Effects of CH2F2 and H2 flow rates on process window for infinite etch selectivity of silicon nitride to ArF PR in dual-frequency CH2F2/H2/Ar capacitively coupled plasmas

The process window for the infinite etch selectivity of silicon nitride (Si3N4) layers to ArF photoresist (PR) and ArF PR deformation were investigated in a CH2F2/H2/Ar dual-frequency superimposed capacitive coupled plasma (DFS-CCP) by varying the process parameters, such as the low frequency power (PLF), CH2F2 flow rate, and H2 flow rate. It was found that infinitely high etch selectivities of the Si3N4 layers to the the ArF PR on both the blanket and patterned wafers could be obtained for certain gas flow conditions. The H2 and CH2F2 flow rates were found to play a critical role in determining the process window for infinite Si3N4/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 (CHxFy) layer and the nitrogen on the Si3N4 surface, leading to the formation of HCN etch by-products, results in a thinner steady-state hydrofluorocarbon layer and, in turn, in continuous Si3N4 etching, due to enhanced SiF4 formation, while the hydrofluorocarbon layer is deposited on the ArF photoresist surface.