Patent Publication Number: US-2023154845-A1

Title: Interconnect Structures

Description:
PRIORITY CLAIM AND CROSS-REFERENCE 
     This application is a continuation of U.S. patent application Ser. No. 17/036,543, filed on Sep. 29, 2020, entitled “Interconnect Structures Having Lines and Vias Comprising Different Conductive Materials,” which is a continuation of U.S. patent application Ser. No. 16/569,912, filed on Sep. 13, 2019, entitled “Interconnect Structures and Methods of Forming the Same,” now U.S. Pat. No. 11,177,208, issued on Nov. 16, 2021, which is a division of U.S. patent application Ser. No. 15/993,726, filed on May 31, 2018, entitled “Interconnect Structures and Methods of Forming the Same,” now U.S. Pat. No. 10,867,905, issue on Dec. 15, 2020, which application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 62/592,646, filed on Nov. 30, 2017, entitled “Interconnect Structures and Methods of Forming the Same,” which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (e.g., the number of interconnected devices per chip area) has generally increased while geometry size (e.g., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. However, scaling down has also led to challenges that may not have been presented by previous generations at larger geometries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIGS.  1  through  10    are cross-sectional views of respective intermediate structures during an example method for forming an interconnect structure in accordance with some embodiments. 
         FIG.  11    is a flow chart of an example method for forming an interconnect structure in accordance with some embodiments. 
         FIG.  12    is a flow chart of an example Atomic Layer Etch (ALE) process in accordance with some embodiments. 
         FIGS.  13  through  18    are cross-sectional views of various details and/or modifications to a portion of the intermediate structure of  FIG.  6    in accordance with some embodiments. 
         FIG.  19    is a cross-sectional view of an interconnect structure in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     Embodiments described herein relate generally to one or more methods for forming an interconnect structure, such as a dual damascene interconnect structure comprising a conductive line and a conductive via, in semiconductor processing. Generally, a conductive via may be selectively deposited in a via opening for the interconnect structure, a nucleation enhancement treatment may then be performed, and a conductive fill material may subsequently be deposited in a trench for the interconnect structure. The nucleation enhancement treatment can cause the deposition of the conductive fill material to be bottom-up and/or conformal, such as by nucleating and being deposited on dielectric surfaces. Some embodiments can obviate using a seed layer for depositing the conductive fill material, and can further obviate using a high resistance metal-containing barrier layer in the interconnect structure. Hence, some process windows for forming the interconnect structure can be increased, and a resistance of the interconnect structure can be decreased. Other advantages or benefits may also be achieved. 
     Some embodiments described herein are in the context of Back End Of the Line (BEOL) processing. Other processes and structures within the scope of other embodiments may be performed in other contexts, such as in Middle End Of the Line (MEOL) processing and other contexts. Various modifications are discussed with respect to disclosed embodiments; however, other modifications may be made to disclosed embodiments while remaining within the scope of the subject matter. A person having ordinary skill in the art will readily understand other modifications that may be made that are contemplated within the scope of other embodiments. Although method embodiments may be described in a particular order, various other method embodiments may be performed in any logical order and may include fewer or more steps than what is described herein. 
       FIGS.  1  through  10    illustrate cross-sectional views of respective intermediate structures during an example method for forming an interconnect structure in accordance with some embodiments.  FIG.  11    is a flow chart of the example method  200  for forming the interconnect structure in accordance with some embodiments. 
       FIG.  1    and operation  202  of the method  200  illustrate the formation of dielectric layers over a semiconductor substrate  20 .  FIG.  1    illustrates a first dielectric layer  22  over the semiconductor substrate  20 . The semiconductor substrate  20  may be or include a bulk semiconductor, a semiconductor-on-insulator (SOI) substrate, or the like, which may be doped (e.g., with a p-type or an n-type dopant) or undoped. In some embodiments, the semiconductor material of the semiconductor substrate  20  may include elemental semiconductor like silicon (Si) and germanium (Ge); a compound semiconductor; an alloy semiconductor; or a combination thereof. 
     Various devices may be on the semiconductor substrate  20 . For example, the semiconductor substrate  20  may include Field Effect Transistors (FETs), such as Fin FETs (FinFETs), planar FETs, vertical gate all around FETs (VGAA FETs), or the like; diodes; capacitors; inductors; and other devices. Devices may be formed wholly within the semiconductor substrate  20 , in a portion of the semiconductor substrate  20  and a portion of one or more overlying layers, and/or wholly in one or more overlying layers, for example. Processing described herein may be used to form and/or to interconnect the devices to form an integrated circuit. The integrated circuit can be any circuit, such as for an Application Specific Integrated Circuit (ASIC), a processor, memory, or other circuit. 
     The first dielectric layer  22  is above the semiconductor substrate  20 . The first dielectric layer  22  may be directly on the semiconductor substrate  20 , or any number of other layers may be disposed between the first dielectric layer  22  and the semiconductor substrate  20 . For example, the first dielectric layer  22  may be or include an Inter-Metal Dielectric (IMD) or an Inter-Layer Dielectric (ILD). The first dielectric layer  22 , for example, may be or comprise a low-k dielectric having a k-value less than about 4.0, such as about 2.0 or even less. In some examples, the first dielectric layer  22  comprises silicon oxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), fluorosilicate glass (FSG), SiO x C y , silicon carbon material, a compound thereof, a composite thereof, or a combination thereof. 
     A conductive feature  24  is in and/or through the first dielectric layer  22 . The conductive feature  24  may be or include a conductive line and/or a conductive via, a gate structure of a transistor, or a contact plug to a gate structure of a transistor and/or to a source/drain region of a transistor. In some examples, the first dielectric layer  22  is an IMD, and the conductive feature  24  may include a conductive line and/or a conductive via (collectively or individually, “interconnect structure”). The interconnect structure may be formed by forming an opening and/or recess through and/or in the IMD, for example, using a damascene process. Some examples of forming an interconnect structure are described further below, although other processes and interconnect structures may be implemented. In other examples, the first dielectric layer  22  may include an ILD, and the conductive feature  24  may include a gate electrode (e.g., tungsten, cobalt, etc.) in the ILD formed using a replacement gate process, for example. In another example, the first dielectric layer  22  may be an ILD, and the conductive feature  24  may include a contact plug. The contact plug may be formed by forming an opening through the ILD to, for example, a gate electrode and/or source/drain region of a transistor formed on the semiconductor substrate  20 . The contact plug can include an adhesion layer (e.g., Ti, etc.), a barrier layer (e.g., TiN, etc.) on the adhesion layer, and a conductive fill material (e.g., tungsten, cobalt, etc.) on the barrier layer. The contact plug can also be made of a less diffusive metal like tungsten, Mo, or Ru without a barrier layer. 
     A first etch stop layer (ESL)  26  is over the first dielectric layer  22  and the conductive feature  24 . Generally, an ESL can provide a mechanism to stop an etch process when forming, e.g., contacts or conductive vias. An ESL may be formed of a dielectric material having a different etch selectivity from adjacent layers or components. The first ESL  26  is deposited on the top surfaces of the first dielectric layer  22  and the conductive feature  24 . The first ESL  26  may comprise or be silicon nitride, silicon carbon nitride, silicon carbon oxide, carbon nitride, the like, or a combination thereof, and may be deposited by Chemical Vapor Deposition (CVD), Plasma Enhanced CVD (PECVD), Atomic Layer Deposition (ALD), or another deposition technique. A thickness of the first ESL  26 , in some examples, is in a range from about 3 nm to about 10 nm. 
     A second dielectric layer  28  is over the first ESL  26 . For example, the second dielectric layer  28  may be or include an IMD. The second dielectric layer  28  is deposited on the top surface of the first ESL  26 . The second dielectric layer  28 , for example, may be or comprise a low-k dielectric having a k-value less than about 4.0, such as about 2.0 or even less. In some examples, the second dielectric layer  28  comprises silicon oxide, PSG, BPSG, FSG, SiO x C y , silicon carbon material, a compound thereof, a composite thereof, or a combination thereof. The second dielectric layer  28  may be deposited using a CVD, such as PECVD or Flowable CVD (FCVD); spin-on coating; or another deposition technique. In some examples, a Chemical Mechanical Planarization (CMP) or another planarization process may be performed to planarize the top surface of second dielectric layer  28 . A thickness of the second dielectric layer  28 , in some examples, is in a range from about 4 nm to about 30 nm. 
     A second ESL  30  is over the second dielectric layer  28 . The second ESL  30  is deposited on a top surface of the second dielectric layer  28 . The second ESL  30  may comprise or be silicon nitride, silicon carbon nitride, silicon carbon oxide, carbon nitride, the like, or a combination thereof, and may be deposited by CVD, PECVD, ALD, or another deposition technique. A thickness of the second ESL  30 , in some examples, is in a range from about 3 nm to about 10 nm. 
     A third dielectric layer  32  is over the second ESL  30 . For example, the third dielectric layer  32  may be or include an IMD. The third dielectric layer  32  is deposited on the top surface of the second ESL  30 . The third dielectric layer  32 , for example, may be or comprise a low-k dielectric having a k-value less than about 4.0, such as about 2.0 or even less. In some examples, the third dielectric layer  32  comprises silicon oxide, PSG, BPSG, FSG, SiO x C y , silicon carbon material, a compound thereof, a composite thereof, or a combination thereof. The third dielectric layer  32  may be deposited using a CVD, such as PECVD or FCVD; spin-on coating; or another deposition technique. In some examples, a CMP or another planarization process may be performed to planarize the top surface of third dielectric layer  32 . A thickness of the third dielectric layer  32 , in some examples, is in a range from about 20 nm to about 50 nm, such as about 45 nm. 
     The configuration of the second dielectric layer  28 , second ESL  30 , and third dielectric layer  32  of  FIG.  1    is an example. In other examples, the second ESL  30  may be omitted between the second dielectric layer  28  and the third dielectric layer  32 . Further, in some examples, a single dielectric layer  34  (see  FIG.  19   ) may be formed in the place of the second dielectric layer  28 , second ESL  30 , and third dielectric layer  32 . A person having ordinary skill in the art will readily understand these and other modifications that may be made. 
       FIG.  2    and operation  204  of the method  200  illustrate the formation of a via opening  42  and a trench  40  in and/or through the first ESL  26 , second dielectric layer  28 , second ESL  30 , and third dielectric layer  32 . The via opening  42  and trench  40  can be formed using photolithography and etch processes, such as in a dual damascene process. For example, a photo resist can be formed on the third dielectric layer  32 , such as by using spin-on coating, and patterned with a pattern corresponding to the trench  40  by exposing the photo resist to light using an appropriate photomask. Exposed or unexposed portions of the photo resist may then be removed depending on whether a positive or negative resist is used. The pattern of the photo resist may then be transferred to the third dielectric layer  32 , such as by using a suitable etch process, which forms the trench  40  in the third dielectric layer  32 . The etch process may include a reactive ion etch (RIE), neutral beam etch (NBE), inductive coupled plasma (ICP) etch, the like, or a combination thereof. The etch process may be anisotropic. The second ESL  30  may be used as an etch stop for the etch process. Subsequently, the photo resist is removed in an ashing or wet strip process, for example. Then, another photo resist can be formed on the third dielectric layer  32  and in the trench  40 , such as by using spin-on coating, and patterned with a pattern corresponding to the via opening  42  by exposing the photo resist to light using an appropriate photomask. The pattern of the photo resist may then be transferred through the second ESL  30 , second dielectric layer  28 , and first ESL  26 , such as by using one or more suitable etch process, which forms the via opening  42  through the second ESL  30 , second dielectric layer  28 , and first ESL  26 . The etch process may include a RIE, NBE, ICP etch, the like, or a combination thereof. The etch process may be anisotropic. Subsequently, the photo resist is removed in an ashing or wet strip process, for example. 
     The sidewalls of the trench  40  and the via opening  42  are illustrated as being substantially vertical with rounding at corners. For example, linear portions of the sidewalls form an angle measured interior to the respective second dielectric layer  28  or third dielectric layer  32  that is in a range from about 85° to about 90°, such as about 85° to about 89°, and more particularly about 87°. In other examples, sidewalls of one or both of the trench  40  and the via opening  42  may be vertical or may taper together in a direction toward or away from the bottom of the via opening  42 . For example, the via opening  42  may have a positive taper profile or a reentrant profile. Various examples of configurations for the via opening  42 , and details thereof, are illustrated in and described with respect to  FIGS.  13  through  18   . 
     In the example configuration of  FIG.  2   , the trench  40  has a first width W 1  in a plane of a top surface of the third dielectric layer  32  and has a second width W 2  along a bottom surface of the trench  40 . The first width W 1 , in some examples, is in a range from about 20 nm to about 40 nm, and the second width W 2 , in some examples, is in a range from about 18 nm to about 36 nm. The trench has a depth that is, in this example, equal to a first thickness T 1  of the third dielectric layer  32 . The first thickness T 1 , in some examples, is in a range from about 20 nm to about 50 nm, as stated previously. A first aspect ratio of the first thickness T 1  to the first width W 1  can be in a range from about 0.5 to about 2.5, and a second aspect ratio of the first thickness T 1  to the second width W 2  can be in a range from about 0.56 to about 2.78. 
     In an example configuration where the sidewalls of the trench are vertical, widths corresponding to the first width W 1  and the second width W 2  in  FIG.  2    are equal, and each can be in a range from about 20 nm to about 40 nm. An aspect ratio of the first thickness T 1  to the width of the trench  40 , in this example, can be in a range from about 0.5 to about 2.5. In an example configuration where the sidewalls of the trench taper (e.g., a positive taper profile), the width corresponding to the first width W 1  in  FIG.  2    may be a function of the width (W lower ) corresponding to the second width W 2  in  FIG.  2    and the angle (θ) of the sidewall measured interior to the third dielectric layer  32  (e.g., W upper =W lower +[2T1(tan θ) −1 ]). The width corresponding to the second width W 2  in  FIG.  2    can be in a range from about 18 nm to about 36 nm, and the angle can be in a range from about 85° to about 89°, or may be less than 85°. An aspect ratio of the first thickness T 1  to the width corresponding to the second width W 2  of  FIG.  2    can be in a range from about 0.56 to about 2.78. 
     A person having ordinary skill in the art will readily understand that the dimensions, ratios, and angles described herein are merely examples. Dimensions, ratios, and angles can vary based on technology generation nodes in which various aspects are implemented and/or based on various processes used. Such variations are within the scope of this disclosure. 
       FIG.  3    and operation  206  of the method  200  illustrate the formation of a liner layer  50  conformally along sidewalls of the via opening  42  and the trench  40 , along respective bottom surfaces of the via opening  42  and the trench  40 , and along a top surface of the third dielectric layer  32 . The liner layer  50  can be formed by conformal deposition. The liner layer  50  may be or comprise silicon nitride (SiN), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), silicon oxygen carbon nitride (SiOCN), a silicon-containing low-k dielectric, a carbon-containing low-k dielectric, the like, or a combination thereof, and may be deposited by CVD, ALD, or another deposition technique. A thickness of the liner layer  50 , in some examples, is in a range from about 1 nm to about 4 nm, and more particularly, from about 2 nm to about 3 nm. 
       FIG.  4    and operation  208  of the method  200  illustrates the formation of respective liners  52  along sidewalls of the via opening  42  and along sidewalls of the trench  40  from the liner layer  50 . The liners  52  can be formed by anisotropically etching the liner layer  50 . The etch process for anisotropically etching the liner layer  50  may include a RIE, NBE, ICP etch, the like, or a combination thereof. The liners  52 , and the second ESL  30 , if implemented, may be diffusion barriers that can reduce or prevent out-diffusion of a conductive fill material subsequently deposited in the trench  40  and via opening  42  to, e.g., the second dielectric layer  28  and third dielectric layer  32 . The liners  52  and second ESL  30  can form a dielectric diffusion barrier. 
     Profiles of the liners  52  can vary depending on, among other things, the profiles of the sidewalls of the trench  40  and via opening  42 . In the example of  FIG.  4   , at rounded corners at the sidewalls where the slope of the corner is approximately 45°, a second thickness T 2  can substantially equal the thickness (t liner ) of the liner layer  50  minus the thickness (t etched ) removed by the anisotropic etch in a vertical direction times the square root of two divided by two (e.g., t liner −[t etched ×2 −(1/2) ]). Further, a third thickness T 3  along a substantially vertical portion of a respective sidewall at the bottom of the trench  40  or via opening  42  can be equal to the thickness of the liner layer  50 . In some examples, the second thickness T 2  is in a range from about 0.3 nm to about 1.2 nm, and the third thickness T 3  is in a range from about 1 nm to about 4 nm. A person having ordinary skill in the art will readily understand the relationship that the thicknesses of the liners  52  can have with the underlying slope angles of the sidewalls. 
     In an example configuration where the sidewalls of the trench are vertical, thicknesses corresponding to the second thickness T 2  and the third thickness T 3  in  FIG.  4    are equal (which may further be substantially equal to the thickness of the liner layer  50 ), and each can be in a range from about 1 nm to about 4 nm. In an example configuration where the sidewalls of the trench taper (e.g., a positive taper profile) at a constant slope angle, the thicknesses corresponding to the second thickness T 2  and the third thickness T 3  in  FIG.  4    are equal. The thicknesses can be a function of the thickness of the liner layer  50  and the angle of the sidewall similar to described above as a person having ordinary skill in the art would understand. The width corresponding to the second width W 2  in  FIG.  2    can be in a range from about 1 nm to about 4 nm. 
     Profiles of the liners  52  can further vary depending on step coverage of the deposition process used to deposit the liner layer  50 . For example, a thickness of the liner  52  along sidewalls of the via opening  42  can vary from a thickness of the liner  52  along sidewalls of the trench  40  due to step coverage variation. 
     In operation  210  of the method  200 , after forming the liners  52 , optionally, a cleaning process may be performed to clean exposed surfaces of, e.g., the trench  40  and via opening  42 . The cleaning process can include a plasma treatment, an etch process, another cleaning process, or a combination thereof. In an example, the cleaning process includes a plasma treatment (operation  212 ) followed by an Atomic Layer Etch (ALE) (operation  214 ). The plasma treatment in operation  212  can include using a hydrogen (H 2 ) gas with a carrier gas, such as argon (Ar). The plasma treatment, in some instances, can reduce an oxide that may be formed on a surface of the conductive feature  24  exposed through the via opening  42  and can remove organic material that may be formed on various surfaces. A flow rate of the hydrogen gas in the plasma treatment can be in a range from about 5 sccm to about 1,000 sccm, and a flow rate of the carrier gas in the plasma treatment can be in a range from about 0 sccm to about 1,000 sccm. A pressure of the plasma treatment can be in a range from about 10 mTorr to about 200 mTorr. A temperature of the plasma treatment can be in a range from about −20° C. to about 100° C. A power of the plasma generator of the plasma treatment can be in a range from about 20 W to about 400 W, and a frequency of the plasma generator can be about 13.56 MHz or greater. The substrate during the plasma treatment can be biased in a range from about 20 V to about 100 V. A duration of the plasma treatment can be in a range from about 5 seconds to about 120 seconds. 
     The ALE in operation  214  is illustrated in further detail in  FIG.  12   . The ALE in operation  214  can include performing multiple cycles, such as in a range from 2 cycles to 25 cycles. A cycle of the ALE can include sequentially flowing a reactant gas (operation  250 ), such as boron trichloride (BCl 3 ) gas, with a carrier gas (e.g., argon (Ar)); purging (operation  252 ) the reactant gas; flowing an etchant gas (operation  254 ), such as hydrogen (H 2 ) gas, with a carrier gas (e.g., argon (Ar)) and possibly with plasma enhancement; and purging (operation  256 ) the etchant gas. In some examples, the reactant gas, e.g., boron trichloride (BCl 3 ) gas, is adsorbed on dielectric surfaces to form a monolayer and is not significantly adsorbed on metal surfaces, and the monolayer is etched by the flowing of the etchant gas, e.g., hydrogen (H 2 ) gas. An example provided here implements boron trichloride (BCl 3 ) gas as the reactant gas and hydrogen (H 2 ) gas as the etchant gas; other gases may be used. During the flowing of the boron trichloride (BCl 3 ) gas, a flow rate of the boron trichloride (BCl 3 ) gas can be in a range from about 20 sccm to about 180 sccm, and a flow rate of the carrier gas can be in a range from about 200 sccm to about 800 sccm. Further, during the flowing of the boron trichloride (BCl 3 ) gas, a pressure of the ALE can be in a range from about 15 mTorr to about 100 mTorr, and a temperature of the ALE can be in a range from about −20° C. to about 60° C. After the boron trichloride is purged, the hydrogen (H 2 ) gas begins to flow and a plasma is ignited. During the flowing of the hydrogen (H 2 ) gas, a flow rate of the hydrogen (H 2 ) gas can be in a range from about 5 sccm to about 1,000 sccm, and a flow rate of the carrier gas can be in a range from about 50 sccm to about 400 sccm. Further, during the flowing of the hydrogen (H 2 ) gas, a pressure of the ALE can be in a range from about 10 mTorr to about 200 mTorr, and a temperature of the ALE can be in a range from about −20° C. to about 20° C. A power of the plasma generator of the ALE can be in a range from about 10 W to about 800 W, and a frequency of the plasma generator can be about 13.56 MHz or greater. The substrate during the plasma of the ALE can be biased in a range from about 50 V to about 300 V. 
     In operation  216  of the method  200 , after the cleaning process in operation  210  is optionally performed, a selectivity enhancement treatment can optionally be performed on exposed dielectric surfaces of, e.g., the trench  40  and via opening  42 . The selectivity enhancement treatment can, for example, treat and/or passivate dielectric surfaces so that a subsequent deposition of metal has a higher selectivity to deposit the metal at a greater rate on a metallic surface than the dielectric surfaces compared to without such treatment. For example, the selectivity enhancement treatment can cause the dielectric surfaces to be hydrophobic, which can improve selectivity during a subsequent deposition of metal. The selectivity enhancement treatment can include flowing a silicon-containing hydrocarbon gas over the dielectric surfaces. The selectivity enhancement treatment can be a tri-methylsiloxy (TMS) treatment, a di-methylsiloxy (DMS) treatment, the like, or a combination thereof. Example silicon-containing hydrocarbon gases include 1,1,1,3,3,3-hexamethyldisilazane (HDMS), chlorotrimethylsilane (TMCS), N, O-bis(trimethylsilyl)acetamide (BSA), N-(trimethylsilyl)dimethylamine (TMS-DMA), TMS-imidazole (SIM, N-trimethylsilylimidazole), 1,1,3,3-tetramethyldisilazane (TMDS), chlorodimethylsilane (DMCS), the like, or a combination thereof. The selectivity enhancement treatment can cause a silylation process in which an atom or group of atoms terminated at the dielectric surface can be substituted by a species of the silicon-containing hydrocarbon, which can cause the dielectric surface to be rendered hydrophobic. A flow rate of the silicon-containing hydrocarbon can be in a range from about 5 sccm to about 100 sccm, and a flow rate of a carrier gas flowed with the silicon-containing hydrocarbon can be in a range from about 0 sccm to about 400 sccm. A pressure during the flowing the silicon-containing hydrocarbon can be in a range from about 1 mTorr to about 100 mTorr, and a temperature can be in a range from about 20° C. to about 300° C. The selectivity enhancement treatment can treat or passivate the exposed dielectric surfaces of the liners  52 , the second ESL  30 , and the third dielectric layer  32  to improve selectivity of a subsequent selective deposition on the conductive feature  24 . 
       FIG.  5    and operation  218  of the method  200  illustrate the formation of a conductive via  60  in the via opening  42 . The formation of the conductive via  60  can include a selective deposition. The selective deposition can use the conductive feature  24  exposed through the via opening  42  as a seed, for example. The selective deposition can include electroless deposition or plating, selective CVD, or another technique. The conductive via  60  can be or include a metal, such as cobalt (Co), ruthenium (Ru), the like, or a combination thereof. In an example, the conductive via  60  is cobalt deposited using electroless deposition or plating. The electroless deposition or plating of cobalt (Co) may be at a temperature in a range equal to or less than about 200° C., such as in a range from room temperature (e.g., about 23° C.) to about 200° C. The selective CVD can include using a precursor gas comprising Ru 3 (CO) 12 , C 10 H 10 Ru, C 7 H 9 RuC 7 H 9 , Ru(C 5 (CH 3 ) 5 ) 2 , the like, or a combination thereof, and a carrier gas, such as argon (Ar). A flow rate of the precursor gas can be in a range from about 5 sccm to about 100 sccm, and a flow rate of the carrier gas can be in a range from about 10 sccm to about 400 sccm. A pressure of the selective CVD can be in a range from about 0.2 mTorr to about 20 mTorr. A temperature of the selective CVD can be less than or equal to about 200° C., such as in a range from room temperature (e.g., about 23° C.) to about 200° C. 
     As illustrated in  FIG.  5   , an upper surface of the conductive via  60  is convex. In other examples, an upper surface of the conductive via  60  can be concave or planar. Various examples of configurations for the conductive via  60  formed in the via opening  42 , and details thereof, are illustrated in and described with respect to  FIGS.  13  through  18   . 
     As illustrated in  FIG.  5   , some residual deposition sites  62  may be formed during the selective deposition used to form the conductive via  60 . The residual deposition sites  62  may be formed on various surfaces, such as surfaces of the second ESL  30  and the liner  52  in the trench  40 . 
       FIG.  6    and operation  220  of the method  200  illustrate the performance of a selective etch back that removes the residual deposition sites  62 . The etch back can be a dry (e.g., plasma) etch process, a wet etch process, or a combination thereof. A plasma etch process can include using a fluorocarbon (C x F y ) gas, a chlorofluorocarbon (C x Cl y F z ) gas, a carbon chloride (C x Cl y ) gas, the like or a combination thereof. A wet etch process can include using one or more solutions of standard clean-1 (SC1), standard clean-2 (SC2), sulfuric acid-hydrogen peroxide mixture (SPM), diluted hydrofluoric (dHF) acid, hydrogen peroxide (H 2 O 2 ), buffered oxide etch (BOE) solution, hydrochloric (HCl) acid, the like, or a combination thereof. A temperature of the solution can be in a range from about 20° C. to about 90° C., and a duration of immersion of the substrate in the solution can be in a range from about 10 seconds to about 120 seconds. 
       FIG.  7    and operation  222  of the method  200  illustrate the performance of a nucleation enhancement treatment along, e.g., exposed surfaces in the trench  40  including an upper surface of the conductive via  60 , to form treated surfaces  70 . Generally, the nucleation enhancement treatment breaks bonds along, e.g., exposed surfaces in the trench  40  to enhance the ability for adsorption of material in a subsequent deposition process. In some examples, the nucleation enhancement treatment includes sputtering (operation  224 ), implantation (operation  226 ), a plasma treatment (operation  228 ), an ultra-violet (UV) treatment (operation  230 ), plasma doping (operation  232 ), the like, or a combination thereof. The nucleation enhancement treatment can be directional (e.g., anisotropic) or conformal (e.g., isotropic). In some examples, the nucleation enhancement treatment can treat, e.g., vertical surfaces, albeit to a lesser extent than, e.g., horizontal surfaces. The extent to which the nucleation enhancement treatment is performed (e.g., the extent to which bonds are broken along surfaces) can affect a number of nucleation sites and, therefore, at least an initial deposition rate for a later deposited conductive fill material  80 , as will be described subsequently. Generally, the more bonds that are broken and the more dangling bonds that are created, the more nucleation sites may be available for adsorption and nucleation of the conductive fill material  80  for an increased deposition rate, at least initially in the deposition. In some examples, the nucleation enhancement treatment can be directional to treat substantially only horizontal surfaces (e.g., a top surface of the second ESL  30  and upper surface of the conductive via  60  exposed by the trench  40 ), which can enable bottom-up deposition of a conductive fill material in the trench  40  and reduce seams and voids being formed in the conductive fill material in the trench  40 . 
     In an example, the nucleation enhancement treatment is sputtering (operation  224 ) using argon (Ar) gas. A flow rate of the argon gas can be in a range from about 10 sccm to about 2,000 sccm. A pressure of the sputtering can be in a range from about 0.5 mTorr to about 50 mTorr, and a temperature of the sputtering can be in a range from about −20° C. to about 120° C. A power of the plasma generator of the sputtering can be in a range from about 100 W to about 2,000 W, and a frequency of the plasma generator can be about 13.56 MHz or greater. The substrate can be biased during the sputtering in a range from about 50 V to about 300 V. The sputtering can be directional (e.g., treats horizontal surfaces), although in some examples, the sputtering can be conformal. The sputtering can cause argon to be deposited on the treated surfaces  70  and/or embedded in the respective materials to a depth below the treated surfaces  70 . For example, the species used for the sputtering (e.g., argon) can be embedded into the materials that form the treated surface  70  (e.g., the conductive via  60 , the second ESL  30 , the liners  52  in the trench  40 , and the third dielectric layer  32 ) to a depth of the respective materials from the treated surfaces  70  equal to or less than about 2 nm and at a concentration in a range from about 1×10 18  cm −3  to about 1×10 19  cm −3 . The concentration of the species can decrease from a peak proximate to the respective treated surfaces  70  to a depth in the material. The sputtering can break bonds by the species colliding with atoms of the material that is exposed (e.g., the treated surfaces  70 ). 
     In another example, the nucleation enhancement treatment is a beam line implantation (operation  226 ). The species implemented for the beam line implantation can include silicon (Si), germanium (Ge), carbon (C), nitrogen (N), argon (Ar), the like, or a combination thereof. An implantation energy can be in a range from about 2 keV to about 10 keV. A dosage of the implantation can be in a range from about 10 13  cm −2  to about 2×10 15  cm −2 . The implantation can be to a depth from a respective exposed surface in a range from about 1 nm to about 4 nm and to a concentration of the implanted species in a range from about 5×10 18  cm −3  to about 5×10 21  cm −3 . The concentration of the species can decrease from a peak proximate to the respective treated surfaces  70  to a depth in the material. The beam line implantation can be directional, although in some examples, multiple implantations may be performed to achieve a more conformal treatment. The beam line implantation can break bonds by the implanted species colliding with atoms of the material that is implanted (e.g., the treated surfaces  70 ). 
     In a further example, the nucleation enhancement treatment is a plasma treatment (operation  228 ). The plasma treatment can include using a gas comprising xenon (Xe), argon (Ar), hydrogen (H 2 ), nitrogen (N 2 ), the like or a combination thereof. A flow rate of the gas can be in a range from about 10 sccm to about 2,000 sccm. A pressure of the plasma treatment can be in a range from about 10 mTorr to about 100 mTorr, and a temperature of the plasma treatment can be in a range from about −20° C. to about 60° C. A power of the plasma generator of the plasma treatment can be in a range from about 20 W to about 200 W, and a frequency of the plasma generator can be about 13.56 MHz or greater. The substrate during the plasma treatment can be biased in a range from about 50 V to about 300 V. The species of the plasma can damage the exposed surfaces and can diffuse into the exposed surfaces. The plasma treatment can be conformal or directional. The plasma treatment can cause the species of the plasma to be embedded on the treated surfaces  70  and/or diffused in the respective materials to a depth below the treated surfaces  70 . For example, the species used for the plasma (e.g., xenon, argon, hydrogen, etc.) can be diffused into the materials that form the treated surface  70  (e.g., the conductive via  60 , the second ESL  30 , the liners  52  in the trench  40 , and the third dielectric layer  32 ) to a depth of the respective materials from the treated surface  70  equal to or less than about 5 nm and at a concentration in a range from about 1×10 18  cm −3  to about 1×10 20  cm −3 . The concentration of the species can decrease from a peak proximate to the respective treated surfaces  70  to a depth in the material. 
     In a yet further example, the nucleation enhancement treatment is a UV treatment (operation  230 ). The UV treatment can include exposing the substrate to UV light in an ambient. The ambient can include a gas comprising argon (Ar), neon (Ne), xenon (Xe), the like, or a combination thereof. An energy of the UV light exposure can be in a range from about 3.4 eV to about 10 eV. A duration of the UV light exposure can be equal to or less than about 300 seconds, such as in a range from about 15 seconds to about 300 seconds. The UV treatment can cause bonds on the exposed surfaces to break thereby damaging the exposed surfaces. The species of the ambient during the UV treatment can diffuse into the exposed surfaces. For example, the species of the ambient (e.g., xenon, argon, neon, etc.) can diffuse into the materials that form the treated surface  70  (e.g., the conductive via  60 , the second ESL  30 , the liners  52  in the trench  40 , and the third dielectric layer  32 ) to a depth of the respective materials from the treated surface  70  equal to or less than about 5 nm. A concentration of the species can decrease from a peak proximate to the respective treated surfaces  70  to a depth in the material. The UV treatment can be directional, although in some examples, multiple UV treatment may be performed to achieve a more conformal treatment. 
     In an even further example, the nucleation enhancement treatment is plasma doping (operation  232 ). The species implemented for the plasma doping can include boron (B), argon (Ar), the like, or a combination thereof. The doping can be to a depth from a respective exposed surface in a range from about 1 nm to about 5 nm and to a concentration in a range from about 1×10 19  cm −3  to about 1×10 20  cm −3 . The concentration of the species can decrease from a peak proximate to the respective treated surfaces  70  to a depth in the material. The plasma doping can break bonds by the implanted species colliding with atoms of the material that is implanted (e.g., the treated surfaces  70 ). 
       FIG.  8    and operation  234  of the method  200  illustrates the formation of a conductive fill material  80  on the treated surfaces  70 , e.g., filling the trench  40 . The formation of the conductive fill material  80  may be by a deposition process that deposits the conductive fill material  80  on dielectric surfaces as well as metallic surfaces. The nucleation enhancement treatment described with respect to  FIG.  7    can create nucleation sites on dielectric surfaces (e.g., on the treated surfaces  70 ) on which the conductive fill material  80  can be adsorbed during deposition. Hence, the deposition of the conductive fill material  80  can be a bottom-up deposition and/or a conformal deposition, such as depending on the directionality of the nucleation enhancement treatment. In a bottom-up deposition, seams can be avoided by having a single growth front of the conductive fill material  80  that propagates vertically in the trench  40 . 
     As a result of a conformal deposition, seams  82  can be formed in the conductive fill material  80  in the trench  40 . The seams  82  can result from the merging or coalescing of different growth fronts of the conductive fill material  80  during the conformal deposition. For example, a growth front originating from a sidewall surface of the liner  52  along a sidewall of the third dielectric layer  32  can coalesce or merge with a growth front originating from a top surface of the second ESL  30  to form at least a portion of a seam  82 . The seams  82  may each include, for example, one or more voids, grain boundaries of the conductive fill material  80 , and/or other indications of the coalescing or merging of growth fronts. A seam  82  can have an angle  86  with respect to a vertical direction (e.g., perpendicular to the top surface of the second ESL  30 ). The angle  86  can be in a range from about 25° to about 75°, and more particularly, from about 30° to about 60°. The angle  86  can be affected by the proximity of the sidewall surface of the liner  52  to the conductive via  60 . In some examples, the growth rate of the conductive fill material  80  is greater from the conductive via  60  than from dielectric surfaces, such as the sidewall of the liner  52 , such as by about two to about three times. Hence, in such examples, the closer the sidewall of the liner  52  is to the conductive via  60 , the smaller the angle  86  may be. 
     In some examples, the deposition of the conductive fill material  80  includes using a CVD, an electroless plating or deposition, or another deposition process. The conductive fill material  80  can be or include a metal, such as ruthenium (Ru), nickel (Ni), molybdenum (Mo), cobalt (Co), tungsten (W), copper (Cu), the like, or a combination thereof. In some examples, the conductive fill material  80  is or includes ruthenium (Ru), molybdenum (Mo), cobalt (Co), or tungsten (W) deposited by CVD. Example precursors for ruthenium include triruthenium dodecacarbonyl (Ru 3 (CO) 12 ), CHORUS, the like, or a combination thereof. Example precursors for molybdenum include molybdenum(V) chloride (MoCl 5 ), Mo(CO) 5 , the like, or a combination thereof. Example precursors for cobalt include dicobalt hexacarbonyl tert-butylacetylene (CCTBA), the like, or a combination thereof. Example precursors for tungsten include tungsten hexafluoride (WF 6 ), tungsten(V) chloride (WCl 5 ), the like, or a combination thereof. A flow rate of the precursor gas during the CVD can be in a range from about 10 sccm to about 200 sccm, and a flow rate of a carrier gas (e.g., argon (Ar)) can be in a range from about 100 sccm to about 800 sccm. A pressure of the CVD can be in a range from about 0.2 mTorr to about 20 mTorr. A temperature of the CVD can be less than or equal to about 175° C., such as in a range from 120° C. to 170° C. (particularly for ruthenium deposition, for example). In other examples, nickel can be deposited using electroless plating or deposition. An anneal or reflow may be performed after the conductive fill material  80  is deposited. 
     In some examples, a silicide and/or a carbide can be formed along the treated surfaces  70  of dielectric material that includes silicon and/or carbon, respectively. For example, assuming that the liner  52  and second ESL  30  include silicon, the nucleation enhancement treatment can cause the silicon to have a dangling bond at the treated surfaces  70 , and a metal of the conductive fill material  80  can attach to the dangling bond and/or react with the silicon of the treated surfaces  70  to form a silicide at an interface between the conductive fill material  80  and the liner  52  or second ESL  30 . The metal of the conductive fill material  80  can attach to the dangling bond and/or react with the silicon of the treated surfaces  70  during the deposition of the conductive fill material  80  (e.g., when a precursor is flowed on the treated surfaces  70 ) and/or subsequent to the deposition of the conductive fill material  80 . Similarly, for example, assuming that the liner  52  and second ESL  30  include carbon, the nucleation enhancement treatment can cause the carbon to have a dangling bond at the treated surfaces  70 , and a metal of the conductive fill material  80  can attach to the dangling bond and/or react with the carbon of the treated surfaces  70  to form a carbide (e.g., a metal carbide) at an interface between the conductive fill material  80  and the liner  52  or second ESL  30 . The metal of the conductive fill material  80  can attach to the dangling bond and/or react with the carbon of the treated surfaces  70  during the deposition of the conductive fill material  80  (e.g., when a precursor is flowed on the treated surfaces  70 ) and/or subsequent to the deposition of the conductive fill material  80 . With the dangling and/or broken bonds of the silicon and/or carbon of the treated surfaces  70 , a silicide and/or carbide can be formed at the treated surfaces  70  to enhance nucleation of the conductive fill material  80  and to promote adhesion of the conductive fill material  80  to dielectric layers, such as the liner  52  and the second ESL  30 . 
     In some examples, a metal of the conductive via  60  may form a metal alloy or compound with a metal of the conductive fill material  80  at the treated surface  70  of the conductive via  60 . The nucleation enhancement treatment may break bonds at the treated surface  70  of the conductive via  60  to permit the mixing and/or reacting of metals of the conductive via  60  and the conductive fill material  80  at the treated surface  70  of the conductive via  60 . The metal of the conductive fill material  80  can mix and/or react with the metal of the conductive via  60  at the treated surfaces  70  during the deposition of the conductive fill material  80  (e.g., when a precursor is flowed on the treated surfaces  70 ) and/or subsequent to the deposition of the conductive fill material  80 . The conductive via  60  and the conductive fill material  80  may be electrically connected without significant resistance caused by the species used in the nucleation enhancement treatment to form the treated surface  70 . 
     Even further, in some examples, a species used in the nucleation enhancement treatment may be embedded in or on the treated surfaces  70 , such as by adsorption, diffusion, and/or implantation, and the species may react with the conductive fill material  80 . For example, silicon or germanium implanted in the treated surfaces  70  can react with a metal of the conductive fill material  80  to form a metal-semiconductor compound (e.g., silicide or germanocide, respectively). As another example, carbon implanted in the treated surfaces  70  can react with a metal of the conductive fill material  80  to form a metal carbide, or nitrogen implanted in the treated surfaces  70  can react with a metal of the conductive fill material  80  to form a metal nitride. Other compounds can be formed in other examples. 
     In some examples, a species used in the nucleation enhancement treatment may be embedded in or on the treated surfaces  70  and may remain un-reacted with other material. For example, inert species, such as argon, can remain un-reacted at or proximate to the treated surfaces  70 . Un-reacted species can diffuse into the respective dielectric layers. Depending on the nucleation enhancement treatment, a highest concentration of the un-reacted species may be at the treated surface  70  (e.g., of a dielectric layer or the conductive via  60 ) and decrease from the treated surface  70  in a direction into the respective dielectric layer or the conductive via  60 , or can increase from the treated surface  70  in a direction into the respective dielectric layer or the conductive via  60  to a peak concentration before decreasing along that direction, such as when the species is implanted by beam line implantation, plasma doping, or a similar technique. 
     The extent to which a species used in the nucleation enhancement treatment may be embedded in or on different treated surfaces  70  may depend on the directionality of the nucleation enhancement treatment. For example, a highly directional nucleation enhancement treatment, such as a beam line implantation, can cause some surfaces to have more of the species embedded therein or thereon than other surfaces. Specifically, in some examples, horizontal surfaces (e.g., a top surface of the second ESL  30 ) can have more of the species embedded therein or thereon than vertical surfaces (e.g., sidewalls of the liner  52 ). In some examples, multiple directional nucleation enhancement treatments can be performed at different directions to obtain a more even treatment between different surfaces, such as multiple beam line implantations at different implant angles. 
       FIG.  9    illustrates the removal of excess conductive fill material  80  to form a conductive line  84  in the third dielectric layer  32 . Excess conductive fill material  80  and the treated surface  70  of the third dielectric layer  32  can be removed using a planarization process, such as a CMP. The third dielectric layer  32  may further be thinned by the planarization process, which may remove the rounded corners of the trench  40  in some examples. The third dielectric layer  32  is thinned to a thickness in a range from about 10 nm to about 30 nm in some examples. The removal of the excess conductive fill material  80  and treated surface  70  of the third dielectric layer  32  can form the top surfaces of the conductive fill material  80  and the third dielectric layer  32  to be coplanar. The seams  82 , as described above, can remain in the conductive line  84 . In some examples, the seams  82  may be cured or removed by an anneal or other thermal process used during processing. An interconnect structure, such as a dual damascene interconnect structure, can be formed, as illustrated in  FIG.  9   , comprising a conductive via  60  and a conductive line  84 . 
       FIG.  10    illustrates the formation of a third ESL  90  and fourth dielectric layer  92  over the third dielectric layer  32 , conductive line  84 , and liner  52  along the sidewalls of the trench  40 , and with a conductive feature  94  through the third ESL  90  and fourth dielectric layer  92  contacting the conductive line  84 . The third ESL  90  can be deposited on the third dielectric layer  32 , conductive line  84 , and liner  52 . The third ESL  90  may comprise or be silicon nitride, silicon carbon nitride, silicon carbon oxide, carbon nitride, the like, or a combination thereof, and may be deposited by CVD, PECVD, ALD, or another deposition technique. The fourth dielectric layer  92  is deposited over the third ESL  90 . For example, the fourth dielectric layer  92  may be or include an IMD. The fourth dielectric layer  92 , for example, may be or comprise a low-k dielectric having a k-value less than about 4.0, such as about 2.0 or even less. In some examples, the fourth dielectric layer  92  comprises silicon oxide, PSG, BPSG, FSG, SiO x C y , silicon carbon material, a compound thereof, a composite thereof, or a combination thereof. The fourth dielectric layer  92  may be deposited using a CVD, such as PECVD or FCVD; spin-on coating; or another deposition technique. In some examples, a CMP or another planarization process may be performed to planarize the top surface of the fourth dielectric layer  92 . 
     The conductive feature  94  contacting the conductive line  84  may be or include, for example, a conductive via or another conductive feature. The conductive feature  94  may be formed using a damascene process, such as a dual damascene process. For example, the conductive feature  94  may be formed using the process described above with respect to and illustrated in  FIGS.  2  through  9    or using a similar process. 
     As is apparent from the foregoing, a seed layer and a metal-containing barrier layer are not deposited in the described examples for forming the conductive via  60  and conductive line  84 . In the illustrated and described examples, no seed layer and no metal-containing barrier layer is deposited (i) between the conductive line  84  and any dielectric layer on or in which it is disposed (e.g., the third dielectric layer  32  or second ESL  30 ), (ii) between the conductive via  60  and any dielectric layer in which it is disposed (e.g., the second ESL  30 , second dielectric layer  28 , or first ESL  26 ), or (iii) between the conductive via  60  and the conductive line  84 . Some embodiments can implement a seed layer and/or a metal-containing barrier layer. Further, although a species of the nucleation enhancement treatment may react with a metal of the conductive line  84  (e.g., the conductive fill material  80 ) and/or the conductive via  60 , such as at the treated surface  70  of the conductive via  60  (e.g., an interface between the conductive via  60  and the conductive line  84 ), the resulting material may be thinner and/or have a lower concentration of the species than a deposited barrier layer, and hence, may, in some instances, not be a diffusion barrier. For example, in some examples implementing a nucleation enhancement treatment, the species can have a concentration of less than or equal to about 5 atomic percent (at. %), such as in a range from about 0.1 at. % to about 5 at. %, in the conductive line  84  (e.g., the conductive fill material  80 ) and/or the conductive via  60  at the respective treated surfaces. The concentration of the species in the conductive line  84  (e.g., the conductive fill material  80 ) and/or the conductive via  60  can be discontinuous because of the low concentration of the species therein. Further, the species and conductive material of the conductive line  84  and/or the conductive via  60  may not be in a stable phase of a corresponding compound of the materials (e.g., a metal compound). 
       FIGS.  13  through  18    illustrate various details and/or modifications to a portion of the cross-sectional view of the intermediate structure of  FIG.  6   , in accordance with some embodiments.  FIGS.  13  through  18    illustrate additional details and/or modifications to the via opening  42  formed in  FIG.  2    and the corresponding conductive via  60  formed in the via opening  42  in  FIGS.  5  and  6   .  FIGS.  13  through  18    each illustrate the first ESL  26  over the conductive feature  24 , the second dielectric layer  28  over the first ESL  26 , and the second ESL  30  over the second dielectric layer  28 . Although the via opening  42  is not specifically identified in  FIGS.  13  through  18   , a person having ordinary skill in the art will readily understand, upon viewing the figures, that sidewalls of the first ESL  26 , second dielectric layer  28 , and second ESL  30 , between which the conductive via  60  is disposed, are sidewalls of the via opening  42  formed in  FIG.  2   . The via opening  42  in  FIGS.  13  through  18    has a first dimension D 1  (e.g., a depth) from a top surface of the conductive feature  24  exposed by the via opening  42  to the top surface of the second ESL  30 . The first dimension D 1  may correspond to a combined thickness of the first ESL  26 , second dielectric layer  28 , and second ESL  30 . The first dimension D 1  can be in a range from about 8 nm to about 40 nm, and more particularly, from about 10 nm to about 30 nm, such as about 25 nm. 
     In  FIGS.  13  and  14   , the via opening  42  has sidewalls (e.g., the sidewalls of the first ESL  26 , second dielectric layer  28 , and second ESL  30  on which the liner  52  is formed) that are substantially vertical with rounding at upper corners. The via opening  42  has a second dimension D 2  (e.g., width) at a bottom of the via opening  42  (e.g., at the top surface of the conductive feature  24 ) in  FIGS.  13  and  14   , and has a third dimension D 3  (e.g., width) in a plane of a top surface of the second ESL  30 . The second dimension D 2 , in some examples, is in a range from about 8 nm to about 14 nm, and the third dimension D 3 , in some examples, is in a range from about 13 nm to about 19 nm. A first aspect ratio of the first dimension D 1  to the second dimension D 2  can be in a range from about 0.7 to about 3.75, and a second aspect ratio of the first dimension D 1  to the third dimension D 3  can be in a range from about 0.53 to about 2.31. 
     In  FIGS.  15  and  16   , the via opening  42  has vertical sidewalls (e.g., the sidewalls of the first ESL  26 , second dielectric layer  28 , and second ESL  30  on which the liner  52  is formed are vertical). Hence, a cross-section of the via opening  42  is rectangular. The via opening  42  has a sixth dimension D 6  (e.g., width) at a bottom of the via opening  42  (e.g., at the top surface of the conductive feature  24 ) in  FIGS.  15  and  16   . The dimension (e.g., width) of the via opening  42  in a plane of a top surface of the second ESL  30  is equal to the sixth dimension D 6  due to the vertical sidewalls. The sixth dimension D 6 , in some examples, is in a range from about 8 nm to about 14 nm. An aspect ratio of the first dimension D 1  to the sixth dimension D 6  can be in a range from about 0.7 to about 3.75. 
     In  FIGS.  17  and  18   , the via opening  42  has non-vertical or sloped sidewalls (e.g., the sidewalls of the first ESL  26 , second dielectric layer  28 , and second ESL  30  on which the liner  52  is formed are non-vertical or are sloped). Hence, a cross-section of the via opening  42  can have a positive taper profile, as illustrated, and in other examples, a cross-section of the via opening  42  can be a reentrant profile. The via opening  42  has a ninth dimension D 9  (e.g., width) at a bottom of the via opening  42  (e.g., at the top surface of the conductive feature  24 ) in  FIGS.  17  and  18   , and has a tenth dimension D 10  (e.g., width) in a plane of a top surface of the second ESL  30 . The ninth dimension D 9 , in some examples, is in a range from about 8 nm to about 14 nm, and the tenth dimension D 10 , in some examples, is in a range from about 13 nm to about 19 nm. A first aspect ratio of the first dimension D 1  to the ninth dimension D 9  can be in a range from about 0.7 to about 3.75, and a second aspect ratio of the first dimension D 1  to the tenth dimension D 10  can be in a range from about 0.53 to about 2.13. 
     In  FIGS.  13 ,  15 , and  17   , the conductive via  60  has a convex upper surface  100 ,  104 , and  108  (e.g., convex meniscus) that protrudes above the top surface of the second ESL  30 . A cross section of the convex upper surface  100 ,  104 , and  108  can be a partial circle (e.g., semi-circular), a partial ellipse (e.g., semi-ellipse), or another shape. The convex upper surface  100 ,  104 , and  108  can have an upper-most point at a level above the top surface of the second ESL  30 , for example, and a bottom portion of the convex top surface can be at a level above, at a level of, or at a level below the top surface of the second ESL  30 . As illustrated, an upper-most point of the convex upper surface  100 ,  104 , and  108  protrudes above the top surface of the second ESL  30  by a fourth dimension D 4 , a seventh dimension D 7 , and an eleventh dimension D 11 , respectively. The fourth dimension D 4 , seventh dimension D 7 , and an eleventh dimension D 11  can be in a range from about 0 nm to about the respective second dimension D 2 , sixth dimension D 6 , and ninth dimension D 9 . In other examples, an upper-most point of the convex upper surface  100 ,  104 , and  108  can be at a level of or at a level below the top surface of the second ESL  30 . 
     In  FIGS.  14 ,  16 , and  18   , the conductive via  60  has a concave upper surface  102 ,  106 , and  110  (e.g., concave meniscus) that is below the top surface of the second ESL  30 . A cross section of the concave upper surface  102 ,  106 , and  110  can be a partial circle (e.g., semi-circular), a partial ellipse (e.g., semi-ellipse), or another shape. The concave upper surface  102 ,  106 , and  110  can have a lower-most point at a level below the top surface of the second ESL  30 . Upper portions of the concave upper surface  102 ,  106 , and  110  can be at a level above, at a level of, or at a level below the top surface of the second ESL  30 . In some examples, a lower-most point of the concave upper surface  102 ,  106 , and  110  is at a level above or at a level of the top surface of the second ESL  30 . As illustrated, a lower-most point of the concave upper surface  102 ,  106 , and  110  is below the top surface of the second ESL  30  by a fifth dimension D 5 , an eighth dimension D 8 , and a twelfth dimension D 12 , respectively. The fifth dimension D 5 , eighth dimension D 8 , and twelfth dimension D 12  can each be in a range from about 0 nm to about two-thirds of the first dimension D 1  (e.g., (⅔)×D 1 ). In further examples, the top surface can have other shapes, such as being planar, and can be at any level with respect to the top surface of the second ESL  30  and/or another dielectric layer. 
     Some embodiments may achieve advantages. As previously described, a seed layer and/or barrier layer may be obviated by some embodiments. Without a seed layer and/or barrier layer, resistance of an interconnect structure can be reduced, thereby reducing a resistance-capacitance (RC) delay and increasing device speed. Further, deposition of a conductive fill material in forming the interconnect structure may be by a bottom-up deposition and/or a conformal deposition as a result of the nucleation enhancement treatment. The bottom-up deposition and/or conformal deposition can decrease an amount of time to fill a trench, which can increase throughput during processing and decrease costs. Example embodiments may be applied at any technology node, and may be particularly applicable to advanced technology nodes, such as 20 nm and smaller. 
     An embodiment is a method. An interconnect opening is formed through one or more dielectric layers over a semiconductor substrate. The interconnect opening has a via opening and a trench over the via opening. A conductive via is formed in the via opening. A nucleation enhancement treatment is performed on one or more exposed dielectric surfaces of the trench. A conductive line is formed in the trench on the one or more exposed dielectric surfaces of the trench and on the conductive via. 
     Another embodiment is a structure. The structure includes a semiconductor substrate, one or more dielectric layers over the semiconductor substrate, and an interconnect structure disposed in the one or more dielectric layers. The interconnect structure includes a conductive via and a conductive line over the conductive via. The conductive line is disposed over a horizontal surface of the one or more dielectric layers. A same species is disposed at the horizontal surface of the one or more dielectric layers and a surface of the conductive via at an interface between the conductive via and a conductive fill material of the conductive line. 
     A further embodiment is a method. A dual damascene opening is formed through one or more dielectric layers over a semiconductor substrate. The dual damascene opening includes a trench and a via opening. A conductive via is formed in the via opening. A number of nucleation sites on dielectric surfaces exposed in the trench is increased by breaking chemical bonds of the dielectric surfaces exposed in the trench. A conductive fill material is deposited in the trench by adsorbing the conductive fill material on the increased number of nucleation sites. Depositing the conductive fill material does not include using a seed layer. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.