Kinetic study of low energy ion-enhanced polysilicon etching using Cl, Cl2, and Cl+ beam scattering

Abstract

The chlorine ion-enhanced etching yield of polysilicon in the low ion energy regime was characterized as a function of Cl ion energy, ion flux, neutral-to-ion flux ratio, and the ion impingement angle by utilizing Cl+, Cl, and Cl2 beam scattering. The chlorine ionic, atomic, and molecular fluxes were controlled independently over more than an order of magnitude and at flux levels within an order of magnitude of that typically used in high density plasma processes. The etching yield increased with the increase of Cl/Cl+ flux ratio but gradually saturated at higher flux ratios as the surface became saturated with chlorine. The ion energy dependence was a linear function of (Eion1/2−Eth1/2), where the threshold energy Eth was found to be approximately 10 eV. With Cl+ ion bombardment, the etching yield of Cl was two to three times higher than that of Cl2 at higher flux ratios. The angular dependence of ion-enhanced etching yield was also measured. The etching yield was reduced by approximately 30% and 50% when ion impingement angles of 60° and 70° off-normal were used, respectively.