The role of extended defects on the formation of ultra-shallow junctions in ion implanted 11B+, 49BF 2, 75As+ and 31P+

Ion implants of ¹¹B⁺ (0.25 keV to 2.0 keV), ⁴⁹BF₂⁺ (1.1 keV to 8.9 keV), 75As⁺ (2.0 keV to 5.0 keV); and ³¹P⁺ (1.0 keV to 5.0 keV) at a dose of 1e15/cm² were investigated by TEM to determine defect type and concentrations after a 750°C, 15 min furnace baseline anneal and then after rapid thermal annealing (RTA) using “slow” and “fast” spike anneals (<0.1 s) at 1050°C. Trapped interstitial densities were calculated from the measured defect concentration, type and size and are compared to the observed changes in junction depth. The effect of the changing trapped interstitial densities on transient enhanced diffusion (TED) for various B and BF₂ implants are discussed. In the case of BF₂ , the combined effect associated with the trapped interstitial density and the residual fluorine level is also discussed. To minimize all other diffusion effects such as oxidation enhanced diffusion (OED), oxygen related diffusion effects and thermal diffusion effects, the B and BF₂ comparison was conducted on wafers which were “spike” annealed in an ambient of 33 ppm O₂ in N ₂. For all species a defect free energy threshold is identified where, after the 750°C, 15 min (and confirmed at 600°C to 800°C) furnace base-line anneal, no extended-defects or loops formed (i.e. <1e7/cm²). Implants below this threshold allow complete freedom in the choice of RTA conditions to minimize desired sheet resistance and junction depth values without the concern of post-RTA trapped interstitials which could enhance the dopant diffusion during subsequent post-implant processing steps, and for concerns of enhanced leakage current resulting from end-of-range (EOR) damage. Examples of how “spike” anneals in low ppm O₂ in N₂ ambients on implants below this energy threshold can be employed to optimize sheet resistance (R₅) and junction depth (X_j) are presented for: ⁴⁹BF₂ at 2.2 keV (R₅ of 406 Ohms/sq., electrical X_j of 386 Å); ⁴⁹BF₂ at 1.1 keV (R₅ of 669 Ohms/sq., electrical X_j of 234 Å); and 0.25 keV ¹¹B (R₅ of 434 Ohms/sq., electrical X_j of 419 Å)