Abstract:

For lasers used in the computer chip etching process, laser performance, as measured by uniformity in the energy output for etching, is affected by the density of the chamber gas at the laser electrode. The laser produces longitudinal shock waves that propagate transverse acoustic pulses. Acoustic modes of the gas within the laser chamber respond to these pulses and can create a resonant response resulting in a very nonuniform energy output of the laser. These phenomena have been studied using finite-element (FEM) and boundary-element (BEM) methods to model the laser chamber and to predict the forced response. The effectiveness of these two approaches is compared. Accuracy, computing efficiency, and ease of modeling have been considered. The challenge that is addressed is the representation of the internal structure within the chamber. The baffling effects of the internal structure provide the means to shape the response either exaggerating or attenuating the resonance. BEM and FEM methods are explored as design tools to predict the response and achieve the desired uniformity of pressure and density.