Infrared multiple internal reflection (MIR) spectroscopy has been applied here to the characterization (ex situ) of thin amorphous silicon layers on crystalline silicon substrates. The specimens are tightly clamped against a Ge prism with 45°bevel angle for the entrance and exit sides, allowing for up to 25 multiple internal reflections. This greatly enhances the thin-film absorption, and the stretching bands of SiHn bonds in amorphous Si are detected in a range of film thickness from 3 to 600 nm. Very thin films (with thickness less than 50 nm) exhibit a different hydrogen bonding compared to the thin ones, due to hydrogenated sublayers that are not visible in IR spectra for larger film thickness. Sublayers are found both at the film/substrate interface and at the film free surface. Another transitional layer, with increased concentration of SiH2 groups and considerably less than 30 nm, is found at the film/substrate interface. MIR is also applied to study the step-by-step etching in CF4/O2 of a 70-nm-thick amorphous silicon layer. This experiment is able to define the location of the sublayers. © 1995 American Institute of Physics.

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