Reactive Ion Etching of RuO2 Films: The Role of Additive Gases in O2 Discharge

Abstract

In a previous work, we had reported that the etch rate of RuO2 thin films in an oxygen discharge exhibits an anomalously strong increase (1625 A/min) when a small amount of additive gas such as CF3CFH2 (2.5% by mole fraction) is introduced. Furthermore, the etch rate was suppressed by a large factor when the mole fraction of CF3CFH2 gas in the feed was increased. In this work, we have explored the underlying mechanism for this behavior. Several gases, such as CF3CFH2 (HCFC-134), N 2 , and SF 6 were added to the oxygen discharge to investigate the etch mechanism. Atomic oxygen was found to be the dominant active species reacting with RuO 2 films to form volatile RuO 4 products. In low concentrations, additive gases in the oxygen discharge were found to increase the generation rate of O atoms, thereby enhancing the etch rate. This was confirmed through loading effect studies; the etch rate was found to decrease with increasing sample area. HCFC-134 gas had the strongest effect in increasing the generation rate (G), and accordingly, addition of small amount of CF 3 CFH 2 in oxygen discharge yielded the highest etch rate. The decrease in etch rate with increasing mole fraction of CF3CFH2 in the feed (>5%) was attributed to the reaction of F atoms with RuO 2 to form surface residue layers that occupied surface reaction sites thus impeding the reaction between O and RuO 2 . The formation of the surface residue layer was validated through X-ray photoelectron spectroscopy studies.