Ferroelectric Hf0.5Zr0.5O2 (HZO) is a promising material in BEOLnonvolatile memory applications for its low deposition and crystallization temperature, with favorable electrical properties such as low operating voltage and low leakage current compared to conventional charge trap-based flash memory technology. However, as the devices scale down so do the metal electrodes; thin electrodes exert less tensile stress to promote the formation of ferroelectric orthorhombic HZO. This leads to reduced remnant polarization which directly affects device performance, reliability, and endurance. Therefore, further scaling of BEOL-compatible HZO requires an intermediary layer between the electrodes and the HZO that can be deposited at low temperature while exerting sufficient tensile stress that promotes desired crystallinity.
In this work, conducted at UT Dallas, Nb2O5 was deposited via thermal ALD technique using (tert-butylimido)tris(dimethyl)amino)niobium (TBTEA-Nb), and H2O or anhydrous H2O2 (provided by RASIRC) as a co-reactant. The ALD window was determined to be 250~300°C for both co-reactants, with H2O2 resulting in 46% higher growth rate compared to H2O. XPS results indicate near stoichiometric 2:5 Nb to O composition with minimal C impurities. Film density at 4 nm agreed with theoretical density of Nb2O5. MIFM structure fabricated with 1 nm Nb2O5 on top of 7 nm HZO shows improved remnant polarization.