Characteristics of atomic-layer-deposited thin Hfx Zr1-x O2 gate dielectrics

In this study, the authors investigated the addition of zirconium (Zr) into Hf O2 to improve its dielectric properties. Hfx Zr1-x O2 films were deposited by atomic-layer deposition at 200-350 °C and annealed in a nitrogen ambient environment at 1000 °C. Extensive physical characterization of the impact of alloying Zr into Hf O2 is studied using vacuum ultraviolet spectroscopy ellipsometry, attenuated total reflectance Fourier transform infrared spectroscopy, secondary-ion mass spectrometry, transmission electron microscopy, atomic force microscopy, x-ray diffraction, Rutherford backscattering spectrometry, and x-ray reflectometry. Hfx Zr1-x O2 transistors are fabricated to characterize the impact of Zr addition on electrical thickness, mobility, and reliability. Zr addition into Hf O2 leads to changes in film microstructure and grain-size distribution. Hfx Zr1-x O2 films have smaller and more uniform grain size compared to Hf O2 for all deposition temperatures explored here. As Zr content and deposition temperature are increased, stabilization of the tetragonal phase is observed. A monotonic decrease in band gap is observed as Zr O2 content is increased. The chlorine impurity in the films is strongly dependent on deposition temperature and independent of film composition. TEM images of transistors showed excellent thermal stability as revealed by a sharp Hfx Zr1-x O2 Si interface and no Zr silicide formation. Significant improvement in device properties such as lower electrical thickness (higher permittivities), lower threshold voltage (Vt) shift after stress (improved reliability), and higher mobilities are observed with Zr addition into Hf O2. All of these results show Hfx Zr1-x O2 to be a promising candidate for Si O2 replacement.