Field strength degradation in Si-SiO/SUB 2/-polycrystalline Si structures

The single crystal silicon-silicon dioxide-polycrystalline silicon system has been studied both experimentally and theoretically with respect to dielectric breakdown. Degraded dielectric field strength was measured for structures which had polycrystalline silicon deposited at temperatures in excess of 800°C. The extent of degradation was found to increase with temperatures above 800°C. A mathematical model was developed which allowed calculation of interface stress magnitudes for the structure. Comparison of calculated values of stress in the polycrystalline silicon with known values of yield stress for single crystal silicon at high temperatures indicates that valid dielectric field strength degradation for deposition temperatures in excess of 800°C is most likely due to thermally induced surface irregularities due to plastic deformation of the polycrystalline silicon.