Abstract:
A semiconductor device includes a first metallization layer, a first diffusion barrier layer, a first etch stop layer, a dielectric layer and a via extending through the dielectric layer, the first etch stop layer, and the first diffusion barrier layer. The first diffusion barrier layer is disposed over the first metallization layer. The first etch stop layer is disposed over and spaced from the first diffusion barrier layer, and the dielectric layer is disposed over the first etch stop layer. The via can also have rounded corners. A second etch stop layer can also be disposed between the first diffusion barrier layer and the first etch stop layer. A sidewall diffusion barrier layer can be disposed on sidewalls of the via, and the sidewall diffusion barrier layer is formed from the same material as the first diffusion barrier layer. A method of manufacturing the semiconductor device is also disclosed.

Description:
RELATED APPLICATION 
   This application contains subject matter related to the subject matter disclosed in U.S. patent application Ser. No. 09/793,993, filed on Feb. 28, 2001. 
   FIELD OF THE INVENTION 
   The present invention relates to the manufacturing of semiconductor devices, and more particularly, to copper and copper alloy metallization in semiconductor devices. 
   BACKGROUND OF THE INVENTION 
   The escalating requirements for high density and performance associated with ultra large scale integration (ULSI) semiconductor device wiring are difficult to satisfy in terms of providing sub-micron-sized, low resistance-capacitance (RC) metallization patterns. This is particularly applicable when the sub-micron-features, such as vias, contact areas, lines, trenches, and other shaped openings or recesses have high aspect ratios (depth-to-width) due to miniaturization. 
   Conventional semiconductor devices typically comprise a semiconductor substrate, usually of doped monocrystalline silicon (Si), and a plurality of sequentially formed dielectric interlayer dielectrics and electrically conductive patterns. An integrated circuit is formed therefrom containing a plurality of patterns of conductive lines separated by interwiring spacings, and a plurality of interconnect lines, such as bus lines, bit lines, word lines and logic interconnect lines. Typically, the conductive patterns of vertically spaced metallization layers are electrically interconnected by vertically oriented conductive plugs filling via holes formed in the interlayer dielectric layer separating the metallization layers, while other conductive plugs filling contact holes establish electrical contact with active device regions, such as a source/drain region of a transistor, formed in or on a semiconductor substrate. Conductive lines formed in trench-like openings typically extend substantially parallel to the semiconductor substrate. Semiconductor devices of such type according to current technology may comprise five or more levels of metallization to satisfy device geometry and microminiaturization requirements. 
   A commonly employed method for forming conductive plugs for electrically interconnecting vertically spaced metallization layers is known as “damascene”-type processing. Generally, this process involves forming an opening (or via) in the dielectric interlayer, which will subsequently separate the vertically spaced metallization layers. The via is typically formed using conventional lithographic and etching techniques. After the via is formed, the via is filled with a conductive material, such as tungsten (W), using conventional techniques. Excess conductive material on the surface of the dielectric interlayer is then typically removed by chemical mechanical planarization (CMP). 
   A variant of the above-described process, termed “dual damascene” processing, involves the formation of an opening having a lower contact (or via) hole section which communicates with an upper trench section. The opening is then filled with a conductive material to form a conductive plug that electrically contacts the lower metallization layer. As with the previous process, excess conductive material on the surface of the dielectric interlayer is then removed by CMP. An advantage of the dual damascene process is that the conductive plug and the upper metallization layer are formed simultaneously. 
   High performance microprocessor applications require rapid speed of semiconductor circuitry, and the integrated circuit speed varies inversely with the resistance and capacitance of the interconnection pattern. As integrated circuits become more complex and feature sizes and spacings become smaller, the integrated circuit speed becomes less dependent upon the transistor itself and more dependent upon the interconnection pattern. If the interconnection node is routed over a considerable distance, e.g., hundreds of microns or more, as in submicron technologies, the interconnection capacitance limits the circuit node capacitance loading and, hence, the circuit speed. As integration density increases and feature size decreases, in accordance with submicron design rules, the rejection rate due to integrated circuit speed delays significantly reduces manufacturing throughput and increases manufacturing costs. 
   One way to increase the circuit speed is to reduce the resistance of a conductive pattern. Conventional metallization patterns are typically formed by depositing a layer of conductive material, notably aluminum (Al) or an alloy thereof, and etching, or by damascene techniques. Al is conventionally employed because it is relatively inexpensive, exhibits low resistivity and is relatively easy to etch. However, as the size of openings for vias/contacts and trenches is scaled down to the sub-micron range, step coverage problems result from the use of Al. Poor step coverage causes high current density and enhanced electromigration. Moreover, low dielectric constant polyamide materials, when employed as dielectric interlayers, create moisture/bias reliability problems when in contact with Al, and these problems have decreased the reliability of interconnections formed between various metallization layers. 
   One approach to improved interconnection paths in vias involves the use of completely filled plugs of a metal, such as W. Accordingly, many current semiconductor devices utilizing VLSI (very large scale integration) technology employ Al for the metallization layer and W plugs for interconnections between the different metallization levels. The use of W, however, is attendant with several disadvantages. For example, most W processes are complex and expensive. Furthermore, W has a high resistivity, which decreases circuit speed. Moreover, Joule heating may enhance electromigration of adjacent Al wiring. Still a further problem is that W plugs are susceptible to void formation, and the interface with the metallization layer usually results in high contact resistance. 
   Another attempted solution for the Al plug interconnect problem involves depositing Al using chemical vapor deposition (CVD) or physical vapor deposition (PVD) at elevated temperatures. The use of CVD for depositing Al is expensive, and hot PVD Al deposition requires very high process temperatures incompatible with manufacturing integrated circuitry. 
   Copper (Cu) and Cu-based alloys are particularly attractive for use in VLSI and ULSI semiconductor devices, which require multi-level metallization layers. Cu and Cu-based alloy metallization systems have very low resistivities, which are significantly lower than W and even lower than those of previously preferred systems utilizing Al and its alloys. Additionally, Cu has a higher resistance to electromigration. Furthermore, Cu and its alloys enjoy a considerable cost advantage over a number of other conductive materials, notably silver (Ag) and gold (Au). Also, in contrast to Al and refractory-type metals (e.g., titanium (Ti), tantalum (Ta) and W), Cu and its alloys can be readily deposited at low temperatures formed by well-known “wet” plating techniques, such as electroless and electroplating techniques, at deposition rates fully compatible with the requirements of manufacturing throughput. 
   Electroless plating of Cu generally involves the controlled auto-catalytic deposition of a continuous film of Cu or an alloy thereof on a catalytic surface by the interaction of at least a Cu-containing salt and a chemical reducing agent contained in a suitable solution, whereas electroplating comprises employing electrons supplied to an electrode (comprising the surface(s) to be plated) from an external source (i.e., a power supply) for reducing Cu ions in solution and depositing reduced Cu metal atoms on the plating surface(s). In either case, a nucleation/seed layer is required for catalysis and/or deposition on the types of substrates contemplated herein. Finally, while electroplating requires a continuous nucleation/seed layer, very thin and discontinuous islands of a catalytic metal may be employed with electroless plating. 
   A number of different variations of a damascene process have been employed during semiconductor manufacturing. With reference to  FIGS. 1A–1H , an example of a damascene process for forming vias between vertically spaced metallization layers, according to conventional techniques, will be described. This process can be repeated to form multiple metallization levels, i.e., two or more, stacked one on top of another. 
   In  FIG. 1A , a first etch stop layer  12  is deposited over a first metallization layer  10 . The first etch stop layer  12  acts as a passivation layer that protects the first metallization layer  10  from oxidation and contamination and prevents the material of the metallization layer  10  from diffusing into a subsequently formed dielectric layer. The first etch stop layer  12  also acts as an etch stop during subsequent etching of the dielectric layer. A typical material used as an etch stop is silicon nitride, and approximately 500 angstroms of silicon nitride is typically deposited over the metallization layer  10  to form the first etch stop layer  12 . An illustrative process used for depositing silicon nitride is plasma enhanced CVD (PECVD). 
   In  FIG. 1B , a first dielectric layer  14  is deposited over the first etch stop layer  12 . The first dielectric layer  14  is generally formed from silicon oxide although other acceptable materials include silicon nitride and organic polymeric materials. Many techniques are capable of providing a dielectric layer  14  formed from silicon oxide, and an illustrative process is PECVD. 
   In  FIG. 1C , vias  16  are formed in the first dielectric layer  14  using conventional lithographic and etch techniques. The lithographic process involves depositing a resist  17  over the first dielectric layer  14  and exposing and developing the resist  17  to form the desired patterns of the vias  16 . The first etch, which is highly selective to the material of the first dielectric layer  14 , removes the first dielectric layer  14  until the etchant reaches the first etch stop layer  12 . The first etch is typically an anisotropic etch, such as a reactive ion plasma dry etch, that removes only the exposed portions of the first dielectric layer  14  directly below the opening in the resist  17 . By using an anisotropic etch, the via  16  can be formed with substantially perpendicular sidewalls. 
   In  FIG. 1D , a second etch, which is highly selective to the material of the first etch stop layer  12 , then removes the first etch stop layer  12  until the etchant reaches the first metallization layer  10 . The second etch is also typically an anisotropic etch. 
   In  FIG. 1E , the corners  18  of the vias  16  can be rounded using a reverse physical sputtering process. The corners  18  of the vias  16  are rounded to prevent problems of void creation associated with subsequent deposition of the conductive plug, and if necessary, a barrier layer. The reverse sputtering process can also be used to clean the first metallization layer  10  at the bottom of the via  16 . Incomplete etching of the first etch stop layer  12  can leave a portion of the first etch stop layer  12  over the first metallization layer  10 , and this material can prevent good ohmic contact between the material of the conductive plug and the material of the first metallization layer  10 . Use of the reverse sputtering process, however, can remove any remaining material of the first etch stop layer  12  and any other contaminants on the first metallization layer  10 . 
   In  FIG. 1F , an adhesion/barrier material, such as tantalum, titanium, tungsten, tantalum nitride, or titanium nitride, is deposited. The combination of the adhesion and barrier material is collectively referred to as a second diffusion barrier layer  20 . The second diffusion barrier layer  20  acts to prevent diffusion into the first dielectric layer  14  of the conductive material subsequently deposited into the via  16 . 
   In  FIG. 1G , a layer  22  of a conductive material, for example, a Cu or Cu-based alloy, is deposited into the via  16  and over the dielectric layer  14 . A typical process initially involves depositing a “seed” layer on the second diffusion barrier layer  20  subsequently followed by conventional plating techniques, e.g., electroless or electroplating techniques, to fill the via  16 . So as to ensure complete filling of the via  16 , the Cu-containing conductive layer  22  is deposited as a blanket (or “overburden”) layer  24  so as to overfill the via  16  and cover the upper surface  26  of the dielectric layer  14 . 
   In  FIG. 1H , the entire excess thickness of the metal overburden layer  24  over the upper surface  26  of the dielectric layer  14  is removed using a CMP process. A typical CMP process utilizes an alumina (Al 2 O 3 )-based slurry and leaves a conductive plug in the via  16 . The conductive plug has an exposed upper surface  30 , which is substantially co-planar with the surface  26  of the dielectric layer  14 . 
   A problem that can be caused by the use of Cu and Cu-based alloys results from Cu having a relatively large diffusion coefficient into silicon oxide and silicon. Once Cu has diffused into these materials, Cu can cause the dielectric strength of these materials to decrease. Thus, if Cu from a plug or metallization layer diffuses into a silicon oxide layer, the layer can become more conductive, and this increase in conductivity can cause short circuits between adjacent conductive regions. These short circuits can therefore result in failure of the semiconductor device. For this reason, Cu conductors are encapsulated by at least one diffusion barrier to prevent diffusion of the Cu into the silicon oxide layer. 
   The above-described process, however, can still result in copper contamination as a result of the use of reverse physical sputtering to clean the first metallization layer and to round the corners of the trenches and vias. Reverse physical sputtering is a process by which atoms or molecules from the surface of a material are dislocated or removed by the impact energy of gas ions, which are accelerated in an electric field. This process involves the creation of a glow discharge or plasma between an anode and a cathode, such as a semiconductor device, wherein the current therebetween is composed of electron flow to the anode and positive ion flow to the cathode. The ions are created by the ionization of gas molecules, such as argon, existing within the flow discharge region between the anode and cathode. The ionization results from the collision of gas particles with the electron flow from the cathode to the anode. A focused beam of these ions can be directed to a very small point on a semiconductor device and then scanned, raster fashion, over a surface where material is to be removed. As an ion impinges on the semiconductor device surface, momentum is transferred from the ion to the impact surface resulting in the removal of one or more surface atoms. 
   The problem of copper contamination as a result of reverse physical sputtering is illustrated in  FIG. 2 . The reverse physical sputtering process rounds the corners  18  of the vias  16  as a result of ionized argon impacting the corners  18  and dislodging atoms. As the atoms of argon are impacting the corners  18 , the atoms of argon are also impacting all the other exposed surfaces, such as the Cu of the first metallization layer  10 . Thus, the impact of the argon atoms onto the first metallization layer  10  also dislodges atoms of Cu, and the dislodged atoms of Cu are undesirably deposited on other surfaces. In particular, the dislodged Cu atoms can be deposited onto the exposed sidewall surfaces  15  of the first dielectric layer  14 . 
   Once the Cu is deposited on the first dielectric layer  14 , the Cu can then diffuse into the first dielectric layer. As previously stated, the diffusion of Cu into a silicon oxide dielectric layer  14  causes detrimental effects that can result in the failure of the semiconductor device. Accordingly, a need exists for an improved method of forming copper plugs and copper metallization that allows for use of reverse physical sputtering to round corners of vias, so as to minimize the problem of void creation, yet still prevent the dielectric layers from being contaminated with Cu. 
   SUMMARY OF THE INVENTION 
   This and other needs are met by embodiments of the present invention which provide a semiconductor device, which includes a first metallization layer; a first diffusion barrier layer; a first etch stop layer; a dielectric layer; and a via extending through the dielectric layer, the first etch stop layer, and the first diffusion barrier layer. The first diffusion barrier layer is disposed over the first metallization layer. The first etch stop layer is disposed over and spaced from the first diffusion barrier layer, and the dielectric layer is disposed over the first etch stop layer. The via can also have rounded corners. A second etch stop layer can also be disposed between the first diffusion barrier layer and the first etch stop layer. A sidewall diffusion barrier layer can be disposed on sidewalls of the via, and the sidewall diffusion barrier layer is formed from the same material as the first diffusion barrier layer. 
   By providing a first barrier layer to the material of the metallization layer, the material of the barrier layer can be subsequently sputtered onto the sidewalls of the via. The material deposited on the sidewalls forms a new sidewall barrier layer that prevents contamination of the dielectric layer caused by the material of the metallization layer being deposited on the sidewalls when this material is subsequently sputtered off. The sputtering process also advantageously provides the via with round corners, which reduce the formation of voids in the via. 
   In a further aspect of the invention, the material of the first etch stop layer can include silicon nitride, and the material of the second etch stop layer can include silicon oxide. Additionally, the material of the first diffusion barrier layer can include silicon nitride. Furthermore, the dielectric layer can be formed from silicon oxide and the first metallization layer can include copper. 
   In still another aspect of the invention, a second diffusion barrier layer can be disposed over the sidewall diffusion barrier layer. Also, a conductive plug can be disposed within the via, and the material of the conductive plug can include copper. 
   In an additional embodiment of the present invention, a semiconductor device comprises a first metallization layer; a dielectric layer disposed over the first metallization layer; a first sidewall diffusion barrier layer formed from a first material disposed on sidewalls of a via; a second diffusion barrier layer disposed over the first sidewall diffusion barrier layer and formed from a second material; and a conductive plug within the via. The second material is different than the first material. Also, the via extends through the dielectric layer to the first metallization layer and can have rounded corners. 
   In a further embodiment of the present invention, a method of manufacturing a semiconductor device is also disclosed. The method of manufacturing includes depositing a first diffusion barrier layer over a first metallization layer; depositing a dielectric layer over the first diffusion barrier layer; etching the dielectric layer to form a via through the dielectric layer; and sputtering the first diffusion barrier layer. The sputtering rounds corners of the via and also deposits material of the first diffusion barrier layer onto sidewalls of the via to form a sidewall diffusion barrier layer. 
   In an additional aspect of the invention, the method can further include the steps of depositing a second etch stop layer between the first barrier diffusion layer and the dielectric layer; depositing a first etch stop layer between the second etch stop layer and the dielectric layer; and etching the first etch stop layer after the dielectric etching step. A second diffusion barrier layer can also be deposited over the sidewall diffusion barrier layer after the sputtering step, and a conductive plug can then be deposited within the via. 
   In still another embodiment of the present invention, an additional method of manufacturing a semiconductor device is disclosed. The method of manufacturing includes forming a first metallization layer; depositing a first diffusion barrier layer over the first metallization layer; depositing a second etch stop layer over the first barrier diffusion layer; depositing a first etch stop layer over the second etch stop layer; depositing a dielectric layer over the first etch stop layer; depositing a resist over the dielectric layer; patterning the resist; etching through the dielectric layer with a first etchant; etching through the first etch stop layer with a second etchant; depositing a conductive material in a via and over a sidewall diffusion barrier layer; and planarizing a top surface of the dielectric layer. The etching of the dielectric layer and the first etch stop layer forms the via. The sputtering rounds corners of the via and also deposits material of the first diffusion barrier layer onto sidewalls of the via to form the sidewall diffusion barrier layer. 
   Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout, and wherein: 
       FIGS. 1A–1H  schematically illustrate sequential phases of a conventional single damascene process. 
       FIG. 2  illustrates a conventional via during a sputtering process. 
       FIGS. 3A–3J  schematically illustrate sequential phases of a single damascene process according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention addresses and solves the problem of contamination from copper being deposited onto a silicon oxide dielectric layer as a result of reverse physical sputtering, which is used to round corners of a via and to clean contaminants on the copper metallization layer below the via. This is achieved, in part, by providing a first etch stop layer, a second etch stop layer and a barrier layer below the second etch stop layer. Advantageously, after the first etch stop layer is removed using conventional etching techniques, the second etch stop layer and the barrier layer are sputtered off during the reverse physical sputtering process. Importantly, the material of the barrier layer that is sputtered off is then deposited onto the exposed portions of the dielectric layer and creates a sidewall diffusion barrier. This is accomplished before the copper from the copper layer is sputtered off onto the dielectric layer. Thus, once the copper layer is reached during the sputtering process and copper is then sputtered off, the copper will be deposited on a barrier layer and not on the dielectric layer. 
   An embodiment of the present invention is illustrated in  FIGS. 3A–3J . As illustrated in  FIG. 3A , a first diffusion barrier layer  111  is formed over a first metallization layer  110 . The first diffusion barrier layer  111  can be formed from any material that prevents diffusion of the material from the metallization layer  110  into a subsequently formed dielectric layer. For example, in current embodiments of the invention, the first metallization layer  110  is formed from a Cu or Cu-based alloy. As such, the preferred first diffusion barrier layer  111  for use with Cu or Cu-based alloys acts as a diffusion barrier to Cu. The first diffusion barrier layer  111  can also act as a passivation layer that protects the first metallization layer  110  from oxidation and contamination. The material of the first diffusion barrier layer  111  is also an etch stop for the etchant used to etch the material subsequently formed above the first diffusion barrier layer  111 . 
   The thickness of the first diffusion barrier layer  111  depends upon several factors, which include the depth of a subsequently formed via in the dielectric layer over the first diffusion barrier layer  111  and the percentage of the material of the first diffusion barrier layer  111  that is deposited onto the sidewalls of the dielectric layer. As such, the thickness of the first diffusion barrier layer  111  must be enough so that when the first diffusion barrier layer  111  is subsequently sputtered off, enough of the material of the first diffusion barrier layer  111  is deposited on the sidewalls of the dielectric layer to form an effective diffusion barrier from the material of the first metallization layer  110 . In current embodiments of the invention, the thickness of the first diffusion barrier layer  111  is at least 50 angstroms. 
   In current embodiments of the invention, the first diffusion barrier layer  111  is formed from silicon nitride although the invention is not limited in this manner. Silicon nitride advantageously acts as a diffusion barrier to copper and also as a passivation layer. Furthermore, silicon nitride acts as an etch stop to an etchant that etches silicon oxide. Any process capable of depositing the first diffusion barrier layer  111  is acceptable for use with the invention, and an illustrative process for depositing silicon nitride is PECVD. 
   In  FIG. 3B , a second etch stop layer  113  is deposited over the first diffusion barrier layer  111 . The second etch stop layer  113  acts as an etch stop during etching of a subsequently formed first etch stop layer. The thickness of the second etch stop layer  113  is preferably sufficient to act as an etch stop and not allow the etchant of the first etch stop layer to reach the first diffusion barrier layer  111 . In current embodiments of the invention, the thickness of the second etch stop layer  113  is at least 50 angstroms and is preferably from about 80 to about 120 angstroms. 
   In current embodiments of the invention, the second etch stop layer  113  is formed from silicon oxide although the invention is not limited in this manner. Silicon oxide advantageously acts as an etch stop to an etchant that etches silicon nitride. Any process capable of depositing the second etch stop layer  113  is acceptable for use with the invention, and an illustrative process for depositing silicon oxide is CVD. 
   In  FIG. 3C , a first etch stop layer  112  is deposited over the second etch stop layer  113 . The first etch stop layer  112  acts as an etch stop during subsequent etching of the dielectric layer. In current embodiments of the invention, the first etch stop layer  112  is formed from silicon nitride although the invention in not limited in this manner. The thickness of the first etch stop layer  112  is preferably sufficient to act as an etch stop during etching of the dielectric layer. In current embodiments of the invention, the thickness of the first etch stop layer  112  is at least 50 angstroms and is preferably from about 400 to about 600 angstroms. Any process capable of depositing the first etch stop layer  112  is acceptable for use with the invention, and an illustrative process for depositing silicon nitride is PECVD. 
   In  FIG. 3D , a first dielectric layer  114  is deposited over the first etch stop layer  112 . The first dielectric layer  114  is generally formed from silicon oxide although other acceptable materials include silicon nitride and organic polymeric materials. Many techniques are capable of providing a dielectric layer  114  formed from silicon oxide, and an illustrative process for depositing silicon oxide is PECVD. 
   In  FIG. 3E , vias  116  are formed in the first dielectric layer  114  using conventional lithographic and etch techniques. The lithographic process involves depositing a resist  117  over the first dielectric layer  114  and exposing and developing the resist  117  to form the desired patterns of the vias  116 . The first etch, which is highly selective to the material of the first dielectric layer  114 , removes the first dielectric layer  114  until the etchant reaches the first etch stop layer  112 . The first etch is typically an anisotropic etch, such as a reactive ion plasma dry etch, that removes only the exposed portions of the first dielectric layer  114  directly below the opening in the resist  117 . By using an anisotropic etch, the via  116  can be formed with substantially perpendicular sidewalls. 
   In  FIG. 3F , a second etch, which is highly selective to the material of the first etch stop layer  112 , then removes the first etch stop layer  112  until the etchant reaches the second etch stop layer  113 . The second etch is also typically an anisotropic etch. 
   In  FIG. 3G , a reverse sputtering process is employed to etch through the second etch stop layer  113  and the first diffusion barrier layer  111  to expose the first metallization layer  110 . After the second etch stop layer  113  has been removed, the sidewalls of the via  116  include material from the second etch stop layer  113 . During the sputtering of the first diffusion barrier layer  111 , material of the first diffusion barrier layer  111  liberated during the sputtering process is deposited on the sidewalls of the via  116 . The material of the first diffusion barrier layer  111  deposited on the sidewalls of the via  116  forms a sidewall diffusion barrier layer  119 . This sidewall diffusion barrier layer  119  acts as a diffusion barrier that prevents the material of the first metallization layer  110  from diffusing into the first dielectric layer  114  after the sputtering process reaches the level of the first metallization layer  110  and the material of the first metallization layer  110  is sputtered off. 
   The reverse sputtering process also advantageously rounds the corners  118  of the via  116 . The corners  118  of the via  116  are rounded to prevent problems associated with subsequent deposition of the conductive plug, and if necessary, a barrier layer. For example, when the material of the conductive plug or the barrier layer is deposited in a via  116  having sharp corners  118 , the material tends to build up more quickly at the corners  118  than at the vertical sidewalls of the via  116 . Consequentially, the material at opposing corners  118  can form cantilevered bridges that eventually meet in the middle of the via  116 . When this occurs, the via  116  is blocked and further deposition of material within the via  116  is prevented, thereby leaving a void in the via  116 . The creation of such a void can disadvantageously cause a malfunction in the semiconductor device. However, by rounding the corners  118  of the vias  116 , excess buildup of material at the corners  118  is counteracted and the problem of void creation is reduced. 
   The reverse sputtering process can also be used to clean the first metallization layer  110  at the bottom of the via  116 . As such, any dielectric material or contaminants formed over the first metallization layer  110  can be removed by the reverse sputtering process to allow for good ohmic contact between the material of the conductive plug and the material of the first metallization layer  110 . 
   In  FIG. 3H , an adhesion/barrier material, such as tantalum, titanium, tungsten, tantalum nitride, or titanium nitride, is deposited in the via  116  and over the sidewall diffusion barrier layer  119 . The combination of the adhesion and barrier material is collectively referred to as a second diffusion barrier layer  120 . The second diffusion barrier layer  120  acts to prevent diffusion into the first dielectric layer  114  of the conductive material subsequently deposited into the via  116 . 
   In  FIG. 3I , a layer  122  of a conductive material is deposited into the via  116  and over the dielectric layer  114 . In current embodiments of the invention, the conductive material is a Cu or Cu-based alloy, and any process capable of depositing Cu into the via  116  is acceptable for use with this invention. An illustrative example of a process acceptable for use with this invention involves depositing a “seed” layer on the second diffusion barrier layer  120 . After the seed layer has been formed, conventional plating techniques, e.g., electroless or electroplating techniques, are used to fill the via  116 . So as to ensure complete filling of the via  116 , the Cu-containing conductive layer  122  is deposited as a blanket (or “overburden”) layer  124  so as to overfill the via  116  and cover the upper surface  126  of the dielectric layer  114 . 
   In  FIG. 3J , the entire excess thickness of the metal overburden layer  124  over the upper surface  126  of the dielectric layer  114  is removed using a CMP process. A typical CMP process utilizes an alumina (Al 2 O 3 )-based slurry and leaves a conductive plug in the via  116 . The conductive plug has an exposed upper surface  130 , which is preferably substantially co-planar with the surface  126  of the dielectric layer  114 . 
   By providing a barrier layer above a copper metallization layer, the material of the barrier layer can be subsequently sputtered onto the sidewalls of a via. The barrier material deposited on the sidewalls during sputtering forms a new barrier layer that advantageously prevents copper contamination of the dielectric layer caused by copper being deposited on the sidewalls when copper from the copper metallization layer is also subsequently sputtered off. The sputtering process also advantageously provides a via with round corners, which reduce the formation of voids in the via. 
   The present invention can be practiced by employing conventional materials, methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention can be practiced without resorting to the details specifically set forth. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the present invention. 
   Only the preferred embodiment of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.