Characterization of Thin Films

In the following there is a listing of the physical and analytical methods of thin film characterization being employed by PT&B.

Profilometry :: Film Thickness | Roughness | Stress

By means of profilometers (optical 3D white-light interferometer as well as a stylus instrument) the surface topography of the layers is investigated. The direct measurement of the thickness is possible for films deposited through a mask generating a sharp transition between the uncoated substrate and the layer (a “step”). The surface profile permits the direct computation of roughness. From the bending of specific silicon substrates (“stress bars”) the internal stress of a layer is calculated.

Nanoindenter :: Hardness | Young's Modulus | Elasticity

Measuring the load-dependent penetration depth for a Vickers-type diamond, the mechanical properties of the coatings are determined according to DIN EN ISO 14577-1. For thin films, the typical forces range between some mN and some 10 mN. The typical penetration depth is up to several 100 nm. The main parameters obtained by the nanoidentation are the universal (Martens) hardness, the Vickers hardness, the elastic reduced penetration modulus (which is about the Young's modulus) and the portion of elastic deformation work of the penetrating diamond tip.

Optical Spectrometry :: Refractive Index | Absorption

Optical transmission and reflection spectra are taken in the ultra-violet, visible and near-infrared (UV/VIS/NIR) spectral range. By means of these spectra the index of refraction, the absorption coefficient and the film thickness are determined. Typical substrate materials used for optical investigations are quartz glass, borosilicate glass or plastic foils.

Electrical Measurements :: Specific Resistivity or Conductivity | Dielectric Strength

From current-voltage curves taken for samples of specific geometric shape, their basic electronic properties are determined. For metallic and dielectric films these are usually expressed in term of the specific resistivity. The specific conductivity being the inverse value is preferred for semiconducting films.

XPS and SIMS :: Quantitative Analysis

The chemical composition of a thin film has fundamental influence on its performance. For this reason, the precise knowledge of the elemental composition is of great importance. The x-ray photoelectron spectroscopy (XPS) employs the element-specific electrons, which are generated by x-rays. Secondary ion mass-spectroscopy (SIMS) bases on the detection of ions from a sputter-removal of the thin film. Both technologies of quantitative analysis result in the atomic composition of the film, which is expressed as fraction of atoms of one specific element to the total number of atoms. The unit is referred to as atomic% (abbr. at%).