Nestler Peter, Helm Christiane A
Opt Express. 2017 Oct 30;25(22):27077-27085. doi: 10.1364/OE.25.027077.
Ellipsometric measurements give information on two film properties with high precision, thickness and refractive index. In the simplest case, the substrate is covered with a single homogenous, transparent film. Yet, with ellipsometry, it is only possible to determine the two film properties thickness and refractive simultaneously if the layer thickness exceeds 15 nm - a restriction well known for a century. Here we present a technique to cross this limitation: A series expansion of the ellipsometric ratio ρ to the second order of the layer thickness relative to the wavelength reveals the first and second ellipsometric moment. These moments are properties of the thin film and independent of incident angle. Using both moments and one additional reference measurement enables to determine simultaneously both thickness and refractive index of ultra-thin films down to 5 nm thickness.
椭偏测量能够高精度地给出有关薄膜的两个特性的信息，即厚度和折射率。在最简单的情况下，衬底上覆盖着一层单一的均匀透明薄膜。然而，对于椭偏测量来说，只有当层厚度超过15纳米时，才有可能同时确定薄膜的厚度和折射率这两个特性——这一限制已为人所知达一个世纪之久。在此，我们提出一种突破这一限制的技术：将椭偏比率ρ相对于波长的层厚度展开至二阶的级数展开式，揭示了一阶和二阶椭偏矩。这些矩是薄膜的特性，且与入射角无关。使用这两个矩以及一次额外的参考测量，能够同时确定厚度低至5纳米的超薄薄膜的厚度和折射率。
