Barrier polishing solution

#The invention relates to chemical mechanical planarizing (CMP) formulations for removing barrier metals and, more particularly, to polishing compositions for selectively removing barrier metals in the presence of interconnect structures in integrated circuit devices.

#In recent years, the semiconductor industry has increasingly relied upon copper electrical interconnects in forming integrated circuits. These copper interconnects have a low electrical resistivity and a high resistance to electromigration. Since copper is very soluble in many dielectric materials, such as silicon dioxide and low-K or doped versions of silicon dioxide, a diffusion barrier layer is necessary to prevent the diffusion of copper into the underlying dielectric material. Typical barrier materials include, tantalum, tantalum nitride, tantalum-silicon nitrides, titanium, titanium nitrides, titanium-silicon nitrides, titanium-titanium nitrides, titanium-tungsten, tungsten, tungsten nitrides and tungsten-silicon nitrides.

#In response to increasing demands for high density integrated circuits, semiconductor producers now fabricate integrated circuits containing multiple overlying layers of metal interconnect structures. During device fabrication, planarizing each interconnect layer improves packing density, process uniformity, product quality and most importantly, enables manufacturing of multiple layer integrated circuits. Semiconductor producers rely upon chemical-mechanical-planarizing (CMP) as a cost effective means of producing flat substrate surfaces. The CMP process is typically carried out in a two-step sequence. First, the polishing process uses a “first-step” slurry specifically designed to rapidly remove copper. For example, Carpio et al., in “Initial Study on Copper CMP Slurry Chemistries” Thin Solid Films, 262 (1995), disclose the use on a 5 weight percent nitric acid solution for efficient copper removal. Similarly, Kondo et al., in U.S. Pat. No. 6,117,775, disclose the use of nitric acid and BTA for copper removal.

#It has been discovered that complexing agents can improve acidic barrier removal solutions by reducing the yellowing of polishing slurries without adversely affecting wafer uniformity or the selective removal of barrier films in patterned wafers. This increases the pot-life performance of the acidic barrier slurry. For purposes of this specification, complexing agents represent constituents that bond with metal ions, act as chelating agents or otherwise associate with free metal ions to decrease the free metal ion concentration of at least one metal ion in the polishing solution. For purposes of the specification, polishing solution refers to aqueous polishing solutions that may or may not include abrasives. If the polishing solution includes an abrasive, then the polishing solution also is a polishing slurry. The polishing solution can also optionally include surfactants, pH buffers, defoaming agents and biocides.

#For purposes of this specification, dielectric includes silica-base materials such as TEOS, low k and ultra-low k materials (some ultra-low materials are not silica-base). To polish low k and ultra-low k dielectric materials, it is important to maintain low pressure to decrease the delamination and fracture of these materials. However, low pressure yields low barrier material (Ta/TaN) removal rate, which is undesirable for wafer throughput. Fortunately, acidic polishing solutions having a strong oxidizer have demonstrated high barrier removal rates in comparison to conventional alkaline barrier slurries that operate at low pressures. The barrier material may include the following: tantalum, tantalum nitride, tantalum-silicon nitrides, titanium, titanium nitrides, titanium-silicon nitrides, titanium-titanium nitrides, titanium-tungsten, tungsten, tungsten nitrides and tungsten-silicon nitrides.

#The barrier metal polishing composition optionally includes an abrasive for “mechanical” removal of the barrier material. The CMP composition includes an abrasive for “mechanical” removal of barrier layers. The abrasive is preferably a colloidal abrasive. Example abrasives include the following: inorganic oxide, metal boride, metal carbide, metal hydroxide, metal nitride, or a combination comprising at least one of the foregoing abrasives. Suitable inorganic oxides include, for example, silica (SiO2), alumina (Al2O3), zirconia (ZrO2), ceria (CeO2), manganese oxide (MnO2), and mixtures thereof. Alumina is available in many forms such as alpha-alumina, gamma-alumina, delta-alumina, and amorphous (non-crystalline) alumina. Other suitable examples of alumina are boehmite (AlO(OH)) particles and mixtures thereof. Modified forms of these inorganic oxides such as polymer-coated inorganic oxide particles may also be utilized if desired. Suitable metal carbides, boride and nitrides include, for example, silicon carbide, silicon nitride, silicon carbonitride (SiCN), boron carbide, tungsten carbide, zirconium carbide, aluminum boride, tantalum carbide, titanium carbide, and mixtures comprising at least one of the foregoing metal carbides, boride and nitrides. Diamond may also be utilized as an abrasive if desired. Alternative abrasives also include polymeric particles and coated polymeric particles. The preferred abrasive is silica.