Study of plasma-induced “Si recess structure” and its effects on threshold voltage variability in advanced MOSFETs

Si recess structure formed by plasma-induced physical damage and its effects on the device performance were studied. The depth of Si recess region (d_R) was determined from the experiments by using an inductively coupled plasma reactor with simple Ar gas mixtures. Threshold voltage shift (DeltaV_th) of n-ch MOSFETs with the recess structure was modeled by using device simulation for various d_R. The plasma-induced recess structure was found to strongly affect DeltaV_th and the off-state leakage current. The |DeltaV_th| increases with the increase in d_R and the decrease in gate length L_g. From the plasma diagnostics, the correlation between DeltaV_th and plasma parameters was investigated. The results imply that the plasma-induced damage also enhances V_th(DeltaV_th)-variability in advanced devices.