Patent Publication Number: US-11398406-B2

Title: Selective deposition of metal barrier in damascene processes

Description:
PRIORITY CLAIM AND CROSS-REFERENCE 
     This application claims the benefit of the following provisionally filed U.S. Patent application: Application Ser. No. 62/738,414, filed Sep. 28, 2018, and entitled “Selective Deposition of Metal Barrier in Damascene Processes,” which application is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     Integrated circuits include interconnect structures, which comprise metal lines and vias to serve as three-dimensional wiring structures. The function of the interconnect structures is to properly connect densely packed devices together. 
     Metal lines and vias are formed in the interconnect structure. Metal lines and vias are typically formed by damascene processes, in which trenches and via openings are formed in dielectric layers. A barrier layer is then deposited, followed by the filling of the trenches and via openings with copper. After a Chemical Mechanical Polish (CMP) process, the top surfaces of the metal lines are leveled, leaving metal lines and vias. 
    
    
     
       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 9  illustrate the cross-sectional views of intermediate stages in the formation of a metal line and a via in accordance with some embodiments. 
         FIG. 10  illustrates a chemical structure of Benzotriazole (BTA) in accordance with some embodiments. 
         FIG. 11  illustrates a chemical structure of Bis-triazolyl indoleamine in accordance with some embodiments. 
         FIG. 12  illustrates a schematic top view of discrete portions of a conductive barrier layer at the bottom of a via opening in accordance with some embodiments. 
         FIG. 13  illustrates a contact angle of water with a BTA surface in accordance with some embodiments. 
         FIG. 14  illustrates a contact angle of water with a bare copper surface in accordance with some embodiments. 
         FIG. 15  illustrates experimental results revealing resistance values of vias formed by a plurality of formation processes in accordance with some embodiments. 
         FIG. 16  illustrates the growth delay of barrier layers formed in a plurality of formation processes in accordance with some embodiments. 
         FIG. 17  illustrates the comparison of thicknesses of conductive barrier layers on different surfaces (and formed by different processes) in accordance with some embodiments. 
         FIG. 18  illustrates a process flow for forming a metal line and a via in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. 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 “underlying,” “below,” “lower,” “overlying,” “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. 
     A method of selectively forming a conductive barrier layer for a conductive feature is provided in accordance with various embodiments. The intermediate stages in the formation of the conductive feature are illustrated in accordance with some embodiments. Some variations of some embodiments are discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements. In accordance with some embodiments of the present disclosure, the formation of the conductive feature includes selectively forming a conductive barrier layer in an opening, filling a metallic material, and performing a planarization. The selective formation of the conductive barrier layer is achieved through forming an inhibitor film on an underlying metal feature, depositing the conductive barrier layer, with a delayed growth achieved on the inhibitor film, so that the conductive barrier layer is selectively grown on the sidewalls of the via opening, with very little (if any) conductive barrier layer being formed on the inhibitor film. After the conductive barrier layer is formed, a treatment is performed to remove the inhibitor film. The remaining opening is then filled with a metallic material such as copper. 
       FIGS. 1 through 9  illustrate the cross-sectional views of intermediate stages in the formation of a via in accordance with some embodiments of the present disclosure. The corresponding processes are also reflected schematically in the process flow  200  as shown in  FIG. 18 . 
       FIG. 1  illustrates a cross-sectional view of package component  100 . In accordance with some embodiments of the present disclosure, package component  100  is a device wafer (such as a logic device wafer) including active devices such as transistors and/or diodes, and possibly passive devices such as capacitors, inductors, resistors, or the like. In accordance with alternative embodiments of the present disclosure, package component  100  is an interposer wafer, which may or may not include active devices and/or passive devices. In accordance with yet alternative embodiments of the present disclosure, package component  100  is a package substrate strip, which may include package substrates with cores therein or core-less package substrates. In subsequent discussion, a device wafer is used as an example of the package component  100 . The teaching of the present disclosure may also be applied to interposer wafers, package substrates, packages, etc. 
     In accordance with some embodiments of the present disclosure, package component  100  includes semiconductor substrate  20  and the features formed at a top surface of semiconductor substrate  20 . Semiconductor substrate  20  may comprise crystalline silicon, crystalline germanium, silicon germanium, a III-V compound semiconductor such as GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, GaInAsP, or the like. Semiconductor substrate  20  may also be a bulk silicon substrate or a Silicon-On-Insulator (SOI) substrate. Shallow Trench Isolation (STI) regions (not shown) may be formed in semiconductor substrate  20  to isolate the active regions in semiconductor substrate  20 . Although not shown, through-vias may be formed to extend into semiconductor substrate  20 , wherein the through-vias are used to electrically inter-couple the features on opposite sides of package component  100 . 
     In accordance with some embodiments of the present disclosure, package component  100  is used to form a device die. In these embodiments, integrated circuit devices  22  are formed on the top surface of semiconductor substrate  20  The examples of integrated circuit devices  22  include Complementary Metal-Oxide Semiconductor (CMOS) transistors, resistors, capacitors, diodes, or the like. The details of integrated circuit devices  22  are not illustrated herein. In accordance with alternative embodiments, package component  100  is used for forming interposers. In accordance with these embodiments, substrate  20  may also be a dielectric substrate. 
     Further illustrated in  FIG. 1  is dielectric layer  24 . Dielectric layer  24  may be an Inter-Layer Dielectric (ILD) or an Inter-Metal Dielectric (IMD). In accordance with some embodiments of the present disclosure, Dielectric layer  24  is an ILD, in which contact plugs are formed. The corresponding dielectric layer  24  may be formed of Phospho Silicate Glass (PSG), Boro Silicate Glass (BSG), Boron-Doped Phospho Silicate Glass (BPSG), Fluorine-Doped Silicate Glass (FSG), a silicon oxide layer (formed using Tetra Ethyl Ortho Silicate (TEOS)), or the like. Dielectric layer  24  may be formed using spin-on coating, Atomic Layer deposition (ALD), Flowable Chemical Vapor Deposition (FCVD), Chemical Vapor Deposition (CVD), Plasma-Enhanced Chemical Vapor Deposition (PECVD), Low-Pressure Chemical Vapor Deposition (LPCVD), or the like. In accordance with some embodiments of the present disclosure, Dielectric layer  24  is an IMD, in which metal lines and/or vias are formed. The corresponding dielectric layer  24  may be formed of a carbon-containing low-k dielectric material, Hydrogen SilsesQuioxane (HSQ), MethylSilsesQuioxane (MSQ), or the like. In accordance with some embodiments of the present disclosure, the formation of dielectric layer  24  includes depositing a porogen-containing dielectric material, and then performing a curing process to drive out the porogen, and hence the remaining dielectric layer  24  is porous. 
     In accordance with some embodiments of the present disclosure, Dielectric layer  24  is an IMD, in which metal lines and/or vias are formed. The corresponding dielectric layer  24  may be formed of a carbon-containing low-k dielectric material, Hydrogen SilsesQuioxane (HSQ), MethylSilsesQuioxane (MSQ), or the like. In accordance with some embodiments of the present disclosure, the formation of dielectric layer  24  includes depositing a porogen-containing dielectric material, and then performing a curing process to drive out the porogen, and hence the remaining dielectric layer  24  is porous. 
     Conductive feature  30  is formed in dielectric layer  24 . Conductive feature  30  may be a metal line, a conductive via, a contact plug, or the like. In accordance with some embodiments, conductive feature  30  includes diffusion barrier layer  26  and conductive filling material  28  over diffusion barrier layer  26 . Diffusion barrier layer  26  may be formed of a conductive material such as titanium, titanium nitride, tantalum, tantalum nitride, or the like. Conductive region  28  may be formed of copper, a copper alloy, aluminum, or the like. Diffusion barrier layer  26  has the function of preventing the diffusion of the material (such as copper) in conductive region  28  from diffusing into dielectric layer  24 . In accordance with some embodiments of the present disclosure, the formation of conductive feature  30  may also adopt the methods as discussed subsequently, so that the bottom portion of diffusion barrier layer is either not formed, or formed as discontinued including isolated islands. 
     As also shown in  FIG. 1 , etch stop layer  32  is formed over dielectric layer  24  and conductive feature  30 . The respective process is illustrated as process  202  in the process flow shown in  FIG. 18 . Etch stop layer  32  is formed of a dielectric material, which may include, and is not limited to, aluminum oxide, aluminum nitride, silicon nitride, silicon carbide, silicon oxynitride, silicon carbo-nitride, or the like. Etch stop layer  32  is formed of a material that has a high etching selectivity with relative to the overlying dielectric layer  34 , and hence etch stop layer  32  may be used to stop the etching of dielectric layer  34 . 
     Dielectric layer  34  is formed over etch stop layer  32 . The respective process is illustrated as process  204  in the process flow shown in  FIG. 18 . In accordance with some embodiments, dielectric layer  34  is an IMD or an ILD. Dielectric layer  34  may comprise a dielectric material such as an oxide, a nitride, a carbon-containing dielectric material, or the like. For example, dielectric layer  34  may be formed of PSG, BSG, BPSG, FSG, TEOS oxide, HSQ, MSQ, or the like. Dielectric layer  34  may also be a low-k dielectric layer having a low dielectric constant value lower than about 3.5 or lower than about 3.0. 
       FIGS. 2 through 8  illustrate the process for forming a metal line and a via in accordance with some embodiments. It is appreciated that the examples as shown in  FIGS. 2 through 8  recite a dual damascene process. In accordance with alternative embodiments, a single damascene process, in which a metal line, a via, a contact plug, or the like, is formed, which is also contemplated. 
     As shown in  FIGS. 2 and 3 , via opening  42  and trench  44  are formed through etching. The respective process is illustrated as process  206  in the process flow shown in  FIG. 18 . Via opening  42  and trench  44  may be formed using, for example, photolithography techniques. In an example of the formation process of via opening  42  and trench  44 , metal hard mask  37  is first formed and patterned, as shown in  FIG. 2 . Metal hard mask  37  may be formed of titanium nitride, boron nitride, or the like. Metal hard mask  37  is patterned to form an opening  38  therein, wherein opening  38  defines the pattern of the trench that is to be filled to form a metal line. Next, photo resist  40  is formed on metal hard mask  37 , and is then patterned to form an opening, through which dielectric layer  34  is formed. Dielectric layer  34  is then etched to form opening  42 . In accordance with some embodiments of the present disclosure, the etching of dielectric layer  34  is performed using a process gas comprising fluorine and carbon, wherein fluorine is used for etching, with carbon having the effect of protecting the sidewalls of the resulting opening. With an appropriate fluorine and carbon ratio, opening  42  may have a desirable profile. For example, the process gases for the etching include a fluorine and carbon-containing gas(es) such as C 4 F 8 , CH 2 F 2 , and/or CF 4 , and a carrier gas such as N 2 . In an example of the etching process, the flow rate of C 4 F 8  is in the range between about 0 sccm and about 50 sccm, the flow rate of CF 4  is in the range between about 0 sccm and about 300 sccm (with at least one of C 4 F 8  having a non-zero flow rate), and the flow rate of N 2  is in the range between about 0 sccm and about 200 sccm. In accordance with alternative embodiments, the process gases for the etching include CH 2 F 2  and a carrier gas such as N 2 . In an example of the etching process, the flow rate of CH 2 F 2  is in the range between about 10 sccm and about 200 sccm, and the flow rate of N 2  is in the range between about 50 sccm and about 100 sccm. 
     During the etching process, package component  100  may be kept at a temperature in the range between about 30° C. and about 60° C. In the etching process, plasma may be generated from the etching gases. The Radio Frequency (RF) power of the power source for the etching may be lower than about 700 Watts, and the pressure of the process gases is in the range from about 15 mTorr and about 30 mTorr. 
     The etching for forming opening  42  may be performed using a time-mode. As a result of the etching, opening  42  is formed to extend to an intermediate level between the top surface and the bottom surface of dielectric layer  34 . Next, photo resist  40  is removed, followed by the further etching of dielectric layer  34  using metal hard mask  37  as an etching mask. In the etching process, which is an anisotropic etching process, opening  42  extends down until etch stop layer  32  is exposed. At the same time opening  42  is extended downwardly, trench  44  is formed to extend into dielectric layer  34 , and the resulting structure is illustrated in  FIG. 3 . In the resulting structure, the final opening  42  is referred to as via opening  42 , which is underlying and connected to trench  44 . 
     In accordance with alternative embodiments, via opening  42  and trench  44  are formed in separate photo lithography processes. For example, in a first photo lithography process, via opening  42  is formed extending down to etch stop layer  32 . In a second lithography process, trench  44  is formed. The order for forming via opening  42  and trench  44  may also be inversed. 
     Next, referring to  FIG. 4 , etch stop layer  32  is etched-through. The respective process is illustrated as process  208  in the process flow shown in  FIG. 18 . The respective process may also be referred to as a wet clean process when the etching-through of etch stop layer  32  involves a wet etching. In accordance with some embodiments of the present disclosure, the etching solution includes glycol, dimethyl sulfide, amine, H 2 O 2 , and the like. Glycol may be used as a surfactant, dimethyl sulfide may be used as a solvent, amine may be used for removing undesirable organic substance on the surface of package component  100 , and H 2 O 2  and amine may be used etching etch stop layer  32 . 
     In addition to the above-recited chemicals, the etching solution may also include an inhibitor, which is used to protect the exposed portion of conductive filling material  28  (such as copper) from being undesirably etched once etch stop layer  32  is etched through. In accordance with some embodiments, the inhibitor includes benzotriazole (BTA). An example of the chemical structure of the BTA is illustrated in  FIG. 10 , which includes a benzo ring and three hydrogen atoms attached to the benzo ring. The chemical formula of the BTA is C 6 H 5 N 3 . 
     In accordance with other embodiments, the inhibitor is selected from other chemicals. These candidate inhibitor materials are hydrophobic, and are preferred to include non-polar groups. The hydrophobic property and the non-polar groups desirably make the candidate inhibitor materials difficult for the adsorption of precursor gases in subsequent deposition processes. The candidate inhibitor materials also have good chelation stability during and after the etching of etch stop layer  32 , and during the subsequent deposition of the conductive barrier layer. Also, the candidate inhibitor materials are removable during the subsequent post-deposition treatment, as will be discussed. For example, bis-triazolyl indoleamine may be used as inhibitor also. An example of the chemical structure of bis-triazolyl indoleamine is illustrated in  FIG. 11 . In  FIG. 11 , the symbol “R” represents a phenol group. The benzo rings in bis-triazolyl indoleamine also results in the hydrophobic and steric hindrance property, which properties are desirable. 
     As a result of adding the inhibitor into the etching solution, the inhibitor has residue left on the exposed surface of conductive region  28  (such as copper), resulting in the formation of inhibitor film  48 . Inhibitor film  48  is thin, and may have thickness T 1  in the range between about 1 nm and about 2 nm, while the thickness T 1  may be greater or smaller. The thickness T 1  is related to the type of inhibitor. Inhibitor film  48  may be a mono layer of the inhibitor such as a mono layer of the BTA.  FIG. 5  schematically illustrates a portion of the inhibitor film  48  and the underlying conductive region  28 . For example, when conductive region  28  comprises copper, copper atoms  29  at the surface of conductive region  28  are bonded to the nitrogen atoms in the BTA. The benzo rings of the BTA face outwardly. Since the benzo rings are unable to be bonded to other atoms (such as Ta atoms and nitrogen atoms in subsequently formed conductive barrier layer), steric hindrance is resulted. 
     It is desired that inhibitor film  48  has a good coverage, for example, 100 percent, or at least 90 percent or greater, of the exposed portion of conductive region  28 , so that no (or at least little) surface of conductive region  28  is exposed after the formation of inhibitor film  48 . The increase in the coverage may be achieved by prolonging the time for etching the etch stop layer and/or increasing the concentration of the inhibitor in the etching solution. It is realized, however, the prolonging of the etching time and the increase in the concentration are limited by other factors. For example, prolonging the etching time too much may cause undercuts to be formed in etch stop layer  32 , and increasing the concentration of inhibitor too much may cause the difficulty in etching the etch stop layer  32  due to the formation of the inhibitor film on etch stop layer  32 . In accordance with some embodiments of the present disclosure, the etching time is in the range between about 50 seconds and about 100 seconds. The concentration of the inhibitor in the etching solution may be in the range between about 0.5 weight percent and about 1.0 weight percent. 
     In accordance with some embodiments of the present disclosure, to increase the coverage of the inhibitor film  48  without causing the problems as aforementioned, additional processes are performed. In an example of the processes, the etch stop layer  32  is first etched. The etching solution may adopt what is discussed in preceding paragraph, which includes the inhibitor and other chemicals. The etching time and the concentration of the inhibitor are not excessive. As a result, the coverage of the inhibitor film is less than 100 percent of the exposed surface of conductive region  28 . For example, the coverage may be lower than about 50 percent. Next, package component  100  is taken out of the etching solution, followed by a cleaning process, for example, using de-ionized water, so that the residue etching solution is removed, while inhibitor film  48  is left unremoved. Next, an inhibitor film formation process is performed using an inhibitor-forming solution. Since this process is used for further growing inhibitor film  48 , but not for etching etch stop layer  32 , the chemicals that are used for etching etch stop layer  32  are not included in the inhibitor-forming solution. For example, amine and H 2 O 2  may not be included. Some other chemicals such as glycol, dimethyl sulfide, etc., however, may be added in the inhibitor-forming solution. An inhibitor (such as BTA), which may be the same or different from the inhibitor used in the etching chemical of etch stop layer  32 , is added into the inhibitor-forming solution. Package component  100  is then soaked in the inhibitor-forming solution to further grow, and to increase the coverage of, inhibitor film  48 . In accordance with some embodiments of the present disclosure, the soaking time is in the range between about 30 seconds and about 60 seconds. The concentration of the inhibitor in the inhibitor-forming solution may be in the range between about 0.5 weight percent (wt %) and about 2.0 wt %. After the soaking, inhibitor film  48  may achieve 100 percent coverage, or substantially 100 percent coverage (for example, more than 95 percent or more than 99 percent coverage). 
     Referring back to  FIG. 4 , at the same time inhibitor film  48  is formed on the surface of conductive region  28 , inhibitor film  48  may also be formed on the (sidewall) surface of etch stop layer  32 , with the corresponding portion of inhibitor film  48  having thickness T 2  smaller than thickness T 1 . The coverage of the corresponding portion of inhibitor film  48  on the sidewalls of etch stop layer  32  may be smaller than 100 percent, for example, smaller than about 50 percent, and is also smaller than the coverage on conductive region  28 . There is no inhibitor film  48  grown on the exposed surface of dielectric layer  34 . There may be, or may not be, inhibitor film  48  grown on metal hard mask  37 . Also, when inhibitor film  48  is grown on metal hard mask  37 , its thickness is smaller than thickness T 1 , and/or the coverage of the portions of inhibitor film  48  on metal hard mask  37  is smaller than 100 percent, for example, smaller than about 50 percent. 
     Next, referring to  FIG. 6 , conductive barrier layer  50  is deposited lining via opening  42  and trench  44 , for example, using Atomic Layer Deposition (ALD). The respective process is illustrated as process  210  in the process flow shown in  FIG. 18 . Conductive barrier layer  50  may include titanium, titanium nitride, tantalum, tantalum nitride, or the like, and has the function of preventing copper in the subsequently deposited copper-containing material  56  ( FIG. 9 ) from diffusing into dielectric layer  34 . In accordance with some embodiments of the present disclosure, conductive barrier layer  50  comprises TaN formed using ALD. The corresponding ALD cycle includes conducting a Ta-containing process gas such as Pentakis Dimethylamino Tantalum (C 10 H 30 N 5 Ta) into the respective ALD chamber, purging the Ta-containing process gas, conducting a nitrogen-containing process gas such as ammonia into the process chamber, and purging the nitrogen-containing process gas. There are a plurality of ALD cycles. After the formation of conductive barrier layer  50 , thickness T 4  of the portion of conductive barrier layer  50  on the sidewalls of dielectric layer  34  is great enough to act as a diffusion barrier. For example, thickness T 4  may be greater than about 15 Å. 
     An example of the reaction equations for forming TaN is as follows:
 
Ta(NMe 2 ) 5 +NH 3 →Ta(NH 2 ) 5 +Me 2 NH  [Eq. 1]
 
 x Ta(NH 2 ) 5 →-[Ta—N(H)-Ta] y -+ z NH 3  outgassing(heating)  [Eq. 2]
 
     Wherein “Me” represents methyl groups (CH 3 ). In accordance with other embodiments, the conductive barrier layer  50  may comprise other materials such as TiN. The corresponding process gases may include tetrakis dimethylamido titanium and ammonia, for example, which may be used in ALD cycles to form TiN. 
     Inhibitor film  48  delays the growth of conductive barrier layer  50 . This is due to the steric hindrance of the inhibitor film  48 , and the steric hindrance is at least partially due to its heterocyclic structure. For example, on inhibitor film  48 , there is a very small possibility of having a TaN molecule (assuming conductive barrier layer  50  comprises TaN) grown thereon in a ALD cycle, while on dielectric layer  34 , a full layer of TaN is grown in each ALD cycle. Accordingly, after one ALD cycle, a very small percentage of the exposed surface of inhibitor film  48  has the TaN grown thereon, which acts as the seed for the subsequent growth. Once the TaN is grown, the TaN will grow at the same rate as on dielectric layer  34 . After each cycle, a very small additional area of inhibitor film  48  is covered by the newly grown TaN. Accordingly, a large percent of the inhibitor film  48  does not have TaN grown thereon until after multiple ALD cycles. This effect is referred to as growth delay (or incubation delay) on the inhibitor film  48 , while there is no grow delay on dielectric layer  34  since no inhibitor film  48  is formed on dielectric layer  34 . There is a delay of the growth of conductive barrier layer  50  on the exposed surfaces of etch stop layer  32  and metal hard mask  37 , and the growth delay is less significant than the growth delay directly over conductive region  28 . 
     Due to the growth delay, and the random seeding of conductive barrier layer  50  on inhibitor film  48 , after the formation of conductive barrier layer  50  is finished, there may be substantially no conductive barrier layer  50  grown on inhibitor film  48 . Alternatively stated, conductive barrier layer  50  may not extend onto conductive region  28 . It is possible that a small amount of conductive barrier layer  50  is grown on inhibitor film  48 , with the coverage smaller than 100 percent and higher than 0 percent. In accordance with some embodiments, the coverage is in the range between about 20 percent and about 80 percent, or in the range between about 40 percent and about 60 percent. Conductive barrier layer  50  also forms discrete islands  50 ′ on the surface of conductive region  28 , which have random and irregular patterns. For example,  FIG. 12  schematically illustrates a top view of the randomly formed islands  50 ′ of conductive barrier layer  50 , which is viewed through via opening  42 . 
     A post-deposition treatment  52  is performed to remove inhibitor film  48 . The respective process is illustrated as process  212  in the process flow shown in  FIG. 18 . The resulting structure is illustrated in  FIG. 7 . The post-deposition treatment  52  may be performed through a plasma treatment and/or a thermal treatment. The process gas may include hydrogen (H 2 ) and a carrier gas such as argon. In accordance with some embodiments of the present disclosure, a plasma treatment is performed. During the plasma treatment, the temperature of the package component  100  may be higher than about 200° C., for example, in the range between about 200° and about 300° C. The treatment duration may be in the range between about 30 seconds and about 60 seconds. In accordance with alternative embodiments of the present disclosure, a thermal treatment is performed (with no plasma being generated). During the thermal treatment, the temperature of the package component  100  may be higher than about 300° C., for example, in the range between about 300° and about 350° C. The treatment duration may be in the range between about 30 seconds and about 60 seconds. 
     As a result of the post-deposition treatment, inhibitor film  48  is removed. The resulting structure is shown in  FIG. 7 . In the post-deposition treatment, inhibitor film  48  is decomposed into gases, which are removed. In addition, the oxide of conductive region  28 , if any, is reduced back to elemental metal. With the inhibitor film  48  being removed, the islands  50 ′ of conductive barrier layer  50  land on conductive region  28 . 
     An advantageous feature of performing the post-deposition treatment after the deposition of conductive barrier layer  50  is that conductive barrier layer  50  is condensed by the post-deposition treatment. By increasing the density of conductive barrier layer  50 , its ability of blocking the diffusion of the material (such as copper) in conductive region  56  ( FIG. 9 ) into dielectric layer  34  is improved. 
     Referring to  FIG. 8 , conductive material  56  is deposited to fill via opening  42  and trench  44 . The respective process is illustrated as process  214  in the process flow shown in  FIG. 18 . The processes as shown in  FIGS. 6 and 7  may be in-situ performed in a same vacuum environment, with not vacuum break in between. A part or all of the deposition process in  FIG. 8  may also be performed in-situ in the same vacuum environment as the processes shown in  FIGS. 6 and 7 , with no vacuum break in between. In accordance with some embodiments, the deposition of conductive material  56  includes performing a blanket deposition to form a metal seed layer (which may be a copper layer) using Physical Vapor Deposition (PVD), and filling the rest of via opening  42  and trench  44  using, for example, electro-plating, electro-less plating, deposition, or the like. A planarization process such as a Chemical Mechanical Planarization (CMP) process or a mechanical polish process may be performed to remove excess portions of conductive material  56 , hence forming via  58  and metal line  60 , as shown in  FIG. 9 . Each of via  58  and metal line  60  includes a portion of conductive barrier layer  50  and a portion of conductive material  56 . 
     In the resulting structure, islands  50 ′ ( FIG. 9 ) may be isolated from each other by conductive region  28  and conductive material  56 , and islands  50 ′ are in contact with conductive region  28  and conductive material  56 . Depending on the materials and the formation processes of conductive region  28  and conductive material  56 , the interface between conductive region  28  and conductive material  56  may or may not be distinguishable. Islands  50 ′ may be in physical contact with the interface. 
     As shown in  FIG. 9 , due to the selective formation of conductive barrier layer  50 , conductive barrier layer  50  includes the portions contacting dielectric layer  34  to perform the diffusion-blocking function, and does not have significant portions to separate the conductive material  56  in via  58  from conductive region  28 . Since the resistivity of conductive barrier layer  50  is significantly higher (such as two orders to four orders higher) than the resistivity of conductive material  56 , not forming conductive barrier layer  50  on conductive region  28  may significantly reduce the contact resistance of via  58 . 
       FIG. 9  also illustrates the formation of dielectric etch stop layer  62 , which covers and contacts dielectric layer  34  and metal line  60 . The respective process is illustrated as process  216  in the process flow shown in  FIG. 18 . In accordance with some embodiments, dielectric etch stop layer  62  is formed of a metal oxide, a metal nitride, a metal carbo nitride, silicon nitride, combinations thereof, and/or multi-layers thereon. 
       FIG. 13  demonstrates the hydrophobic property of inhibitor film  124  when it is formed of BTA. Layer  120  is a copper layer. Inhibitor film  124  is formed on copper layer  120 , and is formed of BTA. Water droplet  122  is dispensed on inhibitor film  124 . The contact angle α 1  is about 60, indicating the inhibitor film  124  is hydrophobic. As comparison,  FIG. 14  illustrates that when water droplet  122  is disposed on copper layer  120  directly, the contact angle α 2  is about 20 degrees. This reveals that inhibitor film  124  is significantly more hydrophobic than copper. Accordingly, the growth delay of conductive barrier layer  50  on inhibitor film  48  is more significant than on bare copper. This proves that the effect of depositing conductive barrier layer  50  on inhibitor film  48  results in more significant growth delay than on bare copper. 
       FIG. 15  illustrates the normalized via contact resistance values of a plurality of via samples, wherein the cumulative percentages of the samples are illustrated as a function of the via resistance values. A plurality of samples are formed, with some of the formation process including pre-clean using H 2 , which results in the full or partial removal of inhibitor film (if any) in the samples. The data marked as  130  are obtained from the sample vias formed through performing pre-clean (to fully remove the inhibitor film), followed by depositing a TaN layer through PVD. The data marked as  132  are obtained from the sample vias formed through performing pre-clean (to fully remove the inhibitor film), followed by forming a TaN layer through ALD and then performing a plasma treatment using H 2 . The data marked as  134  are obtained from the sample vias formed through performing weak pre-clean (to partially remove the inhibitor film), followed by forming a TaN layer, and then performing a plasma treatment using H 2 . The data marked as  136  are obtained from the sample vias formed by adopting the embodiments of the present disclosure. The results indicate that the embodiments of the present disclosure have lowest resistance values. Furthermore, comparing the results of samples  130 ,  132 ,  134 , and  136 , it was revealed that the via contact resistance is directly related to the amount of inhibitor film left when the TaN layer is deposited, and the more inhibitor film is left, the deposition of the TaN layer is more selective, and the lower via contact resistance is achieved. This is revealed by the low contact resistance values of samples  134  and  136  compared to the high contact resistance values of samples  130  and  132 . 
       FIG. 16  illustrate the thicknesses of the TaN layers deposited on different surfaces when ALD is used. The Y-axis represents the thickness of the TaN layers. The X-axis represents the number of ALD cycles. Line  140  represents the results obtained from the samples formed by depositing TaN layers on BTA films. Line  142  represents the results obtained from the samples formed by forming BTA films, performing pre-clean to remove the BTA films, and then depositing the TaN layers. Line  144  represents the results obtained from the samples formed by depositing the TaN layers on bare copper. Line  146  represents the results obtained from the samples formed by depositing the TaN layers on the oxidized copper (Cu 2 O) or bare copper exposed to air (with CuOH at surface). It is shown that line  140  corresponds to the lowest thickness, indicating the significant growth delay of the TaN layers on BTA. Furthermore, line  142  indicates that the remaining BTA&#39;s has effect on the growth-delay of the TaN layer. 
     Table 1 illustrates the results in a table format, which results are also shown in  FIG. 16 . The check marks in the fields “wet” and “pre-clean” indicate whether the wet clean (with BTA film formed) is performed or not, and whether the pre-clean, in which the BTA film (if formed) is removed, is performed or not. For the data corresponding to samples  140 , BTA films are not formed and pre-clean is also not performed. For the data corresponding to samples  142 , BTA films are not formed, while the pre-clean is performed. For the data corresponding to samples  144 , BTA films are formed and not removed when the TaN layer is formed. For the data corresponding to samples  146 , BTA films are formed and then removed in pre-clean before the TaN layers are formed. The TaN thickness after 17 ALD cycles for line  144  is 7.3 Å, which is a half of the line  146 , in which the formed BTA films are removed before the formation of the TaN layers. This proves the effect of the BTA film in delaying/reducing the growth of the TaN. Also, the slope of samples  144  is significantly smaller than other samples. Indicating the growth rate of samples  144  is lower than other samples. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Process 
                   
                 Data 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Wet 
                 Pre-clean 
                 Slope 
                 Thickness (Å) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 140 
                   
                   
                 0.589 
                 19.09 
               
               
                 142 
                   
                 x 
                 0.577 
                 14.92 
               
               
                 144 
                 x 
                   
                 0.262 
                 7.3 
               
               
                 146 
                 x 
                 x 
                 0.468 
                 14.56 
               
               
                   
               
            
           
         
       
     
       FIG. 17  illustrate the comparison of the thicknesses of TaN layers on different surfaces, with the thicknesses of TaN layers on copper, aluminum oxide, and low-k dielectric illustrated. Bar  150  represents the thickness of TaN grown on copper, with the BTA film removed through pre-clean prior to the TaN deposition. Bar  152  represents the thickness of TaN grown on a BTA film formed on copper. Bar  154  represents the thickness of TaN grown on aluminum oxide, with the BTA film removed through pre-clean prior to the TaN deposition. Bar  156  represents the thickness of TaN grown on a BTA film formed on aluminum oxide. Bar  158  represents the thickness of TaN grown on a low-k dielectric layer, with no BTA film removed (since no BTA is formed on low-k). Bar  160  represents the thickness of TaN grown on a low-k dielectric layer (with no BTA formed also). Comparing bar  150  to bar  152 , bar  154  to bar  156 , and bar  158  to bar  160 , it is shown that inhibitor films cause significant delay of the growth of TaN layers on copper, the partial-coverage inhibitor film on the aluminum film causes some but smaller growth delay of TaN layers on aluminum oxide, and there is no growth delay of TaN layers on low-k dielectric layer since no BTA film is formed on the low-k dielectric layer.  FIG. 17  explains the different growth delay behavior on conductive region  28 , etch stop layer  32 , and low-k dielectric layer  34  ( FIG. 6 ). 
     The embodiments of the present disclosure have some advantageous features. By forming the conductive barrier layer after the formation of the inhibitor film, since the growth of the inhibitor film on different materials is selective, the resulting conductive barrier layer is selectively formed on the sidewalls of the low-k dielectric layer to perform the diffusion-blocking function, and is not (or substantially not) formed on the underlying conductive region to cause the undesirable increase in the via contact resistance. In addition, by performing the post-deposition treatment after the formation of the conductive barrier layer, not only the inhibitor film is removed, the conductive barrier layer is also condensed, and the diffusion-blocking ability is improved. In conventional processes, pre-clean processes, which may be performed using H 2 , is performed prior to the formation of conductive barrier layers to reduce oxides, and do not have the function of condensing the conductive barrier layers. 
     In accordance with some embodiments of the present disclosure, a method of forming an integrated circuit structure comprises forming an etch stop layer over a conductive feature; forming a dielectric layer over the etch stop layer; forming an opening in the dielectric layer to reveal the etch stop layer; etching the etch stop layer through the opening using an etchant comprising an inhibitor, wherein an inhibitor film comprising the inhibitor is formed on the conductive feature; depositing a conductive barrier layer extending into the opening; after the conductive barrier layer is deposited, performing a treatment to remove the inhibitor film; and depositing a conductive material to fill a remaining portion of the opening. In an embodiment, the method further comprises, after the etch stop layer is etched, soaking a respective wafer comprising the etch stop layer and the inhibitor film in a chemical solution to increase a thickness of the inhibitor film, wherein during the soaking, the etch stop layer is not etched. In an embodiment, the etchant and the chemical solution comprises a same type of inhibitor. In an embodiment, the treatment comprises a plasma treatment using hydrogen (H 2 ) as a process gas. In an embodiment, the treatment comprises a thermal treatment using hydrogen (H 2 ) as a process gas. In an embodiment, the inhibitor in the etchant comprises Benzotriazole, and the conductive feature comprises copper. In an embodiment, the conductive barrier layer form isolated islands on the inhibitor film. In an embodiment, after the treatment, the isolated islands are in contact with an interface between the conductive feature and the conductive material. In an embodiment, the discrete islands are in contact with an interface between the conductive feature and the conductive material. 
     In accordance with some embodiments of the present disclosure, a method of forming an integrated circuit structure includes forming an etch stop layer over a conductive feature; forming a dielectric layer over the etch stop layer; forming an opening in the dielectric layer to reveal the etch stop layer; etching the etch stop layer; and selectively depositing a conductive barrier layer extending into the opening, wherein the selective depositing results in the conductive barrier layer to have a first thickness on a sidewall of the dielectric layer, and the conductive barrier layer is at least thinner at a bottom of the opening than on the sidewall of the dielectric layer. In an embodiment, the conductive barrier layer comprises discrete islands at the bottom of the opening. In an embodiment, the conductive barrier layer does not extend to the bottom of the opening. In an embodiment, the etching the etch stop layer results in an inhibitor film to be formed on a top surface of the conductive feature, and the method further comprises: after the conductive barrier layer is formed, removing the inhibitor film; and depositing a conductive material to fill a remaining portion of the opening. In an embodiment, the removing the inhibitor film comprises a plasma treatment using hydrogen (H 2 ) as a process gas. In an embodiment, the removing the inhibitor film comprises a thermal treatment using hydrogen (H 2 ) as a process gas. 
     In accordance with some embodiments of the present disclosure, an integrated circuit structure comprises a conductive feature; an etch stop layer over the conductive feature; a dielectric layer over the etch stop layer; and a conductive feature extending into the dielectric layer and the etch stop layer, wherein the conductive feature comprises: a conductive barrier layer comprising a first portion on sidewalls of the dielectric layer, wherein the first portion forms a continuous layer, and second portions on a top surface of the first conductive feature, wherein the second portions are thinner than the first portion; and a conductive region encircled by the first portions of the conductive barrier layer, wherein the conductive region is over and contacting the second portions of the conductive barrier layer. In an embodiment, the second portions are discrete islands separated from each other by the conductive region. In an embodiment, the discrete islands are at, and in contact with, an interface between the conductive feature and the conductive region. In an embodiment, the conductive barrier layer comprises TaN. In an embodiment, the conductive barrier layer has a coverage smaller than about 50 percent. 
     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.