Microstructure and chemical analysis of Hf-based high-k dielectric layers in metal-insulator-metal capacitors

The microstructure and chemistry of the high-k gate dielectric significantly influences the performance of metal-insulator-metal (MIM) and metal-oxide-semiconductor devices. In particular, the local structure, chemistry, and inter-layer mixing are important phenomena to be understood. In the present study, high resolution and analytical transmission electron microscopy are combined to study the local structure, morphology, and chemistry in MIM capacitors containing a Hf-based high-k dielectric. The gate dielectric, bottom and gate electrodes were deposited on p-type Si(100) wafers by electron beam evaporation. Four chemically distinguishable sub-layers were identified within the dielectric stack. One is an unintentionally formed 4.0 nm thick interfacial layer of Ta2O5 at the interface between the Ta electrode and the dielectric. The other three layers are based on HfNxOy and HfTiOy, and intermixing between the nearby sub-layers including deposited SiO2. Hf-rich clusters were found in the HfNxOy layer adjacent to the Ta2O5 layer.