The effect of CeO₂ abrasive size on dishing and step height reduction of silicon oxide film in STI-CMP

The effect of the CeO₂ abrasive size during chemical mechanical polishing (CMP) of shallow trench isolation (STI) structures was investigated, in order to minimize the amount of oxide dishing and to improve the planarization efficiency. Three slurry samples were prepared based on a 1.0 wt.% abrasive concentration with different sizes of ceria particles. The step height and dishing reduction were investigated as a function of the polishing time with pattern wafers in prepared slurries. The reduction in thickness as a function of the polishing time varied between the different slurries. The dependence of the step height reduction of the patterned wafer on the polishing time showed non-linear behavior in all of the tested slurries. The amount of dishing also varied with the type of slurry. The changes in the cross-sectional profiles of the oxide as a function of the polishing time were analyzed, in order to establish a dishing and step height reduction model depending on the abrasive size. The step height variation and dishing were varied with the size of the abrasive. The observed results were explained by the contribution of inactive particles, which depended on relative size of the abrasives and the height of the remaining oxide layer.