In this paper, a new approach of LPCVD reactor modelling and control is pre
sented, based on the use of neural networks. We first present the developme
nt of a hybrid networks model of the reactor. The objective is to provide a
simulation model which can be used to compute online the film thickness on
each wafer. In the second section, the thermal control of a LPCVD reactor
is studied The objective is to develop a multivariable controller to contro
l a space- and time-varying temperature profile inside the reactor. A neutr
al network is designed using a methodology based on process inverse dynamic
s modelling. Good control results have been obtained when tracking space-ti
me temperature profiles inside the LPCVD reactor pilot plant. Finally globa
l software is elaborated to achieve film thickness control in an experiment
al LPCVD reactor pilot plant, in order to get a defined and uniform deposit
ion thickness on the wafers all along the reactor. Experimental results are
presented which confirm the efficiency of the optimal control strategy.