Origin of Electrical Signals for Plasma Etching Endpoint Detection: Comparison of Endpoint Signals and Electron Density
Mark A. Sobolewski, David L. Lahr
Electrical signals are used for endpoint detection in plasma etching, but the origin of the electrical changes observed at endpoint is not well understood. As an etch breaks through one layer and exposes an underlayer, the fluxes and densities of etch products and reactants in the gas phase will change. The resulting perturbation in gas composition may alter the plasma electron density, which in turn may affect the electrical signals. Alternatively, changes in substrate electrical properties or surface properties, such as work function or secondary electron yield, may be involved. To investigate these effects, experiments were performed in an rf-biased, inductively coupled reactor, during CF4/Ar plasma etching of silicon dioxide films on silicon substrates. A complete set of electrical parameters, for the bias as well as the inductive source, was measured and compared. Simultaneously, the plasma electron density was measured using a wave cut-off probe. Factors that limit each electrical signal's sensitivity and reliability for endpoint detection were identified. The fundamental rf bias impedance was found to be the most useful signal. The electron density measurements, together with simple, analytical models of discharge electrical behavior, provide insight into the origin of the electrical changes that occur at endpoint.
and Lahr, D.
Origin of Electrical Signals for Plasma Etching Endpoint Detection: Comparison of Endpoint Signals and Electron Density, Journal of Vacuum Science and Technology A
(Accessed May 29, 2023)