Local lifetime control in silicon power diode by ion irradiation: introduction and stability of shallow donors

Enhanced formation of shallow donors (SDs) in hydrogen or helium-irradiated and subsequently annealed float-zone n-type silicon is investigated. Ion energies, irradiation fluences and annealing temperatures were chosen in ranges typically used for local lifetime control in silicon power devices. Introduced radiation defects and SDs were investigated by deep-level transient spectroscopy and C-V profiling. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when the annealing temperature exceeds 375degC, i.e. when the majority of vacancy-related recombination centres anneal out. Proton irradiation introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Their concentration linearly increases with proton fluence and changes dramatically during post-irradiation annealing between 100 and 200degC since HD constituents are reacting with radiation damage. Their annealing in this temperature range is influenced by the electric field. If annealing temperature exceeds 400degC, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by TDs enhanced by radiation damage. Shallow doping introduced by both hydrogen and helium can have a detrimental influence on blocking voltage of power diodes if high irradiation fluences or wrong annealing conditions are chosen.