NIR diode laser based process control for industrial CVD reactors

Abstract
The proposed new technical approach for CVD 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 a data basis for process control. Diode laser spectroscopy in the near infra red (NIR-DLS) has been successfully applied for monitoring industrial CVD reactors. This technology has some notable potential advantages for production process applications. For example, the technology is robust and simple to operate, interference between species detection can be reduced, and simultaneous multi-point monitoring is readily achieved. The new process control approach is currently being verified on different industrialised CVD coaters. The paper will present some results of recent process monitoring studies on deposition of SnO₂ layers on glass, based on the oxidation of (CH₃)₂SnCl₂, which is used in high volume production for low-E glazings. Kinetic investigations support the empirically determined stiff correlation between gas phase composition and deposition rate.