Christoph Doering, Ann-Kathrin Kleinschmidt, Lars Barzen, Henning Fouckhardt, Michael Wahl, Michael Kopnarski

• Reflectance anisotropy spectroscopy (RAS) enables in-situ monitoring of reactive ion etching (RIE) of monocrystalline III-V semiconductor surfaces. This allows for an etch depth control better than 10 nm without any additional etch stop layer. Moreover, RAS permits the investigation of nanoscopic surface modifications during the etch process. Applicability is demonstrated in connection with a realistic semiconductor device fabrication example, i. e. the highly etch depth sensitive manufacturing of a film lens on the waveguide ridge of a broad area laser (BAL).