MODELING AND IDENTIFICATION OF THE LIQUID ENCAPSULATED CZOCHRALSKI GAAS PROCESS FOR CONTROL

This paper develops an analytic model of the macroscopic dynamics of the liquid encapsulated Czochralski (LEG) GaAs growth process together with a series of system identification experiments that confirm the validity of the model for control system design and analysis. The model combines the meniscus dynamics with a low-order model of the thermal dynamics of the process. The effective heat transfer coefficients used in the model are determined from a steady-state finite-element model of the process. The identification experiments confirm that the model gives accurate predictions of the dominant process dynamics and high frequency phase characteristics. Although the model gain at high frequencies is less accurate, the error can be identified and accommodated in the control system design and analysis process.