Synergetic Effect of Chemical Components in a Tungsten CMP Slurry and the Evolution of Tungsten Surface Species

A novel slurry containing 50 ppm Fe 3+ , 2 wt% H 2 O 2 , 75 ppm oxalic acid, and abrasive nano-silica particles were utilized in a W chemical mechanical planarization process. Using this slurry, a W material removal rate of 710 Å min −1 and surface roughness of 1 nm were achieved. According to X-ray photoelectron spectroscopy data, surface W was first transformed to WO 2 via its dissolution in H 2 O 2 , and then Fe 3+ ions serving as a catalyst promoted the conversion of tungsten to WO 3 through the WO 2 intermediate in the presence of H 2 O 2 . Oxalic acid was added to coordinate with H 2 O 2 and thus improve the slurry stability through a “wrapping” mechanism without decreasing the W material removal rate. Scanning electron microscopy and atomic force microscopy observations revealed that the W surface morphology changed first from coarse elongated grains to a discontinuous structure after the uneven oxidation by H 2 O 2 and then to a wrinkled soft surface by Fe 3+ and H 2 O 2 . Finally, it was ground with abrasive nano-silica particles to achieve a high degree of flatness.