Degradation mechanism of dielectric properties of HfO{sub}(2±x) due to interaction of oxygen composition and strain

摘要

It is known that interfacial degraded layers exist at both the gate-electrode/oxide and the substrate/oxide interfaces. Dangling bonds due to the mismatch at the heterointerface are the main defects that deteriorate the reliability. In addition to this interfacial problem, mechanical strain and intrinsic defects in the dielectric film should be focused on because the volumetric density of defects in the film increases monotonically with the decrease of the film thickness. Mechanical stress or strain has been increasing in the gate oxide film because the structure of the devices has become very complicated three-dimensionally and new gate electrode materials such as high melting point metals hold very high residual stress. The increase of the gradient of the residual strain also deforms the film structure seriously and decreases the band gap of the film and thus, increases the leaking current through the film [1, 2]. One of the most important local defects in the gate oxide film is the compositional fluctuation caused by oxygen vacancies. For example, oxygen vacancies in hafnium oxide (HfO{sub}2), which is considered as a promising candidate for a gate dielectric film for sub-100-nm devices, would trap carriers easily during operation of the devices, and thus, result in the instability of the threshold voltage. Therefore, the detailed understanding of the effect of strain and defects in the gate oxide film on both the structural and dielectric characteristics of the film is a key issue for improving the reliability of devices. In this study, we performed a quantum chemical molecular dynamics analysis for HfO{sub}2 film with different amount of oxygen in order to make clear the effect of the strain and intrinsic defects in the film on the dielectric characteristic of the hafnium dioxide film.