CATHODOLUMINESCENCE MEASUREMENTS OF SUBOXIDE BAND-TAIL AND SI DANGLING BOND STATES AT ULTRATHIN SI-SIO2 INTERFACES

We have directly observed cathodoluminescence (CL) in ultrahigh vacuum over a broad spectral range (0.7-4.0 eV) from ultrathin 5 nm layers o f remote plasma enhanced chemical vapor deposition grown a-SiO2:H depo sited on silicon substrates. In the infrared regime, luminescence is o bserved at 0.8 eV, consistent with the presence in the as-deposited fi lm of Si dangling bond localized states, as well as at 1.1 eV due to b and edge emission. In the optical regime, three peaks (1.9, 2.7, and 3 .4 eV) are observed showing evidence for band tail state emission from an amorphous silicon-oxygen bonded suboxide region in the film, with; smaller contributions from either substrate related c-Si or defect con taining, stoichiometric SiO2. CL spectra with a range of beam voltages indicate that the stoichiometric SiO2 is very close to the free surfa ce of the film, possibly due to oxidation of the air-exposed wafer or due to a nonuniformity in the film. When the films are annealed in sit u in stages up to 500 degrees C, we observe no change in the shape of the a-SiOx:H peak at 1.9 eV, showing the stability of this suboxide to such temperatures. These observations are consistent with CL measurem ents of thicker films of a-SiO2:H and a-SiOx, and demonstrate the util ity of CL spectroscopy for the study of ultrathin dielectric studies. (C) 1998 American Vacuum Society.