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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 measure instantaneous gas temperature at several locations above the wafer as it was heated from room temperature to 475 K. Gas flow rate and wafer temperature correspond to jet Reynolds number Rei=60, wafer maximum Grashof number GrH=4.4×106, and maximum mixed convection parameter GrH/Rei2=1200; all conditions typical of impinging jet reactors common in the numerical literature. Uncertainty of RLS transient temperature from a propagated error analysis was ±2–4 K. Peak gas temperature fluctuations were large (in the order of 25 to 75 °C). Both flow visualization and RLS measurements showed that the flow field was momentum dominated prior to heating initiation, but became unstable by GrH/Rei2=5. It then consisted of buoyancy-induced plumes and recirculations. Up to the peak wafer temperature, the flow field continued to be highly three-dimensional, unsteady, and dominated by buoyancy. RLS measurements are shown to provide information on carrier gas instantaneous temperature and flow field stability, both critical issues in RCVD processing. [S0022-1481(00)02401-4]

A laser-induced Rayleigh light-scattering (RLS) system was assembled and used to noninvasively measure the transient molecular number density in an ideal gas. This information was used to find the transient gas temperature when operating at known pressure. The laser was a 4 W argon ion operating on all lines at a total power of about 2.5 W. The theoretically predicted photon arrival rate at the photomultiplier tube detector was calculated and compared well with the observed photon rates. These rates were high enough that sampling could be averaged over a 1 s period with theoretical uncertainty due to electronic shot noise below 0.1%, and below 2% for a 0.001 s averaging time. A propagated error analysis showed uncertainty in the transient temperature due to all sources was 2–4 K. The RLS system was used to record transient air temperature at several locations above a flat plate during heating from room temperature to 475 K. Results showed buoyancy-induced fluctuations of about 3 Hz, and instabilities in temperature in addition to the overall temperature rise due to plate heating. Excellent transient temperature records were obtained, substantiating the predicted 2–4 K uncertainty.

Instantaneous transient gas temperatures were measured in a simulated rapid thermal chemical vapor deposition (RTCVD) reactor. The gas flow consists of an axisymmetric jet impinging on a heated wafer. The jet momentum is opposed by buoyancy from the heated surface. Temperatures were found non-invasively by laser induced Rayleigh light scattering (RLS). A RLS diagnostic system measures temperature by sensing intensity of light scattered from a control volume. Intensity is related to gas molecular number density, and thus temperature can be found from the ideal gas law. The RLS system was calibrated first with measurements in the potential core of a heated jet, and then in the RTCVD test section operating at ambient temperature but reduced pressure. In both cases, the measured intensity of Rayleigh scattered light had low uncertainty. Measured molecular number density corresponded well with that theoretically predicted from the ideal gas law. Transient temperature measurements were then recorded at several radial locations above the wafer surface as it was heated from ambient temperature to 200°C. Operating conditions consisted of Reynolds number Re, = 60, maximum Grashof number GrH = 4.4 × 106, and maximum mixed convection parameter GrH/Rei2 = 1200. Uncertainty of mean transient temperature was ±2°, while temperature fluctuations were large (T′ ∼ 50°C). Both flow visualization and temperature measurements showed that the flow field consisted of buoyancy dominated recirculations, and was highly three dimensional.