Effects of CH_2F_2 and H_2 flow rates on process window for infinite etch selectivity of silicon nitride to ArF PR in dual-frequency CH_2F_2/H_2/Ar capacitively coupled plasmas

摘要

The process window for the infinite etch selectivity of silicon nitride (Si_3N_4) layers to ArF photoresist (PR) and ArF PR deformation were investigated in a CH_2F_2/H_2/Ar dual-frequency superimposed capacitive coupled plasma (DFS-CCP) by varying the process parameters, such as the low frequency power (P_(LF)), CH_2F_2 flow rate, and H_2 flow rate. It was found that infinitely high etch selectivities of the Si_3N_4 layers to the the ArF PR on both the blanket and patterned wafers could be obtained for certain gas flow conditions. The H_2 and CH_2F_2 flow rates were found to play a critical role in determining the process window for infinite Si_3N_4/ArF PR etch selectivity, due to the change in the degree of polymerization. The preferential chemical reaction of hydrogen with the carbon in the hydrofluorocarbon (CH_xF_y) layer and the nitrogen on the Si_3N_4 surface, leading to the formation of HCN etch by-products, results in a thinner steady-state hydrofluorocarbon layer and, in turn, in continuous Si_3N_4 etching, due to enhanced SiF_4 formation, while the hydrofluorocarbon layer is deposited on the ArF photoresist surface.