Role of O-2 in aluminum etching with BCl3/Cl-2/O-2 plasma in high density plasma reactor

Role of O-2 in aluminum etching process using BCl3/Cl-2/O-2 plasma was inve stigated in inductively coupled plasma (ICP) etching system. Optical emissi on 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 seem s to result in increase of aluminum etchant chlorine radicals and generatio n of BxOy species. Increase of chlorine radicals may play role to enhance a luminum etch rate at relatively low O-2 concentration (less than or equal t o 6%). As the concentration of O-2 increased, local etch stop of aluminum w as 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 surfac e oxidation of aluminum) were postulated and examined. Investigation of the se possibilities shows that the major cause of etch retardation, in the pre sence of O-2, is surface oxidation of aluminum rather than the formation of inhibitor layer via the deposition of BxOy species.