Chemical Effects on Polishing Performance

The physical properties of the pad are heavily determined by its chemical constituents such as polyols, isocyanates, stoichiometric ratio of isocyanate to diol, and cross-link molecular structures (hard and soft segments). They also have a great impact on the mechanical properties of the pad (strength, hardness, stiffness. Young s modulus, etc.) and on the performance of the CMP process. 

CMP is a wet process with DI water and/or polishing slurry present. During polishing, pad is under the attack of water, slurry chemicals, and abrasive particles at elevated temperature due to the friction force among wafer-particle-pad contact. This leads to changes in pad s physical and mechanical properties that influence polishing performance. 

FIGURE 5.11 The oxide thickness removed as a function of cumulative polishing times on the pad. The pads (lot A and lot B) were not conditioned, and cumulative polishing times were obtained using 5 min of polishing [4]. 

FIGURE 5.12 Scanning electron micrograph of IClOOO/Suba IV CMP pad (a) before and (b) after polishing [26]. 

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