Backside medium energy ion scattering study of the lanthanum diffusion in advanced gate stacks for the 32nm node

The insertion of a La"2O"3 capping layer in high-k gate dielectric stacks is a solution for tuning the threshold voltage in nMOSFETs devices. We have investigated TiN/ LaO"x/HfSiON/SiON on Si(001) gate stacks by medium energy ion scattering to determine the La in-depth distribution and highlight the impact of spike-annealing after the complete deposition sequence. A dedicated method of preparation combining both mechanical and chemical thinning of the silicon substrate is applied prior to backside analysis. Results show that lanthanum is the main diffusing element after annealing.