Role of slurry chemicals in chemical mechanical planarization of copper

Copper (Cu) dual damascene process coupled with chemical mechanical planarization (CMP) of over burden Cu has emerged as the only viable technique for patterning Cu lines in the manufacture of Very Large Scale Integration (VLSI) & Ultra Large Scale Integration (VLSI) based devices. With the introduction of low-k dielectric materials as inter level dielectrics (ILD), integration of Cu/low-k dielectric structures has become a serious challenge. The low-k dielectric films are porous, poorly adhere to the metal films and are mechanically weak. Hence, Cu and barrier CMP processes will need to be performed at low down force values, ≤2 psi, compared to much higher down force values used for current processes. If throughput is not to be sacrificed, this calls for increasing the chemical activity of the CMP slurries. A better understanding of the roles of various chemicals used in typical Cu CMP slurries along with the search for novel chemicals is required to achieve this goal.; In this work, MoO3-H2O2 based novel slurries were investigated for Cu CMP. MoO3 dissolves instantaneously in aqueous H2O2 solutions forming different types of peroxo molybdates (yellow colored diperoxo molybdates and reddish brown colored tetraperoxo molybdates). The type of peroxo molybdates formed in aqueous solutions is dependent on the concentration of H2O2 and the pH of the solution. It was found that the diperoxo molybdates act as much powerful oxidizing agents towards Cu than H2O2. However, tetraperoxo molybdates, generally formed at high pH values, are observed to be much less reactive towards Cu. A model slurry containing MoO3, H2O 2 and glycine has been studied to understand the interactions of various slurry constituents among themselves and with Cu surface. It was shown that the addition of glycine to an acidic aqueous solution containing MoO 3 and H2O2 results in the formation of a diperoxo molybdate-glycine complex. Finally, it was demonstrated that by proper choice of the slurry constituents, very high Cu polish rates (1000 nm/min) can be obtained while maintaining very low dissolution rates. (Abstract shortened by UMI.)...