Novel Thermally-Stable Hafnium and Zirconium ALD Precursors

Atomic Layer Deposition (ALD) of Hf and Zr oxide films is of considerable interest and promise for future generation Metal-lnsulator-Metal (MIM) structures in memory applications. Hafnium and zirconium alkylamides such as tetrakis(ethylmethylamino) hafnium (TEMAH) and tetrakis (ethylmethylamino) zirconium (TEMAZ) are the most considered precursors. However, their relatively low thermal stability might become a drawback under heated distribution conditions that could result in vaporizer clogging or insufficient long-term stability. Moreover, these precursors may not be suitable if higher deposition temperature processes are sought. Alternative ALD precursors with improved thermal stability could be viable alternatives. Among the precursor families that could be considered (halides, alkoxides, beta-diketonates, tetranitrates, etc.), metallocenes are particularly attractive. New hafnocenes - dimethyl bis(ethylcyclopentadienyl) hafnium, Hf(EtCp)₂Me₂, and dimethyl bis(methylcyclopentadienyl) hafnium, Hf(MeCp)₂Me₂ - with improved physical properties and thermal stability are studied here. The thermal behavior of these new precursors has been extensively characterized for vapor pressure, thermal stability, and evaporation kinetics. The ALD behavior of Hf(EtCp)₂Me₂ with Cfe as co- reactant was investigated at high temperature (350- 400degC), an ALD deposition rate of 0.72 A/cycle was achieved. Hf(EtCp)₂Me₂ showed the best compromise between thermal stability, physical properties, and deposition behavior. Similar zirconocenes were also studied: ZrCp₂Me₂, Zr(MeCp)₂Me₂, Zr(EtCp)₂Me₂ and Zr(EtCp)(NMe₂)₃.