ESDIAD STUDIES OF FLUORINE AND CHLORINE ADSORPTION AT SI(100)

Electron stimulated desorption ion angular distribution (ESDIAD) patte rns are reported for fluorine and chlorine adsorbed at the silicon (10 0) surface. Analytical and numerical methods of establishing the degre e of angular compression imposed by the sample bias frequently employe d in ESDLAD measurements, are described. Measurements of the two halog en adsorbates contrast strongly, particularly with regard to their res ponse to annealing in the temperature range 300 to 1000 K. In the case of F+ desorption, a minimum in ion intensity occurs along the surface normal. Maxima in the ion production are observed at a polar angle of approximately 30-degrees, and in registry with the principal crystal axes as reported by other workers. Cl+ ion angular distributions howev er, indicate a mixture of normal and off-normal emission for adsorptio n at less-than-or-equal-to 300 K. This pattern transforms, irreversibl y, to a single maximum directed along the surface normal in response t o annealing to approximately 650 K. The transformation is linked to th e thermal depopulation of one adsorption state, leaving a higher bindi ng energy state intact.