Achieving smooth PZT surface via chemical mechanical polishing with ethylenediamine dihydrochloride

摘要

? 2022 Elsevier Ltd and Techna Group S.r.l.Lead zirconate titanate (PZT) has been widely used in microelectromechanical systems and ferroelectric memory, and a high-quality PZT surface is important to the device performance. In this study, chemical mechanical polishing (CMP) was introduced to process PZT-4 (Pb(Zr0.44Ti0.56)O3). A complexing agent ethylenediamine dihydrochloride (EDA·2HCl) was used as a crucial chemical additive in slurries to improve the CMP performance of PZT-4 because it may chelate metal ions of PZT-4, such as Ti4+. The results show that the material removal rate (MRR) of PZT-4 decreases and the surface roughness Sa increases as pH increases. At pH 4.0, with the EDA·2HCl concentration increasing, the MRR first increases, reaches the summit of 498 nm/min at 0.75 mM, and then decreases and levels off. The Sa has a similar trend. With 50 mM EDA·2HCl, the Sa reaches the minimum value of 3.5 nm, and no processing damage occurs in the substrate. For the removal mechanism, EDA can be adsorbed on PZT-4 probably via forming complex with Ti4+. With a low content of EDA·2HCl, the adsorbates of EDA distribute discretely and can be removed easily, and thus the MRR is high. As the content of EDA·2HCl increases, a relatively continuous and uniform film is formed to suppress dissolution and abrasion, and thus the MRR decreases. A two-step CMP process was developed, and a smooth PZT surface can be rapidly achieved. This study provides mechanistic insight of the role of EDA in the CMP of PZT-4, and may open new avenues of developing CMP slurries for achieving smooth surfaces of PZT materials via screening prospective complexing agents.