High Selectivity for Copper CMP

FIGURE 4.4 The removal rates of Cu and TaN films versus alanine concentration in slurry. 

Alanine could exist in aqueous solution in three different forms, namely, CHS CH(NH3+)COOH (cation), CHS CH(NH3+)COO- (zwitterions), and CHS CH(NH2)COO- (anion). These species are denofed as H2L+, HL, and L-, respectively, for brevify. The equilibrium befween fhese may be depicfed, as Babu ef al. (2005) previously reported, the dissolution and removal rate probability of fhe complexing agent, including phthalic acid, citric acid, glycine, oxalic acid, and carboxyl and/or amine functional group, which interact on the Cu film surface should strongly influence the removal rate. 

The suppression of fhe removal rate of TaN film could nof be fully explained through the electrochemical phenomena by chemical reaction between complexing agent and the TaN film surface. We fhought that the TaN film loss and the Cu-to-TaN removal selectivity are directly related to the electrostatic interaction and electrokinetic behavior due to chemical adsorption and steric hindrance of adsorbed organic chemical. 

The surface potentials of the colloidal silica abrasive particles in the aqueous suspension with alanine were strongly negatively charged above 

FIGURE 4.5 Zeta potential of Cu, TaN films, and colloidal silica slurry with alanine as a function of pH. 

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