Characterization of an Ar-TMS microwave discharge using mass spectrometry: effect of the reactor design on free-radical contents

Abstract

A microwave plasma (2.45 GHz) containing Ar-TMS (TMS = tetramethyl silane) gas mixture is investigated by means of a quadrupole mass spectrometer, equipped with a two-stage differential pumping under deposition condition of silicon carbide. An ionization threshold method is used in order to detect and to determine the various species created within the plasma, which are species like SiC x H y or lighter ones like H 2, CH x , and SiH y . The mass spectrometer signal intensity measured for each ion is corrected in order to suppress the contribution of the TMS dissociative ionization in the total signal intensity. We show that contributions due to dissociative ionization of others species SiC x H y can be neglected in comparison with the contribution of the TMS. The effect of the incident microwave power on the plasma composition has also been investigated. The microwave plasma is very efficient for dissociating TMS (80% of TMS is dissociated at 100 W). At a power lower than 40 W, TMS dissociates mainly via Si–C bond breaking; the main species produced in the plasma are Si(Me) x radicals. At a higher power it dissociates via C–H bond breaking and mostly SiH x or CH x radicals are produced. The plasma composition is investigated in four different reactor configurations corresponding to various TMS injectors and analyzer positions within the reactor. The design parameters and the gas mixture (TMS content in Ar-TMS), change the plasma composition and can promote the dissociation of TMS and of the secondary species (SiC x H y ) via Si–C bond breaking or C–H bond breaking.