HfAlO and HfSiO Based Dielectrics for Future DRAM Applications

Abstract

The temperature stability of HfSiOx and HfAlOx films was investigated in the annealing temperature range of 700-1000 {degree sign}C. The main focus of this work is to compare mixed and laminate films in terms of crystallographic phase, capacitance enhancement and leakage current degradation. Single HfO2 layers in the laminate film fully crystallize into monoclinic phase. Mixed films remain nanocrystalline up to a temperature of 800- 900{degree sign}C and fully crystallize in to the cubic phase for higher temperatures. The different crystallization temperatures and crystallographic phases are reflected in the annealing temperature dependence of capacitance and leakage current. Mixed films show a significant increase of capacitance and leakage current after crystallization. For laminates the capacitance remains constant for annealing temperature up to 1000{degree sign}C and the leakage current shows a slight degradation only. Using temperature dependent leakage current measurements the formation of trap states at average levels of 0.2-0.3 eV below conduction band edge of the dielectrics is shown.