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

We demonstrate significantly improved thermal stability of the amorphous phase for hafnium-based gate dielectrics through the controlled addition of Al2O3. The (HfO2)x(Al2O3)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 (HfO2)x(Al2O3)1−x films with Hf:Al∼3:1 (25% Al) remain amorphous up to 900 °C, while films with Hf:Al∼1:3 (75% Al) remain amorphous after a 1050 °C spike anneal.