Optimization of slurry components for a copper chemical mechanical polishing at low down pressure using response surface methodology

Copper replaced aluminium and the low-dielectric constant material (low-k dielectrics) served as a better isolator, which has become the inevitable developing trend of IC technology. Due to the low compression resistance of low-k material, the mechanical strength must be reduced in order to ensure the functional integrity, which is a challenge for the traditional chemical–mechanical polishing (CMP) technology. To solve this issue, it is necessary to develop a chemically dominant CMP process at low down pressure. It is generally known that the implementation of optimum slurry composition is one of the important issues. To achieve a high removal rate (RR) and minimal WIWNU (Within-Wafer Non-Uniformity) at a down pressure of 0.63 psi, the response surface methodology (RSM) was applied to optimize slurry composition which contains silica sols, H2O2 and FA/O chelating agent. A central composite design, which is the standard design of RSM, was used to evaluate the effects and interactions of three factors. The optimal conditions obtained from the compromise of the two desirable responses, RR and WIWNU, were silica sols concentration of 13.88 vol.%, H2O2 concentration of 16.13 ml/L and FA/O chelating agent concentration of 20.22 ml/L, respectively. The RSM was demonstrated as an appropriate approach for the optimization of the slurry components by confirmation experiments.