Impact of high temperature annealing on La diffusion and flatband voltage (Vfb) modulation in TiN/LaOx/HfSiON/SiON/Si gate stacks

We present a detailed analysis of the impact of high temperature annealing on the chemical and electronic properties of TiN/HfSixOyNz/SiOxNy/Si gate stacks, where an ultra-thin LaOx capping layer (0.4–1 nm) is inserted between the TiN metal gate and the HfSixOyNz dielectric. From our experimental results, we demonstrate that La atoms diffuse through the entire nitrided hafnium silicate and reach the SiOxNy interfacial layer to form a La-silicate. In addition, hard x-ray photoelectron spectroscopy analysis highlights the band alignments’ shift of the gate stacks, which is well related to Vfb shifts based on an interfacial dipole and/or fixed charges model. Finally, this study reveals that the Vfb roll-off phenomenon is amplified with an increasing amount of La atoms near the substrate interface. A correlation between LaOx thickness and interface trap density (Dit) is observed, and a mechanism explaining the roll-off behavior is proposed.