Improved thermal stability of nitrogen annealed sputtered hafnium oxide thin films for VLSI technology

Abstract

PurposeHigh‐dielectric thin films are considered as future dielectric for Si based advanced integrated circuit technology and also for the development of organic thin film transistors and micro sensors. The conventional dielectric SiO2 is grown by thermal oxidation of silicon whereas the HfO2 films are grown by both physical and chemical methods. Depending on film deposition technique, the film and interface characteristics are affected. The purpose of this paper is to investigate the effect of thermal annealing in oxygen and nitrogen ambient on the electrical properties of HfO2‐based metal oxide semiconductor (MOS) capacitor and evaluate thermal stability of the characteristics.Design/methodology/approachHfO2 films are deposited by rf sputtering and Al‐HfO2‐Si MOS capacitor fabricated. The electrical I‐V and C‐V characteristics are measured and the effect of temperature in the range of 25‐200°C is evaluated for films annealed in oxygen and nitrogen.FindingsIt is found that thermal annealing in nitrogen reduces oxide trap density and improves the temperature stability compared to the film annealed in oxygen for MOS devices. From the conductance characteristics Dit oxide trap density in the film is estimated to be 2.1×1011/cm2 for nitrogen and 3.23×1011/cm2 for oxygen, which indicates the role of nitrogen in reducing oxide traps. The thermal activation energy of electron traps is found to be about 0.19 eV for nitrogen and 0.58 eV for oxygen annealed films in the temperature range of 25‐150°C.Originality/valueThe paper examines and compares the role and effect of thermal annealing in nitrogen ambient and oxygen ambient on the electrical properties of sputtered HfO2 thin film for improved MOS device reliability.