Positron annihilation spectroscopy as a diagnostic tool for process monitoring of buried oxide layer formation in Si

The sensitivity of positron annihilation spectroscopy (PAS) to process parameters associated with the formation of buried oxide layers in silicon (SIMOX, Separation by IMplantation of OXygen, structures) has been investigated and evaluated. Ion beam current density, implantation temperature, and ion dose and energy were varied over ranges used in standard and low-dose SIMOX formation. Whereas the positron (Doppler broadening) parameter for as-implanted samples was found to have no measurable sensitivity to low-energy ion current density, the results suggest that there is a small dependence on implantation temperature. More significantly, PAS is highly sensitive to ion dose (i.e., to changes in dose of a few percent), and to ion energy. An empirical parameter is proposed as a measure of the former. The results for as-implanted samples suggest that beam-based PAS is an ideal method for improved dose control, particularly during the formation of low-dose SIMOX. Measurements on fully-formed SIMOX samples are also rich in information related to the structure of the samples.