Reduced hydrogen diffusion in strained amorphous SiO2: understanding ageing in MOSFET devices

Abstract

Negative Bias Temperature Instability (NBTI) is one of the main ageing processes in MOSFET devices, and it is related among others to H diffusion within the SiO₂ dielectric layer of the device. In this work we use molecular simulations to study the underlying mechanism that governs the diffusion of H within SiO₂, and suggest how to modify the material to decrease it. The computed diffusion activation energies are in excellent agreement with existing experimental data, and the analysis of the diffusion paths reveals a H hopping mechanism governed by the same orientational constraints as proton exchange in bulk water. Based on this mechanism, we test a hypothetical NBTI ageing retarding modification based on a mechanical deformation of the SiO₂ dielectric. Stretching of the material induces a rearrangement of the silicate units, increasing the O–O distance, and consequently the activation energy required for H diffusion. Hence, stretching of the semiconductor during the MOSFET manufacturing process could reduce significantly the NBTI-driven ageing of the devices.