REACTIVE ION ETCHING OF RUO2 FILMS - THE ROLE OF ADDITIVE GASES IN O-2 DISCHARGE

In a previous work, we had reported that the etch rate of RuO2 thin fi lms in an oxygen discharge exhibits an anomalously strong increase (ap proximate to 1625 Angstrom/min) when a small amount of additive gas su ch as CF3CFH2 (2.546 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 CF3 CFH2 (HCFC-134), N-2, and SF6, mere added to the oxygen discharge to i nvestigate the etch mechanism. Atomic oxygen was found to be the domin ant active species reacting with RuO2 films to form volatile RuO4 prod ucts. In low concentrations, additive gases in the oxygen discharge we re 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-131 : gas had the strongest effect in increasing the generation rate (G), and accordingly, addition of small amount of CF3CFH2 in oxygen dischar ge yielded the highest etch rate. The decrease in etch rate with incre asing mole fraction of CF3CFH2 in the feed (>5%) was attributed to the reaction of F atoms with RuO2 to form surface residue lavers that occ upied surface reaction sites thus impeding the reaction between O and RuO2. The formation of the surface residue layer was validated through X-ray photoelectron spectroscopy studies.