Vacancy enhanced boron activation during room temperature implantation and low temperature annealing

Low temperature annealing combined with pre-damage (or pre-amorphization) implantation is a very promising method to overcome the activation barrier in ultra-shallow junction formation. We have made a 32 nm p⁺/n junction with sheet resistance of 290 Ω/sq. using 20 keV 4×10¹⁴ at./cm² Si followed by 2 keV 1×10¹⁵ at./cm² B implantation and 10 minutes 550°C annealing. This paper studies the boron activation mechanism during low temperature annealing. The result shows that placing B profile in the vacancy-rich region has much better boron activation than placing B profile in interstitial-rich region or without pre-damage. It also shows that a significant portion of boron is in substitutional positions before annealing. The amount of substitutional boron is correlated to the amount of vacancies (damage) by the pre-damage Si implantation. The result supports our speculation that vacancy enhances boron activation.