Role of N2 during chemical dry etching of silicon oxide layers using NF3/N2/Ar remote plasmas

In this work, the role of N2 gas during the chemical dry etching of silicon oxide layers in NF3/N2/Ar remote plasmas was investigated by analyzing the species in the plasma, the reaction by-products in the exhaust, and the chemical properties of the etched surface. Increasing the N2 gas flow rate resulted in an initial increase in the oxide etch rate up to a maximum value, followed by a subsequent decrease. The increased etch rate of the silicon oxide layers was not ascribed to the increased surface arrival rate of fluorine, but to the enhanced oxygen removal from the silicon oxide caused by the formation of NO2 molecules. Presumably, the NO radicals formed from the added N2 gas react chemically with the oxygen in the oxide, leading to the breaking of the Si–O bonds and the effective removal of oxygen, which in turn enhances the formation of SiF4 resulting in an increased etch rate.