X-ray characterization of surfaces and laminated materials

In various types of application, precise surface qualities or very small thicknesses are required, and these need to be characterized. In some cases, the surface layer of interest is the first atomic layer and possibly a few deeper ones; this corresponds to thicknesses in the nanometer range. For other applications, the surface layer, interface or underlying multiple layers to be studied are of the order of tens to hundreds of nanometers, or even a few micrometers. At each of these scales, the most appropriate description may be different, and various techniques are specially adapted. But in all cases, from atomic monolayers to multi-micrometer layers, X-rays can provide non-destructive information on both composition and structure.

The topography of a surface, i.e. its variations in three dimensions, is often referred to as roughness when considering short-range defects. To study it, several complementary methods are needed, as we have to look at spatial frequencies from the millimeter down to the tenth of a nanometer. Mechanical and optical profilometers (interferometry, various types of microscopy) have been developed to meet these diverse needs. Electron microscopy has also been used for surface studies. Much more recently, a range of near-field, tunneling, atomic force and magnetic microscopy techniques have been developed.

In fact, in many applications, not only is the surface topography to be described, but also the thickness of a deposited or formed layer, its chemical nature and that of the interface between the surface layer and its substrate. While electrolytic deposition is relatively old, evaporation deposition is more recent and increasingly used. Microelectronics, for example, uses a large number of thin-film materials whose qualities must be strictly controlled. Macroscopic or microscopic testing of electronic component surfaces and interfaces, for example, enables us to characterize the chemical composition of the surfaces or interfaces of etched patterns and semiconductor substrates.