Roughness measurements of Si and Al by variable angle spectroscopic ellipsometry.

Rough surfaces of silicon and aluminum have been studied by rotating analyzer spectroscopic ellipsometry (RASE). The roughness of a silicon sample similar to that used for the RASE measurements was also studied by cross-sectional transmission electron microscopy. Total integrated scattering was measured on the aluminum specimens to obtain numerical estimates of the rms roughness. The ellipsometry measurements on these specimens were carried out at a number of angles of incidence in the 30-80 degrees range and at a number of discrete wavelengths in the 300-650-nm spectral range. The RASE results were hen analyzed using the Bruggeman effective-medium theory for the Si sample and scalar diffraction theory for the Al samples. This study shows that 70 degrees is the optimum angle of incidence for characterizing the roughness of these Al surfaces using RASE. It also demonstrates the self-consistency of the Bruggeman theory with angular variation for the Si sample. The need for a vector diffraction theory for the retation of the rms roughness using ellipsometric angles Delta and Psi is discussed.

Measurement of the thickness of the surface layer on amorphous Ge films using spectroscopic ellipsometry: validity of effective medium modeling.

Amorphous Ge films prepared using rf-diode sputtering were exposed to air for periods from 15 min to several days. These samples were placed in a windowless cell in which an Ar gas flow was maintained and spectroscopic ellipsometry measurements were performed. The surface of each sample was then rinsed with deionized water and in situ measurements obtained. Differences were interpreted as resulting from partial or complete removal of the layer that formed from air exposure. Changes in the thickness of this layer were determined using (i) effective medium modeling and (ii) the exact equations of ellipsometry. Within the limits for each method, the thickness values are identical.