Annealing Studies on Low Energy As⁺ and As₂ ⁺ Implants

Abstract

2 keV to 10 keV arsenic, As⁺, and arsenic dimer ions, As ₂ ⁺, were implanted into silicon at a dose of le15 cm^-2 and 3e 15 cm^-2 at 0° and 7°' tilt angles. For bare wafers, a low concentration of oxygen is required to provide sufficient capping during anneal to minimize out-diffusion. In the presence of oxygen, enhanced diffusion occurs during the anneal, the extent of which is a function of the concentration of oxygen and the temperature of anneal. The oxidation enhanced diffusion (OED) is significant at anneal temperatures above 1050°C. The extent of OED is observed to be more significant for the samples with lower energy As⁺ implants. An alternative technique for minimizing OED, without much out-diffusion, is the use of higher energy, 5 keV implants through a screen oxide. For identical anneal conditions, 5 keV As⁺ implants through a 40 Å screen oxide offer junction depth and sheet resistance values equivalent to that of 2 keV implants into bare silicon. As the screen oxide is sufficient to cap the out-diffusion of dopants, a nitrogen ambient or a lower temperature could be employed to get shallower junctions without much degradation in the sheet resistance. Further reduction in junction depths can be achieved by using the As ₂ ⁺ implants.