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

Abstract

In this study, sodium periodate (NaIO(4)) was chosen its 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 NaIO(4) 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 RUO(4). Above pH 7.5. the static etch rate decreased due to the formation of insoluble RuO(2)center dot 2H(2)O and the depletion of periodate ions. The highest etching of 20 nm/min was obtained at pH 6. In a slurry of 0.1 M NaIO(4) and 2 wt% alumina particles at pH 6. the removal rate of Ru was about 130 nm/min. 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. (c) 2009 The Electrochemical Society. [DOI: 10.1149/1.3058594] All rights reserved.