Contact resistances in trigate and FinFET devices in a Non-Equilibrium Green's Functions approach

TL;DR

This study uses a Non-Equilibrium Green's Functions approach to analyze contact resistances in trigate and FinFET devices, revealing key factors affecting device performance at nanometer scales.

Contribution

It provides a detailed analysis of contact resistance origins and effects in trigate and FinFET devices, including the impact of design parameters and interface charges.

Findings

Contact resistance is significant in sub-30 nm devices.

Spacers between source/drain and gate are major resistance contributors.

Resistance increases as channel cross section decreases below 50 nm².

Abstract

We compute the contact resistances $R_{\rm c}$ in trigate and FinFET devices with widths and heights in the 4 to 24 nm range using a Non-Equilibrium Green's Functions approach. Electron-phonon, surface roughness and Coulomb scattering are taken into account. We show that $R_{\rm c}$ represents a significant part of the total resistance of devices with sub-30 nm gate lengths. The analysis of the quasi-Fermi level profile reveals that the spacers between the heavily doped source/drain and the gate are major contributors to the contact resistance. The conductance is indeed limited by the poor electrostatic control over the carrier density under the spacers. We then disentangle the ballistic and diffusive components of $R_{\rm c}$, and analyze the impact of different design parameters (cross section and doping profile in the contacts) on the electrical performances of the devices. The contact resistance and variability rapidly increase when the cross sectional area of the channel goes below $\simeq 50$ nm$^2$. We also highlight the role of the charges trapped at the interface between silicon and the spacer material.