Optimization of RTA parameters to produce ultra-shallow, highly activated B+, BF2+, and As+ ion implanted junctions

The effects of time, temperature, ramp-up, and ramp-down rates with rapid t hermal annealing employing a STEAG AST SHS3000 were investigated on 1.0 and 2.0 keV B-11(+), 2.2, 5.0, and 8.9 keV (BF2+)-B-49, and 2 keV As-75(+), 1E 15/cm(2) samples implanted in a Varian VIISion-80 PLUS ion implanter at 0 d egrees tilt angles. These annealed samples were analyzed by four-point prob e, secondary ion mass spectrometry (SIMS), and in select cases by spreading resistance profiling (SRP) and transmission electron microscopy (TEM). To ensure reproducibility and to minimize oxidation enhanced diffusion as an u ncontrolled variable, the O-2 background concentration in N-2 was maintaine d at a controlled low level. Under these conditions, ramp-rates alone were found not to be significant. Spike anneals (1050 degrees C, similar to 0 s) with fast ramp-rates (240 degrees C/s) and fast cool down rates (86 degree s C/s) provided the shallowest junctions, while still yielding good sheet r esistance values. Post annealed samples were examined for extended defect l evels (by TEM) and trapped interstitial concentrations. Fluorine concentrat ion measurements were employed to qualitatively explain differences in the B diffusion from B-11(+) and (BF2+)-B-49 ion implants at various energies. The 2.2 keV (BF2+)-B-49 "fast" spike annealed sample at 1050 degrees C exhi bited limited, if any, enhanced diffusion, yielding a SIMS junction depth o f 490 Angstrom, an electrical junction of 386 Angstrom (by SRP) and a sheet resistance of 406 ohm/sq.