The effect of dicarboxylic acid stabilizers on tungsten chemical mechanical planarization process

The effects of dicarboxylic acids (oxalic acid, malonic acid and succinic acid) on the H2O2 stability during tungsten (W) chemical mechanical planarization (CMP) process were studied for the first time. The dicarboxylic acids can coordinate with Fe3+ in the slurry and impact the reaction process by blocking the interaction between H2O2 molecule and Fe3+, decreasing the Fe-complex redox potential and promoting the reduction of Fe3+ to Fe2+. Among the three dicarboxylic acids, oxalic acid shows the superior coordination ability with Fe3+, resulting in a significant improvement of H2O2 stability in the slurry. Appropriate amount of oxalic acid can improve the wafer surface quality (Ra=1.435 nm) while keeping the high material removal rate (MRR = 917 Å/min) at the same time. An increasing amount of dicarboxylic acids can result in a high degree of coordination between Fe3+ and dicarboxylic acid in the slurry. The results also indicate that the main reaction path from Fe3+ to Fe2+ in this system is the reaction between Fe3+ and H2O2. Meanwhile, the MRR keeps almost unchanged after one-week storage with the 2:1 mole ratio of oxalic acid to Fe3+.