Rayleigh light scattering measurements of transient gas temperature in a rapid chemical vapor deposition reactor

A laser-induced Rayleigh light scattering (RLS) system was used to measure transient gas temperatures in a simulated rapid chemical vapor deposition ( RCVD) reactor. The test section geometry was an axisymmetric jet of carrier gas directed down, impinging on a heated wafer surface. RLS was used to me asure instantaneous gas temperature at several locations above the wafer as it was heated from room temperature to 475 K. Gas flow rate and wafer temp erature correspond to jet Reynolds number Re-i=60, wafer maximum Grashof nu mber Gr(H)=4.4X10(6), and maximum mixed convection parameter Gr(H)/Re-i(2) = 1200; all conditions typical of impinging jet reactors common in the nume rical literature. Uncertainty of RLS transient temperature from a propagate d error analysis was +/-2-4 K. Peak gas temperature fluctuations were large (in the order of 25 to 75 degreesC). Both flow visualization and RLS measu rements showed that the flow field was momentum dominated prior to heating initiation, but became unstable by Gr(H)/Re-i(2)=5. It then consisted of bu oyancy-induced plumes and recirculations. Up to the peak wafer temperature, the flow field continued to be highly three-dimensional, unsteady, and dom inated by buoyancy. RLS measurements are shown to provide information on ca rrier gas instantaneous temperature and flow field stability, both critical issues in RCVD processing.