Hydrogen release at metal-oxide interfaces: A first principle study of hydrogenated Al/SiO$_2$ interfaces

TL;DR

This study uses first-principles DFT calculations to investigate hydrogen release mechanisms at Al/SiO$_2$ interfaces, revealing the roles of various hydrogen bonds and their polarization effects under bias, which impact dielectric breakdown.

Contribution

It provides the first detailed atomic-level understanding of hydrogen release at metal-oxide interfaces, specifically Al/SiO$_2$, using DFT calculations.

Findings

Interstitial hydrogen can break Al-Si and Al-O bonds.

Hydrogenated bonds are polarized and affected by bias.

Al-H and O-H bonds are key to hydrogen release.

Abstract

The Anode Hydrogen Release (AHR) mechanism at interfaces is responsible for the generation of defects, that traps charge carriers and can induce dielectric breakdown in Metal-Oxide-Semiconductor Field Effect Transistors. The AHR has been extensively studied at Si/SiO$_2$ interfaces but its characteristics at metal-silica interfaces remain unclear. In this study, we performed Density Functional Theory (DFT) calculations to study the hydrogen release mechanism at the typical Al/SiO$_2$ metal-oxide interface. We found that interstitial hydrogen atoms can break interfacial Al-Si bonds, passivating a Si $sp^3$ orbital. Interstitial hydrogen atoms can also break interfacial Al-O bonds, or be adsorbed at the interface on aluminum, forming stable Al-H-Al bridges. We showed that hydrogenated O-H, Si-H and Al-H bonds at the Al/SiO$_2$ interfaces are polarized. The resulting bond dipole weakens the O-H and Si-H bonds, but strengthens the Al-H bond under the application of a positive bias at the metal gate. Our calculations indicate that Al-H bonds and O-H bonds are more important than Si-H bonds for the hydrogen release process.