Patterning of Sin and SiO2 Nanostructures for 3D Electronic Devices at Low Temperatures

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Silicon oxide, SiO2, and silicon nitride, SiN, are widely used in memory and logic devices because of their dielectric properties, compatibility with silicon-based devices and etching selectivity. Advanced electronic devices are integrated increasingly in vertical direction, and critical etching challenges must be addressed to advance the technology roadmap. Among the enabling applications are vertical etching of SiO2 and SiN with high aspect ratio as well as lateral or isotropic etching of these films with high selectivity. Hydrofluoric acid gas has been used for over 30 years for isotropic etch of SiO2 (1, 2). The process has many similarities with wet etching using HF and requires the presence of water at the surface. Gas-phase etching of silicon nitride films has been demonstrated using moist HF vapor followed by heating of the wafer to remove ammonium fluorosilicate (NH4)2SiF6 or AFS as an intermediate reaction product (3). Recently, HF is used in high aspect ratio plasma etching of SiO2, SiN and multilayer stacks of these films at wafer temperatures below room temperatures (4). The elementary reactions bare resemblance with the vapor etch analogues. In this paper, we will present experimental results on plasma and vapor etching of SiO2 and SiN. The underlaying etching mechanisms will be explained using molecular dynamics and density functional theory.