Role of O₂ in Aluminum Etching with BCl₃/Cl₂/O₂ Plasma in High Density Plasma Reactor

Abstract

Role of O 2 in aluminum etching process using BCl 3 /Cl 2 /O 2 plasma was investigated in inductively coupled plasma (ICP) etching system. Optical emission spectroscopy (OES) of BCl 3 /Cl 2 /O 2 plasmas shows that reaction between oxygen and boron chloride occurs in the presence of O 2 . This reaction seems to result in increase of aluminum etchant chlorine radicals and generation of B x O y species. Increase of chlorine radicals may play role to enhance aluminum etch rate at relatively low O 2 concentration (≤6%). As the concentration of O 2 increased, local etch stop of aluminum was observed along the aluminum grain boundary at 9% O 2 and it was extended to cause etch stop on all exposed surface at 15% O 2 . Two possible causes of etch stop (i.e. deposition of reaction byproduct B x O y species and surface oxidation of aluminum) were postulated and examined. Investigation of these possibilities shows that the major cause of etch retardation, in the presence of O 2 , is surface oxidation of aluminum rather than the formation of inhibitor layer via the deposition of B x O y species.