Effect of thermal annealing sequence on the crystal phase of HfO₂ and charge trap property of Al₂O₃/HfO₂/SiO₂ stacks

In this study, we investigated the effect of a post annealing sequence on the HfO₂ crystal phase and the memory window of charge trap devices with TiN-Al₂O₃-HfO₂-SiO₂-Si stacks. The charge trap dielectrics of HfO₂ were deposited by atomic layer deposition and were annealed in an oxygen environment with or without Al₂O₃ blocking oxides. X-ray diffraction analysis showed that, after thermal annealing, the predominant crystal phase of HfO₂ is divided into tetragonal and monoclinic phase depending on the presence or absence of Al₂O₃ blocking oxide. In addition, deconvolution of X-ray diffraction spectra showed that, with increasing annealing temperature, the fraction of the tetragonal phase in the HfO₂ film was enhanced with the Al₂O₃ blocking oxide, while it was reduced without the Al₂O₃ blocking oxide. Finally, measurements of program/erase and increase-step-pulse programming showed that the charge trap efficiency and the memory window of the charge trap devices increased with decreasing fraction of tetragonal HfO₂.