Ellipsometric Study of Nanostructured Silicon Materials

Abstract

The incredible development in miniaturization of the last century has lead us today to the domain of nanotechnology. These miniaturization steps to obtain smaller, faster, lighter, denser, and cheaper devices are closely interweaved with the advancement attained in characterization techniques. The ellipsometric technique has followed such a path, with most ellipsometers today being spectroscopic. Ellipsometry is an optical method based on the measurement of the change of polarization upon reflection from, or transmission through a sample. By measuring the polarization change, we obtain not only amplitude, but also phase information of the light interacting with the sample. This remarkable property enables an incredible sensitivity to the properties of thin layers, with a sub-nanometer precision, hence valued in industrial processes as an ex situ feedback between process steps with more and more demand for even in situ measurements. Being an optical technique, spectroscopic ellipsometry (SE) is non-destructive with relatively fast measurements compared to other probing methods. However, it is an indirect technique, meaning that any information on the sample is obtained through the modelling and inversion of the ellipsometric response, often through simulation and iterative fitting. In electronics miniaturization, silicon-based semiconductor technology is approaching its theoretical limits, but silicon industry has grown to such an extent, that it would be hard to imagine the near future without the basic building block of monocrystalline silicon (c-Si). Many different c-Si based nanostructures have emerged in the last two to three decades, that are finding (potential) applications, but industrial ellipsometric characterizations remains limited because the development of highly complex optical models is challenging and often limited to academic research. In my thesis, I aim to show the versatility of SE characterization for some c-Si-based nanostructured materials. I not only wish to increase the understanding of the fundamental properties and formation mechanisms of these materials but also hope to boost their spreading for industrial productions in any modest way by the development of ellipsometric models.