Abstract:
An interconnection scheme employing a dual damascene configuration for coupling multi-layer interconnects is presented. The interconnection structure includes an underlying conductive region, generally comprised of a copper or copper-based alloy having a via hole formed thereupon, with a subsequent trench region formed yet thereupon. The via hole and trench regions are coated both on the horizontal and vertical facet with a barrier material which is thereafter anisotropically etched to remove the horizontal segments of the barrier layer. The horizontal segment attached to the conductive region of the underlying conductor is also removed such that the conductive layer formed within the trench and via hole regions directly contact the underlying conductive region. Such a direct interface forgoes the problems present in material dissimilarities and also provides an improved resistivity match.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. The Field of the Invention  
           [0002]    This invention relates generally to a method of forming multi-level interconnects in an integrated circuit. More specifically, this invention relates to a method for forming an improved dual damascene interconnection.  
           [0003]    2. The Relevant Technology  
           [0004]    An integrated circuit is typically comprised of a series of devices and components which are formed on a substrate and are further insulated from each other through the use of an isolation structure which makes possible the formation of individual circuit structures. These individual devices and components must be electrically connected in order to form higher-level functional circuits. A conventional method for manufacturing interconnects employs conductive layers deposited over the substrate having the devices and components formed thereon. A portion of the conductive layer is then etched away to form a functional wiring pattern. The wiring pattern may then be further protected using an insulation layer to avoid any undesirable connections or shorting with other conductive layers, components or devices. In order to functionally interconnect successive interconnection layers, a vertical via hole is formed through the insulation layer for electrical connection with the next lower wiring layer. This insulation layer, commonly referred to as an inter-metal dielectric (IMD) layer is used as an insulating layer between successive wiring or interconnection layers. The connection, between a first conductive interconnection layer and a second conductive interconnection layer or wiring pattern is achieved through the use of this vertical via.  
           [0005]    One earlier method for fabricating interconnects between adjacent conductive interconnection layers employed separate stages for forming both the layer-connecting via and the routing interconnection wires. In that approach, a dielectric layer was formed over a first conductive interconnection layer with a photoresist layer deposited over the dielectric layer. Etching techniques were used to form a hole in the dielectric, this hole being called a via, and a conductive material was deposited in the via hole to form a conductive plug or via. A second conductive layer was thereafter deposited over the dielectric layer which electrically contacted the via. A follow-up patterning step or process then etched and removed excessive portions of the conductive layer resulting in a desired interconnection conductive pattern.  
           [0006]    A more recent approach for providing interconnection between adjacent conductive layers has become known as the dual damascene process. In such a process, an insulation layer is formed over a lower layer structure in a planarizing manner. The insulation layer is etched to form horizontal trenches defining the wiring pattern as well as vertical via holes. That is to say the vertical profile assumes two distinct levels, one more superficial level defining the inner connection trenches and the second deeper level which defines the via holes which extend down to the lower inner connection level that exposes either a device region or a portion of the metal lines on the lower level. A conductive material is then deposited and fills both the horizontal trench regions and the vertically deeper via holes in a single metalization process. Any excessive metalization extending beyond the horizontal trench region is planarized with the upper isolation or insulating layer using a chemical-mechanical polishing (CMP) process, upon which additional inner connection layers may be placed.  
           [0007]    [0007]FIG. 1 depicts a typical partially processed integrated circuit structure in accordance with a prior art dual damascene process. In FIG. 1, a substrate  100  comprising a first dielectric  101  and a conductive region  102  is depicted. A barrier layer  103  is deposited across first dielectric  101  and conductive region  102 . A second dielectric  104 , typically comprised of silicon oxide, and a barrier layer  106  are formed on first dielectric  101 , conductive region  102  and barrier layer  103 . The barrier layer  106  functions as an etch-stop in a subsequent etching step. In order to remove a portion of barrier layer  106 , a photo-resist layer (not shown) is disposed upon barrier layer  106  and processed so as to allow exposure of the desired portion of barrier layer  106 , aligned over conductive region  102 . Processing thereafter removes a portion of barrier layer  106  depicted as aperture  107  which provides exposure to second dielectric  104 , again aligned vertically over conductive region  102 .  
           [0008]    A third dielectric layer  114  is formed typically through a deposition process and covers barrier layer  106  including the previously etched aperture  107  within barrier layer  106 . Using another patterning process such as through the application of a photo-resist layer and a patterning process, such as through the exposure of certain portions of the photo-resisted layer, not shown, and aperture  115  in the photo-resisted layer is generated which provides a selective exposure to a portion of third dielectric  114  which is aligned over a portion of second dielectric  104  defined by aperture  107 , which in turn is aligned over at least a portion of conductive region  102 .  
           [0009]    Using an etching process, the exposed portion of third dielectric layer  114 , defined by aperture  115 , is removed to form trench  117  and the portion of second dielectric  104 , defined by aperture  107 , is removed to define a via hole  109 . The trench  117  and the via hole  109 , in combination, form a dual damascene structure opening  120 .  
           [0010]    It should be appreciated that via hole  109  may also be another trench and, as used herein, via hole also implies a more broad interpretation of a lower trench region.  
           [0011]    Following the removal of the photo-resist layer defining aperture  115 , a barrier layer  122 , typically referred to as a diffusion barrier comprised of a metal such as TaN, separates the via metal from conductive region  102 . It should be appreciated that barrier layer  122  conforms to the peripheral dimensions of trench  117  and via hole  109  including the bottom portion of via hole  109  that physically interfaces with conductive region  102 . In FIG. 2, trench  117  and via hole  109  are filled with conductive layer  126  in a monolithic process which simultaneously fills via hole  109  and trench  117  to complete the dual damascene process.  
           [0012]    It should be appreciated that there is a need for interconnects and vias to have low resistivity and low electromigration characteristics. Advancements in processing have enabled copper (Cu) to be a natural choice for the replacement of aluminum interconnects and vias. The electromigration characteristics of copper are superior to those of aluminum. Aluminum is approximately ten times more susceptible than copper to degradation and breakdown through electromigration. Additionally, the conductivity of copper is approximately twice that of aluminum enabling the same current to be carried through a copper interconnect having half the width of an aluminum interconnect.  
           [0013]    While copper may appear to be a panacea, copper contaminates many of the materials used in IC processes and, therefore, care must be taken to keep copper from migrating. Several attempts have been proposed which provide some relief to the problem of copper diffusion into integrated circuit material. Several materials, particularly refractory metals, have been suggested for use as barriers to prevent the copper diffusion process. Heretofore, the formation of copper interconnects has required the copper lines to completely be surrounded with barrier layers such as barrier layer  122 . While the utilization of a monolithic conductive layer  126  simultaneously formed within trench  117  and via hole  109  provided an advancement in interconnection architecture, a weakness in the process remains when interfacing with conductive region  102 . For example, interface  126  at the bottom of via hole  109  is the most vulnerable interface with respect to electromigration. That is to say, when interconnection in integrated circuits fail, the failure sights are predominately located at bottom of via hole  109  depicted as interface  126 . Such interconnection failures are primarily resultant from material discontinuity. The barrier layer  122  separates conductive layer  126  from conductive region  102  and in the presence of barrier layer  122  results in an increased resistivity.  
           [0014]    It would be an improvement to advance the interface between conductive layer  126  and conductive region  102  so as to minimize electromigration potential. It would be a further improvement to enhance the interface between conductive layer  126  and conductive region  102  so as to lower the resistivity between conductive region  102  and conductive layer  126 .  
         BRIEF SUMMARY OF THE INVENTION  
         [0015]    A connection scheme using the dual damascene process for providing interconnections for integrated circuits is presented. The present invention includes a structure and method for providing a direct physical coupling of the conductive layer resident within the trench and via hole dual damascene arrangement with the conductive region of a lower level circuit or interconnect portion. In the preferred embodiment, a substrate comprised of a conductive region and a first dielectric in a generally planar and adjacent arrangement provides the basis upon which the interconnect structure is developed. A first barrier layer is disposed upon the conductive region and the first dielectric region in a planar arrangement. A second dielectric structure is overlaid upon the first barrier layer to provide both isolation to the conductive region and to provide a substrate within which a via hole may be formed and into which conductive material may be placed to form a via interconnection with the conductive region.  
           [0016]    A second barrier layer is overlaid upon the second dielectric layer. The second barrier layer is thereafter processed using photoresist-type processes to define an aperture through which an anisotropic process is performed to etch the second dielectric down to the conductive region. A third dielectric layer is thereafter overlaid upon the second barrier layer. The third dielectric layer provides both a dielectric insulator for adjacent interconnection conductors as well as provides a substrate in which a trench is etched to receive conductive material.  
           [0017]    A third barrier layer is overlaid upon the third dielectric using photoresist processes, and aperture defined in the third barrier layer corresponds with the desired trench dimensions to be etched using an anisotropic etching procedure into the third dielectric.  
           [0018]    Following the definition of the void within the third barrier layer, an anisotropic process is performed which etches in a horizontal direction consistent with the defined void or aperture present in the third barrier layer and in a vertical direction consistent with the depth of the second barrier layer which functions as an etch stop for the trench portion of the opening. Additionally, during the same etching step, a via hole is etched into second dielectric  212  having a horizontal dimension consistent with the aperture formed within the second barrier layer and a vertical dimension terminated by the presence of the conductive region.  
           [0019]    Once the opening for both the trench and the via hole have been defined, a barrier layer is disposed upon all horizontal and vertical surfaces of the opening. Such deposition of the barrier layer within the opening further includes applying the barrier layer to the surface of the conductive region aligned with the via hole. Using an etched-back procedure, the horizontal segments of the barrier layer within the opening are removed with the vertical segments of the barrier layer remaining. It should be appreciated that it is desirable to mitigate material discontinuity between a conductive layer deposited within both the trench and via hole area as well as the conductive region. Therefore, the removal of the horizontal segment of the barrier layer resident within the opening that is located directly upon the conductive region is desirable. With only the vertical segments of the barrier layer within the opening remaining, a conductive layer is deposited within the trench and via hole in a monolithic process. Such a process provides a direct coupling of the conductive layer with the conductive region thereby removing the deleterious effects associated with material discontinuity.  
           [0020]    These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    In order that the manner in which the above-recited and other advantages and features of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
         [0022]    [0022]FIGS. 1 and 2 illustrate a barrier layer throughout the entire trench region, in accordance with the prior art;  
         [0023]    [0023]FIG. 3 depicts the formation of barrier and dielectric layers in preparation of the formation of a via hole, in accordance with the interconnect of the present invention;  
         [0024]    [0024]FIG. 4 depicts an etching step for patterning the formation of via hole, in accordance with a preferred embodiment of the present invention;  
         [0025]    [0025]FIG. 5 depicts the formation of the trench region of the interconnect, in accordance with the present invention;  
         [0026]    [0026]FIG. 6 depicts the anisotropic etching of the trench and via for the formation of the interconnect, in accordance with the present invention;  
         [0027]    [0027]FIG. 7 depicts the deposition of a barrier layer within the trench, in accordance with a preferred embodiment of the present invention;  
         [0028]    [0028]FIG. 8 depicts an anisotropic etch-back of the horizontal layers of the barrier, in accordance with the preferred embodiment of the present invention;  
         [0029]    [0029]FIG. 9 depicts the deposition of interconnect material within the trench and via region, in accordance with the present invention; and  
         [0030]    [0030]FIG. 10 depicts an alternate embodiment wherein a barrier layer is etched-back.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    [0031]FIG. 3 depicts an integrated circuit substrate  200  having a first conductive region  202  fabricated thereupon. Conductive region  202  may comprise a metal layer defining an interconnect pattern. Substrate  200  further includes a first dielectric  204  which is formed, for example, of a silicon oxide layer formed through chemical vapor deposition (CVD) or through other processes known by those of skill in the art. Conductive region  202  and dielectric  204  may be configured atop other optional underlying structures  206 . Conductive region  202  is preferably comprised of a copper (Cu) or other copper-based alloys which provide enhanced conductivity. It is however known that copper-based interconnections also suffer from out-diffusion and electromigration problems that require isolation of conductive regions using barrier techniques. Therefore, FIG. 3 depicts a barrier layer  208  for providing isolation between conductive region  202  and dielectric  204 . Conductive region  202  and dielectric  204  may be further planarized in order to provide a more conducive surface for the application of additional layers.  
         [0032]    A first barrier layer  210  is overlaid upon conductive region  202  and dielectric  204  to provide a horizontal barrier for mitigating Cu out-diffusion and electromigration of the material comprising conductive region  202 . A second dielectric  212  is overlaid upon barrier layer  210  to provide an inter-metal dielectric. Dielectric  212  is typically deposited using a chemical vapor deposition process and is most generally comprised of silicon oxide. If necessary, dielectric  212  may also undergo planarization processes prior to the application of additional and successive layers and processes. Such planarization techniques are appreciated by those of skill in the art and the details of such processes are not contained herein. A second barrier layer  214  overlays dielectric  212  and is also a non-conductive barrier layer for providing Cu out-diffusion and electromigration mitigation of subsequent conductive regions.  
         [0033]    [0033]FIG. 4 depicts a patterning structure for implementing the patterning of a via for connecting a subsequently applied conductive layer to conductive region  202 . In FIG. 4, a photoresist layer  216  is applied and processed using techniques known by those of skill in the art to form an opening in the photoresist which allows for exposure of barrier layer  214  to undergo a process wherein an aperture or portion of barrier layer  214  is removed thereby exposing dielectric  212  for a subsequent etching process. It should be noted that opening  218  in barrier layer  214  is aligned so as to facilitate the formation of a via through second dielectric  212  and in vertical alignment with a portion of conductive region  202 . Following the processing to form an opening or aperture  218  in second barrier layer  214 , photoresist  216  is removed to accommodate subsequent processing steps.  
         [0034]    [0034]FIG. 5 depicts formation of a trench for facilitating interconnection, in accordance with the present invention. A third dielectric layer  220  is overlaid upon second barrier layer  214  using conventional integrated circuit processing techniques known by those of skill in the art such as chemical vapor deposition or other suitable processes. Third dielectric  220  is comprised of silicon oxide and provides both isolative separation between hereafter developed conductive interconnection regions as well as providing a mold into which interconnection trenches may be formed for receiving the conductive interconnection material. A third barrier layer  222  overlays third dielectric  220  and is applied using, preferably, a deposition process. In the preferred embodiment, barrier layer  222  is comprised of a nonconductive material. Barrier layer  222  undergoes an etching process through the application of a photoresist  224  and processing of the photoresist  224  in accordance with processes known by those of skill in the art. The processing of photoresist  224  results in a mask wherein barrier layer  222  may be etched to form opening or aperture  226  within barrier layer  222 . Photoresist  224  is thereafter removed leaving the desired patterning and exposure of dielectric  220 .  
         [0035]    [0035]FIG. 6 depicts a cross-sectional view of an anisotropic etched dual damascene structure, in accordance with a preferred embodiment of the present invention. An anisotropic etching process with barrier layer  222  forming the aperture through which third dielectric  220  is anisotropically etched to form a trench  228  defined horizontally by barrier layer  222  and defined vertically by the presence of barrier layer  214  forming an etch stop. The anisotropic etching process further continues, preferably in the same etching process, to etch a via hole  230  through second dielectric  212  and first barrier layer  210 . Via hole  230  is defined horizontally by the aperture previously etched within barrier layer  214  and further defined vertically by the existence of conductive region  202 . Trench  228  and via hole  230  together combine to form an opening  232  into which a monolithic conductive interconnect will be formed with conductive region  202 .  
         [0036]    [0036]FIG. 7 is a cross-sectional view of an integrated circuit depicting a barrier layer lining the dual damascene opening of the interconnection structure, in accordance with the preferred embodiments of the present invention. As described above, conductive interconnects such as those comprised of copper or copper-based alloys, are susceptible to migration and electromigration of the copper into adjacent dielectric layers which greatly impacts the integrity of the integrated circuit. In order to mitigate such deleterious effects, a fourth barrier layer  234  is conformally applied to the surface areas of opening  232 . Fourth barrier layer  234  may be comprised of, for example, titanium (Ti), titanium nitride (TiN) or tantalum (Ta) or tantalum nitride (TaN), or titanium silicon nitride (TiSiN), or other barrier compositions that minimize out-diffusion of Cu into dielectrics. It should be appreciated that fourth barrier layer  234  is applied to both the vertical and horizontal sidewalls of opening  232 .  
         [0037]    [0037]FIG. 8 is a cross-sectional diagram of the integrated circuit of the present invention after having undergone an etch-back process of the barrier layer. Fourth barrier layer  234  undergo an anisotropic etch-back process wherein the horizontal segments of barrier layer  234  undergoes an anisotropic etched-back wherein the horizontal segments of barrier layer  234  are removed with the vertical segments  234 ′- 234 ″″ remaining. It should be noted that the remaining vertical segments of barrier layer  234  result in a capping of exposed dielectric layers which are susceptible to Cu out-diffusion. It should be further apparent that second barrier layer  214  provides a barrier in the horizontal direction for the conductive material that will hereinafter be placed in opening  232 . It should be further apparent that the horizontal segment of barrier layer  234  located over conductive region  202  has further been removed hereby providing a direct contact between the conductive material to be placed in opening  232  with conductive region  202 .  
         [0038]    A direct physical interface of the material of conductive region  202  with the conductive layer material to be placed within opening  232  prevents failures associated with material discontinuity resulting from adjacent placement of dissimilar materials. In traditional dual damascene interconnections, the majority of interconnection failures occur at the interface located at the bottom portion of via hole  230  when the horizontal segment of barrier layer  234  remains as an obstacle between the direct connection of the material filling opening  232  with the material comprising conductive region  202 . Additionally, via resistance, a critical integrated circuit device parameter, is increased when there is an intermediary material isolating conductive region  202 . Therefore, the present invention provides an improvement which enables such similar conductive materials to engage in a direct physical interface. FIG. 9 is a cross-sectional diagram of a dual damascene interconnection incorporating a direct interface between the conductive layer filling the dual damascene opening with the conductive region of the underlying structure, in accordance with the preferred embodiment of the present invention. As shown, a conductive layer  236  fills both via hole  230  (FIG. 6) and trench  228  (FIG. 6) in a single monolithic process that provides a direct coupling of conductive layer  236  with conductive region  202 . Conductive layer  236  is comprised of a similar, if not identical, chemical composition as conductive region  202 . Preferably, conductive layer  236  and conductive region  202  are comprised of copper of copper-based metals. FIG. 9 also depicts third barrier layer  222  being comprised of a dielectric compound such that when excessive portions of conductive layer  232  extend beyond opening  232 , subsequent processing or etching of conductive layer  236  does not affect barrier layer  222 . Barrier layer  222 , being dielectric in nature in the preferred embodiment, facilitates the electromigration barrier that is desirable to mitigate electromigration of any conductive layer overlaid upon third barrier layer  222 .  
         [0039]    [0039]FIG. 10 is a cross-sectional diagram illustrating a dual damascene interconnection for providing direct contact between a conductive layer and a conductive region without an intervening thin film or barrier, in accordance with another embodiment of the present invention. FIG. 10 depicts conductive layer  236  having the direct coupling to conductive region  202  as described in the previous figure, however, in the present embodiment, third barrier layer  222  (FIG. 8) is illustrated as being removed since it was comprised of a conductive material. During the processing of the horizontal segments of barrier layer  234  and during any etching or polishing associated with any excessive profile of conductive layer  236  beyond opening  232 , third barrier layer  222  is removed resulting in the cross-sectional profile as depicted. The absence of a third barrier layer in the present embodiment enables the placement of a single barrier layer over both a portion of third dielectric  220  and conductive layer  236  without the adjacent placement of barrier layers.  
         [0040]    An integrated circuit having a dual damascene interconnection comprised of the various dielectric and barrier layers which facilitates the direct physical coupling of the conductive layer located within the trench and via hole openings with the conductive region of a lower layer has been presented. The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.