Quantification of thin oxid-layers in EPMA

Although the determination of mass thicknesses and depth profiles is a domain of other analytical methods such as secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and ion scattering spectroscopy (ISS) in combination with a sputter process, there are some important advantages of electron probe microanalysis (EPMA). It is a non-destructive method with high lateral resolution which can be used, together with iterative correction software, for thin film determination and even depth profiling. One decisive factor in these algorithms is the depth distribution function f(z) which strongly effects the accuracy of the calculation process. Even for simple bulk samples, f(z) is not exactly known and therefore determined by various fitting functions with more or less sufficient accuracy. However, these models where not designed for multilayer samples or thin films. Although many suited corrections have been published, the so-called "multiple- reflection" model seems to be the most promising correction model which calculates implicitly the depth distribution function using mainly the semi-fundamental parameters such as electron backscattering and transmission coefficients. The angular and energy distribution of backscattered electrons is one of the most sensitive parameter in this model and therefore shall be measured for a number of interesting elements and oxides. Furthermore, these results will be used in a modified multiple-reflection model to improve further investigations on thin films. The results of light element films (oxides) are of great importance for the analysis of corrosion and can be effectively used in the ESEM, because even non-conductive oxides can be measured without the need of coating.

Over the last decades, the technological and industrial progress in the miniature sectors has made the Scanning Electron Microscopy to an irreplaceable analytical measuring method. In order to verify and test constantly changing structures, one has to leave the resolution limit of the light (~ 400 - 800 nm) The Scanning Electron Microscope is able to visualize such small structures (<500nm) and shows even details only a few nanometers in size by using a precise focused electron beam. Besides presenting a highly resolved topography, the integrated X-ray detector also delivers a lateral resolved element analysis. Unfortunately, calculating the exact composition out of the X-ray spectrum only gives limited results. When analysing samples that are heterogeneous within the scatter volume (~m3) (thin Oxidfilms on metal surfaces for example), the used standard algorithms will deliver false results due to the unknown distribution of scattered electrons within the sample. One possibility to calculate the electron distribution for heterogeneous samples is the measurement of the energy- und angle- dependent electron backscatter coefficient and implementing these data into a multi reflexion model. If the Depthdistribution of a thin film system is known and adapted algorithms are used, a quantitative analysis can be formulated. Within this project, a detector was constructed, which enabled the Measurement of the geometric and energetic distribution of the backscattered electrons of various pure element standards. The measurements can be implemented into computer powered algorithms and thus optimize quantitative thin film analysis with Scanning Electron Microscopy.