Reactive Ion Etching of Molybdenum In CF4/O2 Plasma

A mechanistic study of Mo etching in a CF4/O2 plasma has been performed using optical emission spectroscopy, mass spectrometry and x-ray photoelectron spectroscopy.Etching characteristics of Mo for a wide range of conditions relevant to plasma processing are also reported.Addition of small amount of O2 to the CF4 plasma dramatically increases the Mo etch rates, as well as concentrations of 0 and F in plasma.However, further addition of O2 above 50 % leads to decrease in etch rates.Two types of neutral molybdenum oxifluorides and a trace amount of molybdenum hexafluoride were observed in the effluent gas.Comparing the etch rates with the concentration changes of F and 0 with and without Mo present in plasma, it is suggested that Mo is chemically etched by F and 0.Atomic oxygen enhances the etch rate by increasing the F concentration in the plasma as well as by removing a carbon layer forming desorbed CO on the surface.XPS and AES analysis results for the etched surface inferred that chemisorbed fluorocarbon radicals dissociate into carbon and fluorine atoms, which in turn form a passivating graphite-like layer and a volatile molybdenum oxifluoride and molybdenum hexafluoride layer.