In-situ etch depth control with precision around 1 nm via reflectance anisotropy spectroscopy during reactive ion etching of monocrystalline III/V semiconductors

本课题旨在提高反应离子等离子体干刻蚀过程中原位刻蚀深度控制的精度。应采用三种方法。第一个概念（对于普通RIE蚀刻速率为100 nm/min的情况）使用法布里-珀罗振荡，即与蚀刻相关的层厚度收缩的层反射率的周期性变化。振荡将在两个光子能量相差1/10的情况下同时观察到。这与滑动卡尺游标刻度的使用有关。在蚀刻深度测定精度1-2纳米应该是可能的。如果在蚀刻过程中不能足够快地收集和使用RAS数据，可能会出现一个问题。然后蚀刻速率必须降低，例如通过降低离子能量。第二种方法是利用RAS信号的周期性变化，一层一层地变化。这种效应是从外延学中得知的。但是，在干式蚀刻过程中，在不太大的蚀刻速率下，提议者的团队已经看到了平均反射率的振荡。它们在这里被称为单层振荡，以区别于第一种方法的法布里-佩罗振荡。如果第二个概念要工作，最好的精度蚀刻深度的确定将达到，即一个单一的单层。但是，第二种方法的最佳结果只有在蚀刻速率低于通常（如50-100 nm/min）时才会出现。第三个概念是由实践提供的。可以使用RAS信号的差异或由于不同层掺杂的差异而引起的变化。掺杂在光电层序中是很常见的。蚀刻通常要在两层之间的交界处停止。团队的第一个结果将在项目期间进行扩展。问题是：在什么情况下（层和蚀刻参数）可以区分p掺杂和n掺杂？甚至可以从信号中提取兴奋剂水平吗？如果是，精确到什么程度？这些结果可以在线（蚀刻期间）使用吗？数据收集和计算次数是否足够小？

The aim of this project is the improvement of the precision of in-situ etch depth control during reactive ion plasma dry-etching. Three approaches shall be employed.The first concept (for the case of common RIE etch rates of a couple of 100 nm/min) uses Fabry-Perot oscillations, i. e. periodic changes of the reflectivity of a layer for etch-related shrinking layer thickness. The oscillations are to be observed simultaneously at two different photon energies, which differ by 1/10. This relates to the use of a vernier scale of a sliding caliper. Precision of 1-2 nm in etch depth determination should be possible this way. One problem might occur, if the RAS data could not be collected and used fast enough during the etch process. Then the etch rate would have to be reduced, e. g. by reduction of the ion energy. The second approach is going to use periodic changes of the RAS signal with changes monolayer by monolayer. This effect is known from epitaxy. But the proposer-s team has already seen such oscillations in the average reflectivity for not too large etch rates during GaAs dry-etching. They are to be called monolayer oscillations here, in order to distinguish them from the Fabry-Perot oscillations of the first approach. If the second concept was going to work, the best possible precision in etch depth determination would be reached, i. e. a single monolayer. But optimal results for the second approach are only to be expected for etch rates lower than usual (like 50-100 nm/min). A third concept is offered by praxis. Discrepancies in the RAS signal or variations due to differences in doping of different layers can be used. Dopings are common in optoelectronic layer sequences. And oftentimes etching is to be stopped exactly at an interface between two layers. First results of the team are going to be extended during the project. Questions are: Under which circumstances (layer and etch parameters) can p- and n-dopings be distinguished? Can even the doping level be extracted from the signal? If so, with which precision? Can these results be used on-line (during etching)? Are data collection and calculation times small enough?