Oxidation rate reduction in the submicrometer LOCOS process

Experimental and analytical studies on submicrometer LOCOS oxide structures have been carried out. LOCOS oxide thickness reduction in submicrometer nitride windows has been newly observed. However, the bird´s beak length remains constant, in spite of decreasing the nitride window to 0.3 µm. In order to explain these results, a simple oxidation model is experimentally introduced that considers the lateral diffusion of oxidants from the nitride edge. Oxide thickness reduction is due to the decrease of oxidants in the submicrometer nitride window. A locus for the isolation region length in the etched back LOCOS process is also given by using our model. The nitride window sensitivity for LOCOS oxide structures should be considered during the process design for miniature devices with a submicrometer feature size.