Annealing and Diffusion of Boron in Self-Implanted Silicon by Furnace and Electron Beam Heating

ABSTRACTThe annealing and diffusion behaviour of ion implanted boron over a wide range of doses in as-received and pre-amorphised silicon (180 keV 5 × 1015 cm−2 silicon implants) has been studied using conventional furnace annealing and multiple scan electron beam heating in the rapid isothermal annealing mode. The layers obtained have been characterised using spreading resistance profiling (SRP), SIMS and TEM.For furnace annealing the silicon implantation produces improved electrical activation for boron doses in excess of 1015 cm−2. SIMS and SRP data indicate that a higher level of peak activation has been achieved, whilst the overall amount of redistribution has been restricted. The reduction in diffusion achieved (∼0.2 μm) is greater than the maximum difference attributable to the effect of lower ion channelling for the silicon implanted samples. Cross-sectional TEM has been used to determine the resulting defect structure and provides insight into the details of the stable precipitated boron surface peak observed. A numerical diffusion model has been developed to allow interpretation of these experimental findings.Similar samples have been annealed using multiple scan electron beam heating (peak temperatures up to 1100°C for times up to 300 s). For silicon implanted with boron alone, where cooling commenced once the peak temperature of 1100°C had been reached, diffusion was restricted to 0.05 μm while the sheet resistance (32 Ω/square) was reduced by ∼25% compared to furnace anneals at 950°C. Identical annealing of silicon implanted samples produced improved activation with a sheet resistance of 26 Ω/square. Results from SIMS, SRP and TEM analysis of these experiments are reported.