(Invited) Recent Progress in High Aspect Ratio Etching of 3D Memory Devices

Advanced electronic devices are integrated in the vertical direction, and critical challenges in etching deep structures with high aspect ratios must be addressed to advance the technology roadmap. Among the enabling applications, vertical etching of SiO 2 and SiN for flash memory devices features prominently. Recently, HF is used in high aspect ratio plasma etching of SiO 2 , SiN and multilayer stacks of these films at wafer temperatures below room temperature. The etching mechanisms for these so called cryo etch processes are very different from traditional dielectric etching. Instead of reactive fluorocarbon polymers which react with SiO 2 and SiN under ion bombardment, the process forms ammonium fluorosilicate (NH 4 ) 2 SiF 6 or AFS as an intermediate reaction product. In this paper, we will present experimental results on plasma and vapor etching of SiO 2 and SiN. Included in this study are experimental processing regimes characterized by varied ion flux and energy levels with varying degrees of RF power. The underlaying etching mechanisms will be explained using molecular dynamics and density functional theory. The new cryo etching process is fast evolving to meet profile requirements for future nodes and achieves higher etch rates. This is enabled by chemistry and RF technology innovation.