Dose rate and thermal budget optimization for ultrashallow junctions formed by low-energy (2–5 keV) ion implantation

Abstract
High implant dose rates and two-step anneals have been used to optimize ultrashallow junctions (∼60 nm) formed by low-energy (2–5 keV) BF2 ion implantation. Variation in junction depth and dopant profile as a function of beam current density (dose rate) and damage/activation anneal is studied. Junction depths and transient enhanced boron diffusion, as seen from secondary ion mass spectroscopy, are reduced for increasing implant dose rate. In addition, transmission electron microscopy images indicate that implantation at a higher dose rate yields lower residual defect levels following anneal. Dependence of sheet resistance on dose rate seems to be a function of the amorphizing nature of the implant. At a dose of 1×1014 cm−2, use of a low-temperature, 600 °C furnace preanneal, prior to a high-temperature rapid thermal anneal, serves to reduce transient enhanced diffusion. At a dose of 1×1015 cm−2, subtle changes in residual damage are observed while no apparent changes in transient enhanced diffusion or sheet resistance are seen.

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