INSITU MEASUREMENTS OF HYDROGEN MOTION AND BONDING IN SILICON

Hydrogenation of both n- and p-type metal/thin oxide/silicon diodes has been studied using high frequency capacitance profiling. In situ observations of donor and acceptor passivation were made while H ions were implanted through thin gate metallizations at various energies and fluxes. TRIM code simulations of the implantation process as well as studies of the energy, dose, and flux dependence of capacitance data lead us to conclude that irradiation of 400 Å Al gated diodes with 800-1400 eV H ions rapidly establishes a time-independent near-surface H concentration which is proportional to both the ion flux and the implantation depth, and inversely proportional to the hydrogen diffusivity. While direct measurement of ion transits at a variety of electric fields establish that a unique mobility can be assigned to positive H ions, modeling of low and high field data in both n- and p-type samples is consistent with the notion that the positive charge state is occupied only 1/10 of the time. The time dependence of hydrogen penetration for both n- and p-type diodes indicates that hydrogen is, in addition to being trapped at unpassivated shallow donors or acceptors, becoming immobilized at other sites in silicon. The density of these secondary trapping sites correlates well with the shallow dopant population, suggesting that additional hydrogen may become trapped near already-passivated dopant atoms.