Development of a novel chemical mechanical polishing slurry and its polishing mechanisms on a nickel alloy

Conventional chemical mechanical polishing (CMP) slurries of pure nickel (Ni) and its alloys usually consist of toxic and corrosive acids, which is dangerous and contaminative to the operators and environment. It is a big challenge to develop a novel environment friendly CMP slurry for Ni alloys. In this study, a novel environment friendly CMP slurry was developed, containing of silica, hydrogen peroxide (H2O2), malic acid and deionized water. The surface roughness R-a, and peak-to-valley (PV) values are 0.44, and 4.49 nm, respectively with an area of 71 x 53 mu m(2). To the best of our knowledge, surface roughness in this work is the lowest for pure Ni and its alloys at a scan area of 71 x 53 mu m(2). The CMP mechanisms are elucidated by electrochemical, X-ray photoelectron spectroscopy, and infrared measurements. Firstly, H2O2 dominated the oxidation process in CMP, forming oxides of nickel (Ni), chromium (Cr), and molybdenum (Mo) on the surface of Ni alloy. Then, the Ni oxides were dissolved by hydrogen (H) ions. The oxides of Cr and Mo were stable in malic acid. Chelating formulas are proposed between malic acid and Ni ions. Finally, the passivated film was removed by the polishing pad.