Electron beam fluorescence temperature measurements of N2 in a semiconductor plasma reactor

Abstract

The rotational temperature of nitrogen molecules in inductively coupled plasma (ICP) discharge has been measured using the electron beam fluorescence (EBF) technique. The neutral gas temperature is an important parameter in understanding the energy balance and neutral radical uniformity in plasma processing. The EBF technique has been used to study rarefied flows, but has not been applied previously to characterize a semiconductor plasma reactor. In this work an electron beam was integrated into an inductively coupled semiconductor plasma reactor, and was used to excite neutral nitrogen molecules from the N2X 1Σg+ state into the excited molecular ion N2+B 2Σu+ state. The electron beam excitation process maps the rotational population distribution of the original ground state into the excited molecular ion state following a dipole model with ΔK=±1. The rotational temperature, which is thought to be equivalent to the neutral gas translational temperature under plasma reactor conditions, can be determined from the rotational intensity distribution of the fluorescence spectrum from the N2+B 2Σu+ state. For the range of neutral gas temperatures found in the plasma reactor a dipole model of the excitation-emission process provides good agreement with the measured spectrum. A least-square fitting procedure comparing the model and measured emission spectra is used to determine the rotation temperature. In this article the first EBF measurements of gas heating in an ICP reactor at different gas pressures (20, 50 mTorr) and plasma source input powers (250, 500, and 1000 W) are reported.