Study of reverse annealing behaviors of p+/n ultrashallow junction formed using solid phase epitaxial annealing

Abstract

Solid phase epitaxial ͑SPE͒ annealing at low temperature has the advantage of high dopant activation and very little dopant diffusion. However, due to the low thermal budget engaged in SPE, a large amount of defects can exist in the area beyond the original interface of the crystal and the pre-amorphized layer. These defects may cause severe junction leakage. They may also cause dopant diffusion and deactivation in a following higher temperature process. This work studies the reverse annealing behaviors during a second annealing step for SPE-formed p ϩ /n junction using either 1 keV B ϩ or 5 keV BF 2 ϩ implants. Four-point probe, secondary-ion-mass spectroscopy, and transmission electron microscopy are used in this study. The results show that the boron deactivation after second-step annealing is not only correlated with the transmission electron diffraction ͑TED͒, but also correlated with the end of range defect evolution. The results also show that BF2 implanted wafer has slower boron deactivation, less TED and slower defect evolution than the B implanted wafer. In addition, the BF2 implanted wafer shows a much slower SPE regrowth rate at 550°C than the B implanted wafer.

The role of silicon interstitials in the deactivation and reactivation of high concentration boron profiles

“…To better understand the role of EOR Si interstitials in B deactivation and reactivation processes, we analyze the experimental data reported by Jin et al [5] We have simulated a 0.5 keV, 10 15 cm −2 B implant in silicon preamorphized by a 20 keV, 5 × 10 14 cm −2 Si implant, which amorphizes up to 32 nm. The samples were annealed at 550 • C for 40 min to regrow the amorphous layer, and followed by 10 s anneals at temperatures ranging from 550 to 950 • C. Fig.…”

“…3. Simulated and experimental [5] sheet resistance as a function of the annealing temperature for a 0.5 keV, 10 15 cm −2 B implant in preamorphized silicon, after10 s anneals performed after the regrowth of the amorphous layer. The simulated active B dose is also plotted, which is mostly proportional to the inverse of the sheet resistance.…”

“…However, experiments [1,5,6] and theoretical calculations [19] evidence B clustering within the regrown layer for high B concentrations. We assume that only B concentrations up to ∼2 × 10 20 cm −3 [1,5,6] are incorporated into substitutional positions during the regrowth, and B concentrations above that value are in the form of small B clusters [20]. Therefore, the initial simulation conditions for our study correspond to the situation immediately after the regrowth of the amorphous layer.…”

“…Only defects beyond the amorphous/crystalline interface remain from the PAI. However, the activation achieved after SPE regrowth can only reach concentrations in the order of a few times 10 20 cm −3 [1,5,6]. Laser annealing makes electrical activation up to levels ∼10 21 cm −3 possible [7].…”

“…Laser annealing makes electrical activation up to levels ∼10 21 cm −3 possible [7]. However, in the presence of high B concentrations, subsequent thermal treatments results in additional boron deactivation within the regrown layer [1,[5][6][7].…”