Electron-stimulated desorption (ESD) was used to study the hydrogen present on cleaned and oxidized Si(100). Cleaning the surface by ion bombardment and annealing does not completely remove hydrogen from a Si(100) surface. Kinetic energy analysis of the hydrogen ions emitted through ESD shows that multiple states of adsorbed hydrogen are present. Electron beam exposure results in a depopulation of higher energy states. These states are repopulated upon annealing suggesting that the bulk silicon is a source of hydrogen. Oxygen exposure also results in a depopulation of the higher energy desorption states. Angle-resolved, energy-resolved ESD spectra of H + from the cleaned Si(100) surface were also collected. They show that different hydrogen bonding states desorb at different angles relative to the surface plane with differing energy distributions.
INTRODUCTIONAn understanding of the interaction between hydrogen and semiconductors has both technological and scientific importance. Hydrogen has been shown to reduce electrical activity in silicon,'-" germanium and gallium arsenide.' 3 -' 7 For example, Benton et al.' achieved hydrogen passivation of electrically active defects created during laser annealing of crystalline silicon by exposure to atomic hydrogen in a hydrogen plasma. Pearton and Tavendale3 showed that both the deep donor and acceptor levels associated with gold are passivated by exposing silicon samples to a hydrogen plasma. Mechanisms responsible for hydrogen passivation in silicon have been proposed by a number of In addition to the interest in the passivation effects of hydrogen, the interaction of hydrogen and silicon has been studied in order to gain a better understanding of the surface geometry of reconstructed clean silicon surface^.^'--^ The ease with which hydrogen induces surface reconstructions on the low-index planes of silicon has been used to evaluate the various models for reconstruction of the clean surface. For example, Nortonz4 found that changes in the diffraction pattern induced by adsorption of hydrogen on Si(OO1) are consistent with the asymmetric dimer model as opposed to the symmetric dimer model. Numerous calculations of surface electronic properties have also been carried out for both clean and hydrogen-exposed silicon surfaces, 2 1 I 2 6-34 and a variety of experimental studies of the silicon/hydrogen system have been performed, 20.2 3,2 5.3 5-60 Th ese studies show that several surface species (including mono-, di-and trihydrides) can exist depending upon sample history and exposure conditions.Relatively few surface analytical techniques detect hydrogen directly due to its light mass, small cross- section for many processes and lack of core-level electrons. However, electron-stimulated desorption (ESD) is highly sensitive to hydrogen because it is a mass spectrometric technique. ESD is powerful in that it can yield information on surface bonding structure and/or mechanisms of excitation and desorption. Few ESD studies of the silicon/hydrogen system have been published. Ma...
