Post-Poly-Si CMP Cleaning

FIGURE 16.13 Contact angles of poly-Si as a function of oxidizer concentration. 

The adhesion force of pad particles on the poly-Si wafer surfaces was measured in the KOH solution (pH 11) as a function of polysilicon wettability, which was varied by treating the surface with different concentrations of the oxidizer. As shown in Fig. 16.14, the adhesion force decreases and then levels 

FIGURE 16.15 Optical images of polymeric particle contamination on (a) hydrophobic and (b) hydrophilic poly-Si. 

During Cu CMP, wafer surfaces are exposed in two steps to at least two different slurries. During the first step, bulk Cu is removed at a high rate and polishing is stopped when the barrier layer is exposed or thin Cu layer is left. The remaining Cu and barrier layers are removed in the second step. The second-step slurry should have low selectivity between Cu and barrier ( 1 1) and yield minimum dishing and erosion. The most commonly used abrasives in Cu CMP slurries are silica (fumed and colloidal silica) and alumina (AI2O3) 

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