A comparative study of dopant activation in boron, BF/sub 2/, arsenic, and phosphorus implanted silicon

Abstract

Ultra-low energy implants were used in combination with rapid thermal anneals in the temperature range 900/spl deg/C-1050/spl deg/C to study dopant activation in silicon. First, relatively long time anneals were performed in a conventional tungsten-based RTA to investigate the activation mechanisms. The activation was monitored using Hall measurement, where the rate of electrical activation was considered by measuring the time it takes to reach 50% activation. Using Arrhenius fits, an activation energy was extracted, and it was found that while boron has a mean activation energy for electrical activation of 4.7 eV in agreement with previous studies, arsenic and phosphorus have thermal activation energies of 3.6 eV and 4.1 eV, respectively. The 4.7 eV activation energy for boron is believed to be related to a point defect driven mechanism for electrical activation. Electrical activation of arsenic and phosphorus, however, seems to be related to dopant diffusion. In the second set of experiments, an arc lamp system was utilized to perform ultra-sharp spike anneals. For both dopants, it was found that for a given temperature, there is an optimum ramp-rate that produces the desired dopant activation and junction depth.