Sensor location, identification, and multivariable iterative learning control of an RTP process for maximum uniformity of wafer temperature distribution

Comprehensive study on control system design for an RTP process has been conducted with a purpose to obtain uniform temperature distribution across the wafer surface while precisely tracking the temperature trajectory. The study covers from model development, identification, optimum sensor location, to optimum multivariable iterative learning control (ILC). The highlight of the study is the ILC technique that can steer the process to the minimum achievable tracking error overcoming model uncertainty. The proposed T⁴-based dynamic model was found to be effective in enhancing the control performance. In addition, the optimum selection of a small number of sensors and control strategy under this situation was studied, too. The control system has been implemented and evaluated in commercial as well as experimental equipments fabricating 8-inch wafers.