Optimization of RTA parameters to produce ultra-shallow, highly activated B+, BF 2 + , and As+ ion implanted junctions

The effects of time, temperature, ramp-up, and ramp-down rates with rapid thermal annealing employing a STEAG AST SHS3000 were investigated on 1.0 and 2.0 keV ¹¹B⁺, 2.2, 5.0, and 8.9 keV ⁴⁹BF ₂ ⁺ , and 2 KeV ⁷⁵As⁺, 1E15/cm² samples implanted in a Varian VIISion-80 PLUS ion implanter at 0^o tilt angles. These annealed samples were analyzed by four-point probe, 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 uncontrolled variable, the O₂ background concentration in N₂ was maintained at a controlled low level. Under these conditions, ramp-rates alone were found not to be significant. Spike anneals (1050°C, ～ 0 s) with fast ramp-rates (240°C/s) and fast cool down rates (86°C/s) provided the shallowest junctions, while still yielding good sheet resistance values. Post annealed samples were examined for extended defect levels (by TEM) and trapped interstitial concentrations. Fluorine concentration measurements were employed to qualitatively explain differences in the B diffusion from ¹¹B⁺ and ⁴⁹BF ₂ ⁺ ion implants at various energies. The 2.2 keV ⁴⁹BF ₂ ⁺ “fast” spike annealed sample at 1050°C exhibited limited, if any, enhanced diffusion, yielding a SIMS junction depth of 490Å, an electrical junction of 386Å (by SRP) and a sheet resistance of 406 ohm/sq.