MODELING OF SURFACE-ROUGHNESS IN VARIABLE-ANGLE SPECTROSCOPIC ELLIPSOMETRY, USING NUMERICAL PROCESSING OF ATOMIC-FORCE MICROSCOPY IMAGES

Variable-angle spectroscopic ellipsometry is used for ex situ investig ation of thin films deposited on substrates. Calculation of the thickn ess and optical properties of a number of films in a multilayer stack is possible, because a large amount of data is taken over a wide range of wavelengths and incidence angles. However, the authors here confir m that significant surface roughness of the outermost film must be tak en into acount for useful solutions. In our earlier work, the roughnes s was modelled as a single roughness layer at the film ambient interfa ce. This layer was taken to be an effective medium, composed of film a nd voids. The thickness and void fraction were determined from atomic force microscopy (AFM) measurements. Improvement in ellipsometry solut ions has been achieved using a new model of the roughness layer compos ed of six effective medium sublayers. Numerical processing of AFM data is described, considering suface scans ranging from 1 mu m x 1 mu m t o 12 mu m x 12 mu m. The complete deposited film was best modelled as a rough surface layer (70 nm thick) over a continuous layer 350 nm thi ck.