Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/16470
Title: Multiplexed MPC for mutli-zone thermal processing in semiconductor manufacturing
Authors: ANDREAS
Keywords: Photolithography, Critical Dimension, Thermal Processing, MMPC, MPC, Multiplexed MPC
Issue Date: 29-Jan-2009
Source: ANDREAS (2009-01-29). Multiplexed MPC for mutli-zone thermal processing in semiconductor manufacturing. ScholarBank@NUS Repository.
Abstract: During the last two decades, Model Predictive Control (MPC) has established itself as an important form of advanced control due to its advantages over traditional controllers. MPC outperforms other control strategies through its ability to deal with constraints. Most MPC control schemes for Multi Input Multi Output (MIMO) systems assume all the control variables are updated simultaneously. This result in demanding online optimization, hence computing resource can become an issue when applying MPC to complex systems with fast response times. In a recent work, a variant of MPC which called Multiplexed Model Predictive Control (MMPC) was proposed. The multiplexed MPC scheme solves the MPC problem for each subsystem sequentially, and updates subsystem controls as soon as the solution is available, thus distributing the control moves over a complete update cycle. The resulting computational speed-up allows faster response to disturbances and thus may lead to improved performance in some cases, despite finding sub-optimal solutions to the original problem.In semiconductor manufacturing, photolithography process is regarded as the center and the most important process due to its strong influence on cost and performance of a microchip. The most important variable to be controlled is critical dimension (CD) which is the minimum feature size dimension. One major source of CD variation is the thermal processing in lithography, such as Post-exposure Bake (PEB) and Post-apply Bake. Thermal processing of semiconductor wafers is commonly performed by placement of the wafer on a heated plate for a given period of time. A general requirement for these systems is the ability to reject the load disturbance induced by placement of a cold wafer on the bake plate. We have designed Multiplexed MPC (MMPC) feedback controller for bake plate temperature control and conducted the experiment to show the improvement over standard MPC controller. Since the model is important for MPC controller to work properly, we have done system identification to get proper model. The computational advantage of MMPC becomes more significant when constraints are considered and with increasing number of zones and control horizon.
URI: http://scholarbank.nus.edu.sg/handle/10635/16470
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