Chemical-mechanical polish of aluminum alloy thin films: slurry chemistries and polish mechanisms

This study discusses experimentally the effects of slurry formulation and passivating rate on the chemical mechanical polish removal mechanism of aluminum (Al) alloy films. Two regions of material removal with different slurry pH values, namely, one, non-passivating region (pH<4), and the other, passivating region (pH≥4) are investigated. The removal rates of Al alloy films decline with increasing slurry pH. In the non-passivating region (pH=2) where the material removal is a competition between the passivation and mechanical abrasion plus chemical etching, an optimal removal rate occurs in the slurry with hydrogen peroxide (H2O2) concentration ranging from 0 to 15 vol.%. While the slurry pH is increased to 4 arriving in the passivating region where the material removal is a competition between the passivation and mechanical abrasion only, the material removal has weak dependence to the H2O2 concentration. Too low a slurry, pH results in metal loss and scratching, while too high a slurry, pH leads to oxide residue and insignificant removal rate. Furthermore, removal selectivity and performance of Al/barrier metals and Al/oxide are discussed as well.