Effect of pH in Ru Slurry with Sodium Periodate on Ru CMP

In this study, sodium periodate was chosen as both oxidant and etchant on ruthenium (Ru) chemical mechanical planarization (CMP) slurry for the formation of Ru bottom electrodes in dynamic random access memory capacitors. The effect of on etching and polishing behavior was investigated as a function of slurry pH. Below pH 7.5, the high static etch rate was measured due to the dissolution of soluble . Above pH 7.5, the static etch rate decreased due to the formation of insoluble and the depletion of periodate ions. The highest etching of was obtained at pH 6. In a slurry of and alumina particles at pH 6, the removal rate of Ru was about . Even though the highest removal rate was obtained at pH 6, Ru overetching occurred on Ru-patterned wafers due to the high static etch rate of Ru. A selectivity of Ru to oxide of about 23:1 was achieved at pH 8–9. In slurry of pH 9, the planarity and isolation of each capacitor were reached successfully because Ru overetching was prevented due to a low etch rate of Ru.