Abstract
The objective of our study is to investigate the influence of degradation of inhibitor employed in N28 node alkaline-based cleaning solution on the formation of copper oxide during post-Cu CMP cleaning. The effects of the pH and the inhibitor concentration of the cleaning solutions on adhesion force and removal of silica abrasive particles were also studied.We measured the zeta potentials and particle size distribution (PSD) of silica abrasive and copper powder as a function of pH in order to find out the optimal condition of the cleaning solution. The results illustrate that pH around 12 induced strong repulsive force and very fine silica particles, resulting in improved particle removal efficiency. FESEM and AFM images also support the results. Based on this optimal condition, we investigated the effect of inhibitor degradation on copper oxide film formation. In order to observe the formation of Cu oxide film, we did potentiodynamic studies on wafers under different in various air exposure times and found that the degraded cleaning solution failed to maintain the Cu2O passive layer, which resulted in the formation of CuO. XPS spectra also confirm the finding. The results of the XPS and potentiodynamic measurements of Cu wafers in the cleaning solution purged with oxygen indicated that the degradation can be attributed to the oxidative reaction. In future works, we will continue to investigate the degradative mechanism of inhibitor by analyzing the depth profile of oxide film. In addition, we will check the ability of the inhibitor to corrosion inhibition.