Graded Crystalline HfO₂ Gate Dielectric Layer for High-k/Ge MOS Gate Stack

Germanium (Ge) has gained great attention not only for future nanoelectronics but for back-end of line (BEOL) compatible monolithic three-dimensional (M3D) integration recently. For high performance and low power devices, various high-k oxide/Ge gate stacks including ferroelectric oxides have been investigated. Here, we demonstrate atomic layer deposited (ALD) polycrystalline (p-) HfO2/GeOX/Ge stack with an amorphous (a-) HfO2 capping layer. The consecutively deposited a-HfO2 capping layer improves hysteretic behaviors ( ${\Delta } {V}$ ) and interface state density ( $\text{D}_{\mathrm{ it}}$ ) of the p-HfO2/GeOX/Ge stack. Furthermore, leakage current density ( ${J}$ ) is significantly reduced $(\times 100)$ by passivating leakage paths through grain boundaries of p-HfO2. The proposed HfO2 layer with the graded crystallinity suggests possible high-k/Ge stacks for further optimized Ge MOS structures.