FTIR based process control for industrial reactors

Aiming to process control of industrial high yield / high volume CVD reactors, the potential of Fourier transform infrared spectroscopy (FTIR) has been checked as a monitoring tool. Tin oxide deposition on glass by oxidation of dimethyl tin dichlorid in a cold-wall thermal CVD reactor was selected as test case. Four different FTIR monitoring modes have been evaluated and found feasible: transmission, (gas) emission, reflection and surface emission. The most detailed information of the composition of the gas atmosphere in the deposition zone is derived from the transmission and (gas) emission measurements. The emission mode is best suited for high temperature CVD reactors, needs only low effort for optical adaptation of the monitoring system but higher effort in data treatment for process control. Information on both gas composition and surface layer are derivedfrom the reflection and the surface emission modes. Depending on the polarization state of the surface emission, spectra contain information either on the sample surface only or on the reacting gas phase, too.