Recycling a slurry for reuse in chemical mechanical planarization of tungsten wafer: Effect of chemical adjustments and comparison between static and dynamic experiments

Recycling abrasive slurry that has been used in chemical mechanical polishing (CMP) is one of the options for reducing the cost of manufacturing microchip processors. We use ultrafiltration which is a method of choice to recycle silica (SiO2)-based slurry. Taking into account that the chemical composition of abrasive slurry plays an important role in tungsten CMP (W-CMP), chemical adjustments have to be made so that the concentrated after used slurry can be reused. In this study, we investigate the effects of chemical additives (iron catalyst, oxalic acid as complexing agent and surfactants as stabilizers) in slurry that has been retreated by ultrafiltration. Experiments are conducted both under static and dynamic conditions and results are compared to better understand the effect of chemical adjustments on the main performances of W-CMP. An optimal chemical adjustment is proposed through a design of experiments evaluation to obtain a concentrated after used and chemically adjust slurry comparable to the operational point of use slurry