IMPROVEMENTS IN C-PK USING REAL-TIME FEEDBACK-CONTROL

The usual approach to bring the value of the process capability index, C-pk, to an acceptable level is to design equipment and develop a pro cess in which the process variable is robust to external disturbances, However, an alternative approach involves the use of in situ sensors and real-time feedback control, Currently this approach is not widely implemented in the semiconductor industry, In this paper we provide an alytic justification to quantify the potential improvement in C-pk if a real-time feedback control scheme is used instead of the usual open- loop approach, We show that for the case of feedback control the level of C-pk is only limited by the accuracy and reproducibility of the se nsor provided that the target values are indeed achievable by the proc essing equipment, This result also holds in the presence of disturbanc es and nonlinearities. C-pk values for open-loop and real-time feedbac k control strategies are compared for two experimental applications: s ingle-wafer CVD nitride and polysilicon processes.