Quantitative measurement of film thickness, density and stoichiometry of multilayer thin films on thick substrates

Abstract

The analysis of multilayer thin films on thick substrates such as glass or plastics has been difficult to achieve with any accuracy or confidence. At Donnelly Corporation, a number of different multilayer thin film stacks are produced by a variety of methods (sputtering, e-beam, etc.). A knowledge of the physical properties of these films is essential. Film thicknesses typically vary from 10 to 400 nm and are measured by a mechanical surface profiling technique. The structure, density, and stoichiometry of the films are determined by a combination of Rutherford backscattering (RBS) and proton induced X-ray emission (PIXE) experiments. Exact RBS analysis techniques have been developed which, when combined with other analytical tools, have allowed thin film physical properties to be determined quantitatively. One key to this process is the multiple determination of energy loss in a given layer through the multilayer stack. In addition, for any given layer of a metal oxide, e.g., Ta₂O₅, the energy loss of the film constituents, which is proportional to the thickness of the film, is reflected by the width of the tantalum peak in the backscattered spectrum. The integrated area of the tantalum peak, however, is proportional to the tantalum content in the film, leading to a measurement of the film stoichiometry. A strong confidence has been developed in these techniques, since on a variety of standard thin film stacks, the results compare favorably with known values.