Characteristics of very high frequency plasma produced using a ladder-shaped electrode

A very high frequency (VHF) excited H-2 plasma is produced with a ladder-shaped electrode consisted of 17 rods and the plasma parameters are measured with a movable Langmuir probe. When the discharge frequency (similar to 120 MHz) of the RF power source is increased, the plasma density increases while the electron temperature decreases. The position of the RF connections and the shape of the rod, particularly at higher frequencies are found to affect the distribution of the ion saturation current. The uniformity of the ion saturation current of +/-17.2% over a distance of 150 mm is achieved at 120 MHz.