Abstract:
In damascene process integration, a reducing plasma is applied after the etch stop or barrier layer is opened over a copper layer. Currently known methods for opening barrier layers suffer from the disadvantage that they cause at least some of the underlying copper to oxidize to copper oxide.. Because copper oxide is selectively removed by subsequent wet cleaning, voids can form where damaged copper (e.g., copper oxide) is removed, thus compromising the reliability of metal-to-metal contact in vias. The present invention advantageously overcomes this and other disadvantages of the prior art through the use of a hydrogen plasma following the barrier layer opening step, which repairs damaged copper (e.g., reduces copper oxide to copper), thus preventing and/or diminishing defects in metal-to-metal contacts in vias and concomitantly improving the reliability of the same.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to the field of semiconductor device fabrication and, more particularly, to methods for improving metal-to-metal contact in vias by decreasing and/or repairing damage to metal layers during formation of damascene structures in semiconductor devices.  
         [0002]     The integration of a large number of components on a single integrated circuit (IC) chip requires complex interconnects. Ideally, the interconnect structures should be fabricated with minimal signal delay and optimal packing density. The reliability and performance of integrated circuits may be affected by the quality of their interconnect structures. Advanced multiple metallization layers have been used to accommodate higher packing densities as devices shrink below sub-0.25 micron design rules. One such metallization scheme is a dual damascene structure formed by a dual damascene process. The dual damascene process is a sequential mask/etch process to form a two-level structure, such as a via connected to a metal line situated above the via.  
         [0003]     In contrast to a single damascene process, the via and the trench are simultaneously filled with metal. Thus, compared to the single damascene process, the dual damascene process offers the advantage of process simplification and low manufacturing cost.  
         [0004]     To improve the performance, reliability and density of the interconnects, the microelectronics industry has recently begun migrating away from the use of aluminum (Al) and/or its alloys for the interconnects. As such, advanced dual damascene processes have begun using copper (Cu) as the material of choice because copper has high conductivity, extremely low resistivity (about 1.7 μΩcm) and good resistance to electromigration. One difficulty encountered with copper is that copper-to-copper connections between the first level interconnect metal layer and a copper via-filling plug are subject to reliability problems due to chemical and physical damage to the first level interconnect metal layer during formation of the dual damascene structure.  
         [0005]      FIGS. 1A-1C  illustrate a sequence of fabrication steps for a known dual damascene process as applied to interconnect formation. As shown in  FIG. 1A , the process begins with the deposition of a first insulating layer  140  over a first level interconnect metal layer  120 , which in turn is formed over or within a semiconductor substrate  100 . A second insulating layer  160  is next formed over the first insulating layer  140 . Etch stop layers  150 ,  150 ′ are typically formed between the first and second insulating layers  140 ,  160  and between the first insulating layer  140  and the first level interconnect metal layer  120 . The second insulating layer  160  is patterned by photolithography with a first mask (not shown) to form a trench  170  corresponding to a metal line of a second level interconnect. The etch stop layer  150  prevents the upper level trench pattern  170  from being etched through to the first insulating layer  140 .  
         [0006]     As illustrated in  FIG. 1B , a second masking step followed by an etch step is applied to form a via  180  through the etch stop layer  150  and the first insulating layer  140 . The second etch stop layer or barrier layer  150 ′ is formed between the first level interconnect metal layer  120  and the first insulating layer  140  during the formation of the dual damascene structure  125 . Thus, a further step is required to open barrier layer  150 ′ and expose the underlying first level interconnect metal layer  120 . After the etching is completed, both the trench  170  and the via  180  are filled with metal  122  (also referred to as via-filling plug  122 ), which is typically copper (Cu), to form a damascene structure  125 , as illustrated in  FIG. 1C .  
         [0007]      FIGS. 1D-1F  depict one problematic result that arises with known damascene processing techniques. Among other contaminants, copper oxide  121  is formed in the first level interconnect metal layer  120  by the oxidizing etchants conventionally used to open barrier layer  150 ′, as shown in  FIG. 1D . Such damage to first level interconnect metal layer  120  often further includes undercutting (i.e., removal of material from first level interconnect metal layer  120  under barrier layer  150 ′) of the first level interconnect metal layer  120  near the edges of barrier layer  150 ′ (see also  FIG. 1F ). Copper oxide and other contaminants must be removed prior to formation of the via-filling plug  122 , which is typically accomplished with a wet clean process. As shown in  FIGS. 1E-1F , removal of copper oxide  121  in such a wet clean process sometimes causes voids  127  to occur during formation of the via-filling plug  122 . Such voids  127  compromise the reliability of the electrical connection between plug  122  and the first level interconnect metal layer  120  and are particularly likely to occur near or under the edges of the barrier layer  150 ′, as shown in  FIGS. 1E-1F .  
         [0008]      FIG. 1F  is a detail view of region  190  shown in  FIG. 1E .  FIG. 1F  shows the aforementioned undercutting of first level interconnect metal layer  120  near the edges of barrier layer  150 ′, as well as voids  127  that can form due, at least in part, to such undercutting.  
         [0009]     In the past, hydrogen plasmas have been used after the wet clean process described above. However, such an approach is disadvantageous because the wet clean process selectively removes copper oxides  121  from first level interconnect metal layer  120 , thus giving rise to greater potential for incidence of voids  127  and other anomalies in subsequently formed metal-to-metal contacts, e.g., between via-filling plug  125  and first level interconnect metal layer  120 . The present invention advantageously overcomes this problem by at least partly reducing copper oxide to copper before the wet clean process, thus reducing the amount of copper material removed by the wet clean process and concomitantly improving the reliability of subsequently formed metallic connections.  
         [0010]     As mentioned above, copper interconnect is the most promising metallization scheme for the future generation high-speed ULSI, primarily because of lower electrical resistivity (1.7 vs. 2.3 μΩcm) and electro/stress-migration resistance than the conventional aluminum-based materials. However, copper metallization suffers from disadvantages, including those described above. As a result, in order to adopt copper interconnects for ULSI, suitable methods for improving the reliability of copper-to-copper contact in vias are needed.  
         [0011]     As mentioned above, of the several schemes proposed for fabricating copper interconnects, the most promising method appears to be the dual damascene process shown in  FIGS. 1A-1C . Using this method, the trenches for conductors and holes for vias are patterned in blanket dielectrics, and then the desired metal is deposited into the trenches and holes in one step. Chemical mechanical planarization (CMP) is conventionally used to remove the unwanted surface metal extending over the uppermost dielectric, while leaving the desired metal in the trenches and vias. This leaves a planarized surface for subsequent metallization to build multilevel interconnect structures. Unfortunately, this technology not only uses a large amount of expensive consumables for the CMP process and the associated waste disposal problem but also is very wasteful of copper. Typically, the conductors and vias in a given metallization level occupy only a small proportion of the deposited copper, while the bulk of the copper is removed by CMP, rendering the technology very expensive. There is thus a strong economic incentive to minimize waste wherever possible, and losses that can occur due to defective metal-to-metal contact in vias are especially onerous because they occur and/or are discovered only after substantial fabrication is complete.  
         [0012]     The ordinarily skilled artisan will readily appreciate that a number of processes are known for forming dual damascene structures. For instance, trenches may be etched through the upper insulating layer, after which a further mask may be employed to etch the contact vias, or the etch continues through a previously defined, buried hard mask (the so-called “trench first” approach). Alternatively, vias may first be etched through the upper and lower insulating layers, after which the via in the upper insulating layer may be widened to form a trench (the so-called “via first” approach). The “via first” dual damascene approach has been widely adopted for small geometry devices.  
         [0013]     Due to the disadvantageous results (as depicted in  FIGS. 1E-1F ) that can arise in conventional damascene techniques, great care is taken to minimize physical and chemical damage to the first level interconnect metal (copper) layer  120 . Nevertheless, known damascene techniques still frequently result in formation of voids  127 , which are undesirably detrimental to the integrity of the electrical connection between the first level interconnect metal layer  120  and the conductive via-filling plug  122 .  
         [0014]     It can thus be seen that a need exists for improved dual damascene processing techniques that provide improved electrical connections in vias.  
       BRIEF SUMMARY OF THE INVENTION  
       [0015]     The present invention, in an exemplary embodiment, makes advantageous use of the reducing properties of hydrogen plasma to avoid the above-described disadvantages in the prior art. According to an exemplary embodiment of the present invention, a hydrogen plasma is applied after the barrier layer is opened in dual damascene process integration. Currently known methods for opening barrier layers suffer from the disadvantage that they cause at least some of the underlying copper to oxidize to copper oxide. Because copper oxide is selectively removed by subsequent wet cleaning, voids can form where damaged copper (e.g., copper oxide) is removed, thus compromising the reliability of metal-to-metal contact in the via. The present invention advantageously overcomes this and other disadvantages of the prior art through the use of hydrogen plasma following the barrier layer opening step, which heals damaged copper (e.g., reduces copper oxide to copper), thus preventing and/or diminishing defects in subsequently formed metal-to-metal contacts in vias. In currently preferred embodiments, the application of the hydrogen plasma is carried out in the same substantially vacuum environment, most preferably in the same chamber, as the barrier layer opening step to minimize exposure of the copper to oxidation from ambient air and to simplify fabrication processes.  
         [0016]     Following the hydrogen plasma etch step, wet cleaning selectively removes any remaining copper oxide and other contaminants in preparation for formation of the via-filling plug. Since the hydrogen plasma step heals (e.g., reduces copper oxide to copper) the damage to the copper caused by prior processing, less copper is removed by subsequent wet cleaning, and voids are less likely to form in the copper. As a result, improved electrical connection between the first level interconnect metal layer and the conductive plug filling the via is provided by the present invention.  
         [0017]     Further advantages of the present invention will be more apparent to the ordinarily skilled artisan from the ensuing detailed description and accompanying drawings, which illustrate what are currently considered to be preferred embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0018]     In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:  
         [0019]      FIG. 1A  is a cross-sectional view of a conventional dual damascene formation process for a semiconductor device at a preliminary stage of fabrication;  
         [0020]      FIG. 1B  is a cross-sectional view of the semiconductor device of  FIG. 1A  at a subsequent stage of production;  
         [0021]      FIG. 1C  is a cross-sectional view of the semiconductor device of  FIG. 1B  at a subsequent stage of production;  
         [0022]      FIG. 1D  is a cross-sectional view of the semiconductor device of  FIG. 1B  at a subsequent stage of production;  
         [0023]      FIG. 1E  is a cross-sectional view of the semiconductor device of  FIG. 1D  at a subsequent stage of production;  
         [0024]      FIG. 1F  is a detail view of the region indicated at  190  in the semiconductor device of  FIG. 1E ;  
         [0025]      FIG. 2A  is a cross-sectional view of a dual damascene formation process for a semiconductor device according to the present invention at a preliminary stage of fabrication;  
         [0026]      FIG. 2B  is a cross-sectional view of the semiconductor device of  FIG. 2A  at a subsequent stage of production;  
         [0027]      FIG. 2C  is a cross-sectional view of the semiconductor device of  FIG. 2B  at a subsequent stage of production;  
         [0028]      FIG. 2D  is a cross-sectional view of the semiconductor device of  FIG. 2C  at a subsequent stage of production;  
         [0029]      FIG. 2E  is a cross-sectional view of the semiconductor device of  FIG. 2D  at a subsequent stage of production;  
         [0030]      FIG. 2F  is a cross-sectional view of the semiconductor device of  FIG. 2E  at a subsequent stage of production;  
         [0031]      FIG. 2G  is a cross-sectional view of the semiconductor device of  FIG. 2F  at a subsequent stage of production;  
         [0032]      FIGS. 2H-2K  are cross-sectional views illustrating a sequence of fabrication steps of an alternative embodiment of the invention;  
         [0033]      FIG. 3  is a cross-sectional view illustrating yet another embodiment of the invention; and  
         [0034]      FIG. 4  illustrates an electronic system having a memory cell with a copper damascene structure according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     In the following detailed description, reference is made to various specific embodiments in which the invention may be practiced. These embodiments are described with sufficient detail to enable those skilled in the art to practice the invention, but it is to be understood that other embodiments may be employed and structural and electrical changes may be made without departing from the spirit or scope of the present invention. Currently known methods for forming dual damascene structures are described herein in conjunction with the description of the currently preferred embodiments, but the present invention is intended to subsume all methods currently known or discovered in the future for forming dual damascene structures and other like structures and structures requiring like processing.  
         [0036]     The term “substrate” used in the following description may include any semiconductor-based structure that has a semiconductor surface. The term should be understood to include silicon, silicon-on-insulator (SOI), silicon-on-sapphire (SOS), doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. The semiconductor need not be silicon-based. The semiconductor could be silicon-germanium, germanium, or gallium arsenide. When reference is made to a “substrate” in the following description, previous process steps may have been utilized to form regions or junctions in or on the base semiconductor or foundation.  
         [0037]     The term “copper,” as used herein, is intended to include not only elemental copper, but also copper with other trace metals or in various alloyed combinations with other metals as known in the art, as long as such alloy retains the physical and chemical properties of copper. The term “copper” is also intended to include conductive oxides of copper.  
         [0038]     In copper dual damascene etch processes, great care is taken to minimize physical and chemical damage to the lower copper surface. Nonetheless, chemical damage (e.g., oxidation) is unavoidable with known etching techniques. The present invention provides a way to heal surface chemical damage at the end of the dual damascene structure formation loop by applying a hydrogen plasma after the barrier layer removal step exposes the underlying copper layer.  
         [0039]     The barrier layer removal step conventionally uses mixtures of fluorocarbons and oxygen to open the barrier layer and expose the underlying copper layer for the second metallization step (e.g., formation of a via-filling plug). If the copper surface is oxidized, it can be removed by subsequent wet clean chemistries applied prior to metallization, thus giving rise to greater potential for compromised reliability in metal-to-metal connection in the via.  
         [0040]     According to the present invention, a hydrogen plasma is applied after the barrier layer opening step of the etch process to reduce damaged copper (e.g., copper oxide) to copper and thereby heal damage to the copper layer. In currently preferred embodiments, the application of the hydrogen plasma is carried out in the same substantially vacuum environment, more preferably in the same chamber, as the barrier layer removal step to minimize exposure to oxidation from ambient air and to simplify fabrication processes. In this way, the amount of damaged copper removed during wet cleaning is minimized, and the potential for undercutting of copper from beneath the barrier layer (e.g., resulting in the formation of voids) is diminished. As a result, the present invention helps improve metal-to-metal contact in vias in damascene structures formed according to the methods of the invention.  
         [0041]     Rather than removing damaged copper (e.g., copper oxide) formed during the barrier layer opening step, the damaged copper is healed (e.g., reduced) by the methods according to the invention. Consequently, subsequent wet cleaning removes less copper material, thus improving the reliability of metal-to-metal connection formed in the via.  
         [0042]     Conventional etchants used to open the barrier layer damage the underlying copper layer through, for example, oxidation. Oxidizing ions in conventional etchants strike the copper layer during barrier layer removal, thereby oxidizing the copper to copper oxide. The present invention overcomes the disadvantages of the prior art by healing this damage to the copper layer. In currently preferred embodiments, a hydrogen plasma is applied before a wafer is removed from the vacuum environment in which the barrier layer removal step is performed. The hydrogen plasma can be applied in the same chamber as the barrier layer removal step is performed or in a different chamber. It is currently preferred to apply the hydrogen plasma in the same chamber as the barrier layer removal step is performed in order to minimize the exposure of the wafer to ambient air, which can oxidize the copper to copper oxide. In this way, damaged copper (e.g., copper oxide) is healed (e.g., reduced), and further damage is prevented.  
         [0043]     The hydrogen plasma can additionally include inert gases, such as argon and nitrogen, to facilitate contact between hydrogen ions and the damaged copper (e.g., copper oxide). The exposure to the hydrogen plasma is preferably in the range of 10 to 60 seconds, more preferably in the range of 10 to 30 seconds. The ordinarily skilled artisan will be able to determine the appropriate duration of the hydrogen plasma exposure in view of the composition of the plasma and the materials of the wafer being treated.  
         [0044]     The pressure of the hydrogen plasma must be sufficient to create good plasma density, for example, about 100 milliTorr. The energy for the reaction comes from the reduction process, so temperature does not have a significant impact on reaction rate.  
         [0045]     According to current belief, the present invention may be used with metal layers of copper, as well as quasi-noble metals that have less stable oxides, such as, for example, palladium, platinum, nickel, copper, gold, silver, and cobalt, since oxides of these metals are easily reducible.  
         [0046]      FIGS. 2A-2K  are cross-sectional views illustrating a sequence of fabrication steps for forming a dual damascene copper interconnect in association with a semiconductor device according to the teachings of the present invention.  FIG. 2A  depicts a portion of an insulating layer  251  formed over a semiconductor substrate  250 , on or within which a metal layer  252  has been formed. The metal layer  252  may also be formed on or in the substrate  250 . The metal layer  252  represents a lower metal interconnect layer which is to be later interconnected with an upper metal interconnect layer. The metal layer  252  may be formed of copper (Cu), for example, but other conductive materials, such as palladium, platinum, nickel, copper, gold, silver, and cobalt and their alloys, may be used also.  
         [0047]      FIG. 2B  illustrates the structure following the next series of processing steps. As shown in  FIG. 2B , a barrier layer  254  and a first intermetal insulating layer  255  are formed overlying the insulating layer  251  and the metal layer  252 . In an exemplary embodiment of the present invention, the first intermetal insulating layer  255  is blanket deposited by spin coating to a thickness of about 2,000 Angstroms to 15,000 Angstroms, more preferably of about 6,000 Angstroms to 10,000 Angstroms. The first intermetal insulating layer  255  may be cured at a predefined temperature, depending on the nature of the material. Other known deposition methods, such as chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), or physical vapor deposition (PVD), may also be used for the formation of the first intermetal insulating layer  255 , as appropriate for a given circumstance.  
         [0048]     In one embodiment, the first intermetal insulating layer  255  is formed of a conventional insulating oxide, such as silicon oxide (SiO 2 ). In alternative embodiments, the first intermetal insulating layer  255  is formed of a low dielectric constant material such as, for example, polyimide, spin-on-polymers (SOP), parylene, flare, polyarylethers, polytetrafluoroethylene, benzocyclobutene (BCB), SILK, fluorinated silicon oxide (FSG), NANOGLASS® or hydrogen silsesquioxane, among others. The present invention is not limited, however, to the above-listed materials, as other insulating and/or dielectric materials known in the industry may also be used.  
         [0049]      FIG. 2C  illustrates the structure following the next series of processing steps. As shown in  FIG. 2C , a second intermetal insulating layer  257  is formed overlying an optional etch stop layer  256 . According to the present invention, the second intermetal insulating layer  257  can be formed, for example, by deposition to a thickness of about 2,000 Angstroms to about 15,000 Angstroms, more preferably of about 6,000 Angstroms to 10,000 Angstroms. Other deposition methods, such as the ones mentioned above with reference to the formation of the first intermetal insulating layer  255 , can also be used. The second intermetal insulating layer  257  can be formed of the same material used for the formation of the first intermetal insulating layer  255  or a different material.  
         [0050]     The optional etch stop layer  256  and the barrier layer  254  can be formed of any appropriate etch stop material, such as, but not limited to, silicon nitride (Si 3 N 4 ).  
         [0051]      FIG. 2D  illustrates the structure following the next series of processing steps in a “via first” approach to dual damascene process integration. It is to be noted that the present invention is not limited to such a “via first” approach but, rather, is intended to include all methods, currently known or hereafter discovered, for forming damascene structures and structures requiring like processing. As shown in  FIG. 2D , a first photoresist layer  258  is formed over the second intermetal insulating layer  257 . In exemplary embodiments, the first photoresist layer  258  is formed to a thickness of about 2,000 Angstroms to about 3,000 Angstroms. The first photoresist layer  258  is then patterned with a mask (not shown) having images of a via pattern  259 .  
         [0052]     Thus, as shown in  FIG. 2E , a via  265  can be formed by etching through the first photoresist layer  258  and into the second intermetal insulating layer  257  with a first etchant, subsequently etching through optional etch stop layer  256  and into the first intermetal insulating layer  255  with a second etchant, followed by a subsequent barrier layer removal step comprising etching through barrier layer  254 . Removal of the barrier layer  254  is performed at a stage after the trench  267  (see  FIG. 2G ) has been formed. As one of ordinary skill in the art will understand upon reading this disclosure, the etchants (not shown) may be selected in accordance with the characteristics of the first and second intermetal insulating materials  255 ,  257 , optional etch stop layer  256 , and barrier layer  254  so that the insulating materials are selectively etched until the second etchant reaches the metal layer  252 .  
         [0053]     After the formation of the via  265  through the second and first intermetal insulating layers  257 ,  255  and optional etch stop layer  256 , a trench  267 , as shown in  FIG. 2G , is formed by photolithography techniques, as shown in  FIG. 2F . As shown in  FIG. 2F , a second photoresist layer  262  is formed over the second intermetal insulating layer  257 , preferably to a thickness of about 2,000 Angstroms to about 3,000 Angstroms, and then patterned with a mask (not shown) having images of a trench pattern  263 . According to the present invention, the trench pattern  263  is then etched into the second intermetal insulating layer  257  using second photoresist layer  262  as a mask to form trench  267 , as shown in  FIG. 2G . The thickness of the first intermetal insulating layer  255  defines the depth of the via  265 , as shown in  FIGS. 2F-2G . The thickness of the second intermetal insulating layer  257  defines the depth of the trench  267  of  FIG. 2G . As noted above, barrier layer  254  is removed after formation of trench  267 .  
         [0054]     The etching of the trench  267  may be accomplished using the same etchant employed to form the via  265 , as shown in  FIG. 2E , or a different etchant.  
         [0055]     Subsequent to the formation of trench  267 , the second photoresist layer  262  is removed so that further steps to create the copper dual damascene structure  200 , shown in  FIG. 2K , may be carried out.  
         [0056]     Whether a “trench first” or a “via first” approach to damascene process integration is used, a reducing plasma is applied after barrier layer  254  is opened.  FIG. 2G  illustrates a hydrogen plasma being applied after barrier layer  254  is opened to reduce any copper oxide that may have formed from the metal layer  252  during prior processing. The hydrogen plasma is applied in the same substantially vacuum environment as the barrier layer removal step, preferably in the same chamber.  
         [0057]      FIG. 2H  illustrates the structure following the next sequence of fabrication steps in alternative embodiments of the present invention.  FIGS. 2H -2K  show a diffusion barrier layer  272  that may optionally be included in a semiconductor device made according to the present invention. As shown in  FIG. 2H , a diffusion barrier layer  272  is formed on the via  265  and the trench  267  to a thickness of about 50 Angstroms to about 200 Angstroms, more preferably of about 100 Angstroms.  
         [0058]     In one embodiment according to the teachings of the present invention, the diffusion barrier layer  272  is formed of tungsten-nitride (WN 2 ) by atomic layer deposition (“ALD”). One example of a method for depositing tungsten-nitride (WN 2 ) by atomic layer deposition is described in an article by Krause, J. W. et al., entitled “Atomic Layer Deposition of Tungsten Nitride Films Using Sequential Surface Reaction,”  Journal of Electrochemical Soc.,  147:3, 1175-81 (2000). According to the teachings of the invention, a thin layer of WN 2  prepared by ALD is used as the diffusion barrier layer  272  in building copper interconnects for semiconductor devices. According to one embodiment of the invention, the deposition of the tungsten nitride film as the diffusion barrier layer  272  is performed at a temperature of about 600 to 800 degrees Kelvin. In one embodiment according to the teachings of the present invention, a tungsten-nitride (WN 2 ) layer is formed as the diffusion barrier layer  272  such that the diffusion barrier layer  272  is less than five atomic layers thick. According to the teachings of the present invention, these atomic layers are so uniform that a vertical wall as well as a short sidewall obtain an equal thickness. In these embodiments, x-ray photoelectron spectroscopy depth profiling experiments evidence that the film diffusion barrier layer  272  has a WN 2  stoichiometry with low C and  0  impurity concentrations. Further, x-ray diffraction investigation reveals that the tungsten nitride films serving as the diffusion barrier layer  272  are microcrystalline. Atomic force microscopy measurements of the deposited film serving as the diffusion barrier layer  272  evidence a remarkably flat surface indicating smooth film growth for the diffusion barrier layer  272 .  
         [0059]     In one embodiment of the invention, the tungsten-nitride (WN 2 ) diffusion barrier layer  272  is simultaneously deposited in both the via  265  and the trench  267 . However, the invention is not limited to this embodiment. Thus, in an alternative embodiment, the tungsten-nitride (WN 2 ) diffusion barrier layer  272  is deposited first in the via  265  before the formation of the trench  267 , and then in the trench  267  after its respective formation. According to the teachings of the present invention, in the case of either embodiment, after the formation of the diffusion barrier layer  272 , horizontal portions of the tungsten-nitride (WN 2 ) material, serving as the diffusion barrier layer  272 , which formed above a top surface of the second intermetal insulating layer  257  are removed by either an etching or a polishing technique to form the structure illustrated in  FIG. 2I . In one embodiment according to the teachings of the present invention, CMP is used to polish away excess tungsten-nitride (WN 2 ) material above the second intermetal insulating layer  257  and the trench  267  level. According to the teachings of the present invention, the second intermetal insulating layer  257  acts as a polishing stop layer when CMP is used.  
         [0060]      FIG. 2J  illustrates the structure following the next sequence of fabrication steps. As shown in  FIG. 2J , a conductive material  280  comprising, for example, copper (Cu) is deposited to fill in both the via  265  and the trench  267 . In one embodiment according to the teachings of the present invention, the copper is selectively deposited by chemical vapor deposition (CVD) at a low temperature. Some examples of methods for selective deposition of copper by CVD at low temperature are described in an article by Kaloyeros et al., entitled “Blanket and Selective Copper CVD From Cu(fod) 2  For Multilevel Metallization,”  Mat. Res. Soc. Symp. Proc.,  Vol. 181 (1990), and in an article by Eisenbraun et al., entitled “Selective and Blanket Low-Temperature Copper CVD for Multilevel Metallization,”  Materials Research Society Conference Proceedings,  ULSI-VII, 397-401 (1992), the disclosures of each of which are incorporated by reference herein.  
         [0061]     In one embodiment according to the teachings of the present invention, copper films are deposited by selective CVD at a temperature of about 300-400° Celsius in an atmosphere of pure H 2  from the β-diketonate precursor bis (6,6,7,8,8,8-heptafluoro-2,2-dimethyl  1-3,5 -octanedione) copper (II), Cu(fod) 2 . In an alternative embodiment according to the teachings of the present invention, copper films are deposited by selective CVD at a temperature of about 300-400° Celsius in an atmosphere of pure H 2  or Ar from the β-diketonate precursor bis (6,6,7,8,8,8-heptafluoro-2,2-dimethyl  1-3,5 -octanedione) copper (II), Cu(fod) 2 . According to the teachings of the present invention, the reactor is first pumped down to a base pressure of less than 5×10 −7  Torr. Then, the source compound is introduced into the sublimator, which is heated to between 40 and 75° Celsius. A mass flow controller is employed to control the flow of the mixed gas precursor into the reactor. Deposition is carried out using argon and hydrogen as carrier gases. According to the teachings of the present invention, the substrates are heated from 300 to 400° Celsius. The pressure during deposition ranges between 1 and 10 Torr, and gas flow ranges from 30 to 55 sccm.  
         [0062]     Since the temperatures involved in the embodiments of the present invention are relatively low, any low-k dielectric material, including polymers, which can withstand the above temperature range (300-400° C.), can be readily used with this technology as interlayer dielectrics, e.g., the first and second intermetal insulating layers  255 ,  257 .  
         [0063]      FIG. 2K  illustrates the structure following the next sequence of fabrication steps. According to the teachings of the present invention, as shown in  FIG. 2J , after the deposition of the conductive material  280 , excess material formed above the surface of the second intermetal insulating layer  257  may be removed by either an etching or a polishing technique to form the copper dual damascene structure indicated generally at  200  in  FIG. 2K . In one embodiment of the present invention, CMP is used as the technique to polish away excess conductive material above the second intermetal insulating layer  257  and the trench  267  level. In this manner, the second intermetal insulating layer  257  acts as a polishing stop layer when CMP is used.  
         [0064]     As one of ordinary skill in the art will appreciate upon reading this disclosure, the above-described embodiments for selectively depositing conductive material  280  by chemical vapor deposition (CVD) at a low temperature, according to the teachings of the present invention, helps to reduce the amount of wasted copper in the process.  
         [0065]     According to the teachings of the present invention, the selective deposition of copper by CVD described above is not the only method that can be employed for depositing the conductive material  280 . According to another embodiment of the invention, copper can be selectively deposited by an electroless plating technique. In some instance, an electroless plating technique is more attractive than conventional electroplating methods. For example, in some embodiments, electroless plating is more advantageous than electroplating because of the low cost of tools and materials. An example of a study for electroless plating is provided in an article by Shacham-Diamand et al., entitled “Copper Electroless Deposition Technology for Ultra-Large-Scale-Integration (ULSI) Metallization,” Microelectronic Engineering, Vol. 33, pp. 47-48 (1997), the disclosure of which is incorporated by reference herein. As will be understood by one of ordinary skill in the art upon reading this disclosure, electroless plating has a very high selectivity, excellent step coverage and good via/trench filling because of the very thin seed layers formed by the electroless plating method.  
         [0066]     In the article by Shacham-Diamand et al., three practical seeding methods for the electroless deposition of copper, which can be used with the present invention, are presented. The three practical seeding methods for the electroless deposition of copper are: (1) noble metal seeding, typically on gold, palladium or platinum; (2) copper seeding using an aluminum sacrificial layer; and (3) wet activation of surfaces using a contact displacement method. The article by Shacham-Diamand et al. demonstrates the successful use of the third method to deposit copper on Ti/TiN or TiN/AlCu at room temperature.  
         [0067]     Although only one copper dual damascene structure, e.g., structure  200 , is shown in  FIG. 2K , it will be readily apparent to those skilled in the art that, in fact, any number of such copper dual damascene structures may be formed on a substrate. Further, although the exemplary embodiments described above refer to the formation of copper dual damascene structures, the present invention is further applicable to other types of damascene structures, such as, but not limited to, those formed from palladium, platinum, nickel, copper, gold, silver, or cobalt (including alloys of the same).  
         [0068]      FIG. 3  thus illustrates an embodiment, according to the teachings of the present invention, for a triple damascene structure  400 . The triple damascene structure  400 , shown in  FIG. 3 , follows the same processing steps described above in connection with  FIGS. 2A-2K . Thus, the triple damascene structure  400  of  FIG. 3  may optionally include a tungsten-nitride (WN 2 ) material, serving as a diffusion barrier layer  472  and copper  482  selectively deposited by the methods described in detail above. For example,  FIG. 3  illustrates a triple damascene structure  400  with three intermetal insulating layers  455 ,  457 , and  459  (which can comprise the same or different insulating materials), etch stop layers  454 ,  456 , and metal layer  452  formed in insulating layer  451  formed over the substrate  450  and in which vias  465  (not shown) and trenches  467  (not shown) have been formed and then simultaneously filled with the selectively deposited copper  482  by the methods described above.  
         [0069]     As one of ordinary skill in the art will understand from reading this disclosure, further steps to create a functional memory cell or other integrated circuit component having the interconnects of the present invention can be carried out. Hence, additional multilevel interconnect layers and associated dielectric layers can be formed to create operative electrical paths from any of the copper damascene structures  200 ,  400  to appropriate regions of a circuit integrated on a substrate.  
         [0070]      FIG. 4  illustrates an embodiment of an electronic system  500  having such a memory cell with a copper damascene structure according to the present invention. As shown in  FIG. 4 , the electronic system  500  is a processor-based  544  system which includes a memory circuit  548 , for example a DRAM. According to the teachings of the present invention, either the processor  544 , the memory circuit  548 , or both contain damascene structures, such as the copper damascene structures described in connection with  FIGS. 2A-2K  and  3 . The electronic system  500  shown in  FIG. 4  illustrates generally a computer system  500 . Such a computer system  500  generally comprises a central processing unit (CPU)  544 , such as a microprocessor, a digital signal processor, or other programmable digital logic devices, which communicates with an input/output (I/O) device  546  over a bus  552 . The memory circuit  548  communicates with the computer system  500  over bus  552 .  
         [0071]     In the case of a computer system  500 , the processor-based system may include peripheral devices such as a floppy disk drive  554  and a compact disc CD-ROM drive  556 , which also communicates with CPU  544  over the bus  552 . According to the teachings of the present invention, memory circuit  548  can be constructed as an integrated circuit, including one or more copper damascene structures as described above in connection with  FIGS. 1A-1F ,  2 A- 2 K, and  3 , at reference numerals  125 ,  200 ,  400 , respectively. In one embodiment according to the teachings of the present invention, the memory circuit  548  and the processor, for example CPU  544 , can be formed on a single chip as a single integrated circuit.  
         [0072]     Although the present invention has been described with respect to the illustrated embodiments, various additions, deletions and modifications are contemplated as being within its scope. The scope of the invention is, therefore, indicated by the ensuing claims, rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.