NIR laser diode and FTIR based process control for industrial CVD reactors

Aiming toward process control of industrial high yield/high volume CVD reactors, the potential of optical sensors as a monitoring tool has been explored. The sensors selected are based on both Fourier transform infrared spectroscopy (FTIR) and tuneable diode laser spectroscopy (NIR-DLS). The former has the advantage of wide spectral capability and well-established databases. NIRLD spectroscopy has potentially high sensitivity, laser spatial resolution and the benefits of comparatively easier integration capabilities — including optical fibre compatibility. The proposed technical approach for process control is characterised by a ‘chemistry based’ feedback system with in-situ optical data as input information. The selected optical sensors continuously analyse the gas phase near the surface of the growing layer. The spectroscopic data has been correlated with process performance and layer properties, which, in turn establish data basis for process control. The new process control approach is currently being verified on different industrialised CVD coaters. One of the selected applications deals with the deposition of SnO2 layers on glass based on the oxidation of (CH3)2SnCl2, which is used in high volume production for low-E glazings.