Model for Effects of RF Bias Frequency and Waveform on Si Damaged-Layer Formation during Plasma Etching

Abstract

We investigated damaged-layer formation on the Si substrate surface induced by high-energy ion bombardment during plasma processing, by focusing on ion energy distribution function (IEDF). We introduced a modified range theory for the projection of incident ions and applied the model to damaged-layer formation under various plasma conditions – various rf bias frequencies and waveforms, furthermore their single- or dual-frequency bias configurations. Damaged-layer thickness and residual defect site density after the wet-etch process following the plasma treatment were simulated. The IEDF having more high-energy ions induces the formation of thicker damaged layer than in the case of a monochromatic ion energy when the average ion energies are the same. However, we found that, owing to the stochastic effect on the ion-projected range, the effects of bias frequency and the waveform were suppressed, i.e., the thickness of the damaged layer and the density of residual defect sites are weakly dependent on IEDFs under the same average incident ion energy. The present findings obtained by the model prediction are significant and useful for designing bias configurations for future plasma processes.