Effect of Spin-up Acceleration on Onset of Transient Vortices over Rotating Wafer

The purpose of this study is to make clear the effect of the spin-up acceleration on the boundary layer over the rotating wafer surface. In this paper, onset and breakdown of transient vortices are investigated because transient vortices interfere with the formation of uniform thin film. The air flow fields on the wafer surface are measured by a hot-wire anemometer. The onset of transient vortices over the rotating wafer is detected by the spectra of the tangential fluctuating velocity. It is found that transient vortices appear at higher Reynolds number in the case of higher spin-up acceleration of the wafer. On the other hand, transient vortices break down at a certain Reynolds number and the transition of the boundary layer to the turbulent state is independent of the spin-up acceleration.