We investigated the effect of film stress, hardness, and grain size of copper films on copper electropolishing, which was considered as a next-generation technique in copper multilevel interconnects. The copper electropolishing rate was found to increase with an increase in the tensile stress of copper films. It was suggested that the tensile stress weakened metallic bonds between copper atoms and assisted the copper electropolishing rate, whereas the hardness and grain size of polished copper films did not relate directly to the copper electropolishing rate due to a negligible etching effect and no mechanical stress applied during copper electropolishing in a concentrated phosphoric acid electrolyte.

Selective removal of surface passivation on protruded Cu film is a critical factor of Cu planarization. For a stress-free Cu abrasive-free polishing ͑Cu AFP͒ process, due to the lack of mechanical abrasion by abrasives, a polishing pad is used instead of abrasives to remove surface passivation during Cu planarization. Thus, the planarization efficiency in Cu AFP relates to the efficiency of surface passivation removed by a pad. Comparing Cu oxides with a non-native Cu-BTA ͑Cu-Benzotriazole͒ monolayer used as surface passivation, this study found that an oxide-free Cu surface should be required in Cu AFP. When Cu oxides function as surface passivation in Cu AFP, they are removed with greater difficulty by a pad resulting in low planarization efficiency. Contrary to Cu oxides, high planarization efficiency can be obtained with non-native Cu-BTA as surface passivation in Cu AFP.

No abstract

Pattern effect, a critical issue in metal planarization, results from different pattern designs bringing a variation of effective local pressure. In order to optimize the pattern effect in Cu planarization, Cu removal should be pressure independent. Recently, it was found that Cu abrasive-free polishing ͑AFP͒ technology could benefit pressure-independent Cu removal for Cu planarization by controlling the down force. In this study, by using 5-methyl-1H-benzotriazole as a corrosion inhibitor, pressure-independent Cu removal with AFP slurries can be achieved below a 3 psi down force. Thus, the pattern effect in Cu planarization can be optimized with AFP slurries by low down force.In a damascene chemical mechanical polishing ͑CMP͒ process, metal planarization suffers pattern effect due to a variation of effective local pressure on various features. 1 Based on Kaufman's model of metal CMP, the metal removal rate depends on effective local pressure, and it leads to varied metal removal rates on various features. 2 In this case, a metal film is oxidized with oxidizers resulting in the formation of metal oxide on a metal surface during polishing. After selective removal of protruded metal oxide with mechanical abrasion by abrasives, the underlying metal is oxidized again leading to effective removal of the protruded metal film. Consequently, global metal planarization is addressed. However, metal oxide removal depends on mechanical abrasion so that the metal removal rate is proportional to effective local pressure and follows Preston's rule. Thus, at a constant down force, different pattern designs bring a variation of effective local pressure leading to a pattern effect on the metal removal rate. Consequently, varied planarization efficiency on various features is observed in metal planarization.Recently, Cu abrasive-free polishing ͑Cu AFP͒ was developed as an alternative to Cu CMP in order to obtain a scratch-free polished Cu surface and address stress-free Cu planarization. The Cu AFP slurries were comprised only of chemical agents such as oxidizer and corrosion inhibitors, but no abrasives. Owing to the lack of abrasives, Cu AFP technology could significantly reduce strong stress from mechanical abrasion by abrasives leading to stress-free Cu planarization. For a Cu AFP process, Matsuda showed that the Cu removal rate can be nonlinear as a function of down force. 3 In other words, the Cu removal rate can be independent of effective local pressure with adjusting the down force. In our prior study, a similar result was obtained in a Cu AFP slurry formulated with HNO 3 and benzotriazole ͑BTA͒. 4 Moreover, it was found that the pattern effect in Cu planarization could be significantly reduced with pressure-independent Cu removal. However, in a Cu AFP slurry formulated with HNO 3 and BTA, pressure-independent Cu removal needs a down force of more than 5 psi, which would be too high in relation to the porous low-k material used as the dielectric.In this study, in order to reduce the down force required for the pressure ind...