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. (C) 2017 Elsevier B.V. All rights reserved.