Formation of ultra-shallow junction by BF/sub 2//sup +/ implantation and spike annealing

Abstract

Ultra shallow p-type junctions were formed by low energy BF/sub 2//sup +/ implantation and optimized rapid thermal annealing (RTA) at various soak time and temperatures in pure N/sub 2/ 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/spl deg/C/s and 38/spl deg/C/s. The samples implanted BF/sub 2//sup +/ at energy of 2 keV with doses of 6/spl times/10/sup 14/ cm/sup -2/ and 1/spl times/10/sup 15/ cm/sup -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/spl times/10/sup 15/ cm/sup -2/ is higher than one of 6/spl times/10/sup 14/ cm/sup -2/. In the case of 6/spl times/10/sup 14/ cm/sup -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/spl times/10/sup 15/ cm/sup -2/. It is concluded that moderate ramp up rates of spike annealing for low energy and high dose BF/sub 2//sup +/ implant, e.g. 2 keV, 1/spl times/10/sup 15/ cm/sup -2/, can achieve the shallowest junction and lowest sheet resistance.