Hierarchical feedback control of pulsed laser deposition

Abstract

A hierarchical control PLD system controls deposition processes by feedback means, for industrial production of tribological thin films. PLD process system identification, intelligent feedback control architecture, and implementation for ultraviolet pulsed laser deposition processes are provided. This system has three levels of feedback control. The first level of feedback control improves the precision and tracking of sub process variables by linear observer based compensator control. The Mo I plume species density per laser pulse and bulk substrate thickness by the quartz crystal micro balance provide real time sub process data to the observer. The observer based compensator then directly calculates laser energy density per pulse and pulse repetition rate based on the current values predicted by the linear model. The second level consists of a dynamical system design algorithm and nonlinear process map. The nonlinear mapping is used to design a new observer based compensator for each linearization point chosen by the third level of control. The third level features an expert system rulebase and command inputs to achieve a desired product goal. The expert controller decides whether or not the process linearized model used by the first level of control is accurate enough to achieve the desired process goals. Based on controller-process performance, a controller re-design is commanded by the third level to the second level, and then implemented by the first level.