THERMOMETRY OF GAS LAYERS IN THERMAL PLASMA CVD BY PULSED-LASER RAYLEIGH-SCATTERING

The application of Pulsed-Laser Rayleigh Scattering Thermometry (PLRST ) to Chemical Vapor Deposition (CVD) processing of diamond films in a thermal induction plasma is demonstrated. Temperature profiles were me asured in the reactive thermal boundary layer, characteristic features of which are a steep temperature gradient and strong chemical non-equ ilibrium. The temperature in the layer varies between 5000 and 1000 de grees C. The stray light rejection problem typical for Rayleigh scatte ring measurements was solved successfully. In the plasma core, where a tomic emission spectroscopy can be applied to temperature measurement, agreement has been obtained between plasma temperatures measured by e mission spectroscopy and PLRST. In the boundary layer both point-by-po int measurements and laser sheet measurements were made and adequate a greement was obtained. Technical reasons for observed variations were identified. It is concluded that PLRS is a viable non-invasive thermom eter for thin reactive gas layers typical or various CVD deposition pr ocesses and technical improvements are suggested.