Use of multiple analytical techniques to confirm improved optical modeling of SnO2:F films by atomic force microscopy and spectroscopic ellipsometry

Abstract

Variable angle of incidence spectroscopic ellipsometry, reflectance, and transmittance techniques were used to determine the optical constants of a fluorine doped tin oxide film deposited by chemical vapor deposition onto a hot soda-lime-silica glass ribbon. To improve the optical characterization, an additional analytical technique, atomic force microscopy (AFM), was used to incorporate information about surface roughness into the optical model. Our earlier work demonstrated the necessity of including a surface roughness layer as six sublayers in the optical model. The present work further confirms the method and demonstrates its accuracy with additional analytical techniques. These include: (1) cross sectional in-lens field emission scanning electron microscopy to measure total film thickness, determine presence of interface roughness and extent of surface roughness; (2) secondary ion mass spectrometry to give a first approximation of the film layer structure for optical modeling by depth profiling the film composition; (3) Hall measurements to identify the semiconductor carrier density and mobility; (4) x-ray diffraction to identify the crystalline phase and preferential growth orientation. The use of AFM surface images and surface roughness plus the other compositional and structural information to improve ellipsometric modeling of thin films has been confirmed.