CHAPTER 4
MODEL ASSESSMENT
The parameters governing the material removal calculation consist of CMP
operating parameters, slurry parameters, pad and wafer parameters, as listed in Table 4-1.
However, some of these parameters, especially the sub-nanometer thick modified layer
hardness and thickness can not be determined experimentally due to equipment
limitations. The remaining parameters are relatively easy to investigate experimentally
for many CMP systems. Hence, modified layer hardness and thickness are used as the
fitting parameters in the model.
Table 4-1. Parameters included in the revised PERC model.
Operating Parameters Pad properties
Pressure Pad modulus
Velocity Asperity height distribution
Asperity radius
Slurry parameters Asperity density
Particle size distribution
Solids loading Wafer properties
Abrasive density Modified layer thickness
Solvent density Modified layer hardness
Wafer hardness
Model Validation
In this section, PERC II model predictions are compared with experimentally
measured values to assess the reliability of the proposed CMP model. The experimental
literature data is also compared with PERC I predictions to assess the advantage of PERC
II over PERC I. Though PERC II is a refined model compared to PERC I, the model is
still a simplified version of real CMP, mainly in estimating the number of trapped