Numerous significant developments in the semiconductor industry have been achieved in the past 70 years. The capability of exploring and combining different materials and their properties has made many innovative applications possible. Most of these applications require the combination of deposition and subsequent removal of monocrystalline materials on top of a wafer. Due to the nature of the reactive ion etching (RIE) process, unwanted roughness might develop. On the other hand, roughnesses might be desired as effective functional layers. However, controlling the roughnesses of the layers during material removal can be a challenge. With this in mind, the ability to access roughness morphology information during processing is desirable. The significantly higher pressure of reactive ion etching processes when compared to most deposition techniques requires optical methods for monitoring the surface condition. Among the optical measurement techniques, reflectance anisotropy spectroscopy (RAS) stands out. Even small changes to the surface condition can be measured with RAS for the growth and plasma etching of monocrystalline III/V semiconductors. RAS allows for the in-situ and real-time monitoring of roughness evolution upon RIE processes, with the help of valuable statistical tools, i.e., principal component analysis (PCA) and linear discriminant analysis (LDA). This approach enables the distinction of different roughness morphologies and the identification of minor differences in samples of a single roughness morphology.weiterlesen