There are two modes for ion energy analysis at a rf electrode in a plasma chamber. One is a dc mode in which the electric potential of the ion energy analyzer is constant in time, and another is a rf mode in which the electric potential of the analyzer oscillates with same frequency, amplitude, and phase as that of the rf electrode. For correct ion energy analysis at the rf electrode, the rf mode is necessary. For ion mass analysis in the rf mode, the electric potential of the ion mass analyzer also must oscillate. We fabricated such an ion energy and mass analyzer, and confirmed its performance. ©1998 American Institute of Physics.