ATOMIC-HYDROGEN-INDUCED DESORPTION OF FLUORINE FROM SILICON SURFACES

Extraction of fluorine adsorbates on silicon surfaces is induced by exposure to atomic hydrogen. The decay process of fluorine has been investigated with Auger electron microscopy and is discussed in terms of chemical kinetics. The desorption rate depends on the hydrogen exposure time, the substrate temperature, and the supply of atomic hydrogen. In the initial stage, the reaction proceeds with second-order kinetics with an activation energy of about 0.4 eV. Moreover, two hydrogen atoms seem to take part in the reaction at the same time, according to the rate dependence on the supply of atomic hydrogen. With the decrease of the fluorine coverage, a first-order process dominates the reaction, and its activation energy is about 0.56 eV. The fluorine adsorbates on silicon are completely removed by annealing above 200-degrees-C for 30 min, using the atomic hydrogen.