Role of Poly (diallyldimethylammonium chloride) in Selective Polishing of Polysilicon over Silicon Dioxide and Silicon Nitride Films

A cationic polymer, poly(diallyldimethylammonium chloride), or PDADMAC (MW ˜ 200?000), at a concentration of 250 ppm was used to enhance polysilicon removal rates (RRs) to 600 nm/min while simultaneously suppressing both silicon dioxide and silicon nitride RRs to <1 nm/min, both in the absence or in the presence of ceria or silica abrasives during chemical mechanical polishing (CMP). These results suggest that aqueous abrasive-free solutions of PDADMAC are very attractive candidates for several front-end-of-line (FEOL) CMP processes. Possible mechanisms for the enhancement of poly-Si RR and the suppression of oxide and nitride RRs are proposed on the basis of the RRs, contact angle data on poly-Si films, zeta potentials of polishing pads, polysilicon films, silicon nitride particles, and silica and ceria abrasives, thermogravimetric analysis, and UV-vis spectroscopy data.