A method of processing a material layer on a substrate is provided. The method includes delivering RF power from an RF power source through a match network to a showerhead of a capacitively coupled plasma chamber; igniting a plasma within the capacitively coupled plasma chamber; measuring one or more phase angles of one or more harmonic signals of the RF power relative to a phase of a fundamental frequency of the RF power; and adjusting at least one phase angle of at least one harmonic signal of the RF power relative to the phase of the fundamental frequency of the RF power based on the one or more phase angle measurements.