Improving Chemical Mechanical Polishing Efficiency of PZT with Less than 100 ppm SO4 2−

Abstract

Excellent surface quality of lead zirconate titanate (PZT) is required to achieve high performance in micro-electro-mechanical systems. In this work, PZT-4 (Pb(Zr0.44Ti0.56)O3) was processed with chemical mechanical polishing (CMP). K2SO4 was used to enhance the CMP efficiency. The results reveal that at pH 4 and 6, as the K2SO4 concentration increases, the material removal rate (MRR) and surface roughness S a first increase, then decrease and stabilize. Interestingly, at pH 6, after adding only 55 ppm SO4 2−, the MRR increases by 54%. After CMP, the surface becomes smooth. No visible processing damage occurs in the substrate. For the CMP mechanism, SO4 2− in K2SO4 plays an essential role in the MRR enhancement. At pH 6, PbO can dissolve, forming oxygen vacancies. After adding a low concentration of SO4 2−, the negatively charged SO4 2− ions can be attracted by the positively charged oxygen vacancies. Then soluble Zr(SO4)2 can be formed, promoting the dissolution of Zr4+. As a result, the surface integrity can be destroyed. Therefore, the MRR is improved. However, with a high concentration of SO4 2−, the PbSO4 precipitates can inhibit dissolution and wear. Hence, the MRR is suppressed. This research may provide a feasible approach for high-efficiency CMP of PZT.