The effect of subwafer dielectrics on plasma properties in plasma etching reactors

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Nonplanar electrode topographies in plasma etching reactors are known to perturb plasma properties. In this article results from a computational study of plasma etching reactors having nonuniform dielectric structures below the wafer are presented. The system is an inductively coupled plasma reactor having a 13.56 MHz bias applied to the substrate. The model we have used is a hybrid simulation consisting of electromagnetics, electron Monte Carlo and fluid kinetics modules, and an off-line plasma chemistry Monte Carlo simulation. We found that the subwafer dielectric adds a series capacitance to the sheath and wafer resulting in voltage division of the applied potential between the sheath, wafer, and dielectric. This produces a smaller sheath potential and smaller sheath thickness above the dielectric. The ion energy distribution is therefore depressed in the vicinity of the dielectric. The effect is more severe at high plasma densities where the capacitance of the sheath is larger compared to the subwafer dielectric.