Gas Residence Time Effects on Plasma Parameters: Comparison between Ar and C₄F₈

Abstract

The effects of gas residence time on the plasma parameters such as the ion current density (ICD) and hot-electron population have been studied in an inductively coupled plasma (ICP) system employing Ar and C 4 F 8 , separately. The fluorocarbon ionic and radical compositions with respect to the residence time have also been studied in the case of C 4 F 8 ICP. The ion current density with the gas residence time shows a totally opposite behavior in Ar and C 4 F 8 discharge. To elucidate this phenomenon, the hot-electron population with the gas residence time was investigated. The measurement of hot electron population reveals that the energetic electrons are generated much more in Ar discharge but they become less in the case of C 4 F 8 with the decrease of the residence time. Moreover, hot electron population is 3–6 times higher in Ar discharge than in C 4 F 8 . In the C 4 F 8 ICP system, the number of all CF x ( x =1–3) radicals increases but the intensity of the fluorocarbon ionic species [CF x + ( x =1–3)] except for the high-order molecular ions decreases with the decrease of the residence time. All of the diagnostic results show that the effects of the gas residence time must be considered by the characteristics of the plasma parameters as well as the effect of the adsorption and the desorption rate in the etch process.