Optimization and Mechanism on Chemical Mechanical Planarization of Hafnium Oxide for RRAM Devices

Chemical mechanical planarization (CMP) of hafnium oxide including chemical and mechanical factors has been investigated in this paper. We demonstrated that the introduction of sodium fluoroborate (NaBF4) into hafnium oxide CMP has efficiently improved the removal rate from 5 nm/min to 95:5 nm/min. According to the static etch rate and effects of down force and platen rotation rate on hafnium oxide CMP, the Preston equation RR = kPV was modified to RR = kPV + R-c which suggests that the hafnium oxide CMP is determined by the combination of chemical and mechanical process. Moreover, we proposed a possible mechanism that the reaction of introduced NaBF4 with hafnium oxide provides a softer surface layer, enabling hafnium oxide to be easily polished and removed. Therefore, the removal rate of hafnium oxide was substantially enhanced. Using this method, the hafnium oxide surface with sub-nanometric roughness (RMS) was achieved, which can provide the related planarization material and technology for hafnium oxide nano-devices. (C) 2014 The Electrochemical Society., All rights reserved.