Electrical measurement of the lattice damage induced by a-particle implantation in silicon

Recent studies suggest that lattice damage induced by helium or proton ion implantation can be used to control the electrical behavior of bipolar semiconductor devices, such damage directly affecting the mean time (lifetime) of electrons and holes over and above their equilibrium values. However, a lack of knowledge exists regarding the nature of the defects produced by ion implantation, in particular, their stability with time and temperature and effectiveness in controlling recombination processes. In this paper we have reconstructed and characterized the damage profile induced by helium implantation in silicon by making direct measurements of the lifetime profile made on specially fabricated test devices. Results show that the shape of the defect profile differs from that predicted by Monte Carlo simulations. Also, a considerable increase in the resistivity of the layer, not expected with He implantation, has been found. Finally, energy levels affecting the recombination of minority carriers have been given.