Transient dynamics and control of indium phosphide LEC furnaces

A transient 1D model was developed for simulating the dynamics of Liquid en capsulated Czochralski (LEC) growth processes. The model considers a melt-s olid flat interface and a uniform temperature within the four phases (i.e., air, melt, solid and encapsulant) and predicts the crystal shape evolution during growth given the time histories of the heater temperature and of th e pull rate. The model predictions were satisfactorily compared with experi mental InP LEC dynamic growth data. Then, a feedback-feedforward control al gorithm effective to achieve a cylindrical growth of single crystals in LEC systems was developed. In particular, the model to be used in the feedforw ard step was derived linearizing the above dynamic model. The controller ke eps the crystal radius constant by acting on the heater, taking as input va riables heater and air temperature, crystal weight, seed and crucible posit ion. Controller performances have been tested on a transient model of LEC p rocess as controlled system. (C) 2000 Elsevier Science S.A. All rights rese rved.