Post BF/sub 2//sup +/ implant annealing using single wafer rapid thermal furnace

Abstract

49BF2 + implanted wafers were annealed in the temperature range of 900degC and 1100degC using a single wafer rapid thermal furnace for 30 sec to 1800 sec under N2 ambient at atmospheric pressure. Sheet resistance and its uniformity were measured. Boron and fluorine depth profiles at different annealing temperatures and times were analyzed using secondary ion mass spectroscopy (SIMS). The minimum sheet resistance of 67.46 Omega/sq. with a uniformity of 0.57% (1sigma) was achieved at 1000degC for 90 s annealing time. Good uniformity with good productivity was attained with the sheet resistance decreasing as annealing temperature and time increased. Boron moved toward the silicon surface during annealing as was observed through SIMS analysis and fluorine desorption was enhanced with increasing annealing temperature and time. The electrically activated dopant concentration was calculated by evaluation of the sheet resistance and the junction depth estimated from SIMS depth profile. The concentration was on the order of 1020 atoms/cm3 regardless of annealing temperature and was closer to the solid solubility of boron in silicon as reported in the past. It is recommended that the appropriate dosage and implant energy should be selected in order to prevent inactive dopant existence and unnecessary diffusion due to an unnecessarily high gradient of dopant concentration