Abstract:
A semiconductor device includes a first metallization level, a first diffusion barrier layer, a first etch stop layer, a dielectric layer and an opening 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 level. The first etch stop layer is disposed over the first diffusion barrier layer, and the dielectric layer is disposed over the first etch stop layer. The opening can also have rounded corners. A sidewall diffusion barrier layer can be disposed on sidewalls of the opening, and the sidewall diffusion barrier layer is formed from the same material as the first diffusion barrier layer. The first etch stop layer can be formed from a material different than the first barrier layer, and the material of the first barrier layer can be selected from the group consisting of tantalum, titanium, tantalum nitride, titanium nitride, and tungsten nitride. Metal within the opening form a second metal feature, and the metal can comprise copper or a copper alloy. 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. Nos. 09/776,750 and 09/776,749, both filed on Feb. 6, 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 inter-metal dielectric layers 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 levels are electrically interconnected by vertically oriented conductive plugs filling via holes formed in the inter-metal dielectric layer separating the metallization levels, 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 levels is known as “damascene” -type processing. Generally, this process involves forming a via opening in the inter-metal dielectric layer or interlayer dielectric (ILD) between vertically spaced metallization levels which is subsequently filled with metal to form a via electrically connecting the vertically spaced apart metal features. The via opening is typically formed using conventional lithographic and etching techniques. After the via opening is formed, the via is filled with a conductive material, such as tungsten (W), using conventional techniques, and the excess conductive material on the surface of the inter-metal dielectric layer 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 opening section which communicates with an upper trench section. The opening is then filled with a conductive material to simultaneously form a contact or via in contact with a conductive line. Excess conductive material on the surface of the inter-metal dielectric layer is then removed by CMP. An advantage of the dual damascene process is that contact or via and the upper line 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 inter-metal dielectric layers, create moisture/bias reliability problems when in contact with Al, and these problems have decreased the reliability of interconnections formed between various metallization levels. 
     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 level 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 wiping. Still a further problem is that W plugs are susceptible to void formation, and the interface with the metallization level 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 levels. 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 Cucontaining 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. 
     Another technique to increase the circuit speed is to reduce the capacitance of the inter-metal dielectric layers. Dielectric materials such as silicon oxide (SiO 2 ) have been commonly used to electrically separate and isolate or insulate conductive elements of the integrated circuit from one another. However, as the spacing between these conductive elements in the integrated circuit structure has become smaller, the capacitance between such conductive elements because of the dielectric being formed from silicon oxide is more of a concern. This capacitance negatively affects the overall performance of the integrated circuit because of increased power consumption, reduced speed of the circuitry, and cross-coupling between adjacent conductive elements. 
     A response to the problem of capacitance between adjacent conductive elements caused by use of silicon oxide dielectrics has led to the use of other dielectric materials, commonly known as low-k dielectrics. Whereas silicon oxide has a dielectric constant of approximately 4.0, many low-k dielectrics have dielectric constants less than 3.5. Examples of low-k dielectric materials include organic or polymeric materials. Another example is porous, low density materials in which a significant fraction of the bulk volume contains air, which has a dielectric constant of approximately 1. The properties of these porous materials are proportional to their porosity. For example, at a porosity of about 80%, the dielectric constant of a porous silica film, i.e. porous SiO 2 , is approximately 1.5. Still another example of a low-k dielectric material is carbon doped silicon oxide wherein at least a portion of the oxygen atoms bonded to the silicon atoms are replaced by one or more organic groups such as, for example, an alkyl group such as a methyl (CH 3 —) group. 
     A problem associated with the use of many low-k dielectric materials is that these materials can be damaged by exposure to oxidizing or “ashing” systems, which remove a resist mask used to form openings, such as vias, in the low-k dielectric material. This damage can cause the surface of the low-k dielectric material to become a water absorption site, if and when the damaged surface is exposed to moisture. Subsequent processing, such as annealing, can result in water vapor formation, which can interfere with subsequent filling with a conductive material of a via/opening or a damascene trench formed in the dielectric layer. For this reason, the upper surface of the low-k dielectric material is typically protected from damage during removal of the resist mask by a capping layer, such as silicon oxide, disposed over the upper surface. 
     A number of different variations of a damascene process using low-k dielectrics have been employed during semiconductor manufacturing. With reference to Figures  1 A- 1 H, an example of a damascene process for forming vias between vertically spaced metallization levels, 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 level  10 . The first etch stop layer  12  acts as a passivation layer that protects the first metallization level  10  from oxidation and contamination and prevents the material of the metallization level  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 level  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 low-k dielectric layer  14  is deposited over the first etch stop layer  12 . The majority of low-k dielectric materials used for a dielectric layer are based on organic or inorganic polymers. The liquid dielectric material is typically spun onto the surface under ambient conditions to a desired depth. This is typically followed by a heat treatment to evaporate solvents present within the liquid dielectric material and to cure the film to form the first low-k dielectric layer  14 . 
     After formation of the first low-k dielectric layer  14 , a capping layer  13  can be formed over the first low-k dielectric layer  14 . The function of the capping layer  13  is to protect the first low-k dielectric layer  14  from the process that removes a subsequently formed resist layer. The capping layer  13  can also be used as a mechanical polishing stop to prevent damage to the first low-k dielectric layer  14  during subsequent polishing away of conductive material that is deposited over the first low-k dielectric layer  14  and in a subsequently formed via. Examples of materials used as a capping layer  13  include silicon oxide and silicon nitride. 
     In FIG. 1C, vias are formed in the first low-k dielectric layer  14  using conventional lithographic and etch tchniques. The lithographic process involves depositing a resist  17  over the capping layer  13  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 low-k dielectric layer  14  and the capping layer  13 , removes the capping layer  13  and the first low-k 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 low-k 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 , removes the first etch stop layer  12  until the etchant reaches the first metallization level  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 level  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 level  10 , and this material can prevent good ohmic contact between the material of the conductive plug and the material of the first metallization level  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 level  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 low-k 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 capping layer  13 . 
     In FIG. 1H, the entire excess thickness of the metal overburden layer  24  over the upper surface  26  of the capping layer  13  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 capping layer  13 . 
     A number of different variations of a dual damascene process using low-k dielectrics have been employed during semiconductor manufacturing. With reference to FIGS. 2A-2L, a dual damascene process for forming vias and a second metallization level over a first metallization level, 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. 2A, a second etch stop layer  12  is deposited over a first metallization level  10 . The second etch stop layer  12  acts as a passivation layer that protects the first metallization level  10  from oxidation and contamination and prevents diffusion of material from the metallization level  10  into a subsequently formed dielectric layer. The second 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 level  10  to form the second etch stop layer  12 . An illustrative process used for depositing silicon nitride is PECVD. 
     In FIG. 2B, a first low-k dielectric layer  14  is deposited over the second etch stop layer  12 . The majority of low-k dielectric materials used for a dielectric layer are based on organic or inorganic polymers. The liquid dielectric material is typically spun onto the surface under ambient conditions to a desired depth. This is typically followed by a heat treatment to evaporate solvents present within the liquid dielectric material and to cure the film to form the first low-k dielectric layer  14 . 
     In FIG. 2C, a first etch stop layer  40  is deposited over the first low-k dielectric layer  14 . The first etch stop layer  40  acts as an etch stop during etching of a dielectric layer subsequently formed over the first etch stop layer  40 . As with the second etch stop layer  12 , a material typically used as an etch stop is silicon nitride, and approximately 500 angstroms of silicon nitride is typically deposited over the first dielectric layer  40  to form the first etch stop layer  40 . An illustrative process used for depositing silicon nitride is PECVD. 
     In FIG. 2D, a second low-k dielectric layer  42  is deposited over the first etch stop layer  40 . After formation of the second low-k dielectric layer  42 , a capping layer  13  can be formed over the second low-k dielectric layer  42 . The function of the capping layer  13  is to protect the second low-k dielectric layer  42  from the process that removes a subsequently formed resist layer. The capping layer  13  can also be used as a mechanical polishing stop to prevent damage to the second low-k dielectric layer  42  during subsequent polishing away of conductive material that is deposited over the second low-k dielectric layer  42  and in a subsequently formed via and trench. Examples of materials used as a capping layer  13  include silicon oxide and silicon nitride. 
     In FIG. 2E, the pattern of the vias are formed in the second low-k dielectric layer  42  and capping layer  13  using conventional lithographic and etch techniques. The lithographic process involves depositing a resist  44  over the capping layer  13  and exposing and developing the resist  44  to form the desired pattern of the vias. The first etch, which is highly selective to the material of the second low-k dielectric layer  42  and capping layer  13 , removes the capping layer  13  and the second low-k dielectric layer  42  until the etchant reaches the first etch stop layer  40 . The first etch is typically an anisotropic etch, such as a reactive ion plasma dry etch, that removes only the exposed portions of the second low-k dielectric layer  42  directly below the opening in the resist  44 . 
     In FIG. 2F, a second etch, which is highly selective to the material of the first etch stop layer  40 , removes the first etch stop layer  40  until the etchant reaches the first low-k dielectric layer  14 . The second etch is also typically an anisotropic etch. 
     In FIG. 2G, the vias  16  are formed in the first low-k dielectric layer  14  and the trenches  46  of the second metallization level are formed in the second low-k dielectric layer  42  using conventional lithographic and etch techniques. The lithographic process involves depositing a resist  50  over the capping layer  13  and exposing and developing the resist  50  to form the desired pattern of the trenches  46 . The third etch, which is highly selective to the material of the first and second dielectric layers  14 ,  42 , removes the first low-k dielectric layer  14  until the etchant reaches the second etch stop layer  12  and removes the second low-k dielectric layer  42  until the etchant reaches the first etch stop layer  40 . The third etch is typically an anisotropic etch, such as a reactive ion plasma dry etch, that removes only the exposed portions of the first low-k dielectric layer  14  directly below the opening in the first etch stop layer  40  and the exposed portions of the second low-k dielectric layer  42  directly below the opening in the resist  50 . By using an anisotropic etch, the via  16  and the trench  46  can be formed with substantially perpendicular sidewalls. 
     In FIG. 2H, a fourth etch, which is highly selective to the material of the first and second etch stop layers  40 ,  12 , then removes the second etch stop layer  12  until the etchant reaches the first metallization level  10  and removes the first etch stop layer  40  until the etchant reaches the first low-k dielectric layer  14 . The fourth etch is also typically an anisotropic etch. 
     In FIG. 21, the corners  18  of the vias  16  and trenches  46  can be rounded using a reverse sputtering process. The corners  18  of the vias  16  and trenches  46  are rounded to prevent problems of void creation associated with subsequent deposition of the conductive plug and second metallization level, and if necessary, a barrier layer. The reverse sputtering process can also be used to clean the first metallization level  10  at the bottom of the via  16 . Incomplete etching of the second etch stop layer  12  can leave a portion of the second etch stop layer  12  over the first metallization level  10 , and this material can prevent good ohmic contact between the material of the conductive plug and the material of the first metallization level  10 . Use of the reverse sputtering process, however, can remove any remaining material of the second etch stop layer  12  and any other contaminants on the first metallization level  10 . 
     In FIG. 2J, 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 and second dielectric layers  14 ,  42  of the conductive material subsequently deposited into the via  16  and trench  46 . 
     In FIG. 2K, a layer  22  of a conductive material, for example, a Cu or Cu-based alloy, is deposited in the via  16  and trench  46  and over the capping layer  13 . A typical process initially involves depositing a “seed” layer on the barrier layer  20  subsequently followed by conventional plating techniques, e.g., electroless or electroplating techniques, to fill the via  16  and trench  46 . So as to ensure complete filling of the via  16  and trench  46 , the Cu-containing conductive layer  22  is deposited as a blanket (or “overburden”) layer  24  so as to overfill the trench  46  and cover the upper surface  52  of the capping layer  13 . 
     In FIG. 2L, the entire excess thickness of the metal overburden layer  24  over the upper surface  52  of the capping layer  13  is removed using a CMP process. A typical CMP process utilizes an alumina (Al 2 O 3 )-based slurry, which leaves a conductive plug in the via  16  and a second metallization level in the trench  46 . The second metallization level has an exposed upper surface  58 , which is substantially co-planar with the upper surface  52  of the capping layer  13 . 
     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 and cause a lack of uniformity in the overall properties of the semiconductor device produced. This problem is particularly prevalent if the dielectric layer has a high porosity as copper can more easily leach, or migrate, into the pores of the dielectric layer. If Cu from the plug or the metallization level diffuses into the dielectric 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 processes, however, can still result in copper contamination as a result of the use of reverse physical sputtering or sputter etching to clean the first metallization level and to round the corners of the trenches and vias. Reverse physical sputtering or sputter etching 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 sputtering is illustrated in FIG.  3 . The reverse physical sputtering process rounds the corners  18  of the vias  16  and trenches  46  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 level  10 . Thus, the impact of the argon atoms onto the first metallization level  10  also dislodges atoms of Cu, and the dislodged atoms of Cu are free to be redeposited on other surfaces. In particular, the dislodged Cu atoms can be deposited onto the exposed sidewall surfaces  15  of the first and second low-k dielectric layers  14 ,  42 . Once the Cu is deposited on the first and second low-k dielectric layers  14 ,  42 , the Cu can then diffuse into the first and second low-k dielectric layers  14 ,  42 . As previously stated, the diffusion of Cu into a low-k dielectric layer  14 ,  42  causes detrimental effects that can result in the failure of the semiconductor device. The problem of Cu diffusion into the dielectric layers  14 ,  42  is particularly pronounced when the low-k dielectric material is porous. 
     Another problem associated with above-identified processes is the limited choices of material for the etch stop layers. A commonly used material as an etch stop is silicon nitride, which has a dielectric constant of about 7.0. However, the use of a thick etch stop layer of silicon nitride with a low-k dielectric layer partially negates the benefits obtained by use of a low-k dielectric material because of the increased combined capacitance of the etch stop layer and dielectric layer. Accordingly, a need exists for an improved method of forming copper plugs and copper metallization with low-k dielectric layers that allows for use of reverse sputtering to round corners of vias, so as to minimize the problem of void creation, yet still prevent the low-k 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 level; a first diffusion barrier layer; a first etch stop layer; a dielectric layer; and an opening. The first diffusion barrier layer is formed from a first material disposed over the first metallization level. The first etch stop layer is formed from a second material disposed over the first diffusion barrier layer, and the dielectric layer is disposed over the first etch stop layer. The first material is different from the second material. The opening has side surfaces and extends through the dielectric layer, the first etch stop layer, and the first diffusion barrier layer, and the opening can also have rounded corners. A sidewall diffusion barrier layer can also be disposed on sidewalls of the opening, and the sidewall diffusion barrier layer is formed from the same material as the first diffusion barrier layer. The first metallization level includes a first metal feature, and metal within the opening forms a second metal feature. 
     By providing a first diffusion barrier layer to the material of the metallization level, the material of the first diffusion barrier layer can be subsequently sputtered onto the sidewalls of the opening. The material deposited on the sidewalls forms a new sidewall diffusion barrier layer that prevents contamination of the dielectric layer caused by the material of the metallization level being deposited on the sidewalls when this material is subsequently sputtered off. The sputtering process also advantageously provides the opening with round corners, which reduce the formation of voids in the opening. 
     In another aspect of the invention, the dielectric layer is formed from a low-k dielectric material, and this low-k dielectric material can have a dielectric constant of less than about 3.5. Furthermore, the low-k dielectric material can be formed with a porous material. Additionally, the semiconductor device can further comprise a capping layer disposed over the dielectric layer. By providing a dielectric layer formed from a low-k dielectric material, the capacitance of the dielectric layer is reduced as compared to dielectric layers formed using conventional dielectric materials. 
     In a further aspect of the invention, the material of the first diffusion barrier layer can include tantalum, tantalum nitride, tungsten nitride, titanium, or titanium nitride, and the thickness of the first diffusion barrier layer can be from about 80 angstroms to about 120 angstroms. Also, the material of the first etch stop layer can include silicon nitride, and the thickness of the first etch stop layer can be from about 400 angstroms to about 600 angstroms. The metal and the first metallization level can comprise copper or a copper alloy. A second diffusion barrier layer can also be disposed over the sidewall diffusion barrier layer with an interface therebetween. 
     In still another aspect of the invention, the opening can be a via opening, a trench or a dual damascene opening. The dual damascene opening can comprise a lower via opening in communication with an upper trench. Also, the second metal feature can be a via, a line, or a combination of a lower via in contact with an upper line. 
     In an additional embodiment of the present invention, a semiconductor device comprises a first metallization level; a dielectric layer disposed over the first metallization level; a first sidewall diffusion barrier layer formed on sidewalls of an opening; a second diffusion barrier layer disposed on the first sidewall diffusion barrier layer with an interface therebetween; and a conductive plug within the via. The opening extends through the dielectric layer to the first metallization level and can have rounded corners. The first sidewall barrier diffusion layer is formed by sputtering a first diffusion barrier layer disposed over the first metallization level. 
     In a further embodiment of the present invention, a method of manufacturing a semiconductor device is also disclosed. The method of manufacturing includes forming a first diffusion barrier layer over a first metallization level; forming a first etch stop layer over the first diffusion barrier layer; forming a dielectric layer over the first etch stop layer; etching the dielectric layer to form an opening through the dielectric layer and the first etch stop layer; and sputtering the first diffusion barrier layer. The sputtering rounds corners of the via and 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 forming a second diffusion barrier layer over the sidewall diffusion barrier layer and forming a conductive plug within the opening. Also, the dielectric layer can be formed from a low-k dielectric material, and the first metallization level and the conductive plug can include copper. The material of the first diffusion barrier layer can include tantalum, tantalum nitride, tungsten nitride, titanium, or titanium nitride, and the material of the first etch stop layer can include silicon nitride. 
     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 level; forming a first diffusion barrier layer over the first metallization level; forming a first etch stop layer over the first diffusion barrier layer; forming a dielectric layer over the first etch stop layer; forming a capping layer over the dielectric layer; forming a resist over the capping layer; patterning the resist; etching through the capping layer and the dielectric layer with a first etchant; etching through the first etch stop layer with a second etchant; sputtering the first diffusion barrier layer; forming a conductive material in a opening and over a sidewall diffusion barrier layer; and planarizing a top surface of the capping layer. The etching of the capping layer, dielectric layer and the first etch stop layer forms the opening. 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. The material of the first diffusion barrier layer can include tantalum, tantalum nitride, tungsten nitride, titanium, or titanium nitride, and the material of the first etch stop layer can include silicon nitride. 
     In still a further embodiment of the present invention, a semiconductor device comprises a first metallization level, a first diffusion barrier layer, a second etch stop layer, a first dielectric layer, a first etch stop layer, a second dielectric layer, a trench, and a via. The first diffusion barrier layer is formed from a first material disposed over the first metallization level. The second etch stop layer is formed from a second material disposed over the first diffusion barrier layer, and the first dielectric layer is disposed over the second etch stop layer. The first material is different from the second material. The first etch stop layer is disposed over the first dielectric layer, and the second dielectric layer is disposed over the first etch stop layer. The trench extends through the second dielectric layer and the first etch stop layer, and the via extends from the trench through the first dielectric layer, the second etch stop layer, and the first diffusion barrier layer to the first metallization level. The via can also have rounded corners. A sidewall diffusion barrier layer can be disposed on sidewalls of the via and trench, and the sidewall diffusion barrier layer is formed from the same material as the first diffusion barrier layer. 
     By providing a first diffusion barrier layer to the material of the first metallization level, the material of the first diffusion barrier layer can be subsequently sputtered onto the sidewalls of the via and the trench. The material deposited on the sidewalls forms a new-sidewall diffusion barrier layer that prevents contamination of the dielectric layers caused by the material of the metallization level being deposited on the sidewalls when this material is, subsequently sputtered off. The sputtering process also advantageously provides the via and trench with round corners, which reduce the formation of voids in the via and trench. 
     In another aspect of the invention, the dielectric layers are formed from a low-k dielectric material, and this low-k dielectric material can have a dielectric constant of less than about 3.5. Furthermore, the low-k dielectric material can be formed with a porous material. Additionally, the semiconductor device can further comprise a capping layer disposed over the second dielectric layer. By providing dielectric layers formed from a low-k dielectric material, the capacitance of the dielectric layers are reduced over dielectric layers formed with conventional dielectric materials. 
     In a further aspect of the invention, the material of the first diffusion barrier layer can include tantalum, tantalum nitride, tungsten nitride, titanium, or titanium nitride. Also, the material of the first and second etch stop layers can include silicon nitride, and the first metallization level can include copper. A second diffusion barrier layer can also 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 yet another embodiment of the present invention, a semiconductor device comprises a first metallization level; a first dielectric layer disposed over the first metallization level; a second dielectric layer disposed over the first dielectric layer; a first sidewall diffusion barrier layer disposed on sidewalls of a via and trench; a second diffusion barrier layer disposed over the first sidewall diffusion barrier layer and formed from a material different than silicon nitride; and a conductive material within the via and trench. The trench extends through the second dielectric layer to the first dielectric layer, and the via extends from the trench through the first dielectric layer to the first metallization level. The via can also have rounded corners. The first sidewall diffusion barrier layer is formed by sputtering a first diffusion barrier layer disposed over the first metallization level. 
     In a further embodiment of the present invention, a method of manufacturing a semiconductor device is also disclosed. The method of manufacturing includes forming a first diffusion barrier layer over a first metallization level; forming a second etch stop layer over the first diffusion barrier layer; forming a first dielectric layer over the second etch stop layer; forming a second dielectric layer over the first dielectric layer; etching the first and second dielectric layers to form a via and a trench; and sputtering the first diffusion barrier layer. The trench is formed through the second dielectric layer, and the via is formed from the trench through the first dielectric layer. Also, the sputtering rounds corners of the via and trench and also deposits material of the first diffusion barrier layer onto sidewalls of the via and trench to form a sidewall diffusion barrier layer. 
     In an additional aspect of the invention, the method can further include the steps forming a first etch stop layer between the first dielectric layer and the second dielectric layer and etching the first etch stop layer during etching of the second etch stop layer. The material of the first diffusion barrier layer can include tantalum, tantalum nitride, tungsten nitride, titanium, or titanium nitride, and the material of the first and second etch stop layers can include silicon nitride. A second diffusion barrier layer can also be deposited over the sidewall diffusion barrier layer, and a conductive material can then be deposited within the via and trench. The dielectric layers can also be formed from a low-k dielectric material. 
     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 level; forming a first diffusion barrier layer over the first metallization level; forming a second etch stop layer over the first diffusion barrier layer; forming a first dielectric layer over the second etch stop layer; forming a first etch stop layer over the first dielectric layer; forming a second dielectric layer over the first etch stop layer; forming a capping layer over the second dielectric layer; forming a first resist over the capping layer; patterning the first resist; etching through the capping layer and the second dielectric layer with a first etch; etching through the first etch stop layer with a second etch; forming a second resist over the capping layer; patterning the second resist; etching through the capping layer and first and second dielectric layers with a third etch; etching through the first and second etch stop layers with a fourth etch; sputtering the first diffusion barrier layer; forming a conductive material in a via and a trench; and planarizing a top surface of the capping layer. The etchings form the trench through the capping layer, the second dielectric layer, and the first etch stop layer to the first dielectric layer and form the via from the trench through the first dielectric layer and the second etch stop layer to the first barrier diffusion layer. The sputtering rounds corners of the via and trench and deposits material of the first diffusion barrier layer onto sidewalls of the via and trench to form a sidewall diffusion barrier layer. The conductive layer is deposited over the sidewall diffusion barrier layer. The material of the first diffusion barrier layer can include tantalum, tantalum nitride, tungsten nitride, titanium, or titanium nitride, and the material of the first and second etch stop layers can include silicon nitride. Also, the dielectric layers can be formed from a low-k dielectric material. 
    
    
     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. 
     FIGS. 2A-2L schematically illustrate sequential phases of a conventional dual damascene process. 
     FIG. 3 illustrates a conventional via and trench during a sputtering process. 
     FIGS. 4A-4H schematically illustrate sequential phases of a single damascene process according to an embodiment of the present invention. 
     FIGS. 5A-5L schematically illustrate sequential phases of a dual damascene process according to an additional embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention addresses and solves the problem of contamination during single damascene processing 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 level below the via. This is achieved, in part, by providing a first etch stop layer and a barrier layer below the first etch stop layer. Advantageously, after the first etch stop layer is removed using conventional etching techniques, the barrier layer is 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. 
     Furthermore, the present invention addresses problems associated with the high capacitance of inter-metal dielectric layers. This is achieved, in part, by providing a dielectric layer formed from a low-k dielectric material. As used herein, the term low-k dielectric means a dielectric having a dielectric constant of less than about 3.5, e.g., less than about 2.5. 
     An embodiment of the present invention is illustrated in FIGS. 4A-4H. As illustrated in FIG. 4A, a first diffusion barrier layer  111  is formed over a first metallization level  110 . The first diffusion barrier layer  111  can be formed from any material that prevents diffusion of the material from the metallization level  110  into a subsequently formed dielectric layer. For example, in current embodiments of the invention, the first metallization level  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 level  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 level  110 . Also, the thickness of the first diffusion barrier layer  111  is preferably sufficient to act as an etch stop and not allow the etchant of the first etch stop layer to reach the first metallization level  110 . In current embodiments of the invention, the thickness of the first diffusion barrier layer  111  is at least 50 angstroms and is preferably from about 100 to about 200 angstroms. 
     In an aspect of the invention, the first diffusion barrier layer  111  can be formed from tantalum, tantalum nitride, tungsten nitride, titanium, or titanium nitride although the invention is not limited in this manner. These materials advantageously act as a diffusion barrier to copper and also as a passivation layer. Furthermore, the materials also act as an etch stop to an etchant that etches silicon nitride. Any process capable of depositing the first diffusion barrier layer  111  is acceptable for use with the invention, and an illustrative process for depositing tantalum is physical vapor deposition (PVD) and an illustrative process for deposing tantalum nitride is CVD or reactive PVD. 
     After the first diffusion barrier layer  111  is formed, a first etch stop layer  112  is deposited over the first diffusion barrier layer  111 . The first etch stop layer  112  acts as an etch stop during subsequent etching of the dielectric layer formed above the first etch stop layer  112 . In an aspect of the invention, the first etch stop layer  112  is formed from silicon nitride although the invention in not limited in this manner. Silicon nitride, however, has the advantage of acting as an etch stop to many etchants used to etch low-k dielectric materials. 
     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 an aspect of the invention, the thickness of the first etch stop layer  112  is at least 50 angstroms, and in another aspect of the inventionrthhikness of the first etch stop layer  112  is 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 pross for depositing silicon nitride is PECVD. 
     In FIG. 4B, a first dielectric layer  114  is deposited over the first etch stop layer  112 . The first dielectric layer  114  can be formed from any material capable of acting as a dielectric, and illustrative materials include silicon oxide and silicon nitride. In one aspect of the invention, the first dielectric layer  114  is formed from a low-k dielectric material. Illustrative examples of low-k dielectric materials include fluorosilicate glass (FSG or SiOF), hydrogenated diamond-like carbon (DLC), polystyrene, fluorinated polyimides, parylene (AF-4), polyarylene ether, and polytetrafluoro ethylene. In another aspect of the invention, the first dielectric layer  114  is formed from a porous low-k dielectric material, such as siloxanes, silsesquioxanes, aerogels, and xerogels. These low-k dielectric materials can be applied via conventional spin-coating, dip coating, spraying, meniscus coating methods, in addition to other coating methods that are well-known in the art. 
     After formation of the first dielectric layer  114 , a capping layer  113  can be formed over the first dielectric layer  114 . The function of the capping layer  113  is to protect the first dielectric layer  114  from the process that removes a subsequently formed resist layer, and any material so capable is acceptable for use with the invention. The capping layer  113  can also be used as a mechanical polishing stop to prevent damage to the first dielectric layer  114  during subsequent polishing away of conductive material that is deposited over the first dielectric layer  114  and in a subsequently formed via. Examples of materials used as a capping layer  113  include silicon oxide and silicon nitride. In an aspect of the invention, the capping layer  113  is formed from silicon oxide and has a thickness of at least 50 angstroms. In another aspect of the invention, the thickness of the capping layer  113  is from about 400 to about 600 angstroms. 
     In FIG. 4C, vias  116  are formed in the first dielectric layer  114  using conventional lithographic techniques, for example, optical lithography (including, for example, I-line and deep-UV), X-ray, and E-beam lithography, followed by etching. 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 pattern of the vias  116 . The first etch, which is highly selective to the material of the first dielectric layer  114  and capping layer  113 , removes the capping layer  113  and 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. 4D, a second etch, which is highly selective to the material of the first etch stop layer  112 , removes the first etch stop layer  112  until the etchant reaches the first diffusion barrier layer  111 . The second etch is also typically an anisotropic etch. 
     In FIG. 4E, a reverse sputtering process etches through the first diffusion barrier layer  111  to expose the first metallization level  110 . 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 level  110  from diffusing into the first dielectric layer  114  after the sputtering process reaches the first metallization level  110  and the material of the first metallization level  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 level  110  at the bottom of the via  116 . As such, any dielectric material or contaminants formed over the first metallization level  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 level  110 . 
     In FIG. 4F, 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. 4G, a layer  122  of a conductive material is deposited into the via  116  and over the capping layer  113 . In an aspect 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 capping layer  113 . 
     In FIG. 4H, the entire excess thickness of the metal overburden layer  124  over the upper surface  126  of the capping layer  113  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 capping layer  113 . 
     By providing a barrier layer above a copper metallization level, 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 level 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. 
     In an additional embodiment, the present invention addresses and solves the problem of contamination during dual damascene processing from copper being deposited onto silicon oxide dielectric layers as a result of reverse physical sputtering, which is used to round corners of vias and trenches and to clean contaminants on the copper metallization level below the via. This is achieved, in part, by providing a second etch stop layer and a barrier layer below the second etch stop layer. Advantageously, after the second etch stop layer is removed using conventional etching techniques, the barrier layer is 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 layers and creates a sidewall diffusion barrier. This is accomplished before the copper from the copper layer is sputtered off onto the dielectric layers. 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 layers. Furthermore, the present invention addresses problems associated with the high capacitance of inter-metal dielectric layers. This is achieved, in part, by providing first and second dielectric layers formed from low-k dielectric materials. 
     The additional embodiment of the present invention is illustrated in FIGS. 5A-5L. The dual damascene process to be described is illustrative of one sequence of steps, which can be used to practice the invention. In particular, the process provides a dual damascene structure, which includes a first metallization level, over which first and second dielectric layers are disposed, and the first and second dielectric layers respectively include a via and trench filled with a conductive material. However, the invention is not limited as to particular sequence of steps described to provide the dual damascene structure, as other sequence of steps capable of providing the dual damascene structure can be used to practice the invention. 
     As illustrated in FIG. 5A, a first diffusion barrier layer  111  is formed over a first metallization level  110 . The first diffusion barrier layer  111  can be formed from any material that prevents diffusion of the material from the metallization level  110  into a subsequently formed dielectric layer. For example, in current embodiments of the invention, the first metallization level  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 level  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 and trench in the dielectric layers 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 layers. 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 layers to form an effective diffusion barrier from the material of the first metallization level  110 . Also, the thickness of the first diffusion barrier layer  111  is preferably sufficient to act as an etch stop and not allow the etchant of the second etch stop layer to reach the first metallization level  110 . In current embodiments of the invention, the thickness of the first diffusion barrier layer  111  is at least 50 angstroms and is preferably from about 100 to about 200 angstroms. 
     In an aspect of the invention, the first diffusion barrier layer  111  can be formed from tantalum, tantalum nitride, tungsten nitride, titanium, or titanium nitride although the invention is not limited in this manner. These materials advantageously act as a diffusion barrier to copper and also as a passivation layer. Furthermore, the materials also act as an etch stop to an etchant that etches silicon nitride. Any process capable of depositing the first diffusion barrier layer  111  is acceptable for use with the invention, and an illustrative process for depositing tantalum is physical vapor deposition (PVD) and an illustrative process for deposing tantalum nitride is CVD or reactive PVD. 
     After the first diffusion barrier layer  111  is formed, a second etch stop layer  112  is deposited over the first diffusion barrier layer  111 . The second etch stop layer  112  acts as an etch stop during subsequent etching of the dielectric layer formed above the second etch stop layer  112 . In an aspect of the invention, the second etch stop layer  112  is formed from silicon nitride although the invention in not limited in this manner. Silicon nitride, however, has the advantage of acting as an etch stop to many etchants used to etch low-k dielectric materials. 
     The thickness of the second etch stop layer  112  is preferably sufficient to act as an etch stop during etching of the dielectric layer. In an aspect of the invention, the thickness of the second etch stop layer  112  is at least 50 angstroms, and in another aspect of the invention, the thickness of the second etch stop layer  112  is from about 400 to about 600 angstroms. Any process capable of depositing the second etch stop layer  112  is acceptable for use with the invention, and an illustrative process for depositing silicon nitride is PECVD. 
     In FIG. 5B, a first dielectric layer  114  is deposited over the second etch stop layer  112 . The first dielectric layer  114  can be formed from any material capable of acting as a dielectric, and illustrative materials include silicon oxide and silicon nitride. In one aspect of the invention, the first dielectric layer  114  is formed from a low-k dielectric material. Illustrative examples of low-k dielectric materials include fluorosilicate glass (FSG or SiOF), hydrogenated diamond-like carbon (DLC), polystyrene, fluorinated polyimides, parylene (AF-4), polyarylene ether, and polytetrafluoro ethylene. In another aspect of the invention, the first dielectric layer  114  is formed from a porous low-k dielectric material, such as siloxanes, silsesquioxanes, aerogels, and xerogels. These low-k dielectric materials can be applied via conventional spin-coating, dip coating, spraying, meniscus coating methods, in addition to other coating methods that are well-known in the art. 
     In FIG. 5C, a first etch stop layer  140  is deposited over the first dielectric layer  114 . The first etch stop layer  140  acts as an etch stop during subsequent etching of the dielectric layer formed above the first etch stop layer  140 . In an aspect of the invention, the first etch stop layer  140  is formed from silicon carbide although the invention in not limited in this manner. However, as with the second etch stop layer  112 , the dielectric constant of silicon carbide is lower than the dielectric constant of other etch stop materials, such as silicon nitride, and thereby lowers the combined capacitance of the intermetal dielectric layers. 
     The thickness of the first etch stop layer  140  is preferably sufficient to act as an etch stop during etching of the dielectric layer formed above the first etch stop layer  140 . In one aspect of the invention, the thickness of the first etch stop layer  140  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  140  is acceptable for use with the invention, and an illustrative process for depositing silicon nitride is PECVD. 
     In FIG. 5D, a second dielectric layer  142  is deposited over the first etch stop layer  140 . As with the first dielectric layer  114 , the second dielectric layer  142  can be formed from any material suitable for use a dielectric. In one aspect of the invention, however, the second dielectric layer  142  is formed from a low-k dielectric material, and in another aspect of the invention, the second dielectric layer  142  is formed from a porous low-k dielectric material. 
     After formation of the second dielectric layer  142 , a capping layer  113  can be formed over the second dielectric layer  142 . The function of the capping layer  113  is to protect the second dielectric layer  142  from the process that removes a subsequently formed resist layer, and any material so capable is acceptable for use with the invention. The capping layer  113  can also be used as a mechanical polishing stop to prevent damage to the second dielectric layer  142  during subsequent polishing away of conductive material that is deposited over the second dielectric layer  142  and in a subsequently formed via and trench. Examples of materials used as a capping layer  113  include silicon oxide and silicon nitride. In an aspect of the invention, the capping layer  113  is formed from silicon oxide and has a thickness of at least 50 angstroms. In another aspect of the invention, the thickness of the capping layer  113  is from about 400 to about 600 angstroms. 
     In FIG. 5E, the pattern of the vias are formed in the second dielectric layer  142  using conventional lithographic techniques, for example, optical lithography (including, for example, I-line and deep-UV), X-ray, and E-beam lithography, followed by etching. The lithographic process involves depositing a resist  144  over the second dielectric layer  142  and exposing and developing the resist  144  to form the desired pattern of the vias. The first etch, which is highly selective to the material of the second dielectric layer  142  and capping layer  113 , removes the capping layer  113  and second dielectric layer  142  until the etchant reaches the first etch stop layer  140 . The first etch is typically an anisotropic etch, such as a reactive ion plasma dry etch, that removes only the exposed portions of the second dielectric layer  142  directly below the opening in the resist  144 . 
     In FIG. 5F, a second etch, which is highly selective to the material of the first etch stop layer  140 , removes the first etch stop layer  140  until the etchant reaches the first dielectric layer  114 . The second etch is also typically an anisotropic etch. 
     In FIG. 5G, the vias  116  are formed in the first dielectric layer  114  and the trenches  146  of the second metallization level are formed in the second dielectric layer  142  using conventional lithographic and etch techniques. The lithographic process involves depositing a resist  150  over the second dielectric layer  142  and exposing and developing the resist  150  to form the desired pattern of the trenches  146 . The third etch, which is highly selective to the material of the capping layer  113  and first and second dielectric layers  114 ,  142 , removes the first dielectric layer  114  until the etchant reaches the second etch stop layer  112  and removes the second dielectric layer  142  until the etchant reaches the first etch stop layer  140 . The third 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 first etch stop layer  140  and the exposed portions of the second dielectric layer  142  directly below the opening in the resist  150 . By using an anisotropic etch, the via  116  and the trench  146  can be formed with substantially perpendicular sidewalls. 
     In FIG. 5H, a fourth etch, which is highly selective to the material of the first and second etch stop layers  140 ,  112 , removes the second etch stop layer  112  until the etchant reaches the first diffusion barrier layer  111  and removes the first etch stop layer  140  until the etchant reaches the first dielectric layer  114 . The fourth etch is also typically an anisotropic etch. 
     In FIG. 5I, a reverse sputtering process etches through the first diffusion barrier layer  111  to expose the first metallization level  110 . 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  and trench  146 . The material of the first diffusion barrier layer  111  deposited on the sidewalls of the via  116  and trench  146  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 level  110  from diffusing into the first and second dielectric layers  114 ,  142  after the sputtering process reaches the first metallization level  110  and the material of the first metallization level  110  is sputtered off. 
     The reverse sputtering process also advantageously rounds the corners  118  of the via  116  and trench  146 . The corners  118  of the via  116  and trench  146  are rounded to prevent problems associated with subsequent deposition of the conductive plug and second metallization level, 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  or trench  146  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  and trench  146 . Consequentially, the material at opposing corners  118  can form cantilevered bridges that eventually meet in the middle of the via  116  or trench  146 . When this occurs, the via  116  or trench  146  is blocked and further deposition of material within the via  116  or trench  146  is prevented, thereby leaving a void in the via  116  or trench  146 . The creation of such a void can disadvantageously cause a malfunction in the semiconductor device. However, by rounding the corners  118  of the via  116  and trench  146 , 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 level  110  at the bottom of the via  116 . As such, any dielectric material or contaminants formed over the first metallization level  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 level  110 . 
     In FIG. 5J, an adhesion/barrier material, such as tantalum, titanium, tungsten, tantalum nitride, or titanium nitride, is deposited in the via  116  and trench  146  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 and second dielectric layers  114 ,  142  of the conductive material subsequently deposited into the via  116  and trench  146 . 
     In FIG. 5K, a layer  122  of a conductive material is deposited into the via  116  and trench  146  and over the capping layer  113 . 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  and trench  146  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  and trench  146 . So as to ensure complete filling ofthe via  116  and trench  146 , the Cu-containing conductive layer  122  is deposited as a blanket (or “overburden”) layer  124  so as to overfill the trench  146  and cover the upper surface  152  of the capping layer  113 . 
     In FIG. 5L, the entire excess thickness of the metal overburden layer  124  over the upper surface  152  of the capping layer  113  is removed using a CMP process. A typical CMP process utilizes an alumina (A 2 O 3 )-based slurry, which leaves a conductive plug in the via  116  and a second metallization level in the trench  146 . The second metallization level has an exposed upper surface  158 , which is substantially co-planar with the upper surface  152  of the capping layer  113 . 
     By providing a barrier layer above a copper metallization level, the material of the barrier layer can be subsequently sputtered onto the sidewalls of a via and trench. The barrier material deposited onto the sidewalls during sputtering forms a new barrier layer that advantageously prevents copper contamination of the dielectric layers caused by copper being deposited onto the sidewalls when copper from the copper metallization level is also subsequently sputtered off. The sputtering process also advantageously provides a via and trench with round corners, which reduce the formation of voids in the via or trench. 
     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.