High selectivity in dry etching of silicon nitride over Si using a novel hydrofluorocarbon etch gas in a microwave excited plasma for FinFET

Increased etch selectivity of SiN_x over Si is required for the gate spacer formation in miniaturized MISFETs, especially in the FinFET. In this work, the selectivity of SiN_x over Si is evaluated using a novel hydrofluorocarbon etch gas with a microwave excited high-density plasma. By using this novel etchant gas, a higher selectivity of SiN_x over Si was obtained compared to CH₃F. The etch rate of Si was suppressed due to the deposition of a hydrocarbon film on Si surface without O₂ gas. It was found that the selectivity of SiN_x over Si near the SiNx sidewall decreased compared that far from the SiNx sidewall. By using flow rates of more than 12 sccm of the novel C_xH_yF_z gas, the gate spacer was formed without Si recess even after the SiNx was overetched for an equivalent thickness of 40 nm.