Chemical downstream etching of silicon–nitride and polycrystalline silicon using CF4/O2/N2: Surface chemical effects of O2 and N2 additives

By comparing the etching characteristics of silicon and silicon nitride in CF4 /O2 /N2 microwave downstream plasmas we demonstrate clearly how low concentrations of energetic species can play a dominant role in remote plasma processing: Injection of 5% N2 to a CF4 /O2 plasma increases the silicon nitride etch rate by a factor of 7, while not significantly affecting the bulk composition of the discharge. Downstream injection of N2 is ineffective. Using surface spectroscopies we directly show a dramatic enhancement of the reactivity of fluorine and oxygen atoms with silicon and silicon– nitride surfaces upon N2 injection to the discharge. Our results can be explained by the production of energetic metastable species in the discharge region which transport energy to the gas-surface interface. © 1995 American Institute of Physics.