Hydrogen determination in Si-rich oxide thin films

Quantitative in-depth distribution of the elements contained in silicon-rich oxide thin films deposited on single-crystal silicon by low temperature plasma-assisted deposition has been performed by a combination of various MeV ion beam techniques. The quantity of oxygen and nitrogen has been measured by nuclear reactions, the silicon content has been determined by Rutherford backscattering, and elastic recoil detection was used for hydrogen. All the samples contain not only Si and O, but also N and H, which are residuals from the reactions involved in the deposition process. We did find that the MeV beam used in the nuclear techniques can induce a process of hydrogen desorption, which causes the measured H content to be a function of the He dose received by the sample. This phenomenon, not previously reported, must be taken into account to give the comet H content. The study of the kinetics of the He-induced hydrogen desorption has been used to correct the experimental data and to determine the original hydrogen content. The correction factor is in most of the cases close to 2 and outside any experimental error. Moreover the studies of the kinetics give information on the kinds of hydrogen complexes contained in the films. The results suggest that, on the basis of the strength of the binding energies, hydrogen is present in at least two different configurations, weakly and strongly bonded. In the first configuration hydrogen is easily desorbed either under the action of the ion beam or of the heat treatment at 600 degrees C, in the second, hydrogen is lost only after treatment at 900 degrees C.