Optimizing remote plasma sources for selective etching

Abstract

Remote plasma sources (RPS) are used in microelectronics fabrication to produce fluxes of radicals for etching and surface passivation in the absence of damage that may occur by charging and energetic ion bombardment. RPS reactors typically use flow distance and grids to reduce or eliminate charged particle fluxes from reaching the surface of the material being treated. Nitrogen trifluoride (NF3) is frequently used in RPS for the ease with which F atoms are produced by dissociative attachment. RPS sustained only in NF3 typically limits the types of reactive fluxes reaching the processing chamber to only Fx and NFx atoms and molecules. RPS sustained in gas mixtures such as NF3/O2 and NF3/H2, increases the variety of reactive species that can be produced, and so enables some customization of the fluxes to the substrate. For example, the use of NF3/O2 mixtures increases the etch rate of Si3N4 by production of NO which aids in the removal of the N atom from the surface. For certain applications it may be desirable to separately optimize the fluxes of different reactants. This separate optimization could be performed using pulsed power sources or multiple RPS.