Patent Publication Number: US-6709316-B1

Title: Method and apparatus for two-step barrier layer polishing

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the fabrication of semiconductor devices and to chemical mechanical polishing and planarization of semiconductor devices. 
     2. Background of the Related Art 
     Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) of semiconductor devices. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology has placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of this technology require precise processing of high aspect ratio features, such as vias, contacts, lines, and other interconnects. Reliable formation of these interconnects is important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die. 
     In order to further improve the current density of semiconductor devices on integrated circuits, it has become necessary to use conductive materials having low resistivity for conductors and materials having low dielectric constant (low k, defined herein as having dielectric constants, k, less than about 4.0) as insulating layers to reduce the capacitive coupling between adjacent interconnects. Increased capacitative coupling between layers can detrimentally affect the functioning of semiconductor devices. 
     One conductive material gaining acceptance is copper and its alloys, which have become the materials of choice for sub-quarter-micron interconnect technology because copper has a lower resistivity than aluminum, (1.7 μΩ-cm compared to 3.1 μΩ-cm for aluminum), and a higher current carrying capacity. These characteristics are important for supporting the higher current densities experienced at high levels of integration and increased device speed. Further, copper has a good thermal conductivity and is available in a highly pure state. 
     One difficulty in using copper in semiconductor devices is that copper is difficult to etch and achieve a precise pattern. Etching with copper using traditional deposition/etch processes for forming interconnects has been less than satisfactory. Therefore, new methods of manufacturing interconnects having copper containing materials and low k dielectric materials are being developed. 
     One method for forming vertical and horizontal interconnects is by a damascene or dual damascene method. In the damascene method, one or more dielectric materials, such as the low k dielectric materials, are deposited and pattern etched to form the vertical interconnects, i.e. vias, and horizontal interconnects, i.e., lines. Conductive materials, such as copper, and other materials, such as barrier layer materials used to prevent diffusion of conductive material into the surrounding low k dielectric, are then inlaid into the etched pattern. Any excess conductive material and excess barrier layer material external to the etched pattern, such as on the field of the substrate, is then removed. 
     Barrier layer materials include, for example, tantalum (Ta), tantalum nitride (TaN), titanium (Ti), and titanium nitride. 
     As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization. Planarizing a surface, or “polishing” a surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in damascene processes to remove excess deposited material and to provide an even surface for subsequent levels of metallization and processing. Planarization may also be used in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. 
     Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates. In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate urging the substrate against the polishing pad. The pad is moved relative to the substrate by an external driving force. Thus, the CMP apparatus effects polishing or rubbing movement between the surface of the substrate and the polishing pad while dispersing a polishing composition to effect both chemical activity and mechanical activity. 
     Conventionally, in polishing copper features, such as a dual damascenes, the copper material is polished to the barrier layer, and then the barrier layer is polished to the underlying dielectric layer. One challenge which is presented in copper polishing is that the interface between copper and the barrier layer is generally non-planar. Further, the copper material and the barrier materials are often removed from the substrate surface at different rates. These challenges in copper removal often results in the retention of copper containing material, or residue, on the surface of the substrate. To ensure removal of all the copper material and residue before removing the barrier material, it is necessary to overpolish the copper and the interface. Overpolishing of copper and the interface can result in forming topographical defects, such as concavities or depressions, referred to as dishing, and can further lead to non-uniform removal of the barrier layer disposed thereunder. 
     FIG. 5 is a schematic view of a substrate illustrating the phenomenon of dishing. Conductive lines  211  and  212  are formed by depositing conductive material, such as copper or copper alloy, in a feature definition formed in the dielectric layer  210 , typically comprised of silicon oxides or other dielectric materials. After planarization, for example, a portion of the conductive material is depressed by an amount D, referred to as the amount of dishing, forming a concave copper surface. Dishing results in a non-planar surface that impairs the ability to print high resolution lines during subsequent photolithographic steps and detrimentally affects subsequent surface topography of the substrate and device formation. Dishing also detrimentally affects the performance of devices by lowering the conductance and increasing the resistance of the devices, contrary to the benefit of using higher conductive materials, such as copper. 
     Therefore, there exists a need for a method and related CMP composition which facilitates the removal of copper containing material residue and the barrier layer, and provides selectivity therebetween and to the underlying dielectric layer. 
     SUMMARY OF THE INVENTION 
     The invention generally provides a method and composition for planarizing a substrate surface having a barrier layer disposed thereon. In one aspect, the invention provides for planarizing a substrate surface, comprising providing a substrate comprising a dielectric layer with feature definitions formed therein, a barrier layer conformally deposited on the dielectric layer and in the feature definitions formed therein, and a copper containing material deposited on the barrier layer and filling the feature definitions formed therein, chemical mechanical polishing the substrate with a bulk CMP composition to substantially remove excess copper containing materials, chemical mechanical polishing the substrate with a first CMP composition to remove residual copper containing materials and at least a portion of the barrier layer, and chemical mechanical polishing the substrate with a second CMP composition to selectively remove residual barrier layer. 
     In another aspect, the invention provides a method for planarizing a substrate surface, comprising providing a substrate comprising a dielectric layer with feature definitions formed therein, a barrier layer conformally deposited on the dielectric layer and in the feature definitions formed therein, and a copper containing material deposited on the barrier layer and filling the feature definitions formed therein, supplying a bulk polishing composition to the substrate, removing substantially excess copper containing material at a ratio of copper containing material to barrier layer between about 1:0 and about 1:0.01 by a polishing technique, supplying a first polishing composition to the substrate, removing residual copper containing materials and removing a portion of the barrier layer from the substrate at a ratio of copper containing material to barrier layer between about 2:1 and about 1:1 by a polishing technique, supplying a second polishing composition to the substrate, and removing residual barrier layer from the surface of the substrate at a ratio of barrier layer to copper containing material to dielectric layer between about 1:0:0 and about 1:0.2:0.2 by a chemical mechanical polishing technique. 
     Another aspect of the invention provides a method for planarizing a barrier layer comprising a tantalum containing material on a substrate surface, comprising chemical mechanical polishing the substrate to selectively remove residual copper containing material and a portion of the tantalum containing material therefrom, and then chemical mechanical polishing the substrate to selectively remove residual tantalum containing material therefrom. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is a schematic perspective view of a chemical mechanical polishing apparatus; 
     FIGS. 2-4 are schematic diagrams of a substrate illustrating one embodiment of a process for planarizing a substrate surface described herein; and 
     FIG. 5 is a schematic view of a substrate illustrating the phenomenon of dishing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In general, aspects of the invention provide a method and polishing composition for removing conductive material and barrier layer materials while eliminating or substantially reducing dishing. The invention will be described below in reference to the removal of copper and tantalum/tantalum nitride barrier layers from a substrate surface by a chemical mechanical polishing (CMP) technique. CMP is broadly defined herein as polishing a substrate by chemical activity, mechanical activity, or a combination of both chemical and mechanical activity. 
     One apparatus for performing the planarizing process and composition described herein is a Mirra® CMP System available from Applied Materials, Inc., as shown and described in U.S. Pat. No. 5,738,574, entitled, “Continuous Processing System for Chemical Mechanical Polishing,” the entirety of which is incorporated herein by reference to the extent not inconsistent with the invention. Although, the CMP process and composition is illustrated utilizing the Mirra® CMP System, any system enabling chemical mechanical polishing using the composition described herein can be used to advantage. Examples of other suitable polishing apparatus include the Obsidian 8200C System available from Applied Materials, Inc., or a linear polishing system, using a sliding or circulating polishing belt or similar device. An example of a linear polishing system is more fully described in co-pending U.S. patent application Ser. No. 09/244,456, filed on Feb. 4, 1999, and incorporated herein by reference to the extent not inconsistent with the invention. The following apparatus description is illustrative and should not be construed or interpreted as limiting the scope of the invention. 
     FIG. 1 is a schematic perspective view of a chemical mechanical polishing apparatus  20 . The polishing apparatus  20  includes a lower machine base  22  with a table top  28  mounted thereon and a removable outer cover (not shown). The table top  28  supports a series of polishing stations, including a first polishing station  25   a , a second polishing station  25   b , a final polishing station  25   c , and a transfer station  27 . The transfer station  27  serves multiple functions, including, for example, receiving individual substrates  10  from a loading apparatus (not shown), washing the substrates, loading the substrates into carrier heads  80 , receiving the substrates  10  from the carrier heads  80 , washing the substrates  10  again, and transferring the substrates  10  back to the loading apparatus. 
     Each polishing station  25   a - 25   c  includes a rotatable platen  30  having a polishing pad  100  or  110  disposed thereon. Each platen  30  may be a rotatable aluminum or stainless steel plate connected to a platen drive motor (not shown). The polishing stations  25   a - 25   c  may include a pad conditioner apparatus  40 . The pad conditioner apparatus  40  has a rotatable arm  42  holding an independently rotating conditioner head  44  and an associated washing basin  46 . The pad conditioner apparatus  40  maintains the condition of the polishing pad so that it will effectively polish the substrates. Each polishing station may include a conditioning station if the CMP apparatus is used with other pad configurations. 
     The polishing stations  25   a - 25   c  may each have a slurry/rinse arm  52  that includes two or more supply tubes to provide one or more chemical slurries and/or water to the surface of the polishing pad. The slurry/rinse arm  52  delivers the one or more chemical slurries in amounts sufficient to cover and wet the entire polishing pad. Each slurry/rinse arm  52  also includes several spray nozzles (not shown) that can provide a high-pressure fluid rinse on to the polishing pad at the end of each polishing and conditioning cycle. Furthermore, two or more intermediate washing stations  55   a ,  55   b , and  55   c  may be positioned between adjacent polishing stations  25   a ,  25   b , and  25   c  to clean the substrate as it passes from one station to the next. 
     A rotatable multi-head carousel  60  is positioned above the lower machine base  22 . 
     The carousel  60  includes four carrier head systems  70   a ,  70   b ,  70   c , and  70   d . Three of the carrier head systems receive or hold the substrates  10  by pressing them against the polishing pads  100  or  110  disposed on the polishing stations  25   a - 25   c . One of the carrier head systems  70   a - 70   d  receives a substrate from and delivers a substrate  10  to the transfer station  27 . The carousel  60  is supported by a center post  62  and is rotated about a carousel axis  64  by a motor assembly (not shown) located within the machine base  22 . The center post  62  also supports a carousel support plate  66  and a cover  68 . 
     The four carrier head systems  70   a - 70   d  are mounted on the carousel support plate  66  at equal angular intervals about the carousel axis  64 . The center post  62  allows the carousel motor to rotate the carousel support plate  66  and orbit the carrier head systems  70   a - 70   d  about the carousel axis  64 . Each carrier head system  70   a - 70   d  includes one carrier head  80 . A carrier drive shaft  78  connects a carrier head rotation motor  76  (shown by the removal of one quarter of the cover  68 ) to the carrier head  80  so that the carrier head  80  can independently rotate about its own axis. There is one carrier drive shaft  78  and motor  76  for each head  80 . In addition, each carrier head  80  independently oscillates laterally in a radial slot  72  formed in the carousel support plate  66 . 
     The carrier head  80  performs several mechanical functions. Generally, the carrier head  80  holds the substrate  10  against the polishing pad  100  or  110 , evenly distributes a downward pressure across the back surface of the substrate  10 , transfers torque from the drive shaft  78  to the substrate  10 , and ensures that the substrate  10  does not slip out from beneath the carrier head  80  during polishing operations. 
     Chemical Mechanical Polishing Process and Composition 
     CMP is broadly defined herein as polishing a substrate by chemical activity, mechanical activity, or a combination of both chemical and mechanical activity. In some systems, a substrate is polished on a pad in the presence of a polishing fluid, also known as a slurry, which may contain chemicals that pacify or oxidize the layer being polished and abrasives that abrasively remove or polish off the surface of the layer. The interaction of a polishing pad, the chemically reactive polishing fluid, and the abrasive polishing fluid with the surface of the substrate imparts a combination of chemical and mechanical forces to the substrate which planarizes the substrate surface and results in controlled polishing of the exposed layer. In a fixed-abrasive system, a polishing pad called a fixed abrasive pad is used which does not require abrasive particles within the slurry. Typically, a polishing fluid without abrasive particles is used in concert with the fixed abrasive pad to provide the chemical component of the polishing process. 
     A substrate surface processed by the methods and compositions described herein generally comprises a dielectric layer with feature definitions formed therein, a barrier layer deposited on the dielectric layer, and a copper containing material deposited on the barrier layer. The copper containing material includes copper, copper alloys, or doped copper. As used throughout this disclosure, the phrase “copper containing material” and the symbol Cu are intended to encompass high purity elemental copper as well as doped copper, e.g. phosphorous doped copper and copper-based alloys, e.g., copper-based alloys containing at least about 80 wt. % copper. The barrier layer material includes tantalum-containing materials, such as tantalum, tantalum nitride, or tantalum silicon nitride. Other barrier materials conventionally used in the art for aluminum, copper, and tungsten metallization processes are also contemplated by the invention. 
     The dielectric layer can comprise any of various dielectric materials conventionally employed in the manufacture of semiconductor devices. For example, dielectric materials, such as silicon dioxide, phosphorus-doped silicon glass (PSG), boron-phosphorus-doped silicon glass (BPSG), and silicon dioxide derived from tetraethyl orthosilicate (TEOS) or silane by plasma enhanced chemical vapor deposition (PECVD) can be employed. The dielectric layer can also comprise low dielectric constant materials, including fluoro-silicon glass (FSG), polymers, such as polyamides, and carbon-containing silicon dioxide, such as Black Diamond™, commercially available from Applied Materials, Inc., of Santa Clara, Calif. The openings are formed in interlayer dielectrics by conventional photolithographic and etching techniques. 
     In one embodiment of the invention, a two step planarizing process for removing copper containing residues and barrier layer materials from a substrate surface following bulk removal of excess copper containing material disposed thereon is provided. In the first step, a first composition is used to selectively remove residual copper containing material remaining from the bulk removal process and at least a portion of the underlying barrier layer material. A second composition selectively removes residual barrier layer material, which advantageously stops on an underlying dielectric layer, thereby planarizing the surface of the substrate. 
     The bulk of the copper containing material can be selectively removed using a CMP composition comprising one or more chelating agents, one or more oxidizers, one or more corrosion inhibitors, and deionized water. The CMP composition may also further include one or more pH adjusting agents and/or abrasive particles. The CMP composition is well suited for removing copper from the substrate described above with minimal removal of the barrier layer material. Copper can be selectively removed at a ratio between about 1:0 and about 1:0.2 of copper to barrier material. Selectivity is defined broadly herein as the rate of removal of one material in comparison to the rate of removal of a second or additional materials in a CMP process. Selective to a “material” is broadly defined herein as removing the material at an equal or higher rate than other materials or adjacent materials in a CMP process. 
     In the bulk CMP composition, the one or more chelating agents may include one or more amine or amide groups, such as ethylenediaminetetraacetic acid, ethylenediamine or methylformamide. The one or more chelating agents can be present in an amount between about 0.2 vol % to about 3.0 vol % of the CMP composition. The oxidizers can be any of various conventional oxidizers employed in CMP compositions and processes, such as hydrogen peroxide, ferric nitride, or other compounds such as iodates. The oxidizers can be present in an amount between about 0.5 vol % and about 8.0 vol % of the CMP composition. Examples of corrosion inhibitors include any of various organic compounds containing an azole group, such as benzotriazole, mercaptobenzotriazole, or 5-methyl-1-benzotriazole. The corrosion inhibitors can be present in an amount between about 0.02 vol % and about 1.0 vol % of the CMP composition. 
     The pH adjusting agent or agents can be present in an amount sufficient to adjust the pH of the CMP composition to a range of about 2.5 to about 11 and can comprise any of various bases, such as potassium hydroxide (KOH), or inorganic and/or organic acids, such as acetic acid, phosphoric acid, or oxalic acid. The pH is adjusted based on the composition of the various components of the composition, for example if hydroxylamine is used as the reducing agent, potassium hydroxide is added to the composition to produce an alkaline pH, i.e., between a pH of about 7 and about 10. 
     The bulk CMP composition may further comprise up to about 35 wt. % of abrasive particles, such as silica. Other chelating agents, oxidizers, corrosion inhibitors, and pH adjusting agents are contemplated for use with the invention. The above-specified components are illustrative and should not be construed as limiting the invention. The bulk CMP composition is more fully described in co-pending U.S. patent application No. 09/543,777, entitled, “Composition For Metal CMP With Low Dishing And Overpolish Insensitivity,” filed on Apr. 5, 2000, and incorporated herein by reference to the extent not inconsistent with the invention. 
     The first CMP composition used in the first step of the two step barrier layer material planarizing process may remove the residual copper containing material, or copper containing material residue, and a portion of the barrier layer material from the substrate at a ratio of copper containing material to barrier layer between about 1:1 and about 2:1, thereby having a selectivity to copper containing materials between about 1:1 and about 2:1. A selectivity of the copper containing material to the barrier layer material of about 1:1 is used to ensure that the copper containing material and the barrier layer material are removed at about the same rate. 
     The first CMP composition may comprise an abrasive-free CMP composition comprising one or more reducing agents, one or more pH adjusting agents, one or more corrosion inhibitors, one or more chelating agents, and deionized water. The reducing agent can be selected from the group of hydroxylamine, glucose, sulfothionate, potassium iodide, and combinations thereof. The reducing agent can be present in an amount between about 0.005 wt. % to about 10 wt. % of the first CMP composition. In one aspect of the invention, a concentration of about 0.1 wt. % of reducing agent is used in the first composition. 
     The one or more chelating agents may include conventional chelating agents such as iminodiaetic acid or include one or more amine or amide groups, such as ethylenediaminetetraacetic acid, ethylenediamine, or methylformamide, and can include one or more acids, such as oxalic acid and acetic acid. The one or more chelating agents can also include compounds having one or more quinoline groups, such as 8-hydroxyquinoline. The one or more chelating agents can be present in an amount between about 0.005 vol % to about 0.5 vol % of the CMP composition. In one aspect of the invention, the chelating agent comprises about 0.05 wt. % of the composition The pH adjusting agent or agents can be present in an amount sufficient to adjust the pH of the first CMP composition to a range of about 2.5 to about 11 and can comprise any of various bases, such as potassium hydroxide (KOH) or inorganic and/or organic acids, such as acetic acid, phosphoric acid, nitric acid, or oxalic acid. 
     Examples of corrosion inhibitors that may be included in the first CMP composition may be any various organic compounds containing an azole group, such as benzotriazole, mercaptobenzotriazole, 5-methyl benzotriazole, or 5-methyl-1benzotriazole. The one or more corrosion inhibitors can be present in an amount between about 0.01 vol % to about 0.2 vol % of the CMP composition. 
     In one aspect of the first CMP composition, abrasives may be added to the first CMP composition to improve polishing of the substrate surface. The CMP composition may contain up to about 5 wt. % of abrasives. One example of a CMP composition having abrasive particles includes a colloidal suspension of silicon oxide particles, with an average size of about 50 nm. Other abrasive components which may be used in CMP compositions include, but are not limited to, alumina, zirconium oxide, titanium oxide, cerium oxide, or any other abrasives known in the art and used in conventional CMP compositions. 
     An example of the first CMP composition includes between about 0.005 wt. % and about 10 wt. % of a reducing agent, e.g., about 0.1 wt. %., such as hydroxylamine, between about 0.005 wt. % and about 0.5 wt. % e.g., about 0.05 wt. %, of a chelating agent, such as hydroxyquinoline, between about 0.01 wt. % and about 0.2 wt. % corrosion inhibitor, e.g., about 0.05 wt. %, such as 5-methyl benzotriazole, an amount of pH agent, such as acetic acid, to adjust the pH between about 7 and about 10, and the balance being deionized water. 
     The first CMP composition is believed to remove the residual copper containing material disposed on the barrier layer by oxidizing any copper containing material to produce oxidized copper material, such as Cu ions or copper oxide (CuO), during the CMP process. The oxidized copper containing residue is then mechanically abraded by the polishing pad from the substrate surface and may be entrained in the first CMP composition. The barrier layer material is typically mechanically abraded by the polishing pad from the substrate surface. The chelating agent in the first CMP composition chemically reacts with any metal ions produced during the CMP process to form soluble metal complexes to increase the removal of the copper containing residue from the substrate surface. In this manner, all or substantially all of the residual copper containing material is removed from the surface of the substrate and removal of the barrier layer to the dielectric materials on the substrate surface can be performed. 
     The second CMP composition used in the second step selectively polishes, i.e., removes, residual barrier layer material at a higher removal rate than removal of the dielectric material disposed adjacent thereto. The second CMP composition used in the second step may remove the barrier layer material and the dielectric material from the substrate at a ratio of barrier layer material to the dielectric material between about 1:0 and about 1:0.2, thereby having a selectivity to barrier layer materials between about 1:0 and about 1:0.2. 
     The second CMP composition may be selected to polish the barrier layer material at a sufficient selectivity to minimize polishing of the dielectric layer or stop polishing on contact with the dielectric layer as well as reduce dishing in the copper containing features formed in the substrate surface. The barrier layer, the copper containing material and the dielectric layer are removed from the substrate at a ratio of barrier layer to copper containing material to dielectric layer of about 1:0.2:0.2 and about 1:0:0, thereby having a selectivity of about 1:0.2:0.2 and about 1:0:0. A higher barrier layer material removal rate in comparison to the removal rate of the copper containing material and dielectric material has been observed to reduce dishing of the copper containing material and erosion and oxide loss of the dielectric material. 
     The second CMP composition may comprise an abrasive-free CMP composition, or have a low abrasive particle concentration (i.e., &lt;1.0%), comprising at least one reducing agent for reducing ions of at least one transition metal to a lower valence state, ions of the at least one transition metal, at least one pH adjusting agent for providing the composition with a pH between about 4 and about 12, at least one metal corrosion inhibitor, and water. The composition may further comprise abrasive particles, at least one pH buffering agent, at least one metal chelating agent, or combinations thereof. 
     Suitable transition metal ions for use in performing selective CMP of barrier layer materials include, but are not limited to, copper (Cu), iron (Fe) ions, and silver (Ag) ions. The ions of the transition metal are either contained in the aqueous liquid composition when the composition is applied to the substrate surface or to the polishing pad, or are introduced into the composition subsequent to the application of the composition to the substrate surface or to the polishing pad. For example, the requisite Cu transition metal ions are formed in situ during polishing of the copper and tantalum layers and then supplied to the composition for use in polishing of the barrier layer materials in the second CMP step. Additionally, copper residue from an earlier processing step still present on the surface of the substrate may be the source of the metal ions. The requisite transitional metal ions may also be supplied to the second composition by contacting a metal disk, such as a copper disk, with the polishing pad, or by addition of a solution of metal ions to the second composition. 
     The reducing agent can be selected from hydroxylamine, glucose, sulfothionate, potassium iodide, and combinations thereof at a concentration between about 0.005 wt. % to about 10 wt. % of the composition. The at least one pH adjusting agent may be present at a concentration sufficient to provide the composition with a pH between about 4 and about 12, for example a pH between about 8 and about 12 when hydroxylamine is used as the reducing agent in the composition. The metal corrosion inhibitor, typically organic compounds comprising at least one azole group, such as benzotriazo, for moderating metal loss of copper containing materials during the selective CMP, can comprise about 2.0 wt. % or less of the CMP composition. 
     The composition may, if desired in order to enhance the removal rate, also contain a small amount of abrasive particles, e.g., up to about 10 wt. % of abrasive particles, typically about 0.3 to about 1.0 wt. % of abrasive particles, such as of silica (SiO 2 ), alumina (Al 2 O 3 ), or titania (TiO 2 ). 
     The composition may further include about 0.1 to about 8 wt. % of at least one pH buffering agent, such as an alkali metal bicarbonate and tetraborate-tetrahydrate salts, about 0.01 to about 0.5 wt. % of at least one metal chelating agent comprising, for example, carboxylate and/or amino groups, or combinations thereof to improve polishing performance. 
     An example of the second CMP composition includes between about between about 0.005 wt. % and about 10 wt. % of hydroxylamine, glucose, sulfothionate, or potassium iodide, a pH adjusting agent at a concentration sufficient to provide a pH between about 8 and about 12, about 2.0 wt. % or less of 5-methyl benzotriazole, and deionized water. The composition further includes between about 0.3 wt. % and about 1.0 wt. % of silica abrasive particle, between about 0.1 wt. % and about 8 wt. % of an alkali metal bicarbonate and tetraborate-tetrahydrate salt as a buffering agent, and between about 0.01 wt. % and about 0.5 wt. % chelating agent having carboxylate and/or amino groups. 
     The operative mechanism by which the first and second CMP compositions facilitates rapid and selective planarization of tantalum containing barrier layer materials is not known with certainty. However, it is believed that the problems attendant upon CMP of tantalum containing barrier layer materials stem from the chemically inert nature of tantalum and its compounds. Conventional CMP is predicated upon a combination of chemical reaction and mechanical action (abrasion) for material removal. Since tantalum and its related compounds are relatively inert after oxidation, mechanical abrasion is the predominant mechanism for removing tantalum containing barrier layer materials. However, it is believed that the low valence state transition metal ions of the compositions facilitate CMP of the tantalum containing barrier layer materials, even in the absence of abrasive particles. 
     It is believed that the two-step process reduces dishing of the copper containing material disposed in the feature and on the barrier layer materials during chemical mechanical polishing of the substrate surface when copper containing residue is removed prior to polishing the barrier layer material. The two-step removal process with the second step having an increased selectivity to the barrier layer over the copper containing layer and the dielectric layer is observed to have reduced erosion and reduced dielectric material layer loss, particularly with SiO 2  layers and low metal (e.g., Cu) loss at relatively high tantalum removal rates (&gt;750 Å/min.). The process and CMP composition have been observed to produce a good uniformity of planarization on the substrate. Finally, the ability to planarize using an abrasive-free process or a process utilizing a very low concentration of abrasives results in lower production and operation costs. 
     Moreover, the two-step barrier layer removal process described herein can be performed on a single platen rather than having each step performed on two separate platens. This improves the processing efficiency by increasing the number of steps that can be performed on a polishing apparatus and improve equipment usage by minimizing the need for additional equipment. The process is compatible with the requirements for manufacturing throughput on a large scale, and is fully compatible with all other aspects of conventional polishing technology utilized in the manufacture of high integration density semiconductor devices. 
     FIGS. 2-4 are series of schematic cross-sectional views of a substrate illustrating sequential phases of a process for forming an in-laid metallization pattern utilizing the two-step planarization process described herein. 
     Referring to FIG. 2, the substrate includes a dielectric layer  110 , such as a silicon oxide or a carbon-doped silicon oxide, formed on a substrate  100 . A plurality of openings  111  patterned and etched into the dielectric in area A forming features for a dense array of conductive lines with area B being unetched. Typically, the openings  111  are spaced apart by a distance C which can be less than about 1 micron, such as about 0.2 micron, or greater than 10 microns, such as 20 microns. The openings  111  were formed in the dielectric layer  110  by conventional photolithographic and etching techniques. A barrier layer  112  of a conductive material, such as Ta or TaN for a copper metallization, is disposed conformally in openings  111  and on the upper surface of the dielectric layer  110 . A copper layer  113  is disposed on the barrier layer at a thickness (D) between about 8,000 Å and about 18,000 Å. 
     Referring to FIG. 3, the bulk of the copper layer  113  is removed using a CMP copper polishing process with the bulk CMP composition described herein. The bulk CMP composition removes the copper layer  113  to the tantalum containing barrier layer  112 . Removing the copper material by a bulk CMP composition having a selectivity of about 1:0 between copper and tantalum containing allows for effective removal of the copper layer  113  to the tantalum containing layer  112 , minimizes dishing of the copper later  113 , and minimizes formation of a non-planar surface. 
     Referring to FIG. 4, the two step planarization of the barrier layer is performed according to the process and CMP composition disclosed herein. A first composition is used to remove all or substantially all of the residual copper containing material and a portion of the tantalum containing barrier layer  112  from the substrate  100 , and a second CMP composition removes the residual tantalum containing barrier layer  112 . The second CMP composition typically stops on the dielectric layer to prevent excessive removal of the dielectric material, thereby completing planarization. A first CMP composition having a selectivity of copper to barrier of about 1:1 ensures the removal of the residual copper prior to removal of the residual barrier layer  112 . A second CMP composition having a high selectivity to the tantalum containing barrier layer  112  in comparison to the copper layer  113  and the dielectric layer  110  of about 1:0.2:0.2 allows for removal of substantially all of the tantalum containing material while minimizing removal of the dielectric layer  110 . However, the dielectric layer  110  may be polished during the second CMP process to remove or reduce scratching or defects formed on the substrate surface. The resulting copper features comprises a dense array (A) of copper lines  113  bordered by open field B and the planar surface  114  of the copper metallization and substrate  100 . 
     EXAMPLE 
     An example of a two-step polishing process according to aspects of the invention described herein is as follows. A substrate including a low k dielectric layer with feature definitions formed therein, a tantalum containing barrier layer conformally deposited on the low k dielectric layer and in the feature definitions formed therein, and a copper layer deposited on the barrier layer and filling the feature definitions formed therein is provided to the CMP apparatus disclosed above. 
     The substrate is positioned over a first polishing pad of a first platen, and a bulk CMP composition having a selectivity of about 1:0 between the copper and the tantalum containing layer is delivered to the polishing pad. An example of the bulk CMP composition includes between about 0.2 vol % to about 3.0 vol % ethylenediaminetetraacetic acid, between about 0.5 vol % and about 8.0 vol % hydrogen peroxide, between about 0.02 vol % and about 1.0 vol % benzotriazole, and a pH adjusting to adjust the pH of the CMP composition to a range between about 2.5 and about 11. 
     The substrate is then transferred to a second polishing pad on a second platen, and a first CMP composition having a selectivity of about 1:0 between the tantalum containing layer and the dielectric material is delivered to the polishing pad. An example of the first CMP composition includes between about 0.005 wt. % and about 10 wt. % of a reducing agent, e.g., about 0.1 wt. %., such as hydroxylamine, between about 0.005 wt. % and about 0.5 wt. % e.g., about 0.05 wt. %, of a chelating agent, such as hydroxyquinoline, between about 0.01 wt. % and about 0.2 wt. % corrosion inhibitor, e.g., about 0.05 wt. %, such as 5-methyl benzotriazole, an amount of pH agent, such as acetic acid, to adjust the pH between about 7 and about 10, and the balance being deionized water. The first CMP composition may also include up to about 5 wt. % of abrasives. The pressure of the polishing pad pressure of between about 1 to about 8 psi. The substrate is then polished for a requisite amount of time sufficient for complete or substantially complete removal of the copper containing material and a portion of the underlying barrier layer. 
     Then, the second CMP composition having a selectivity of about 10:1:1 of the tantalum containing layer to the copper to the low k dielectric material described herein is delivered to the same polishing pad. An example of the second CMP composition includes between about between about 0.005 wt. % and about 10 wt. % of hydroxylamine, glucose, sulfothionate, or potassium iodide, a pH adjusting agent at a concentration sufficient to provide a pH between about 8 and about 12, about 2.0 wt. % or less of 5-methyl benzotriazole, and deionized water. The composition further includes between about 0.3 wt. % and about 1.0 wt. % of silica abrasive particle, between about 0.1 wt. % and about 8 wt. % of an alkali metal bicarbonate and tetraborate-tetrahydrate salt as a buffering agent, and between about 0.01 wt. % and about 0.5 wt. % chelating agent having carboxylate and/or amino groups. The pressure of the polishing pad pressure of between about 1 to about 8 psi. The substrate is then polished for a requisite amount of time sufficient to remove all or substantially all of the barrier layer to the dielectric layer. 
     While the foregoing is directed to the one or more embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow including their equivalents.