CD control sensitivity analysis

This paper presents the cross-machine direction (CD) control capability and sensitivity with respect to the control actuator response uncertainty and mapping errors. Contrary to common belief, the profile spectrum longer than 2-actuator wavelength may not be controllable for certain types of CD processes. If there is actuator response shape uncertainty or mapping error, the control may become unstable. In this case control with even a conservative tuning may not stabilize the process; it only slows down the time to reach instability. Applying robust control without fully understanding the stability requirements compromises the control performance unnecessarily. Several simulations are performed to illustrate the theoretical basis of the results. Finally, a CD control performance assessment tool based on control capability and sensitivity analysis is also briefly discussed and guidelines to robust control design indicated