Effect of iron(III) nitrate concentration on tungsten chemical-mechanical-planarization performance

Investigating the catalytic effect of Fe(NO3)3 on the performance of tungsten (W) chemical mechanical planarization in H2O2-based acidic slurries, we found that the trend of the polishing rate with increasing Fe(NO3)3 concentration was divided into two regions. The polishing rate in region I (<0.10 wt%) increased rapidly because of the increase of the WO3 layer formed by the reaction of Fe(NO3)3 and H2O2. The polishing rate in region II (>0.10 wt%), on the other hand, increased only slightly with increasing Fe(NO3)3 concentration. We suggest the excess ferric ions in the slurry were rapidly supplied to the W surface. Consequently, the addition of Fe(NO3)3 resulted in the rapid formation of the WO3 layer because of the decomposition of H2O2 into O2 by Fe3+ ion, and polishing rate increased with the Fe(NO3)3 concentration. This polishing trend was explained through the opposite trend of static etch rate, the confirmation of the surface morphology, the trend of the WO3 content on the W surface, and the trend of the corrosion potential and the corrosion current density.