$CF_4$ gas is one of the most useful gases in modern technologies for semiconductor fabrication. However, there are many problems which should be solved in order to fabricate semiconductor device, for example, etching speed drop due to ion charge-up and etching selectivity drop due to the high electron energy. One of useful method in order to suppress their damages above is pulsed-time modulated plasma (PM). However, transient responses of charged particles occur when the source power is turned-on and -off in PM method. To control plasma properties in detail, such a transient phenomenon must be investigated. In this paper, we investigate $CF_4$ RF plasma properties under a one-dimensional fluid model. And also for dynamic and stable control of $CF_4$ plasmas, we investigated the transient behavior of the plasmas after step up or down of the amplitude of the power source voltage $V_s$(t). Fundamental properties of transient $CF_4$ plasmas was discussed. Furthermore, we intend to discuss new method for pulsed-time plasma modulation.