Mist chemical vapor deposition study of 20 and 100 nm thick undoped ferroelectric hafnium oxide films on n+-Si(100) substrates

Abstract

This study effectively synthesized ferroelectric undoped ferroelectric-phase hafnium oxide (HfO2) thin films on n+-Si(100) substrates without the need of any post-annealing for crystallization using mist chemical vapor deposition (CVD) techniques. Metal-ferroelectric highly doped n+-Si stacked capacitors exhibited ferroelectric polarization–electric field hysteresis at 1 kHz owing to the ferroelectric-phase HfO2 with remnant polarization and coercive field values of approximately 7 μC cm−2 and 1.4 MV cm−1, respectively. The resultant endurance cycle reached 1 × 109 after imposing fatigue pulses of 3 MV cm−1, which is an excellent value reported so far. These ferroelectric properties were related to the surface morphology and density of the films, compared to the post-annealed ones. A clear microcrystalline structure in the as-deposited films suggested the formation of intermediate chemical compounds containing carbon. On the contrary, the ferroelectricity was lost by post-anneal enhancing crystallization, especially for paraelectric monoclinic phase. Finally, we expect that the mist CVD HfO2 films will be promising in developing a key technology for Si-based ferroelectric LSIs.