Lifetime effects in ion implanted silicon

Abstract

The damage produced by energetic ions in the space charge region of diffused p⁺n junction diodes is studied. By measuring the diode reverse leakage current, J_r , as a function of the implant parameters (ion mass. energy, post-anneal temperature, etc.) the characteristics of recombination-generation centers introduced by the implant process can be probed. It is these states which strongly affect the operation of lifetime dependent devices. The results can be fit by a single level Shockley-Read-Hall model with the centers lying ∼ 1kT from the centre of the gap. They are seen to be closer to the surface than the L.S.S. range of the implanted carbon ions. Silicon implants have reverse leakage currents which are roughly linearly dependent on dose for low doses while carbon and helium implants have highly super linear dependencies indicating that defects created by separate lighter ions can interact at low doses. The pre-implant reverse leakage current of diodes implanted with 10¹⁵/cm², 300 keV C⁺ can be substantially but not completely recovered after a 75°C anneal.