The Design Of Atomic Layer Deposition System And Its Temperature Control Research Based On Model Predictive Control

Atomic layer deposition is a nano-thin films fabrication technology, through self-limiting precursor alternately saturated reaction to obtain a controlled thickness and uniform films, which are widely used in microelectronics, solar cells, flexible electronics and other fields. Temperature is one of the most important factors affecting the film deposition and efficiency, while the conventional control methods have poor temperature stability, longer settling time, large temperature fluctuation, in external disturbances. The model predictive control (MPC) could improve transient performance through the optimization and output calibration at external disturbance. Due to its processing delays, capacity constraints and the mathematical models requiring low characteristics, MPC has gotten a lot of successful applications in the industry.In this research, the method of model predictive control is used as the theoretical basis, and the temporal atomic layer deposition (T-ALD) system and spatial atomic layer deposi-tion (S-ALD) system are acted as object of study, and controlling the reaction temperature in two different atomic layer deposition systems as the goal, and improving the efficiency and the quality of thin film deposition. The main works are shown as below,Firstly, based on transfer function, the MPC-based closed-loop control system is estab-lished for T-ALD system, in which the disturbances and constraints have been introduced to meet the command of accurate model and actual condition. Meanwhile the MPC-based closed-loop control system is established for S-ALD systems based on the state space form, in which the optimal control increment is computed via Kalman filter for state observation.Secondly, conductive heating T-ALD system is self-designed, in which a Spectra El-lipsometer is integrated for online-situ measurement of film thickness. On the basis of conductive heating T-ALD system, a radiant heating T-ALD apparatus is proposed. An MPC-based close-loop temperature control system for T-ALD system is established, which has a good stability and strong robustness with the disturbances of gas flow, precursor pulse and sample loading/unloading. Comparing with conventional PID control and open-loop control, MPC-based temperature control system reduces the temperature settling time in the sample loading/unloading disturbance, thereby increasing the efficiency of thin-film depo-sition process. Meanwhile the film has better uniformity and consistency with MPC-based temperature control system.Thirdly, highly efficient T-ALD apparatus is designed with modularized injectors, so as to explore the optimal parameters based on simulations and experiments. An MPC- based close-loop temperature control system for S-ALD reactor is established, which has a good stability and strong robustness with gas flow step disturbance and moving speed disturbance. Comparing with conventional PID control, in MPC-based temperature control system, temperature fluctuations are reduced to 25% and to 14% under substrate moving in depositing binary compound thin films, while the settling times have been saved with 206 % and 186% based on MPC temperature control system when the substrate back and forth switching in depositing nano-laminate.Finally, nano-laminates of ZnO/TiO2 have been deposited by S-ALD technology, in which the XRD spectra suggest peaks of ZnO are weaker with the increase of bilayers' number. Meanwhile the optical experiments of ZnO/TiO2 laminates illustrate the optical transmittance is enhanced and the refractive index gets improved with the increase of the bilayers'number.In this thesis, the vacuum T-ALD and atmosphere S-ALD systems have been developed, in which MPC algorithm has been applied to control the temperature in ALD reactors. While the future work will focus on the design of more efficient and large-scale S-ALD system, and roll-to-roll ALD system for flexible substrate. Besides, MPC will be applied to research the temperature in the responding ALD reactors, and control the gap distance between the injector and substrate.