Oxygen Transport in High-k Metal Gate Stacks and Physical Characterization by SIMS Using Isotopic Labeled Oxygen

Abstract

We review the different diffusion pathways for oxygen in high-k/metal gate (HK/MG) stacks and the impact on electric characteristics such as equivalent oxide thickness (EOT), leakage (Jg), and threshold voltage (Vt). We have investigated the distribution and migration of oxygen in HK/MG stacks at different stages of processing using Secondary Ion Mass Spectrometry (SIMS) depth profiling, in combination with 18O isotope labeling. We demonstrate that use of isotope labeling is instrumental to detect low quantities of O and to follow exchange reactions between different O-sources in the HK/MG stack. We reveal that O-atoms can rapidly diffuse along grain boundaries in titanium nitride (TiN) electrodes at intermediate temperatures. This enables to control the O-distribution throughout the HK/MG stack and the related electrical device characteristics by engineering the chemical composition of the stack and/or by choosing the appropriate processing conditions.