer 204 can be deposited by physical deposition (e.g., sputtering) rather than electroplating. Depending on the nature of the deposition process, the copper layer 204 can have a mostly 111 texture and a randomly oriented grain structure.

[0072] exist Figure 7D During the deposition of dielectric layer 74, portions of copper layer 204 and barrier layer 153 above dielectric layer 74 can be removed. For example, portions of copper layer 204 and barrier layer 153 above dielectric layer 74 can be removed by polishing (e.g., chemical mechanical polishing (CMP)) to define a bonding surface 200a of component 200, which includes dielectric layer 74 surface 74a and copper layer 204 surface 204a. In practice, the CMP process used to form dielectric bonding surface 200a may polish away a very small portion of dielectric material 74 during the barrier layer 153 removal step. The CMP process can occur at a lower temperature than the deposition temperature used to deposit copper layer 204. The CMP chemistry or a subsequent etching process can cause copper surface 204a to be recessed below dielectric surface 74a. Aluminum layer 202 and copper layer 204 can together form conductive feature 206. Because upper copper layer 204 and lower aluminum layer 202 have sidewalls or lateral extents defined by the same mask (e.g., the mask used to etch aluminum to form aluminum layer 202 or to etch dielectric layer 74 to fill the aluminum), the sidewalls of the upper and lower portions are continuous, without the typical discontinuities (e.g., corners) that are typical when the upper and lower portions are defined by separate masks. At least lower aluminum layer 202 comprises aluminum. In the illustrated embodiment, copper layer 204 comprises copper or another conductive material (e.g., silver), but in other embodiments, the upper portion may also comprise fine-grained aluminum. Conductive feature 206 may have a first portion (e.g., aluminum layer 73) and a second portion (e.g., upper copper layer 204). The second portion may have a different microstructure than the first portion. The thickness of conductive feature 206 may be in the range of approximately 0.5 μm to 7 μm or 1 μm to 5 μm.

[0073] exist Figure 7EIn some embodiments, the bonding surface 200a of the component 200 can be cleaned and exposed to a plasma and / or etchant to activate the bonding surface 200a. In some embodiments, the bonding surface 200a of the component 200 can be terminated with a substance after activation or during activation (e.g., during a plasma and / or etching process). Without being limited by theory, in some embodiments, the activation process can be performed to break the chemical bonds at the bonding surface 200a of the component 200, and the termination process can provide additional chemicals at the bonding surface 200a, thereby improving the bonding energy during direct bonding. In some embodiments, activation and termination can be provided in the same step, for example, using a plasma to activate and terminate the bonding surface 200a of the component 200. In other embodiments, the bonding surface 200a of the component 200 can be terminated in a separate process to provide additional substances for direct bonding.

[0074] As explained above, the bonding surface 200a may include material concentrations from activation and / or the final chemical treatment process. For example, in embodiments utilizing nitrogen plasma for activation, a nitrogen peak may be formed at the bonding surface 200a. The nitrogen peak may be detected using secondary ion mass spectrometry (SIMS) technology.

[0075] In various embodiments, for example, a nitrogen termination treatment (e.g., exposing the bonding surface to a nitrogen-containing plasma) can replace OH groups on the hydrolyzed (OH-terminated) surface with NH2 molecules, thereby producing a nitrogen-terminated surface. In embodiments utilizing oxygen plasma activation, an oxygen peak can be formed at the bonding surface 200a. In some embodiments, the bonding surface 200a can include silicon oxynitride, silicon carbonitride oxide, or silicon carbonitride.

[0076] As with the elements 76 , 150 in the previous embodiments, the element 200 may be a die or a wafer, and the element 200 may be bonded to another element (eg, a wafer or a die). Figure 7FFIG2 is a schematic cross-sectional side view of a bonded structure 5 , which includes a wafer-shaped component 200 and a second component 220 (another wafer) bonded to component 200 along a bonding interface 221 . Second component 220 may include a BEOL layer 222 , a dielectric layer 224 , and a conductive feature 232 , which may also include a lower portion 228 (e.g., aluminum) and an upper portion 230 (e.g., copper), as shown. Dielectric layer 74 and dielectric layer 224 may be directly bonded together without an intermediate adhesive; and copper layer 204 and upper layer 230 (e.g., a copper layer) may also be directly bonded together without an intermediate adhesive. In other embodiments, additional wafers or substrates (e.g., 1 to 8 wafers) may be mechanically and electrically bonded to second component 220 . The bonded wafer or substrate stack may be singulated for subsequent processing. Similarly, additional dies (e.g., 1 to 40 dies) may be bonded or stacked to second component 220 . The wafer or substrate with the bonded dies can be singulated for subsequent processes. One of the subsequent processes can include encapsulating the sides of the singulated stack in a dielectric layer. In some embodiments, the encapsulating dielectric layer includes a molding material.

[0077] and Figure 6I and Figure 6J Like the element 150 shown in FIG. 1 , in some embodiments, the element 200 can be singulated into singulated elements before bonding. These singulated elements can be bonded to another element (eg, a wafer or die) as described herein.

[0078] The various embodiments disclosed herein or their features can be combined to provide additional embodiments. For example, any two or more elements disclosed herein can be joined to define various joint structures. For example, any two or more elements in elements 76, 150, 200 can be joined to define a joint structure.

[0079] In the above embodiments, aluminum-based features such as contact pads can be processed to achieve efficient direct metal bonding, including direct hybrid bonding. In the illustrated embodiment, aluminum features can be defined and processed for direct hybrid bonding without additional high temperature deposition or masking steps. For example, with Figures 3A-3D The process is different, after defining the aluminum features (e.g. Figure 5E ), without any masking steps or insulating layer deposition shown. Thus, in all illustrated embodiments, the metal contact features prepared for direct hybrid bonding can have continuous sidewalls, a characteristic defined by a single masking process, with the contact features having a lower aluminum portion, a fluorine-treated upper aluminum portion, or an upper copper portion. Figures 5A-5HIn the embodiment of FIG, no deposition or masking steps are shown after the aluminum features are defined at the surface, and fluorination facilitates low-temperature direct hybrid bonding of the aluminum features. Figures 6A-6L and Figures 7A-7F Embodiments may employ recessing and redeposition of metal to form an upper portion of a contact feature that is different than the lower portion (e.g., a different aluminum grain structure, or copper on top and aluminum on the bottom), but even these embodiments do not rely on additional insulator deposition or masking steps, such that a contact feature having a lower aluminum portion and a different metal upper portion still has continuous sidewall characteristics defined by a single masking process. Furthermore, compared to oxide deposition, Figures 6A-7F The recessing, metal redeposition and CMP steps can all be performed at low temperatures.

[0080] In one aspect, a method for forming a bonding surface for direct hybrid bonding is disclosed. The method may include providing a component 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.

[0081] In one embodiment, exposing the surface of the aluminum feature to fluorine inhibits the formation of aluminum oxide.

[0082] In one embodiment, the method further includes providing an aluminum layer over the back end of line (BEOL) layer, removing at least a portion of the aluminum layer to define an aluminum feature, and providing a dielectric material adjacent the aluminum feature to define a non-conductive field region.

[0083] In one embodiment, the aluminum feature includes a first portion and a second portion, the second portion being located above the first portion and at least partially defining the surface of the aluminum feature. The second portion may include an average grain size that is smaller than the average grain size of the first portion. The method may also include: removing metal from the initial aluminum feature to leave the first portion below a recess of approximately 0.1 μm to 0.3 μm relative to the surface of the non-conductive field region, and depositing the second portion into the recess above 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 of less than about 100°C. A majority of the grains in the second portion may have a width in the range of 10 nm to 500 nm. The aluminum feature may have a continuous sidewall along the sidewalls of the first portion and the sidewalls of the second portion.

[0084] 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 may be in the range of about 1 μm to 5 μm.

[0085] In one embodiment, the component includes an aluminum interconnect structure electrically connected to the aluminum feature.

[0086] In one embodiment, exposing the surface of the aluminum feature to fluorine includes forming aluminum fluoride, aluminum fluoride oxide, or aluminum fluoride boron oxide. Exposing the surface of the aluminum feature to fluorine may include forming at least a portion that is free of aluminum oxide.

[0087] In one embodiment, exposing the surface of the aluminum feature to fluorine comprises exposing the surface to a rinse solution comprising 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, tetramethylammonium tetrafluoroborate, tetramethylammonium tetrafluoroborate, or hydrogen fluoride (HF).

[0088] In one embodiment, the surface of the aluminum feature is exposed to fluorine without exposing the aluminum feature to a nitrogen plasma or an ammonia immersion solution.

[0089] In one embodiment, a method of forming a bonded structure is disclosed. The method includes providing a component formed using the method; providing a second component 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 intermediate adhesive; and directly bonding the aluminum feature and the conductive feature without an intermediate adhesive.

[0090] In one aspect, a direct hybrid bond structure is disclosed. The bond structure may 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 bond structure may 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 along a bonding interface without an intermediate adhesive, and the surface of the second aluminum feature is directly bonded to the second aluminum feature along a bonding interface without an intermediate adhesive. The surface of the first aluminum feature includes a higher fluorine content than a portion of the first aluminum feature distal from the surface.

[0091] In one embodiment, the bonding interface between the first aluminum feature and the second aluminum feature includes one or more fluorine peaks.

[0092] In one embodiment, the first aluminum feature includes a first fluorine concentration gradient that decreases away from the bonding interface. The second aluminum feature may include a second fluorine concentration gradient that decreases away from the bonding interface.

[0093] In one embodiment, a first aluminum feature includes a first portion and a second portion, the second portion being located above the first portion and at least partially defining a surface of the first aluminum feature. The second portion may include an average grain size that is smaller than an average grain size of the first portion. A majority of the grains in the second portion may have a width in a range of 10 nm to 500 nm. The first aluminum feature may also include a barrier layer between the first portion and the second portion.

[0094] In one embodiment, the bonding interface between the first aluminum feature and the second aluminum feature includes less than 1000 ppm of oxygen.

[0095] In one embodiment, the bonding interface between the first aluminum feature and the second aluminum feature includes less than 100 ppm nitrogen.

[0096] In one embodiment, the first aluminum feature has a thickness in the range of 0.5 μm to 5 μm.

[0097] In one aspect, the present invention discloses a component having a bonding surface configured for direct hybrid bonding to another component. The component may 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 component. The surface of the aluminum feature includes aluminum and fluorine.

[0098] 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 may be in the range of approximately 1 μm to 3 μm.

[0099] In one embodiment, the aluminum feature includes a first portion and a second portion located above the first portion. The second portion may define a surface of the aluminum feature. The second portion may include an average grain size that is smaller than the average grain size of the first portion. A majority of the grains in the second portion may have a width in a range of 10 nm to 500 nm. The second portion may have a thickness in a range of 0.1 μm to 0.3 μm.

[0100] In one embodiment, the surface of the aluminum feature is recessed by approximately 2 nm to 20 nm from the surface of the non-conductive field region.

[0101] In one aspect, a bonding structure is disclosed. The bonding structure may 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, the second portion being located above the first portion and at least partially defining a surface of the first conductive feature. The first portion includes aluminum. The first conductive feature has a continuous sidewall along the first portion and the second portion. 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 may include a second element having a second non-conductive field region and a second conductive feature. The surface of the second non-conductive field region is directly bonded to the first non-conductive field region along a bonding interface without an intermediate adhesive, and the surface of the second conductive feature is directly bonded to the second conductive feature along a bonding interface without an intermediate adhesive.

[0102] In one embodiment, the second portion has an average grain size that is smaller than an average grain size of an average grain size of the second portion.A majority of the grains in the second portion may have a width in the range of 10 nm to 500 nm.

[0103] 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 may have different metal structures. The second portion may include aluminum. The surface of the conductive feature may include aluminum fluoride. The second portion may include copper.

[0104] In one aspect, a component having a bonding surface configured to directly bond to another component is disclosed. The component may include a non-conductive field region and a conductive feature, the conductive feature including a first portion and a second portion, the second portion being located above the first portion and at least partially defining a surface of the conductive feature. The first portion comprises aluminum. The conductive feature has a continuous sidewall extending along the first and second portions. The second portion comprises a different metal composition than the first portion or includes fluorine at 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 component.

[0105] In one embodiment, the second portion has an average grain size that is smaller than an average grain size of the second portion.A majority of the grains in the second portion may have a width in the range of 10 nm to 500 nm.

[0106] 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 may include aluminum. The surface of the conductive feature may include aluminum fluoride. The second portion may include copper.

[0107] The present invention discloses a method for forming a component having a bonding surface configured to directly bond to another component. The method may include forming a non-conductive field region and a first portion of a conductive feature. The first portion includes aluminum. The method may include forming a second portion of the conductive feature above the first portion. The second portion at least partially defines a surface of the conductive feature. The first portion and the second portion are defined by a single mask process. The second portion includes a different metal composition than the first portion or includes fluorine at 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 component.

[0108] In one embodiment, the second portion comprises fine grain aluminum.

[0109] In one embodiment, the second portion comprises copper.

[0110] In one embodiment, the second portion includes aluminum and fluorine.

[0111] In one embodiment, the method further comprises 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 nitrogen plasma or an ammonia immersion solution.

[0112] Unless the context clearly requires otherwise, throughout the specification and claims, the words "comprise," "comprising," "include," "including," and the like are to be interpreted in an inclusive sense, and not in an exclusive or exhaustive sense; that is, in the sense of "including but not limited to." The word "coupled," as generally used herein, means that two or more elements can be connected directly, or can be connected with the aid of one or more intermediate elements. Similarly, the word "connected," as generally used herein, means that two or more elements can be connected directly, or can be connected with the aid of one or more intermediate elements. In addition, the words "herein," "above," "below," and the like, and words of similar meaning, when used in this application, shall refer to the entire application, not to any particular part of this application. Where the context permits, words used in the singular or plural in the above specific embodiments may also include the plural or singular, respectively. The word "or" refers to a list of two or more items, and the word covers all of the following interpretations: any item in the list, all items in the list, and any combination of items in the list.

[0113] Furthermore, conditional language used herein, such as "can," "may," "could," "may," "for example," "such as," and the like, unless expressly stated otherwise or understood otherwise from the context, is generally intended to convey that some embodiments include certain features, elements, and / or states, while other embodiments do not. Thus, such conditional language is generally not intended to imply that features, elements, and / or states are in any way essential to one or more embodiments.

[0114] While certain 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 provisions for direct hybrid bonding, those skilled in the art will appreciate that the techniques taught herein can also be used for direct metal bonding even in the absence of direct dielectric bonding. Indeed, the novel devices, methods, and systems herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit of the present disclosure. For example, while the blocks are presented in a given arrangement, alternative embodiments may utilize different components and / or circuit topologies to perform similar functionality, and blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each block may be implemented in a variety of different ways. Any suitable combination of the elements and actions of the various embodiments described above may be combined to provide additional embodiments. Furthermore, various combinations or subcombinations of the specific features and aspects of the embodiments are contemplated and still fall within the scope of the present disclosure. The accompanying claims and their equivalents are intended to cover any form or modification falling within the scope and spirit of the present disclosure.

Claims

1. A method of forming a joining surface for direct hybrid joining, the method comprising: Providing a component having a non-conductive field region and aluminum features; as well as The surface of the aluminum feature is exposed to fluorine, wherein the surface of the aluminum feature and a surface of the non-conductive field region define the direct bonding surface.

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

3. The method according to claim 1, further comprising: Providing an aluminum layer on top of the back-end-of-line (BEOL) layer; removing at least a portion of the aluminum layer to define the aluminum feature; as well as A dielectric material is provided adjacent the aluminum feature to define the non-conductive field region.

4. The method of claim 1 , wherein the aluminum feature comprises a first portion and a second portion, the second portion being located above the first portion and at least partially defining the surface of the aluminum feature, the second portion comprising an average grain size that is smaller than an average grain size of the first portion.

5. The method according to claim 4, further comprising: removing metal from the initial aluminum feature to leave the first portion below a recess of approximately 0.1 μm to 0.3 μm relative to the surface of the non-conductive field region; as well as The second portion is deposited into the recess above the first portion, the second portion having a different microstructure than the first portion. The method of claim 5 , wherein the second portion is deposited at a deposition temperature below about 100° C. 7 . The method according to claim 5 , wherein a majority of the grains in the second portion have a width in the range of 10 nm to 500 nm.

8. The method of claim 4, wherein the aluminum feature has a continuous sidewall 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 a range of approximately 0.5 μm to 7 μm.

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

11. The method of claim 1 , wherein the component comprises 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: Aluminum fluoride, aluminum fluoride oxide or aluminum fluoride boron oxide is formed.

13. The method of claim 12, wherein exposing the surface of the aluminum feature to fluorine comprises: At least a portion is formed that does not contain aluminum oxide.

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

15. The method of claim 1, wherein the surface of the aluminum feature is exposed to fluorine without exposing the aluminum feature to a nitrogen plasma or an ammonia immersion solution.

16. A method of forming a bonded structure, the method comprising: providing the element formed using the method according to claim 1; providing a second element having a second non-conductive field region and a conductive feature; directly joining the non-conductive field region and the second non-conductive field region without an intermediate adhesive; and The aluminum feature and the conductive feature are directly bonded without an intermediate adhesive.

17. A direct hybrid joint structure comprising: a first component 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 component; as well as a second component having a second non-conductive field region and a second aluminum feature, a surface of the second non-conductive field region being directly bonded to the first non-conductive field region along a bonding interface without an intermediate adhesive, and a surface of the second aluminum feature being directly bonded to the second aluminum feature along the bonding interface without an intermediate adhesive, wherein the surface of the first aluminum feature comprises a higher fluorine content than portions of the first aluminum feature distal from the surface.

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

19. The bonded structure of claim 17, wherein the first aluminum feature comprises a first fluorine concentration gradient that decreases away from the bonded interface.

20. The bonded structure of claim 19, wherein the second aluminum feature comprises a second fluorine concentration gradient that decreases away from the bonded interface.

21. The bonded structure of claim 17, wherein the first aluminum feature comprises a first portion and a second portion, the second portion being located above the first portion and at least partially defining the surface of the first aluminum feature, the second portion comprising an average grain size smaller than an average grain size of the first portion. 22 . The bonded structure according to claim 21 , wherein a majority of the grains in the second portion have a width in the range of 10 nm to 500 nm.

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

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

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

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

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

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

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

30. The element of claim 27, wherein the aluminum feature comprises a first portion and a second portion located above the first portion, the second portion defining the surface of the aluminum feature, the second portion comprising an average grain size that is smaller than the average grain size of the first portion, wherein a majority of the grains in the second portion have a width in the range of 10 nm to 500 nm. 31 . The element according to claim 30 , wherein the thickness of the second portion is in the range of 0.1 μm to 0.3 μm.

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

33. A joining structure comprising: a first element having a first non-conductive field region and a first conductive feature, a surface of the first non-conductive field region and a surface of the first conductive feature at least partially defining a bonding surface of the first element, the first conductive feature including a first portion and a second portion, the second portion being located above the first portion and at least partially defining a surface of the first conductive feature, the first portion comprising aluminum, the first conductive feature having a continuous sidewall 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 second element having a second non-conductive field region and a second conductive feature, a surface of the second non-conductive field region being directly bonded to the first non-conductive field region along a bonding interface without an intermediate adhesive, and a surface of the second conductive feature being directly bonded to the second conductive feature along the bonding interface without an intermediate adhesive. 34 . The bonded structure according to claim 33 , wherein the second portion has an average grain size smaller than an average grain size of the second portion, a majority of grains in the second portion having a width in the range of 10 nm to 500 nm.

35. The bonded 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. The joint structure of claim 35, wherein the first portion and the second portion have different metal structures.

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

38. The bonded structure of claim 37, wherein the surface of the conductive feature comprises aluminum fluoride. The bonded structure of claim 35 , wherein the second portion comprises copper.

40. A component having a joining surface configured to directly join to another component, the component comprising: non-conductive field regions; as well as a conductive feature comprising a first portion and a second portion, the second portion being located above the first portion and at least partially defining a surface of the conductive feature, the first portion comprising aluminum, the conductive feature having a continuous sidewall along the first portion and the second portion, the second portion comprising a different metal composition than the first portion or comprising fluorine at the surface of the first conductive feature, the surface of the non-conductive field region and the surface of the aluminum feature together defining the bonding surface of the element.

41. The element of claim 40, wherein the second portion has an average grain size smaller than an average grain size of the second portion, a majority of the grains in the second portion having a width in the range of 10 nm to 500 nm.

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

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

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

46. ​​A method of forming a component having a joining surface configured to directly join to another component, the method comprising: forming a non-conductive field region and a first portion of a conductive feature, the first portion comprising aluminum; as well as forming a second portion of the conductive feature over the first portion, the second portion at least partially defining a surface of the conductive feature; wherein the first portion and the second portion are defined by a single mask process; the second portion comprises a different metallic composition than the first portion or comprises fluorine at the surface of the conductive feature; and The surface of the non-conductive field region and the surface of the conductive feature together define the bonding surface of the element.

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

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

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

50. The method of claim 46, further comprising: The surface of the conductive feature is exposed to fluorine.

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

52. The method of claim 50, wherein the surface of the aluminum feature is exposed to fluorine without exposing the aluminum feature to a nitrogen plasma or an ammonia immersion solution.

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