Abstract
At ASML, engineers are driven to make technological advancements in lithographic scanner systems to increase the performance of the manufactured chips. One of the factors the performance of these chips depends on, is the combined error or the synchronization error of the reticle and the wafer stage.Bi-directional Feed-through (bi-Ft) controllers are introduced in the control system of these stages to synchronize the stage errors and achieve increased performance beyond the performance of the individual stages. One of the problems with the bi-Ft is the robust stability analysis. That is, adding the bi-Ft the open-loop matrix of the system becomes full, which resulted in the loss of its nominal robust stability properties. This made the overall system stability very vulnerable in presence of plant uncertainty and interactions. Robust stability of the wafer scanner system with bi-Ft has been studied using a double-
Youla parameterization approach of plant and controller. A modified robust stability criterion has been derived based on this approach. Furthermore, the extent of conservatism in the criterion has been analyzed and compared to existing robust stability criteria. The new modified criterion was concluded
to give the least conservative robust stability margins. The robust stability approach studied has been implemented on the NXT3 OFP1 system to robustly stabilize it using its FRFs measurements. Feedthrough Factors for a system with bi-Ft, which are its performance measurement, are derived through a universal definition. Also, tuning bi-Ft controllers can result in a system with open-loop RHP poles, which puts the system under additional design constraints. Hence, guidelines are derived to prevent suchpoles during tuning.
| Date of Award | 14 Dec 2021 |
|---|---|
| Original language | English |
| Supervisor | Marcel F. Heertjes (Supervisor 1) & Bas Roset (External coach) |