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 (HfO 2 ) 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 HfO 2 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 × 10 9 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 HfO 2 films will be promising in developing a key technology for Si-based ferroelectric LSIs.

A preliminary study on mist CVD-derived ferroelectric Hf1−x Zr x O2 films featuring its possibility of suitable operation for non-volatile analog memory

“…Especially the fatigue pulse of 2.5 MV cm −1 seems to be large enough because the corresponding P-E curves became fatty and degraded. Similar to our previous work, 29,30) HfO 2 film showed again good endurance properties until pulse count of 10 9 cycles. It should be noted that for fatigue pulse bias of both 0.5 and 2.5 MV cm −1 , wakeup phenomenon was little observed until 10 9 cycles.…”

“…Our mist CVD apparatus and its typical process for HfO 2 film preparation were explained elsewhere in detail. 29,30) First, metal-ferroelectric-n + -Si (resistivity: 1.7 × 10 −3 Ω cm) stacked capacitors were fabricated using mist CVD Hf 1−x Zr x O 2 thin films (20 nm in thickness) with Pt top electrodes (150 nm in thickness). Hafnium acetylacetonate {Hf(C 5 H 7 O 2 ) 4 } and zirconium acetylacetonate {Zr(C 5 H 7 O 2 ) 4 dissolved in methanol (CH 3 OH) were used as precursors during the process, where the precursor concentration in the solution was 0.02 M. Thereafter, a mist of the source solution was atomized using an ultrasonic transducer at 2.4 MHz and was carried into the mixing part of the solution mist gas area of the apparatus carried by nitrogen gas at a flow rate of 7.5 l min −1 with a growth time of 2 min.…”

“…In view of the situation, we have reported, for the first time, its application for undoped HfO 2 film in detail. 29,30) As the mist CVD enables alloying through the simple dissolution of multiple precursors in a solution, the method is advantageous to dope and control the ferroelectricity of o-phase HfO 2 thin films.…”