Wafer Redeposition Impact on Etch Rate Uniformity in IPVD System

Abstract

The liner and seed deposition and feature coverage in an ionized physical vapor deposition (IPVD) technique depends on the background gas pressure and an RF bias power applied to the substrate electrode. Under such conditions, a redeposition (RD) occurs at the increased pressures, and it has a noticeable impact on the actual feature coverage and performance nonuniformity (NU) across the wafer. An analytical 2-D plasma fluid model, combined with analytical thermalization model, and experimental validation were used to investigate the impact of the wafer RD on the intrinsic and apparent etch rates (ERs) and their NU in the IPVD system. The model comprised the Cu+Ar collisional mechanism, including charge exchange and Penning ionization, considering gas rarefaction effect and variable ion mobility approach. The analytical approach was implemented to describe the mechanism of the thermalization of sputtered Cu. The experiment encompassed pressure range from 0.6 to 8.7 Pa and the table power from 100 to 800 W, showing the dramatic effect of the RD on the ER uniformity. Depending on the pressure, the apparent ER NU (one with contribution of the RD) can vary from ~6% (min-max) to over 20% (min-max). An intrinsic ER NU (contribution of the RD is extracted) is from 5% (min-max) to over 16% (min-max), shifted with respect to the pressure. The most significant impact of the RD effect has been observed at the edge of a 300-mm wafer. The evaluation on Ta (TaN) liners exhibits similar trends in RD, but a shift in the performance curves shows that the key factor in RD uniformity is the mean free path of the etched material