Formation of ultra-shallow junction by BF2+ implantation and spike annealing

Ultra shallow p-type junctions were formed by low energy BF₂ ⁺ implantation and optimized rapid thermal annealing (RTA) at various soak time and temperatures in pure N₂ atmosphere. Especially, the spike annealing was defined as a fraction of a second soak time at the peak temperature. The dependence of junction depth and sheet resistance on ramp-up rate were investigated for rates of 23°C/s and 38°C/s. The samples implanted BF₂⁺ at energy of 2 keV with doses of 6×10¹⁴ cm^-2 and 1×10¹⁵ cm^-2 were annealed. The peak carrier concentration was calculated from sheet resistance and SIMS profile. The carrier concentration depends on the implant dose strongly; the carrier concentration of 1×10¹⁵ cm^-2 is higher than one of 6×10¹⁴ cm ^-2. In the case of 6×10¹⁴ cm^-2 lower thermal budget by decreasing the soak time or increasing the ramp-up rate results in shallower junction depth monotonously. It is observed that junction depth is deeper and peak carrier concentration decreases by decreasing thermal budget with extremely high ramp-up rate of spike annealing at dose of 1×10¹⁵ cm^-2. It is concluded that moderate ramp up rates of spike annealing for low energy and high dose BF₂⁺ implant, e.g. 2 keV, 1×10¹⁵ cm^-2, can achieve the shallowest junction and lowest sheet resistance