Physical and electrical characterization of a SILO isolation structure

The main drawback of the otherwise attractive sealed interface local oxidation (SILO) technology is the occurrence of dislocations in the substrate beneath the edges of the nitride mask. For the present study, a mask consisting of three layers, namely Si3N4/SiO2/ Si3N4, has been used and the field oxide has been slightly recessed. Both physical and electrical results for SILO structures made by using masks with varying thicknesses of the upper Si3N4layer are presented. Oxidation was carried out in a wet O2ambient at temperatures from 750 to 950°C and pressures of 1 and 20 bar. TEM observations show that association of a thin (< 0.1 µm) upper Si3N4film and high-temperature oxidation significantly improves SILO structures. Oxidation pressure, on the other hand, was found to have no significant effect on the generation of dislocations. In diodes fabricated to determine the influence of dislocations on electrical parameters, high leakage currents were detected. Based on these findings, an improved defect-free SILO structure exhibiting near-zero "bird\´s beak" is proposed for VLSI applications.