The etching properties of MgO thin films in Cl2/Ar gas chemistry

Abstract

The metal–ferroelectric–semiconductor (MFS) structure is widely studied for nondestructive readout (NDRO) memory devices, but conventional MFS structure has two critical problems. First, the one that is difficult to obtain ferroelectric films like PZT on Si substrate without interdiffusion of impurities such as Pb, Ti and other elements. Diffusion of Pb or Ti induces increased trap density and Fermi-level pinning. The other one is that PZT/Si structure generates nonferroelectric and low-dielectric constant layer at the interface. In order to solve these problems, the metal–ferroelectric–insulator–semiconductor (MFIS) structure has been proposed with a buffer layer of high dielectric constant such as MgO, Y2O3, and CeO2. Buffer layer candidate should meet the following requirements of low lattice mismatch, low leakage current, low interface-state density, high dielectric constant, chemical stability, and prevention of interdiffusion.In this study, the etching characteristics (etch rate, selectivity) of MgO thin films were etched using Cl2/Ar plasma. The maximum etch rate of 85 nm/min for MgO thin films was obtained at Cl2(30%)/Ar(70%) gas mixing ratio. Moreover, the etch rate was measured by varying the etching parameters such as ICP rf power, dc-bias voltage, and chamber pressure. Plasma diagnostics was performed by Langmuir probe (LP) and optical emission spectroscopy (OES).