Evolution of the electron energy distribution and E-H mode transition in inductively coupled nitrogen plasma

Electron energy distribution function (EEDF) measurements were conducted in nitrogen gas inductively coupled plasma (ICP). At a low ICP power (capacitive mode) and a high gas pressure, the measured EEDF had an unusual distribution with a hole near this electron energy of 3 eV. This distribution is primarily due to vibrational excitation collisions because the vibrational cross section has a sharp peak at the electron energy in nitrogen gas. However, the EEDF evolved into a Maxwellian distribution and the hole disappeared, when the discharge mode transition from E mode to H mode occurred. This evolution of the EEPF can be understood by the electron-electron collision effect, and it occurs when the electron-electron collision time become shorter than the electron residence time.