HfO ₂/metal stacks: Determination of energy level diagram, work functions & their dependence on metal deposition

Abstract

We report the following results for metal/HfO 2/oxide stacks, (i) The energy level band diagram of HfO 2/SiO 2 stacks is experimentally determined for the first time; the conduction band offset between HfO 2 and interfacial SiO 2 is estimated to be 2.05 eV. (ii) Work functions of W, Re and TaSiN are measured for HfO 2/SiO 2/Si and SiO 2/Si stacks: work functions exhibit no Fermi pinning effect in HfO 2, unlike previous report [1]. (iii) The impact of metal gate deposition on its work function and the oxide charge density is investigated. Measurements show that the tungsten work function is independent of deposition time and method (CVD vs. sputtering). However, oxide charge density (Q ox) depends both on the deposition time and method: Q ox is positively charged for CVD and negatively charged for sputtered depositions. Also, Q ox increases with W deposition time.