Evolution of Ferroelectricity With Annealing Temperature and Thickness in Sputter Deposited Undoped HfO$_{\text{2}}$ on Silicon

Ferroelectricity in sputtered undoped HfO $_{\text{2}}$ is attractive for composition control for low power and nonvolatile memory and logic applications. Unlike doped HfO $_{\text{2}}$ , the evolution of ferroelectricity with annealing and film thickness effect in sputter deposited undoped HfO $_{\text{2}}$ on Si is not yet reported. In the present study, we have demonstrated the impact of postmetallization annealing temperature and film thickness on ferroelectric properties in dopant-free sputtered HfO $_{\text{2}}$ on Si substrate. A rich correlation of polarization (2 $\textit{P}_{\textit{r}}$ ) with phase, lattice constant, and crystallite size and interface reaction is observed. First, anneal temperature shows o-phase saturation beyond 600 $^{\circ}$ C followed by interface reaction beyond 700 $^{\circ}$ C to show an optimal temperature window on 600 $^{\circ}$ C–700 $^{\circ}$ C. Second, thickness study at the optimal temperature window shows an alluring o-phase crystallite scaling with thickness till a critical thickness of 20 nm, indicating that the films are completely o-phase. However, the lattice constants (volume) are high in the 15–20 nm thickness range, which correlates with the enhanced value of 2 $\textit{P}_{\textit{r}}$ . Beyond 20 nm, crystallite scaling with thickness saturates with the correlated appearance of m-phase and reduction in 2 $\textit{P}_{\textit{r}}$ . The optimal thickness-temperature window range of 15–20-nm films annealed at 600 $^{\circ}$ C–700 $^{\circ}$ C shows 2 $\textit{P}_{{\textit{r}}}$ of $\sim$ 35.5 $\mu$ C/cm $^{\text{2}}$ is comparable to state of the art. The robust endurance of $\sim$ 108 cycles with negligible wakeup showcased in the promising temperature-thickness window has been identified systematically for nonvolatile memory applications.