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

Abstract In this study, we investigated the effect of a post annealing sequence on the HfO 2 crystal phase and the memory window of charge trap devices with TiN-Al 2 O 3 -HfO 2 -SiO 2 -Si stacks. The charge trap dielectrics of HfO 2 were deposited by atomic layer deposition and were annealed in an oxygen environment with or without Al 2 O 3 blocking oxides. X-ray diffraction analysis showed that, after thermal annealing, the predominant crystal phase of HfO 2 is divided into tetragonal and monoclinic phase depending on the presence or absence of Al 2 O 3 blocking oxide. In addition, deconvolution of X-ray diffraction spectra showed that, with increasing annealing temperature, the fraction of the tetragonal phase in the HfO 2 film was enhanced with the Al 2 O 3 blocking oxide, while it was reduced without the Al 2 O 3 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 HfO 2 .