Role of the Functional Groups of Complexing Agents in Copper Slurries

Abstract

We investigate the role of -NH 2 and -COOH functional groups of complexing agents in H 2 O 2 -based slurries in controlling copper ͑Cu͒ removal rates. Slurries containing complexing agents with two of the same functional groups ͑succinic acid: HOOC-CH 2 CH 2 -COOH, ethylene diamine: H 2 N-CH 2 CH 2 -NH 2 ͒ and a complexing agent containing one each of the functional groups ͑␤-alanine: H 2 N-CH 2 CH 2 -COOH͒, all with the same carbon chain length, were investigated. Along with dissolution and disk polish experiments, potential-pH diagrams were constructed for these three systems in the presence of H 2 O. The dissolution and polish rates are consistent with the known activity of carboxylic acids ͑with -COOH groups͒ at acidic conditions and that of amines ͑with -NH 2 groups͒ in an alkaline environment. The observed trends in the removal rates with all these slurries are explained using potential-pH diagrams, UV/visible spectra, and electrochemical experiments. When compared to glycine ͑H 2 N-CH 2 -COOH͒, ␤-alanine ͑H 2 N-CH 2 CH 2 -COOH͒ produced higher removal rates at acidic pH values and lower removal rates at alkaline pH values. Finally, succinic acid and ␤-alanine-based slurries were found to result in lower dissolution rates and higher polish rates compared to glycine-based slurries at pH 4.Chemical mechanical planarization ͑CMP͒ is widely used to planarize metal and dielectric films during integrated circuit fabrication. 1,2 Damascene process 3 is currently used in conjunction with CMP in the fabrication of multilevel copper ͑Cu͒ interconnects for advanced logic and memory devices. In this fabrication scheme, trenches are first patterned in a dielectric material at each level. After the barrier, seed, and copper fill are sequentially deposited in the dielectric trenches, 4 CMP is used to remove excess copper and create a planar surface for subsequent fabrication of additional levels of metallization.Cu CMP involves removal of material by the combined action of chemical and mechanical means to achieve planarization. Chemicals aid in material removal by modifying the surface film while abrasion between the particles in the slurry, pad, and the modified film facilitates mechanical removal. Material removal solely involving chemicals usually leads to uniform etching of both elevated and recessed regions and does not level the topography. The synergistic interplay between chemical and mechanical components in the slurry facilitates effective planarization. An important requirement of any successful copper CMP slurry is a high polishing rate leading to short copper overburden polishing times while minimizing dishing and erosion and other surface defects.With the introduction of low-k dielectric materials, integration of Cu/low-k dielectrics has become a serious challenge. These low-k dielectric films are porous, poorly adhere to Cu/Ta, are mechanically weak, and hence are prone to damage during CMP. 5 These problems can be mitigated by performing Cu and the barrier CMP at "low" pressures. 6,7 Because throughput can...

Investigation of dissolution inhibitors for electrochemical mechanical planarization of copper using beta-alanine as a complexing agent

“…The advantage of using b-alanine as a complexing agent is that it might be useful to increase the polish rates while maintaining relatively low Cu dissolution, which is a main requirement for achieving high planarization efficiencies. This has been noted in a recent study, where b-alanine in comparison with glycine (at pH = 4.0) was found to yield lower dissolution rates but similar polish rates in CMP of Cu [12,13]. This effect has been attributed to the increased chain length of b-alanine, based on the observation that the degree of complex formation by Cu and Cu oxides with certain amino acids decreased with increasing distances between the functional groups of the amino acid molecules [12,14].…”

“…By noting that CuHL 2+ is the predominant form of the dissociated copper-b-alanine complex at pH = 4.0, we expect the following reactions in the Ref solution [12,14]:…”

“…More recently, we have tested b-alanine as an alternative complexing agent of glycine [12], together with ADS and BTAH used as inhibitors for CMP of Cu [13]. In our present work, we extend our investigation of the b-alanine system to the case of voltage activated Cu dissolution for ECMP.…”

Perspective—Electrochemical Assessment of Slurry Formulations for Chemical Mechanical Planarization of Metals: Trends, Benefits and Challenges

“…Stabilized OCPs recorded in pH-varied slurries are useful to construct OCP-pH correlation charts, which can be mapped onto Pourbaix diagrams to categorize the CMP-specific primary surface species for a given test system. 22,23 Raman, optical absorption and X-ray photoelectron spectroscopies can be combined with MRR and electrochemical measurements 24,25 to further analyze the CMP specific surface species.…”

Key Chemical Components in Metal CMP Slurries

“…The influence of pH on the roles of amino and carboxylic groups has been studied by Babu and coworkers [50,51]. It was demonstrated that, in the basic regime, the removal rate decreases as the pH increases for a citric acid based slurry due to a competition between hydroxide and citrate for complexation with copper ions.…”