Formation mechanism of sidewall striation in high-aspect-ratio hole etching

We investigated the formation mechanism of sidewall striations in etched holes with high aspect ratios, with focus on the roles of energetic ions and fluorocarbon radicals. Striations were observed on the sidewalls of holes with high aspect ratios in stacked dielectric films, despite the smooth sidewall of the mask. Argon plasma treatment increased the degree of striation on the carbon mask, while striation was prevented with a cyclic process consisting of a fluorocarbon deposition step and an argon plasma treatment step. The blanket films were irradiated with oblique ion beams in order to simulate the surface reactions on the sidewalls of high aspect ratio holes. Argon ion beams oriented 85° from the surface normal formed severe striations on the blanket fluorocarbon film surface, despite the low roughness of the SiO 2 film surface. A thicker fluorocarbon film was observed in regions with striations than deeper regions with smooth sidewalls. The striations formed on the fluorocarbon films at the sidewalls of high aspect ratio holes and transferred to the dielectric films laterally as the hole diameters increased. In addition, as etching proceeded, striations began to form at the deeper regions, depending on the aspect ratios.