Controllable formation of HfO₂thin film in 20 nm thick lateral trenches with high aspect ratio up to 30

Ultimate-vertical-gate-all-around (UVGAA) MOSFET represent an advanced evolution of VGAA architectures, featuring source-drain symmetry enabled by simultaneous formation of both terminals. Derived from the fabrication methods of three dimensional (3D) NAND flash memory, UVGAA MOSFET offer potential for vertically stacked logic circuits. However, their implementation demands ultra-thin sacrificial Si₃N₄layers and higher lateral-high-aspect-ratio (LHAR) trench structures compared to 3D NAND flash memory. In this study, 20 nm thick multilayer LHAR trench structures with aspect ratio up to 30 were successfully fabricated via a combined dry and wet etching approach applied to SiO₂-Si₃N₄-SiO₂multilayer stacks. Hafnium dioxide (HfO₂) thin films were subsequently deposited within these confined geometries and on planar silicon surfaces using atomic layer deposition. By systematically optimizing key process parameters: precursor pulse time and purge duration-optimal conditions for uniform and conformal film growth were established. The comprehensive deposition behavior of HfO₂films in different geometric structures has been qualitatively analyzed using the molecular diffusion theory and the surface adsorption kinetics model. Resulting HfO₂films exhibited predominantly amorphous structure, ultra-low surface roughness, and excellent electrical properties. This study establishes a theoretical framework and process foundation for the miniaturization and performance optimization of next-generation 3D integrated circuits.