Investigation of oxide layer removal mechanism using reactive gases

In a CMOS technology, the removal of silicon oxide and nitride layer is one of the critical steps as it represents a possible source of high contact resistance and a decrease of gate oxide reliability. In high aspect ratio (HAR), it is very difficult to remove SiO₂ with wet etching. In the present study, the effect of the gases such as plasma dry etching of ammonia (NH₃) and nitrogen trifluoride (NF₃) on the SiO₂ and Si₃N₄ substrates were analyzed and the etch rate was measured. The measurement of the SiO₂ and Si₃N₄ thickness was measured by Ellipsometer. Various factors such as chamber pressure, electrode power and NH₃/NF₃ gas ratio were affected by the combination and dissociation of NH₄F molecules. The existence of the by-product was analyzed by using a contact angle analyzer and scanning electron microscope, respectively. In this study we have found that, the removal efficiency was mainly dependent on the reaction mechanism and the effect of the by-product.