Plasma Surface Treatment of GeSn Layers and Its Subsequent Impact on Ni / GeSn Solid-State Reaction

The plasma surface treatment of GeSn layers was monitored by quasi in-situ parallel angle-resolved X-ray photoelectron spectroscopy (pAR-XPS) and atomic force microscopy (AFM). The combination of a wet cleaning and an Ar plasma treatment appeared to be the best compromise to reduce the quantity of native oxides on GeSn surfaces without impacting the surface roughness. In particular, the passivation effect of HCl was particularly beneficial to control the regrowth of oxides at the GeSn surface before the plasma treatment and to obtain a final relative low amount of oxides. The impact of surface treatment on the solid-state reaction between Ni thin films and GeSn layers was also studied. The phase formation sequence was followed by in-situ X-ray diffraction and the morphological and electrical properties were discussed. If the overall phase formation sequence remained the same, the addition of a preclean step prior to metallization influenced the temperatures at which the Ni-rich phase appeared. As far as morphological and electrical properties were concerned, the impact of surface preparation treatments remained moderate, except for HF-treated samples which suffered from an increase of dewetting and Ni(GeSn) film agglomeration phenomena.