Role of O2 in aluminum etching with BCl3/Cl2/O2 plasma in high density plasma reactor

Role of O-2 in aluminum etching process using BCl3/Cl-2/O-2 plasma was investigated in inductively coupled plasma (ICP) etching system. Optical emission spectroscopy (OES) of BCl3/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 BxOy species. Increase of chlorine radicals may play role to enhance aluminum etch rate at relatively low O-2 concentration (less than or equal to 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 BxOy 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 BxOy species.