Transient Scanning Electron Beam Annealing Methods Used to Study Diffusion and Defects in Implanted Silicon

Abstract

AbstractRapid thermal annealing of arsenic and boron difluoride implants, such as those used for source/drain regions in CMOS, has been carried out using a scanning electron beam annealer, as part of a study of transient diffusion effects. Three types of e-beam anneal have been performed, with peak temperatures in the range 900-1200°C; the normal isothermal e-beam anneals, together with sub-second fast anneals and ‘dual-pulse’ anneals, in which the sample undergoes an isothermal pre-anneal followed by rapid heating to the required anneal temperature in less than O.5s.The diffusion occuring during these anneal cycles has been modelled using SPS−1D, an implant and diffusion modelling program developed by one of the authors. This has been modified to incorporate simulated temperature vs. time cycles for the anneals. Results are presented applying the usual equilibrium clustering model, a transient point-defect enhancement to the diffusivity proposed recently by Fair and a new dynamic clustering model for arsenic. Good agreement with SIMS measurements is obtained using the dynamic clustering model, without recourse to a transient defect model.Defects remaining in diodes fabricated with the forementioned implants after these anneal cycles have been studied using DLTS techniques. Trap densities for the three types of e-beam anneal are comparable to those for furnace annealed diodes, as are the reverse leakage currents measured (typically 2–5nA for a 0.85mm2 diode at -5V).