Electrical characterization of polysilicon surface roughness in double polysilicon EPROMS

Data retention in floating gate double-polysilicon erasable programmable read-only memories (EPROMs) strongly depends on the insulating properties of the interpolyoxide layer. The author describes a method for rapid evaluation of the interpolyoxide quality and the surface texture of the underlying polysilicon by simple electrical measurements. First, the electrical conduction mechanism in the interpolyoxide is discussed. A simple quantitative model relating the increased conductivity of polyoxides to the polysilicon surface morphology is presented. The test structures used in this study, the interpolyoxide conductivity measurements, and the proposed characterization technique are described. The results are discussed, and the predicted poly surface roughness is compared to that obtained by transmission electron microscopy (TEM)