Chapter 7 - Film Thickness

Abstract

The thickness of an individual film, or of a series of many films, represents a dimension that figures in practically all equations used to characterize thin films. The geometrical thickness, often called physical thickness, is defined as the step height between the substrate surface and the film surface. This step height multiplied by the refractive index of the film is termed as the optical thickness and is expressed generally in integer multiples of fractional parts of a desired wavelength. If the density and the optical data of a thin film are known, its mass thickness can be converted into the corresponding geometrical as well as optical thickness. Although film thickness is a length, its measurement cannot be accomplished with conventional methods for length determinations. The great efforts that were made to overcome this problem led to a remarkable number of different, often highly sophisticated, film-thickness measuring methods. Many of the methods cannot be employed for all film substances, and there are various limits to the range of thickness and measuring accuracy. Furthermore, with these methods, the film to be measured is often specially prepared or dissolved during measurement, and therefore it becomes useless for additional investigations or applications.