Oxalic acid was investigated as a complexing agent in H 2 O 2 -based slurries for chemical mechanical planarization ͑CMP͒ of Cu. At pH ϳ 1.5, oxalic acid acts as an inhibiting agent by forming an easily abraded soft bluish film on the copper surface. The high removal rate and low dissolution rates make it a desirable complexing agent, except for the strongly acidic pH condition. In the pH range 2.0-6.0, oxalic acid etches copper with the maximum dissolution rate occurring at pH ϳ 3.0. Cu removal rates and some electrochemical measurements that shed more light on these results are presented.As silicon semiconductor device feature size scales down to less than 0.5 µm, signal processing speeds are determined by interconnect delay. 1 The latter is a function of the dimensions of metal wires that interconnect different devices on a chip, the resistivity of the metal and the dielectric constant of the intermetal dielectric ͑IMD͒. The increase in this delay with a decrease in feature sizes can be overcome by decreasing the length of metal lines using multilevel metallization ͑MLM͒ structures, incorporating metals of low resistivity and dielectric materials of low dielectric constants. 2 Chemical mechanical planarization ͑CMP͒ has made the replacement of aluminum with copper, a metal with lower electric resistivity and better electromigration resistance than the former, feasible for all interconnections in advanced integrated circuits ͑ICs͒. Copper interconnections are fabricated using the damascene or the dual damascene process. 3 Successful fabrication of such interconnects requires the removal of the overburden Cu and barrier layer with minimal dishing of the metal lines and erosion of the underlying dielectric film. Optimization of the abrasive characteristics and the chemical composition of the slurry used to remove Cu and the barrier layer can help reduce the above defects.Cu CMP slurries typically contain sub-micrometer size abrasives dispersed in aqueous chemical solutions of oxidizing agents, complexing agents ͑etchants and inhibiting agents͒, and surfactants. 4 The complexing agents form complexes with the oxidized metal layer. They may etch the metal from its surface and/or dissolve the abraded metal debris ͑e.g., Glycine, 5 citric acid 6 ͒. They may also inhibit further oxidation of the metal surface by the oxidant and decrease the dissolution rates by forming a passivation layer, acting as an inhibiting agent ͑e.g., Benzotriazole 7 ͒. Both an etchant and an inhibiting agent are used in Cu CMP slurries to attain high removal rates and better planarity, respectively. Though considerable progress has been made in exploring different chemicals as additives in Cu CMP slurries, 4-14 a comprehensive understanding of their interactions would help not only in designing better CMP slurries but also in determining the factors that contribute to defect formation.Oxalic acid is an inexpensive, environmentally benign bicarboxylic compound that can form complexes with copper. 15 Its potential as a complexing agent in coppe...
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