Fluorocarbon high density plasmas. VII. Investigation of selective SiO₂-to-Si₃N₄ high density plasma etch processes

Abstract

A comparison of the plasma etching characteristics of SiO2 and Si3N4 in high-density fluorocarbon discharges with the goal of identifying an etching chemistry with a very high SiO2-to-Si3N4 etch selectivity has been initiated. High-density plasmas were excited in an electron cyclotron resonance apparatus equipped with a cooled rf powered electrostatic chuck. Gas mixtures of either CF4/H2, CHF3/H2 (low carbon/fluorine ratio fluorocarbon gases), or C2F4/H2, C2F6/H2, and C3F6/H2 (high C/F ratio) were used in this work. We will show that a carbon-rich fluorocarbon gas like C2F4 and a modest amount of H2 are useful in achieving high SiO2TSi3N4 etch selectivity (>28). On the other hand, hydrogen-rich fluorocarbon gas mixtures which contain less carbon, e.g., CHF3/H2, are not useful for achieving SiO2 over Si3N4 etch selectivity although they will enable SiO2TSi etch selectivity. The gas phase and surface chemical aspects of the different gas mixtures were studied by optical emission spectrometry and line of sight mass spectrometry and by post plasma x-ray photoelectron spectroscopy. The results of these measurements can explain the etch rate data by selective deposition of fluorocarbon films on Si3N4 and Si surfaces. © 1996 American Vacuum Society.