MODELING AND INDUCTIVELY-COUPLED PLASMA SOURCE

Inductively coupled plasma (ICP) sources are becoming increasingly popular for etching submicrometer features, soft-cleans for physical vapor deposition cluster tools, and plasma-enhanced chemical-vapor deposition. Here, we report on a discharge model for argon for the ICP which combines an electromagnetic field distribution model with an ambipolar diffusion model. The model provides a self-consistent solution for the spatial distribution of the charged species in the bulk plasma, which permits the spatial distribution of the ion flux to the wafer surface to be calculated. The variations of the peak electron concentration, the ion flux, and its uniformity at the wafer have been simulated as a function of the rf power, antenna geometry, and chamber geometry. The electron number density increases linearly with rf power in accordance with experimental observations. The ion flux uniformity is primarily dependent on die diameter of the antenna and is only slightly dependent on the number of turns. The uniformity generally is relatively invariant with rf power above a threshold power level. Contouring the antenna or the dielectric separating the antenna from the plasma is useful for improving ion flux uniformity. The minimum thickness of the dielectric cap is constrained by the maximum allowable sheath potential. The induced electric field at the wafer can cause substantial wafer heating at high antenna power levels. Increasing the wafer to antenna spacing mitigates this problem without sacrificing the ion flux and its uniformity.