## 초록

In this work, the deviation of energy distribution function of energetic ions from the predetermined value in an inductively coupled plasma (ICP) ion gun source is discussed. An abnormal plasma potential increase at an extraction voltage 400 V caused a beam energy shift of up to 50 eV compared to the preset value. The ion energy peak position was found to be more affected by pressure at higher extraction voltages on the acceleration grid. The energy of primary and secondary ions was measured with an ion energy analyzer. The evolution of the ion energy distribution function during the accelerating voltage change was studied in the pressure range from $3~\times~10^{-3}$ to $1.1~\times~10^{-2}$ Torr.