We have investigated diffusion and activation of boron implanted with 6 keV energy to a maximum concentration of 8.0×1020atoms∕cm3 in crystalline germanium (c-germanium) and preamorphized germanium, employing rapid thermal annealing in the range of 400–600 °C. As-implanted boron profiles in preamorphized germanium are shallower than the ones in c-germanium due to channeling suppression. While boron diffusion is not observed either in c-germanium or during the germanium regrowth from amorphous state, the boron activation level achieved from the two starting phases is significantly different. A boron activation level of 2.4×1020atoms∕cm3 has been found in regrown germanium, while a level of only 1.2×1019atoms∕cm3 is observed in c-germanium. Remarkably, there is no evidence of any residual extended defectivity at the original crystalline/amorphous interface, when preamorphization is performed.

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An overview of the existing two-dimensional carrier profiling tools using scanning probe microscopy includes several scanning tunneling microscopy modes, scanning capacitance microscopy, Kelvin probe microscopy, scanning spreading resistance microscopy, and dopant selective etching. The techniques are discussed and compared in terms of the sensitivity or concentration range which can be covered, the quantification possibility, and the final resolution, which is influenced by the intrinsic imaging resolution as well as by the response of the investigated property to concentration gradients and the sampling volume. From this comparison it is clear that, at present, none of the techniques fulfills all the requirements formulated by the 1997 Semiconductor Industry Association roadmap for semiconductors [National Technology Roadmap for Semiconductors (Semiconductor Industry Association, San Jose, CA, 1997)]. Most methods are limited to pn-junction delineation or provide a semiquantitative image of the differently doped regions. However, recent comparisons have shown that the techniques can provide useful information, which is not accessible with any other method.

We have studied implant-induced damage, defect annealing, and recrystallization of B, Ga, P, As, and Sb introduced in Ge by ion implantation at high doses, such that dopant chemical concentrations are above the corresponding solubility in Ge, with energies that target about 100-nm junction depths. It is shown that the amount of damage induced in the Ge lattice increases with the mass of the implanted ion, as expected. Implanted B produces local amorphous regions, although crystalline Ge zones are present in the implanted layer. P is a self-amorphizing ion, creating a continuous amorphous layer during implantation. However, a low thermal budget is sufficient to fully regrow the amorphous layer, without evidence of residual extended defects, as evaluated by crosssectional transmission electron microscopy. Conversely, high concentrations of As cause a significant decrease of the regrowth rate of the damaged layer during rapid thermal annealing in the 400-600°C range studied. Finally, high-dose implantation of heavy ions such as Sb induces dramatic morphologic changes in Ge that are not recovered by post-implant rapid thermal annealing.

Time evolution of the chemical profile, electrical activity, and regrowth of P implanted in Ge at a concentration above the maximum equilibrium solubility is investigated at 500°C rapid thermal annealing temperature. During the first anneal, a second, epitaxial regrowth of a part of the amorphous layer leads to P trapping in substitutional sites at a level of about 4×1020atoms∕cm3. However, nonsubstitutional P atoms frozen in the crystal at high concentration during recrystallization form large, inactive precipitates of peculiar circular shape. Simultaneously, long annealing time leads to continuing, extensive P out- and indiffusion affecting both the P chemical profile and junction sheet resistance.