Transient Behaviors of Gaseous and Surface Reactions in a Cycle of Pasivation and Etch Steps Using Ar-Based C₄F₈ and SF₆ Plasma

In the fabrication of high-aspect-ratio (HAR) Si features, a cycle of passivation and etch using a temporal modulation of bias-application and gas exchange is used. The cycle is comprised that a passivating film on interior of the HAR feature by the C₄F₈ based plasma is deposited and the feature bottom is etched of by the SF₆-added plasma. As the period for one cycle is shortened, the temporal modulations of the external control variables, such as the bias supply and the gas flow, are interferred due to slow responses of evacuation and the wall memory effect. To control the etch profiles, decouple of the etch reactions between sidewall and bottom in the etched feature is effective. A change in the bias application timing has demonstrated a control of the etch rates and HAR shape profiles in accordance with dynamic measurements of densities of electron, ion, and radical at real time.