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

Abstract

Ultimate-Vertical-Gate-All-Around (UVGAA) MOSFET represent an advanced evolution of vertical GAA (VGAA) architectures, featuring source-drain symmetry enabled by simultaneous formation of both terminals. Derived from the fabrication methods of 3D NAND flash memory, UVGAA MOSFET offer potential for vertically stacked logic circuits. However, their implementation demands ultra-thin sacrificial Si3N4 layers 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-SiO2 multilayer stacks. Hafnium dioxide (HfO₂) thin films were subsequently deposited within these confined geometries and on planar silicon surfaces using atomic layer deposition (ALD). 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 HfO₂ films in different geometric structures has been qualitatively analyzed using the molecular diffusion theory and the surface adsorption kinetics model. Resulting HfO₂ films 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.