Developing and implementing an advanced CMP run-to-run controller

摘要

An innovative model for R2R control of CMP processes was developed based on the Mesa microscale polish simulator. The model accurately predicts planarization rate―that is, the polishing of high wafer-surface features relative to low features as a function of critical recipe variables (e.g., polishing time, downforce, and platen speed) and important incoming product characteristics (e.g., prepolish feature height and pattern density). In addition, the model captures the nonlinear dependence of planarization rate on polishing time. The model represents a significant improvement over typical CMP control models, which employ a rudimentary description of polishing rate as constant over polishing time and do not model downforce, platen speed, or critical product characteristics such as feature height and density. The new R2R controller provides an accurate, device-dependent prediction of planarization rate on new products before the first polish. It tracks the state of the CMP tool across recipes with differing downforces and platen speeds, enabling the automated system to update the controller consistently. Moreover, by correctly describing the nonlinear dependence of planarization rate on polishing time, the system can automate the calculation of the polishing time required to rework underpolished wafers.