Paper PS-TuP4
Highly Selective Etching of Silicon Nitride to CVD a-C in Dual-Frequency Capacitively Coupled CH₂F₂/H₂ Plasmas

Tuesday, November 10, 2009, 6:00 pm, Room Hall 3

For the fabrication of a multilevel resist (MLR) based on amorphous carbon (a-C) layer and Si₃N₄ hard-mask layer (underlayer), etch selectivity of the Si₃N₄/a-C layer becomes increasingly critical with the feature size reduction. In this work, therefore, the highly selective etching process of the Si₃N₄ layer using chemical-vapor-deposited (CVD) a-C etch-mask was investigated by varying the following process parameters in CH₂F₂/H₂/Ar plasmas: etch gas flow ratio, high-frequency source power (P_HF) and low-frequency source power (P_LF) in a dual-frequency superimposed capacitively coupled plasma etcher. It was found that infinitely high etch selectivities of the Si₃N₄ layers to the CVD a-C on both the blanket and patterned wafers could be obtained for certain process conditions. In particular, the etch gas flow ratio was found to play a critical role in determining the process window for infinite Si₃N₄/CVD a-C etch selectivity, due to the change in the degree of polymerization. The etch results of patterned ArF PR/BARC(bottom anti-reflective coating)/SiO_x/CVD a-C/Si₃N₄ MLR structure supported the possibility of using a infinitely high selective etch processes of the Si₃N₄ layer using a very thin CVD a-C etch-mask for reduced overall aspect ratio of MLR structure during patterning.