Surface diagnostics of nanostructured silicon by CF4/H2 plasmas

Nanostructured silicon obtained by a RF CF4/H2 maskless plasma process showed outstanding properties such as reflectance lower than 10% in the visible region as well as in near-IR region. SEM analyses showed a peculiar surface morphology made of irregular trenched texture that can be higher than 400 nm forming light trapping cavities. A selective etching process can be envisaged to explain the above cavities formation. To investigate on it, surface and bulk XPS and SIMS analyses have been carried out on three samples obtained at 100, 200 and 280 W of RF power. Both the techniques showed a C-FX film, typical of such depositions, only for the first 100 nm of the trenches that can support the rationale of the selective etching process. Surface elemental composition is locally assessed by Auger electron micro-spectroscopy.