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

• An advanced high-k/metal gate stack is examined by medium energy ion scattering.
• The effect of the dopant activation anneal on the La2O3 capping layer is studied.
• Substrate thinning is carried out to enable the backside in-depth investigation.
• Diffusion of La up to the bottom SiON layer is observed after spike anneal at 1065 °C.

The insertion of a La2O3 capping layer in high-k gate dielectric stacks is a solution for tuning the threshold voltage in nMOSFETs devices. We have investigated TiN/ LaOx/HfSiON/SiON on Si(0 0 1) 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.

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