Role of polycation adsorption in poly-Si, SiO2 and Si3N4 removal during chemical mechanical polishing: Effect of polishing pad surface chemistry

The dramatic differences in the effects of two different polishing pads (IC1000 and Politex) on the removal rates (RRs) of poly-Si, SiO2, and Si3N4 films during chemical mechanical polishing using aqueous abrasive-free solutions of a cationic polymer, poly(diallyldimethyl ammonium chloride) (PDADMAC), are described. For example, with a 250 ppm of aqueous PDADMAC solution, poly-Si RR is <1 nm/min with a Politex pad but is about 500 nm/min using an IC1000 pad. The difference in the RRs is attributed to differences in the strengths of PDADMAC-mediated bridging interactions between the pads and the substrates. Also, when the same 250 ppm of PDADMAC was used as an additive in either silica- or ceria-based dispersions, the RRs of both SiO2 and Si3N4 films were suppressed to less than 1 nm/min for both pads. Possible mechanisms for the observed differences in the RRs of poly-Si, SiO2, and Si3N4 on the two pads are discussed based on elemental analysis of the pads, X-ray photoelectron spectroscopy, and zeta potential measurements (of the pads in the absence and presence of PDADMAC). Also, the results of exposure to eosin Y, a dye that changes color on exposure to PDADMAC provided useful insights into the strength of the bridging attraction between the pads and PDADMAC.