Influence of the surrounding ambient on the reliability of the electrical characterization of thin oxide layers using an atomic force microscope

Abstract

Physical and electrical properties of thin oxide films have been studied using the atomic force microscope (AFM). Experiments have been done in three different surroundings: in air and in secondary vacuum (∼10 −6 mbar) without and with a heating stage in order to study the influence of the surrounding ambient on the reliability of the electrical characterization of thin oxide films. It is shown that by applying a positive voltage at the AFM tip and in the presence of a water layer at the oxide’s surface in air ambient, the behavior of the oxide film is very different compared to the same experiment conducted in secondary vacuum. It is thought that in air, H + ions are injected through the oxide, forming attached hydrogen defects in it. These electrically active defects form a path in the oxide between the tip and the substrate facilitating the passage of charges through the oxide, which can be described by a Trap Assisted Tunneling (TAT) mechanism. The results show that working in vacuum with a heating stage is an important condition for the reliability of the characterization of oxides since the breakdown phenomenon is largely reduced due to the absence of the water layer. Moreover, the creation of hillocks (protrusions appearing on the surface after the electrical stress) on the oxide’s surface is decreased under vacuum.