Suppressed crystallization of Hf-based gate dielectrics by controlled addition of Al2O3 using atomic layer deposition

Abstract

We demonstrate significantly improved thermal stability of the amorphous phase for hafnium-based gate dielectrics through the controlled addition of ${\mathrm{Al}}_2{\mathrm{O}}_3.$ The $({\mathrm{HfO}}_2{)}_x({\mathrm{Al}}_2{\mathrm{O}}_3{)}_{\text{1−x}}$ films, deposited using atomic layer deposition, exhibit excellent control over a wide range of composition by a suitable choice of the ratio between the Al and Hf precursor pulses. By this method, extremely predictable hafnium aluminate compositions are obtained, with Hf cation fractions ranging from 20% up to 100%, as measured by medium energy ion scattering. Using x-ray diffraction, we show that $({\mathrm{HfO}}_2{)}_x({\mathrm{Al}}_2{\mathrm{O}}_3{)}_{\text{1−x}}$ films with $\mathrm{Hf:Al}\text{∼3:1}$ (25% Al) remain amorphous up to 900 °C, while films with $\mathrm{Hf:Al}\text{∼1:3}$ (75% Al) remain amorphous after a 1050 °C spike anneal.