On-line control of process uniformity in single wafer processes

摘要

A methodology for on-line process control of uniformity isndeveloped based on the division of process variability into twoncategories: that which can be effectively controlled on-line and thatnwhich must be optimized off-line. This categorization is based on thenphysics of the process and equipment. In the case of axisymmetric singlenwafer processing, the radial uniformity can be controlled on-line, as annumber of process parameters will have a direct influence on the radialnuniformity. However, circumferential uniformity is not directlyninfluenced by any process parameters and must be optimized off-line. Thenchoice of process parameters to effect on-line control is designed tondecouple the successive stages of optimization and control and is guidednby the formulation of appropriate performance metrics. The methodologynpresented simplifies on-line control and recommends a narrower goal fornits implementation, one that can be achieved with minimum risk ofninadvertently degrading the performance of the process. The methodologynis applied to single wafer plasma oxide and polysilicon etchingnprocesses. It is shown that radial uniformity is improved by applyingnon-line control while minimizing the impact on circumferentialnuniformity, with the result that overall uniformity within a wafer isnimproved. The methodology is also successfully applied to effect a stepnchange in the radial profile of etching rate