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

Abstract

Ion implants of /sup 11/B/sup +/ (0.25 keV to 2.0 keV), /sup 49/BF/sub 2//sup +/ (1.1 keV to 8.9 keV), 75As/sup +/ (2.0 keV to 5.0 keV); and /sup 31/P/sup +/ (1.0 keV to 5.0 keV) at a dose of 1e15/cm/sup 2/ were investigated by TEM to determine defect type and concentrations after a 750/spl deg/C, 15 min furnace baseline anneal and then after rapid thermal annealing (RTA) using slow and fast anneals (<0.1 s) at 1050/spl deg/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 BF/sub 2/ implants are discussed. In the case of BF/sub 2/, 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 BF/sub 2/ comparison was conducted on wafers which were spike annealed in an ambient of 33 ppm O/sub 2/ in N/sub 2/. For all species a defect free energy threshold is identified where, after the 750/spl deg/C, 15 min (and confirmed at 600/spl deg/C to 800/spl deg/C) furnace base-line anneal, no extended-defects or loops formed (i.e. <1e7/cm/sup 2/). 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 O/sub 2/ in N/sub 2/ ambients on implants below this energy threshold can be employed to optimize sheet resistance (R/sub 5/) and junction depth (X/sub j/) are presented for: /sup 49/BF/sub 2/ at 2.2 keV (R/sub 5/ of 406 Ohms/sq., electrical X/sub j/ of 386 /spl Aring/); /sup 49/BF/sub 2/ at 1.1 keV (R/sub 5/ of 669 Ohms/sq., electrical X/sub j/ of 234 /spl Aring/); and 0.25 keV /sup 11/B (R/sub 5/ of 434 Ohms/sq., electrical X/sub j/ of 419 /spl Aring/).