Abstract: An apparatus for use in semiconductor fabrication that includes use of a photo-excitation process and is provided with a revolving gas chamber for forming spiral vortices flow of purge gas located at the upper or side part of a gas reaction chamber, an internal or external light source, a partition having a centrally located circular opening provided between the revolving gas chamber and the gas reaction chamber, or without the partition when the revolving gas chamber is made smaller than the gas reaction chamber. The revolving gas chamber has a multiplicity of gas inlets oriented at an angle with respect to the center of the revolving gas chamber to produce a gas flow in one direction to form spiral vortices that revolves and thereby prevents the light source or light transmitting window from becoming contaminated by process reactions.