Abstract:
One or more aspects of the subject disclosure pertain to forming single or dual damascene interconnect structures in the fabrication of semiconductor devices. The interconnect structures are formed in manners that mitigate one or more adverse effects associated with conventional techniques. One or more aspects of the invention may be employed, for example, to facilitate better via critical dimension (CD) control, improve selectivity of etch-stop layer to inter layer dielectric (ILD) and/or intra-metal dielectric (IMD) material, and/or to simplify and make the fabrication process more efficient and/or cost effective.

Description:
RELATED APPLICATIONS  
       [0001]     This application is related to U.S. patent application Ser. No. 10/313,491, (Attorney Docket No. TI-34486), filed on Dec. 5, 2002, entitled “METHODS FOR FORMING SINGLE DAMASCENE VIA OR TRENCH CAVITIES AND FOR FORMING DUAL DAMASCENE VIA CAVITIES”, the entirety of which is hereby fully incorporated by reference. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention relates generally to semiconductor processing and more particularly to implementing in-situ ashing in association with damascene processing in forming interconnect structures in the fabrication of semiconductor devices.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the manufacture of semiconductor products such as integrated circuits, individual electrical devices are formed on or in a semiconductor substrate, and are thereafter interconnected to form electrical circuits. Interconnection of these devices is typically accomplished by forming a multi-level interconnect network structure in layers formed over the electrical devices, by which active elements of the devices are connected to one another to create the desired circuits. Individual wiring layers within the multi-level network are formed by depositing an insulating or dielectric layer over the discrete devices or over a previous interconnect layer, and patterning and etching contact holes or openings such as vias. Conductive material, such as tungsten is then deposited into the vias to form inter-layer contacts. A conductive layer may then be formed over the dielectric layer and patterned to form wiring interconnections between the device vias, thereby creating a first level of basic circuitry. Dielectric material is then deposited over the patterned conductive layer, and the process may be repeated any number of times using additional wiring levels laid out over additional dielectric layers with conductive vias therebetween to form the multi-level interconnect network.  
         [0004]     As device densities and operational speeds continue to increase, reduction of the delay times in integrated circuits is desired. These delays are related to the resistance of interconnect metal lines through the multi-layer interconnect networks as well as to the capacitance between adjacent metal lines. In order to reduce the resistivity of the interconnect metal lines formed in metal layers or structures, recent interconnect processes have employed copper instead of aluminum. However, difficulties have been encountered in patterning (etching) deposited copper to form wiring patterns. Furthermore, copper diffuses rapidly in certain types of insulation layers, such as silicon dioxide, leading to insulation degradation and/or copper diffusion through the insulation layers and into device regions.  
         [0005]     Copper patterning difficulties have been avoided or mitigated through the use of single and dual damascene interconnect processes in which cavities are formed (etched) in a dielectric layer. Copper is then deposited into the trenches and over the insulative layer, followed by planarization using a chemical mechanical polishing (CMP) process to leave a copper wiring pattern including the desired interconnect metal lines inlaid within the dielectric layer trenches. In a single damascene process copper trench patterns or vias are created which connect to existing interconnect structures thereunder, whereas in a dual damascene process, both vias and the trenches are filled at the same time using a single copper deposition and a single CMP planarization.  
         [0006]     Copper diffusion issues have been addressed using copper diffusion barriers formed between the copper and the dielectric layers as well as between the copper and the silicon substrate. Such barriers are typically formed using conductive compounds of transition metals such as tantalum nitride, titanium nitride, and tungsten nitride as well as the various transition metals themselves. Insulators such as silicon nitride and silicon oxynitride have also been used as barrier materials between copper metallurgy and insulative layers. More recently, silicon carbide (SiC) has been used as a copper diffusion barrier material, as well as in etch-stop layers employed during trench and/or via cavity formation.  
         [0007]     RC delay times have also been reduced by recent developments in low dielectric constant (low-k) dielectric materials formed between the wiring metal lines, in order to reduce the capacitance therebetween and consequently to increase circuit speed. Examples of low-k dielectric materials include spin-on-glasses (SOGs), as well as organic and quasi-organic materials such as polysilsesquioxanes, fluorinated silica glasses (FSGs) and fluorinated polyarylene ethers. Totally organic, non silicaceous materials such as fluorinated polyarylene ethers, are seeing an increased usage in semiconductor processing technology because of their favorable dielectric characteristics and ease of application. Other low-k insulator materials include organo-silicate-glasses (OSGs), for example, having dielectric constant (k) as low as about 2.6-2.8, and ultra low-k dielectrics having dielectric constant below 2.5. OSG materials are low density silicate glasses to which alkyl groups have been added to achieve a low-k dielectric characteristic.  
         [0008]     Conventional single and dual damascene interconnect processing typically includes the formation of via cavities through a dielectric layer, in which the via etch process stops on an etch-stop layer underlying the dielectric. A resist ashing process is then employed to remove a via etch photoresist mask, and an optional wet clean operation is then performed to remove polymers and other residual materials from the via cavity. In the single damascene case, an etch-stop layer etch process is then performed to expose the underlying structure, such as a conductive feature (e.g., copper feature) in a pre-existing interconnect layer. The via cavity is then filled with copper and the wafer is planarized, after which further interconnect levels may then be fabricated. In the dual damascene case, after the via ashing and wet clean operations, a trench cavity is patterned and etched, followed by another ashing operation and optionally another wet clean. Thereafter an etch-stop layer etch is performed to expose the underlying structure, and the via and trench cavities are simultaneously filled with copper and the wafer is planarized.  
         [0009]     In the conventional single and dual damascene interconnect processes, however, the etch-stop layer etch process not only etches the etch-stop layer, but also recesses the exposed dielectric material. As a result, the inter level or inter layer dielectric (ILD) and/or intra-metal dielectric (IMD) becomes thinner. In addition, in the single damascene case, the etch-stop layer etch and subsequent cleaning steps (e.g., ashing and wet clean) often change the via profile and increase the critical dimensions (CDs) thereof. As new technologies demand ever smaller CDs in semiconductor devices, CD control becomes more important. Furthermore, the conventional via sidewalls become bowed during the etch-stop etch and intervening cleaning after the via etch process, leading to via profile distortion. In the dual damascene case, the etch-stop etch and subsequent cleaning also affect the top dielectric surface and sidewalls of the trench cavity. Consequently, the effective dielectric constant of the resulting structure can be increased. Thus, there remains a need for improved methods for fabricating single and/or dual damascene interconnect structures in semiconductor wafers by which these and other adverse effects can be mitigated or overcome, while concurrently streamlining the fabrication process to become more efficient in terms of cycle times, cost effectiveness, etc.  
       SUMMARY OF THE INVENTION  
       [0010]     The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.  
         [0011]     One or more aspects of the present invention relate to forming single or dual damascene interconnect structures in the fabrication of semiconductor devices in manners that mitigate the above mentioned and other adverse effects. One or more aspects of the invention may be employed, for example, to facilitate better via critical dimension (CD) control, improve selectivity of etch-stop layer to inter layer dielectric (ILD) and/or intra-metal dielectric (IMD) material, and/or to simplify and make the flow of the fabrication process more efficient and/or cost effective.  
         [0012]     In accordance with one or more aspects of the present invention, a method of performing an ashing act in an interconnect structure formation process that is integral with forming one or more semiconductor devices is disclosed. The method includes forming a via for the interconnect structure including etching via ILD layer and etch-stop layer in-situ, and then performing an in-situ ashing in forming the via.  
         [0013]     To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIGS. 1A-1F  are partial side elevation views in section illustrating a conventional single damascene via formation flow.  
         [0015]      FIGS. 2A-2F  are partial side elevation views in section illustrating a conventional via-first dual damascene formation flow.  
         [0016]      FIG. 3  is a flow diagram illustrating an exemplary method of forming a single damascene interconnect structure in accordance with one or more aspects of the present invention.  
         [0017]      FIGS. 4A-4P  are partial side elevation views in section illustrating fabrication of an exemplary single damascene via or trench in accordance with one or more aspects of the present invention.  
         [0018]      FIG. 5A  is a cross-sectional side elevation view scanning electron microscope (SEM) image of single damascene vias formed according to conventional processes following ex-situ etch-stop etching.  
         [0019]      FIG. 5B  is a cross-sectional side elevation view SEM image of single damascene vias formed according to related application (Ser. No. 10/313,491) following in-situ etch-stop etching and conventional ex-situ ashing and utilizing the same ILD film stack as that used as in  FIG. 5A .  
         [0020]      FIG. 5C  is a cross-sectional side elevation view SEM image of single damascene vias formed according to related application (Ser. No. 10/313,491) following in-situ etch-stop etching, conventional ex-situ ashing and wet solvent clean.  
         [0021]      FIG. 5D  is a cross-sectional side elevation view SEM image of single damascene vias formed according to one or more aspects of the present invention following in-situ etch-stop etching, in-situ ashing and wet solvent clean and utilizing the same ILD film stack as that used as in  FIG. 5C .  
         [0022]      FIG. 5E  is a top view SEM image of single damascene vias formed according to related application (Ser. No. 10/313,491) following in-situ etch-stop etching and conventional ex-situ ashing.  
         [0023]      FIGS. 5F and 5G  are top view SEM images of single damascene vias formed according to one or more aspects of the present invention following in-situ etch-stop etching and in-situ ashing.  
         [0024]      FIGS. 6A and 6B  provide a flow diagram illustrating an exemplary method of forming a dual damascene interconnect structure in accordance with one or more aspects of the present invention.  
         [0025]      FIGS. 7A-7N  are partial side elevation views in section illustrating fabrication of an exemplary via-first dual damascene interconnect structure in accordance with one or more aspects of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     The present invention will now be described with reference to the attached drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the various structures are not necessarily drawn to scale. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects of the present invention. It may be evident, however, that one or more aspects of the present invention may be practiced with a lesser degree of these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more aspects of the present invention.  
         [0027]     One or more aspects of the present invention relate to forming single and/or dual damascene interconnect structures, including via and/or trench cavities or openings during interconnect processing of integrated circuits and other semiconductor devices. One or more implementations of the invention are hereinafter illustrated and described in the context of single or dual damascene trench and/or via cavity formation in low-k organo-silicate-glass (OSG) structures, where silicon carbide (SiC) etch-stop layers are employed. However, it will be appreciated by those skilled in the art that the invention is not limited to the exemplary implementations illustrated and described hereinafter. In particular, the various aspects of the invention may be employed in association with processing of devices using OSG, fluorinated silica glasses (FSG), or other low-k or ultra low-k dielectric materials, and other types of etch-stop layer materials. Further, the dual damascene formation methods of the invention may be employed in association with via-first and/or trench-first implementations.  
         [0028]     Referring initially to  FIGS. 1A-1F , one or more problems or shortcomings of conventional single damascene interconnect processing are illustrated and described to provide an appreciation of the benefits possible with the invention.  FIG. 1A  illustrates a wafer  2  comprising a silicon substrate  4 , in which a conductive silicide structure  5  is formed. An initial contact layer is formed over the substrate  4 , including a dielectric  6  with a tungsten contact  7  extending therethrough. A first interconnect structure is formed over the contact layer, including an etch-stop layer (not shown), over which a dielectric  8  is deposited. A conductive feature  10  is formed through the dielectric  8  and the etch-stop layer to provide electric coupling to the contact  7 . To form a single damascene interconnect level, a SiN or SiC etch-stop layer  12  is formed over the dielectric  8  and the conductive feature  10 , and a dielectric layer  14  is formed over the etch-stop layer  12  to a thickness  14 ′ of about 5000-6000 Å. A bottom anti-reflective coating (BARC) layer  16  is deposited over the dielectric  14  and a resist mask  18  is formed over the BARC layer  16 . In  FIG. 1A , a via etch process  22  is performed to form an aperture or via cavity  24  in the BARC and dielectric layers  16  and  14 , respectively, which is stopped on the etch-stop material  12 .  
         [0029]     Thereafter in  FIG. 1B , a resist ashing process  26  is used to remove the mask  18  and BARC  16 , and a wet clean operation  28  is performed in  FIG. 1C . The resulting via cavity  24  has a critical dimension (CD)  20 . In  FIG. 1D , an etch-stop etch process  30  is performed to etch the exposed etch-stop layer material  12  at the bottom of the via cavity  24 , which also removes dielectric material from the exposed top of the layer  14 , as well as from the sidewalls of the cavity  24 . Thereafter in  FIG. 1E , another ashing operation  32  is performed and a wet clean  34  is performed in  FIG. 1F . Following this conventional single damascene process, the resulting via cavity  24  has a critical dimension  20 ′ ( FIG. 1F ), which may be significantly larger than the original dimension  20  ( FIG. 1C ). In addition, the etch-stop etch and cleaning processes  30 ,  32 , and  34  have reduced the dielectric (e.g., ILD) thickness of the layer  14  to a smaller dimension  14 ″ ( FIG. 1F ), which may be significantly less than the starting dimension  14 ′ ( FIG. 1A ). For low-k dielectrics, the etch-stop etch and cleaning processes  30 ,  32  and  34  can also affect low-k film properties of top surface and sidewalls, thus increasing the effective dielectric constant. Further, the ashing acts  26  and  32  are performed ex-situ, or rather in fabrication components that are separate from the chamber or chambers wherein the other acts (e.g., deposition, etching, etc.) are performed. Such ex-situ ashing adds complexity to the process flow and increases cycle times and equipment costs, among other things, as wafers have to be moved back and forth between processing tools. Ex-situ ashing may also, at times, fail to adequately remove etch residues.  
         [0030]     Referring now to  FIGS. 2A-2F , similar problems are seen in conventional dual damascene processing.  FIG. 2A  illustrates a wafer  52  comprising a substrate  54 , in which a conductive silicide structure  55  is formed. An initial contact layer is formed over the substrate  54 , including a dielectric  56  and a conductive contact  57 . A first interconnect structure is formed over the contact layer, including an etch-stop layer (not shown), and a dielectric  58  in which a conductive feature  60  is formed to provide electric coupling to the contact  57 . An etch-stop layer  62  is formed over the dielectric  58  and over the contact  60 , and a dielectric layer  64  is formed over the etch-stop layer  62  to a thickness of about 7000-8000 Å. A BARC layer  66  is then formed over the dielectric  64  and a resist mask  68  is formed over the BARC layer  66 . A via etch process  72  is performed in  FIG. 2A  to form a hole or via cavity  74  in the layers  66  and  64 , stopping on the etch-stop layer  62 . In  FIG. 2B , a resist ashing process  76  and a wet clean  78  are performed to remove the mask  68  and the BARC  66 , resulting in via cavity  74  having a critical dimension of  70 .  
         [0031]     In  FIG. 2C , a second BARC layer  80  and a trench resist mask  82  are formed over the wafer  52 , and a trench etch operation  84  is performed to form a trench cavity or opening  86  leaving a CD of  71 , and leaving a trench bottom surface thickness  88  of about 3000-4000 Å above the previous interconnect dielectric material  58 . Another ashing operation  90  and wet clean  92  are performed in  FIG. 2D , and an etch-stop etch process  94  is then performed in  FIG. 2E  to etch the exposed etch-stop layer material  62  at the bottom of the via cavity  74 . As illustrated in  FIG. 2E , the etch-stop etch  94  also removes dielectric material from the exposed top of the layer  64 , from the bottom and sidewalls of the trench cavity  86 , and also from the sidewalls of the via cavity  74 . Thereafter in  FIG. 2F , another ashing operation  96  and a wet clean  98  are performed. Thus the dielectric layer  64  has a reduced trench bottom surface thickness  88 ′ from it&#39;s original thickness  88  ( FIG. 2C ), and CDs have been increased to  70 ′ and  71 ′ for the via  74  and the trench  86  from their original dimensions  70  and  71  ( FIG. 2C ).  
         [0032]     In the conventional single and dual damascene processes illustrated in  FIGS. 1A-1F  and  2 A- 2 F, respectively, it is thus seen that the etch-stop layer etch steps in  FIGS. 1D and 2E  adversely affect the profiles and CDs of the interconnect cavities and structures, leading to thinning of the ILD/IMD layers and corresponding increase in the effective dielectric constant of the finished structures. In order to reduce the capacitance between interconnect routing lines and vias and consequently to increase circuit speed in modern semiconductor devices, the present invention provides methods for single and dual damascene interconnect structure formation by which these difficulties can be mitigated or avoided, while the number of acts in these processes are also reduced, thus streamlining the processes and making them more efficient and cost effective, among other things.  
         [0033]     Referring now to  FIG. 3 , an exemplary method  100  is illustrated and described hereinafter for forming a single damascene interconnect structure, such as a via or a trench. Although the method  100  and other methods herein are illustrated and described below as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methods according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated.  
         [0034]     The exemplary method  100  is described hereinafter in the context of a single damascene via formation in a semiconductor wafer. However, it will be appreciated that the exemplary method  100 , and other single damascene methodologies of the present invention, may be employed alternatively or in combination in forming a single damascene trench structure. Beginning at  102 , the method  100  comprises forming an etch-stop layer over an existing interconnect structure at  104  (e.g., over a previous damascene structure or over an initial contact level), and forming a low-k dielectric layer over the etch-stop material at  106 . Any appropriate etch-stop and dielectric materials and layer fabrication techniques may be employed at  104  and  106 , respectively, such as depositing SiN or SiC etch-stop material to a thickness of about 600 Å using any appropriate deposition technique such as chemical-vapor deposition (CVD) or the like. A hardmask or cap layer can be optionally used. A BARC (bottom anti-reflective coating) layer is optionally deposited at  108  of any appropriate organic material having anti-reflective properties to a thickness of about 800 Å over the dielectric layer. A resist mask is then deposited and patterned at  110 , having an opening in a prospective via region of the wafer, for example, using known photolithographic techniques and photoresist materials.  
         [0035]     The dielectric layer may be formed at  106  via any appropriate technique, for example, by deposition of organo-silicate-glass (OSG) material to a thickness of about 5000 Å over the SiC etch-stop layer. Any appropriate deposition process may be employed in forming the OSG layer at  106 . In operation, the low-k dielectric layer provides insulation between overlying and underlying conductive features, such as between a conductive feature in an existing interconnect structure and later-formed features above or in trenches in the low-k dielectric. In this regard, it is noted that OSG material provides relatively low dielectric constant characteristics desirable in avoiding or mitigating RC delays and cross-talk between signals in the finished semiconductor device. In addition, it will be appreciated that any dielectric materials may be used in forming the dielectric layer at  106 , including but not limited to OSG, FSG, ultra low-k dielectrics, or the like, wherein the invention is not limited to use in association with the OSG materials discussed herein.  
         [0036]     Thereafter, an in-situ process flow  112  is performed wherein a via cavity is formed through the BARC, dielectric, and etch-stop layers, which may be performed in a single reactive ion etch (RIE) tool, for example, without breaking vacuum. At  114   a , the exposed BARC layer is etched, using the patterned resist as a mask, and a via main etch is performed at  114   b  to remove a portion of the dielectric layer, creating a via cavity or opening therein. Thereafter, a via over-etch process is performed at  114   c  to remove the remaining portion of the dielectric material in the cavity and to expose a portion of the underlying etch-stop layer material. At  116 , the exposed portion of the etch-stop material is etched to extend the cavity and to expose a conductive feature in the underlying interconnect structure, with substantially no intervening processing between the via etch acts of  114   a - 114   c  and the etch-stop etch of  116 .  
         [0037]     In the exemplary method  100 , the via etch at  114   a - 114   c  and the etch-stop etch at  116  are performed in-situ within a single reactive ion etching (RIE) tool. However, other implementations are possible within the scope of the invention, wherein the etch-stop etch at  116  is performed concurrently with the via etch  114  or immediately thereafter. In addition, the invention also contemplates alternative implementations in which the via and etch-stop etch acts are performed with substantially no processing steps therebetween. For example, no ashing or wet etch operations are performed between the via etch  114  and the etch-stop layer etch at  116  in the illustrated method  100 . Thus, compared with the conventional single damascene methods (e.g.,  FIGS. 1A-1F  above), the exemplary method  100  streamlines the process by removing an intermediate act (e.g., ashing  26  in  FIG. 1B ). Additionally, performing the etch-stop etch with the patterned resist mask in place mitigates damage to the via cavity (e.g.,  20  vs  20 ′,  FIGS. 1C and 1F ) as the mask affords some protection to the dielectric layer.  
         [0038]     It is further noted that while the exemplary method  100  provides in-situ etching of the via cavity through the dielectric layer (e.g.,  114 ) and etch-stop etching to extend the via cavity through the etch-stop layer, that other implementations are possible within the scope of the present invention where these or equivalent acts are performed in different etch tools. Moreover, one or more process steps or acts may be performed between the via and etch-stop etch acts in accordance with the invention where the dielectric layer is covered with the resist mask during the etch-stop etch. In the illustrated method  100 , the resist mask from the via etch steps remains during the etch-stop etch  116 . However, other implementations are possible within the scope of the invention, wherein all or a portion of the dielectric is covered by any means during the entirety of, or during a portion of, the etch-stop etch  116 . Also, while the exemplary method  100  provides a multi-step etch (e.g.,  114   b ,  114   c ) through the dielectric layer, other implementations are contemplated, wherein the BARC etch, the via etch, and/or the etch-stop etch acts may individually comprise single step and/or multi-step operations, within the scope of the present invention.  
         [0039]     In the illustrated example, the acts  114   a - 114   c  and  116  are performed in a single RIE etch tool, with appropriate etch chemistries being changed accordingly, in order to remove material from the layer currently exposed in the prospective via region (e.g., the BARC layer, then the dielectric layer, then the etch-stop layer). Furthermore, while illustrated and described with respect to organic BARC materials, OSG type low-k dielectric material, and SiC or SiN etch-stop layer materials, any appropriate materials may be employed in forming these layers in accordance with the invention, where appropriate etch chemistries and selectivities may be selected in performing the etch operations  114 - 116  to form and extend the via cavity. Furthermore, although illustrated in the context of a single damascene via formation flow, the invention contemplates implementations for forming single damascene trench structures and cavities, wherein the above described etch techniques may be employed to form a trench opening or cavity through the BARC, dielectric, and etch-stop layers.  
         [0040]     In one exemplary implementation of the method  100 , the via etch through the dielectric layer at  114   b  and  114   c  comprises a two-step process having different etch chemistries for each such step. The main etch at  114   b  is performed to etch the majority of the dielectric material in the cavity, and leaves about 1000-2000 Å of dielectric material remaining. The process parameters are then switched to the over-etch at  114   c , which is time controlled to stop on the etch-stop layer, although other forms of process control may be employed to stop on the etch-stop material, wherein the exemplary over-etch at  114   c  has a higher selectivity to the etch-stop layer than does the main etch at  114   b.    
         [0041]     Once the etch-stop layer has been exposed, the etch process parameters are again adjusted for etching the etch-stop material with a selectivity to the underlying (e.g., pre-existing) interconnect structure, so as to expose an underlying conductive feature (e.g., copper structure). It is noted that the method  100  provides a resist mask over the dielectric layer while etching the exposed portion of the etch-stop layer at  116 , since there is no intervening ashing or wet etch process to remove the via resist mask. This, in turn, advantageously mitigates or avoids etch-stop etch related damage to the dielectric material during the etch-stop etch at  116 , by which the via CD and profile, and the dielectric layer thickness are protected.  
         [0042]     Following the in-situ process at  112 , the method  100  proceeds to  118 , where a resist stripping or ashing operation is performed to remove the resist mask initially formed at  110 , as well as the BARC material deposited at  108 . However, unlike conventional ashing operations (e.g.,  32 ,  FIG. 1E ) which are performed ex-situ, ashing operation  118  is performed in the same processing chamber as the via etch  114   a - 114   c  and etch-stop etch  116 , or in a different chamber on the same etcher. In the latter situation, the wafers would likely be transferred under vacuum. Performing the ashing operation  118  in-situ according to one or more aspects of the present invention, allows the process to be further streamlined as wafers do not have to be transferred between different processing tools. In-situ acts  114   a ,  114   b ,  114   c ,  116  and  118  are thus referenced as  112 ′ in the exemplary flow  100 .  
         [0043]     Such an in-situ ash  118  may also be performed with an RIE plasma asher that can remove tough residues more effectively as compared to ex-situ plasma ashers using downstream plasmas. The in-situ ash is also performed at a relatively low power and low pressure as compared to conventional systems. For example, the ash ing operation  118  may be performed at a power of about 150 to 400 W and a pressure of about 20 to 80 mT. Further, the operation  118  may be performed for a time of about 15 to 60 seconds with an oxygen (O 2 ) flow of about 100 to 500 sccm and at a chuck temperature of about 20 to 40 degrees Celsius. Additionally, other ash chemistries such as H 2 /Ar, H 2 /He, H 2 /N 2  O 2 /H 2 , O 2 /N 2  can also be used. The in-situ ash thus allows the operation to be more effective and to be performed more efficiently and cost effectively as fewer actions have to be taken, less equipment is needed, and cycle time is thereby reduced.  
         [0044]     A wet clean operation is then optionally performed at  120 , such as using a wet solvent to remove any residue from the RIE etch acts which may still remain after the ashing operation at  118 . A copper diffusion barrier layer is then formed at  122 , which serves to line the via cavity, examples of which include conductive compounds of transition metals such as tantalum nitride, titanium nitride, and tungsten nitride as well as the various transition metals themselves. A seed copper layer is then deposited over the diffusion barrier at  124 , to facilitate subsequent copper filling of the via cavity.  
         [0045]     An electro-chemical deposition (ECD) process is then performed at  126  to deposit a copper layer over the wafer, which fills the via cavity, and overlies the barrier layer on top of the remaining dielectric. Any appropriate copper deposition process or acts  124 - 126  may be employed, which may be a single step or a multi-step process. Thereafter at  128 , a chemical mechanical polishing (CMP) process is performed to planarize the upper surface of the device, which ideally stops on the dielectric layer and reduces the diffusion barrier and the deposited copper. In this manner, the planarization process  128  electrically separates the conductive (e.g., copper) via from other such vias formed in the device, whereby controlled connection of the underlying conductive feature with subsequently formed interconnect structures can be achieved, after which the method  100  ends at  130 .  
         [0046]     Referring also to  FIGS. 4A-4P , an exemplary wafer  202  is illustrated undergoing single damascene interconnect structure formation processing in accordance with this aspect of the invention.  FIGS. 4A-4P  illustrate formation of a single damascene via structure. However, the invention may also be employed in formation of a single damascene trench structure (not shown) according to the principles illustrated and described herein.  FIG. 4A  illustrates the wafer  202  at an intermediate stage of fabrication, comprising a silicon substrate  204 , in which a conductive silicide structure  205  is formed. An initial contact layer is formed over the substrate  204 , comprising a dielectric  206  with a tungsten contact  207 , for example, extending therethrough, and electrically contacting the silicide  205 . A previously formed interconnect structure is formed over the contact layer, comprising an etch-stop layer (not shown) and a dielectric  208  in which a conductive feature (e.g., copper trench metal)  210  is formed to provide electric coupling to the contact  207 . The invention may be employed in association with any existing interconnect structure to provide electrical coupling to a conductive feature therein. In  FIG. 4B , a SiN or SiC etch-stop layer  212  is formed over the dielectric  208  and the conductive feature  210  of the existing interconnect structure to a thickness  212 ′ of about 500-800 Å via a deposition process  213 . A dielectric layer  214 , such as a low-k OSG dielectric material or the like, is formed via a deposition process  215  in  FIG. 4C  over the etch-stop layer  212  to a thickness  214 ′ of about 5000-6000 Å.  
         [0047]     An organic BARC layer  216  is deposited in  FIG. 4D  over the dielectric  214  via a deposition process  217  to a thickness  216 ′ of about 600-800 Å. Thereafter in  FIG. 4E , a resist mask  218  is formed over the BARC layer  216  having an opening  220  in a prospective via region. In  FIG. 4F , a via BARC etch process  222  is performed to remove material from the BARC layer  216  in the via region  220 . A via main etch process  224  is then employed in  FIG. 4G  to form a via cavity  226  in the dielectric layer  214 , leaving a thickness  228  of dielectric material  214  unetched at the bottom of the via cavity  226 , wherein the via main etch  224  has a substantial etch rate and is substantially anisotropic. A via over-etch process  230  (e.g., which is highly selective with respect to the etch-stop layer  212 ) is then performed in  FIG. 4H  to further form the cavity  226  through the rest of the dielectric layer  214 , stopping on and exposing a portion of the underlying etch-stop layer  212 . At this point the via  226  has a width or critical dimension (CD) of  231 . An etch-stop etch  232  is performed immediately thereafter (e.g., concurrently with the over-etch  230 ) in  FIG. 4I .  
         [0048]     Thereafter in  FIG. 4J , a resist ashing process  234  is used to remove the remaining resist mask  218  and the BARC layer  216 , and a wet clean operation  236  is performed in  FIG. 4K . It is noted in  FIG. 4K , that unlike the conventional single damascene process (e.g.,  FIG. 1F  above), the profile and CD  231  of the via cavity  226  remains essentially the same as prior to the etch-stop etch  232 , since the resist mask  218  was maintained during the etch-stop etch  232  ( FIG. 4I ). In this regard, having the resist  218  over the dielectric  214  helps preserve the CD and profile of the via  226 . Additionally, unlike conventional ashing operations which are performed on separate fabrication tools and that require wafers to be moved back and forth between different tools, ashing operation  234  is performed in the same processing chamber as the etch-stop etch  232 , or in a different chamber on the same etcher. In the latter situation, the wafers would likely be transferred under vacuum. Performing the ashing operation  234  in-situ in accordance with one or more aspects of the present invention, allows the process to be streamlined as wafers do not have to be transferred between different processing tools.  
         [0049]     An in-situ ash also allows a RIE plasma to be utilized at  234 . A RIE plasma ash process can remove tough residues more effectively as compared to ex-situ plasma ash using downstream plasmas. The in-situ ash is also performed at a relatively low power and low pressure as compared to conventional systems. For example, the ashing operation  234  may be performed at a power of about 150 to 400 W and a pressure of about 20 to 80 mT. Further, the operation  234  may be performed for a time of about 15 to 60 seconds with an oxygen (O 2 ) flow of about 100 to 500 sccm and at a chuck temperature of about 20 to 40 degrees Celsius. Additionally, other ash chemistries such as H 2 /Ar, H 2 /He, H 2 /N 2  O 2 /H 2 , O 2 /N 2  can also be used. The in-situ ash thus allows the operation to be more effective and to be performed more efficiently and cost effectively as fewer actions have to be taken, less equipment is needed, and cycle time is thereby reduced.  
         [0050]     In  FIG. 4L , a copper diffusion barrier layer  238  is formed via a deposition process  237 , and a copper seed layer  240  is formed in  FIG. 4M  via a deposition process  239 . An ECD, for example, copper deposition process  241  is then performed in  FIG. 4N  to deposit copper  242 , thereby filling the via cavity  226  and overlying the remainder of the wafer  202 , after which a CMP planarization process  243  is employed in  FIG. 4O  to planarize the wafer  202 , thus completing the conductive single damascene via structure.  
         [0051]     Thereafter, as illustrated in  FIG. 4P , a subsequent interconnect level or layer may be constructed, for example, using the above-described single damascene techniques, comprising another etch-stop layer  244 , a low-k dielectric layer  245 , and a trench structure comprising a copper diffusion barrier layer  246 , a copper seed layer  247 , and ECD deposited copper fill material  248 . Any number of such layers or levels may be fabricated in accordance with the present invention, to provide electrical coupling to the conductive feature  210  in the existing interconnect structure of the wafer  202 .  
         [0052]     Referring also to  FIGS. 5A and 5B , scanning-electron microscope (SEM) images are provided to illustrate some of the advantages which may be realized in practicing the single damascene methods of the invention, including the exemplary method  100  above, as contrasted with conventional techniques.  FIG. 5A  provides a cross-sectional SEM image  250  of single damascene vias after etch-stop etching, formed according to conventional processes (e.g.,  FIGS. 1A-1F  above).  FIG. 5B  is a cross-sectional SEM image  262  (at the same scale and utilizing the same ILD film stack as the image  250  of  FIG. 5A ) of single damascene vias formed according to the present invention (e.g.,  FIGS. 3 and 4 A- 4 P) with in-situ etch-stop etching and ashing.  
         [0053]     As can be seen from  FIGS. 5A and 5B , the conventional single damascene technique ( FIG. 5A ) provides significant reduction in the dielectric thickness  251  (e.g., due to the exposure of the dielectric material during the etch-stop etch or a poor selectivity to the top dielectric), whereas the thickness  251 ′ of the dielectric in the image  262  ( FIG. 5B ) is maintained according to the invention. This allows process flow steps (e.g., such as the dielectric layer formation in  FIG. 4C  above) to be adjusted to provide the desired final thickness, without having to compensate for etch-related reduction as experienced in the past. Further, the via profiles are better in the image  262  than in the conventional case of the image  250  (e.g., less bowing in  FIG. 5B  than in  FIG. 5A , corresponding to  231  in  FIG. 4J  vs.  20 ′ in  FIG. 1F , for example). Furthermore, the CDs in the image  262  of  FIG. 5B  are smaller than those in  FIG. 5A .  
         [0054]     By way of further example,  FIGS. 5C and 5D  similarly illustrate the effectiveness of in-situ ashing in accordance with one or more aspects of the present invention as compared to conventional techniques. In particular,  FIG. 5C  is a cross sectional SEM image  266  of vias  267  formed with in-situ etch-stop etching, conventional ex-situ ashing and wet solvent clean.  FIG. 5D , on the other hand, depicts such vias formed as a result of in-situ ashing according to one or more aspects of the present invention. More particularly,  FIG. 5D  is a cross sectional SEM image  270  of single damascene vias  271  formed at the same scale as  FIG. 5D  and with in-situ etch-stop etching, in-situ ashing and wet solvent clean, where the vias  271  are formed in the same ILD film stack as the vias  267  of  FIG. 5C . In the example shown in  FIG. 5D , the in-situ ashing occurs in the same processing chamber as the in-situ etching. It will be appreciated, however, that the in-situ ashing could also occur in the same tool, but in a different chamber than the in-situ etching (with wafer transferred under vacuum) in accordance with one or more aspects of the present invention. It can be seen that the same, if not an improved, level of quality results from the in-situ ashing as compared to conventional ex-situ ashing. For example, the profile of the vias  271  in  FIG. 5D  is the same if not better than those  267  of  FIG. 5C  and are substantially uniform with very little, if any, bowing.  
         [0055]      FIGS. 5E, 5F  and  5 G are top view SEM images  574 ,  576 ,  578 , respectively, that also illustrate the effects of in-situ ashing according to one or more aspects of the present invention versus conventional ex-situ ashing. For example, the SEM image  574  in  FIG. 5E  is a top view of vias  575  formed with conventional ex-situ ash processing. It can be seen that a generous amount of residue  577  exists around the vias (and more particularly down in the vias along the sidewalls) and on the top surface between the vias.  FIGS. 5F and 5G , on the other hand, illustrate vias formed with in-situ ashing according to one or more aspects of the present invention. The vias  579  in  FIG. 5F  were ashed in the same tool and in the same chamber as other processing (e.g., etching), whereas the vias  580  in  FIG. 5G  were ashed in the same tool, but in a different chamber. Regardless, it can be seen that less residue  581 ,  582  (if any) is present in FIGS.  5 F and  5 G, respectively, as compared to the ex-situ ash case presented in  FIG. 5E .  
         [0056]     It is to be appreciated that one or more aspects of the present invention (e.g., in-situ low power, low pressure ash) allows a RIE plasma to be utilized. This, among other things, facilitates the decreased CD bias from in-situ ash as compared to conventional ex-situ ash due to, among other things, a substantially anisotropic nature of the RIE plasma. Additionally, adding O 2  to the low power ash facilitates oxidizing possible Cu residues left over from the in-situ etch-stop etch. The oxidized Cu residues can then be more easily removed by the subsequent wet clean operation further facilitating the improved residue removal.  
         [0057]     According to another aspect of the invention, methods are provided for forming a dual damascene interconnect structure overlying an existing interconnect structure in a semiconductor wafer, which may be employed in a via-first implementation or in a trench-first dual damascene implementation to provide electrical coupling to a conductive feature in the existing interconnect structure. An exemplary via-first method  300  is illustrated in  FIGS. 6A and 6B . While the method  300  is illustrated and described below as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methods according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated.  
         [0058]     Beginning at  302 , the method  300  comprises forming an etch-stop layer over an existing interconnect structure at  304 , forming a low-k dielectric layer over the etch-stop material at  306 , and optionally forming a first BARC layer at  308  over the dielectric layer, in a manner similar to the acts  104 - 108  above. A via resist mask is then formed and patterned at  310 , having an opening in a prospective via region of the wafer. An in-situ process flow  312  is then performed in accordance with this aspect of the invention, wherein a via cavity is formed through the BARC, dielectric, and etch-stop layers, for example, concurrently in a single RIE tool. At  314   a , the exposed BARC layer is etched, using the patterned resist as a mask, and a via main etch is performed at  314   b , creating a via cavity or opening in the dielectric layer. A via over-etch process is then performed at  314   c  to remove the remaining portion of the dielectric material in the via cavity and to expose a portion of the underlying etch-stop layer material. At  316 , an etch-stop layer etch (e.g., an RIE etch operation) is then performed to remove the exposed portion of the etch-stop material, thereby extending the cavity and exposing a conductive feature in the underlying interconnect structure.  
         [0059]     As with the above single damascene case (e.g.,  FIG. 3  above), substantially no other processing is performed between the via etch acts of  314   a - 314   c  and the etch-stop etch of  316 . The via etch at  314   a - 314   c  and the etch-stop etch at  316  may, but need not be, performed in-situ within a single RIE etch tool, wherein other implementations are possible within the scope of the invention, in which the etch-stop etch at  316  is performed concurrently with the via etch  314  or immediately thereafter. In addition, the invention also contemplates alternative implementations in which the via and etch-stop etch acts are performed with substantially no processing steps therebetween. For example, no ashing or wet etch operations are performed between the exemplary via etch  314  and the etch-stop layer etch at  316  in the illustrated method  300 . In this regard, the exemplary method  300  provides coverage of the upper dielectric surface during the etch-stop etch at  316  because the patterned resist mask remains until after the etch-stop etch  316 .  
         [0060]     Although the exemplary method  300  provides in-situ etching of the via cavity through the dielectric layer (e.g.,  314 ) and etch-stop etching to extend the via cavity through the etch-stop layer, other implementations are possible within the scope of the present invention where these or equivalent acts are performed in different etch tools. Moreover, one or more process acts may be performed between the via etch and the etch-stop etch acts in accordance with the invention where the dielectric layer is covered during the etch-stop etch. In the illustrated method  300 , the resist mask from the via etch steps remains during the etch-stop etch  316 . However, other implementations are possible within the scope of the invention, wherein the all or a portion of the dielectric is covered by any means during the entirety of, or during a portion of, the etch-stop etch  316 . Further, although the exemplary method  300  provides a multi-step etch (e.g.,  314   b ,  314   c ) through the dielectric layer, other implementations are contemplated, wherein any of the BARC etch, the via etch, and/or the etch-stop etch acts may be single step or multi-step operations, within the scope of the present invention.  
         [0061]     In the exemplary method  300 , the etching acts  314   a - 314   c  and  316  are performed in a single RIE etch tool, with appropriate etch chemistries being changed accordingly, to remove material from the exposed layer (e.g., from the BARC layer, then the dielectric layer, and then the etch-stop layer). Furthermore, while illustrated and described with respect to organic BARC materials, OSG type low-k dielectric material, and SiC or SiN etch-stop layer materials, any appropriate materials may be employed in forming these layers in accordance with the invention, where appropriate etch chemistries and selectivities may be selected in performing the etch operations  314 - 316  to fabricate the via cavity. In the illustrated method  300 , the main etch at  314   b  removes the majority of the dielectric material in the cavity, leaving about 1000-2000 Å of OSG low-k dielectric material remaining. The process parameters are then switched to the over-etch at  314   c , which is time controlled to stop on the etch-stop layer, wherein the exemplary via over-etch at  314   c  has a higher selectivity to the etch-stop layer than does the via main etch at  314   b.    
         [0062]     With the etch-stop layer exposed, the etch process is again adjusted for etching the etch-stop material at  316  with a selectivity to the underlying (e.g., pre-existing) interconnect structure, so as to expose an underlying conductive feature (e.g., copper structure). As with the single damascene case, the dual damascene method  300  preserves the resist mask over the dielectric layer while etching the exposed portion of the etch-stop layer at  316 , since there is no intervening ashing or wet etch process to remove the via resist mask. Consequently, etch-stop etch related damage to the dielectric material is mitigated or avoided during the etch-stop etch at  316 , by which the via CD and profile are protected.  
         [0063]     After the in-situ process at  312 , the method  300  proceeds to  318 , where an ashing operation is performed to remove the resist mask initially formed at  310 , and the BARC material deposited at  308 . As discussed above with regard to the single damascene case, according to one or more aspects of the present invention, the ashing  318  is performed in-situ in the same tool either in the same or a different chamber. The in-situ ashing allows a RIE plasma to be utilized to more effectively remove residues. Similarly, oxygen can be added to facilitate removing Cu residues. Also, the in-situ process allows the via etch  314   a - 314   c , etch-stop etch  316  and ash  318  to be done more efficiently, cost effectively and with less actions. For example, the ashing  318  can be performed at a power of about 150 to 400 W and a pressure of about 20 to 80 mT. Further, the operation  318  may be performed for a time of about 15 to 60 seconds with an oxygen (O 2 ) flow of about 100 to 500 sccm and at a chuck temperature of about 20 to 40 degrees Celsius. Other ash chemistries such as H 2 /Ar, H 2 /He, H 2 /N 2  O 2 /H 2 , O 2 /N 2  can also be used. As a matter of reference, in-situ acts  314   a ,  314   b ,  314   c ,  316  and  318  are depicted as  312 ′ in the exemplary flow  300 . A wet clean operation is then optionally performed at  320  to remove any residue remaining from the RIE etch and ash acts.  
         [0064]     Referring also to  FIG. 6B , a second BARC layer is then formed at  322 , and a trench resist mask is formed and patterned at  324 . A two step trench etch  326  is then performed, comprising a trench BARC etch at  328   a  and a patterned trench main etch at  328   b . Thereafter at  330 , another ashing operation is performed to strip the trench resist mask and the second BARC layer, followed by another wet clean operation at  332 . The ashing operation  330  is once again performed in-situ according to one or more aspects of the present invention (e.g., as set forth above with regard to operations  318 ,  118 ). As a matter of reference, in-situ acts  328   a ,  328   b  and  330  are depicted as  326 ′ in the exemplary flow  300 . It will be appreciated, however, that the ashing  330  can also be performed according to conventional ex-situ ash processes.  
         [0065]     A diffusion barrier is then formed at  334 , and a seed copper layer is deposited over the diffusion barrier at  336 , to facilitate subsequent copper filling of the via and trench cavities. The trench and via cavities are then filled with copper using an ECD process at  338 , and a CMP process is performed at  340  to planarize the upper surface of the device, before the method  300  ends at  342 . It is noted that alternative implementations are possible within the scope of the invention, wherein the trench is formed prior to formation of the via cavity, wherein the via etch and etch-stop etch operations are performed concurrently, and/or with substantially no processing operations therebetween, and/or with the dielectric layer at least partially covered during the etch-stop etch, as described above.  
         [0066]     Referring now to  FIGS. 7A-7N , another exemplary wafer  402  is illustrated undergoing dual damascene interconnect processing in accordance with the invention.  FIG. 7A  illustrates the wafer  402  at an intermediate stage of fabrication, comprising a silicon substrate  404 , in which a conductive silicide structure  405  is formed. An initial contact layer is formed over the substrate  404 , comprising a dielectric  406  with a tungsten contact  407  extending therethrough, and electrically contacting the silicide  405 . An existing interconnect structure overlies the contact layer, including an etch-stop layer (not shown) and a dielectric  408  in which a conductive feature  410  is formed, such as copper trench metal, to provide electric coupling to the tungsten contact  407 . As with the single damascene methods of the invention, the dual damascene processing of the present invention may be carried out in fabricating an interconnect structure over an initial contact structure, such as illustrated in  FIG. 7A , and/or in forming such a structure over another single or dual damascene structure in a multi-layer interconnect network structure.  
         [0067]     A SiN or SiC etch-stop layer  412  is formed over the existing interconnect dielectric material  408  and over the conductive feature  410 , for example, to a thickness  412 ′ of about 600-800 Å, and a dielectric layer  414 , such as a low-k OSG dielectric material or the like, is formed over the etch-stop layer  412  to a thickness  414 ′ of about 7000-8000 Å. An organic BARC layer  416  overlies the dielectric  414 , having a thickness of about 600-800 Å, and a via resist mask  418  is formed over the BARC layer  416 , having an opening  420  in a prospective via region. In  FIG. 7B , a via BARC etch process  422  is performed to remove the BARC layer  416  in the via region  420 . In  FIG. 7C , a via main etch process  424  is used to form a via cavity  426  in the dielectric layer  414 , leaving a thickness  428  of dielectric material  414  unetched at the bottom of the via cavity  426  (e.g., about 1000-2000 Å). A via over-etch process  430  is employed in  FIG. 7D  to further form the cavity  426  through the rest of the dielectric layer  414 , stopping on and exposing a portion of the underlying etch-stop layer  412 . An etch-stop etch  432  is performed immediately thereafter (e.g., concurrently with the over-etch  430 ) in  FIG. 7E  to expose the underlying conductive contact  410 .  
         [0068]     Thereafter in  FIG. 7F , a resist ashing process  434  is used to remove the remaining resist mask  418  layer and the BARC layer  416 , and a wet clean operation  436  is performed in  FIG. 7G . According to one or more aspects of the present invention, the ashing process  434  is performed in-situ in the same processing tool that performs the other operations (e.g., etching) in either the same or a different processing chamber within the tool. The ashing  434  is performed in an efficient and cost effective manner by utilizing a RIE plasma and oxygen that more effectively removes Cu and other residues as compared to conventional ex-situ ashing. Additionally, the ashing can be done at a power of about 150 to 400 W and a pressure of about 20 to 80 mT, for example. Further, the operation  434  may be performed for a time of about 15 to 60 seconds with an oxygen (O 2 ) flow of about 100 to 500 sccm and at a chuck temperature of about 20 to 40 degrees Celsius. Other ash chemistries such as H 2 /Ar, H 2 /He, H 2 /N 2  O 2 /H 2 , O 2 /N 2  can also be used.  
         [0069]     As illustrated in  FIG. 7H , a second BARC layer  438  is then formed over the wafer  402 , wherein some of the BARC material  438 ′ is formed at the bottom of the via cavity  426 . A trench resist mask  440  is formed over the BARC layer  438 , and a trench BARC etch process  442  is performed in  FIG. 7I  to remove the BARC material in the prospective trench region of the wafer  402 , with a portion of the BARC  438 ′ remaining in the via cavity  426 . Thereafter in  FIG. 7J , an RIE trench etch process  444  is employed to form a trench cavity  446  in the dielectric layer  414 , wherein a certain amount of residual BARC material  438 ′ may still remain in the bottom of the via cavity  426  during the trench etch process  444 . Following the trench etch process  444 , another ashing process  448  is performed in  FIG. 7K  to remove the trench resist mask  440  and any remaining BARC material (e.g., BARC  438 ′ in the via cavity  426 ), after which another wet clean process  450  is performed in  FIG. 7L . According to one or more aspects of the present invention, the ashing process  448  is performed in-situ rather than ex-situ, such as is described above with regard to  434  and  234 . The ashing operation  448  can also be performed according to conventional ex-situ ash processes.  
         [0070]     As illustrated in  FIG. 7M , a copper diffusion barrier layer  452  and a copper seed layer  454  are formed, after which copper fill material  456  is deposited over the wafer  402  to fill the trench and via cavities  446  and  426 , respectively, for example, using an ECD process. Thereafter in  FIG. 7N , the wafer  402  is planarized, for example, using a CMP process, to complete the conductive dual damascene trench and via structure. One or more subsequent interconnect levels or layers may thereafter be constructed over the structure of  FIG. 7N , for example, using the above-described or other single and/or dual damascene fabrication techniques. Any number of such layers or levels may be fabricated in accordance with the present invention, to provide electrical coupling to the conductive feature (e.g., silicide structure  406 ) in the wafer  402 .  
         [0071]     Although the invention has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings and the present invention is intended to include the same. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” Also, the term “exemplary” as utilized herein merely means an example, rather than the best.