Improved ferroelectric characteristics of ALD lanthanum-doped hafnium oxide thin film by controlling post-cooling time

Abstract

A study was conducted on how the subsequent cooling time affects the ferroelectric (FE) characteristics of atomic layer deposited (ALD) lanthanum (La) doped HfO2 thin films after the crystallization heat treatment in the form of TiN/La-doped HfO2/TiN metal-ferroelectric-metal (MFM) device structure. The ALD La-doped HfO2 thin film was cooled to room temperature in a chamber (“chamber cooling” - slower cooling) or in an air atmosphere (“air cooling” - faster cooling). Based on the polarization vs electric field (P-E) hysteresis curve, the double remanent polarization (2Pr) values of the chamber cooling and air-cooling are 9.5 μC/cm2 and 40 μC/cm2, respectively. This drastic improvement stems from more orthorhombic phase formation within La-doped HfO2 thin film, which is confirmed by smaller grain size, higher amount of oxygen vacancies, and more tensile stress within HfO2 thin film. Our results suggest that FE properties of La-doped HfO2-based thin film can be significantly modulated by post cooling processes.