Selective Polishing of Polysilicon during Fabrication of Microelectromechanical Systems Devices

During a typical microelectromechanical systems device fabrication process, a polysilicon top layer has to be polished with a slurry that yields a high polysilicon removal rate (0.5 mu m/min or more) and a high selectivity over the underlying silicon dioxide and silicon nitride layers (>50:1). In this work, polysilicon polish rates as high as 550 nm/min and selectivity over silicon dioxide and nitride of similar to 130 and similar to 260, respectively, have been achieved using colloidal silica and calcined ceria-based slurries containing arginine or lysine mono hydrochloride, at 4 psi down pressure. At 8 psi, polysilicon polish rates close to 900 nm/min and selectivities over both oxide and nitride that are close to 300 have been achieved. xi potential, infrared spectroscopy, and contact angle data are used to explain the role of the amino acid additives in achieving the desired removal rate selectivities of polysilicon over silicon dioxide and silicon nitride.