Design and operation of an Omegatron mass spectrometer for measurements of positive and negative ion species in electron cyclotron resonance plasmas

Abstract

The Omegatron mass spectrometer, originally developed for measuring atomic constants, was employed for measuring both positive ions and negative ions in high density, electron cyclotron resonance etching plasmas. The main disadvantages of the conventional design of the Omegatron include the observation of resonance frequency shifts and poor mass resolution in a relatively weak magnetic field. Based on 2D numerical analysis, several modifications were carried out to overcome these limitations: the (±) ion collector, differential pumping, different RF excitation methods, an additional magnet for uniform magnetic field, etc. Experimental results indicated the presence of H − and H − 2 in H 2 plasmas, and F − and CF − in CF 4 plasmas.