Comprehensive Modeling of Threshold Voltage Variability Induced by Plasma Damage in Advanced Metal-Oxide-Semiconductor Field-Effect Transistors

摘要

Threshold voltage shift (Δ V_(th)) and its variation induced by plasma processing were investigated in detall. Two damage mechanisms occurring in an inductively coupled plasma reactor were focused on in this study; the charging damage induced by the conduction current from plasma and the physical damage attributed to the bombardment of high-energy ions. Regarding the charging damage, Δ V_(th) was found to show a power-law dependence on antenna ratio for both SiO_2 and high-k gate dielectrics in metal-oxide-semiconductor field-effect transistors (MOSFETs). The observed dependence was also confirmed from the results of a constant-current stress test, indicating that the plasma plays the role of the current source in terms of the charging damage. As for the physical damage, the recess structure in source/draln extension regions was focused on as a possible cause of ΔV_(th) The depth of the recess (or) formed by the physical damage was studied using Si wafers exposed to various plasma conditions and subsequently analyzed for surface damage. The recess depth determined from the experiments and classical molecular dynamics simulations exhibits a power-law dependence on potential drop across the sheath between the plasma and the device surface (V_p - V_(dc)), which is used as a practical measure of the damage. On the basis of the above results, Δ V_(th) due to the physical damage was calculated by technology computer-ALDed design (TCAD) device simulation for n- and p-channel MOSFETs with the recess structure. ΔV_(th), shows a linear dependence on recess depth for both n- and p-channel MOSFETs, resulting in the power-law dependence on (V_p - V_(dc)) via d_R. These findings provide a simple relationship among the variations of Δ V_(th), antenna ratio, and plasma parameters. By taking into account the findings that the MOSFET with high-k dielectrics shows a larger Δ V_(th) due to the charging than that with SiO_2, and that the MOSFETs with a smaller gate length indicate a larger Δ V_(th) due to the Si recess structure, we can conclude that larger amount of plasma damage induces the larger ΔV_(th), variations, i.e., the V_(th) variability induced by the plasma damage is difficult to suppress and will become crucial to the fabrication of future advanced devices. The proposed relationship is useful as a guideline to suppress the Δ V_(th) variations caused by plasma damage.