Evaluating the Effect of Photogeneration Nonuniformity on the Accuracy of Laser Simulation of the Transient Radiation Response in Semiconductor Devices and Circuits

摘要

The effect is investigated of photogeneration nonuniformity, both vertical and horizontal, on the accuracy of laser simulation of the transient radiation response (dose-rate effects) in silicon devices and circuits. It is shown that vertical nonuniformity, due to optical absorption by the substrate, has an insignificant effect if the wavelength is selected to be 1.06-1.08 μm, the first harmonic of a Nd laser. Horizontal nonuniformity, due to the metallization pattern, is shown to disappear on a timescale comparable with the laser pulse width for most practical ICs, as a result of lateral flow of excess carriers by diffusion and drift. When this is the case, the influence of the metallization pattern is found to be fully determined by the area of metallization relative to the overall chip area. Using a diffuser of laser radiation is proposed as a way to reduce this effect. An optical model is developed to calculate equivalent dose for the diffuse radiation. It is demonstrated that this approach indeed alleviates the horizontal nonuniformity of equivalent dose rate related to the metallization pattern. The predictions are verified by experiment.