Practical Scaling of Multi-Frequency Capacitive Discharges for Etch Applications

Summary form only given. Multi-frequency RF capacitive discharges are the current state-of-the-art technology in dielectric etch. Very high frequency (VHF) sources are used for controlling plasma density. Low frequency sources are used to control ion dynamics in the sheath in front of the processing wafer. These two frequency selections allow for nearly independent control of ion flux and ion energy impinging the wafer. Another configuration utilizes just two low frequency sources (without VHF) to control ion dynamic in the sheath. By varying the relative RF current from these two sources, the modification of ion energy distribution on the wafer surface can be achieved while maintaining nearly the same mean ion energy. Recently, systems with three frequencies (one high frequency for bulk plasma control, and two low frequencies for time average sheath control and sheath dynamic control) have been introduced that provide independent control of bulk plasma properties, mean ion energy, and ion energy distribution function width. The purpose of this work is to present the scaling laws for these three configurations. Using a simple plasma model that incorporates the power deposition and energy loss, the static and dynamic plasma and sheath parameters can be inferred from RF measurement of the discharge impedance. A method will be shown for estimating basic plasma and sheath parameters, including the ion flux characteristics, using off-the-shelf RF metrology. These plasma and sheath parameters are then used to establish empirical scaling laws for the multi-frequency systems suitable for a real-time tracking of plasma parameters