We have examined nanovoid formation, Fe gettering, and Fe clustering phenomena occurring in epitaxial silicon layers implanted with MeV Si ions. Insights into these phenomena as a function of depth have been gained from detailed analyses by Z-contrast imaging in conjunction with electron energy-loss spectroscopy. Our work has shown at the nanoscale structural and chemical levels that the defects produced by MeV self-ion implantation between the surface and the ion projected range Rp (i.e., in the so-called Rp/2 region) are voids, which provide extremely efficient and aggressive metallic impurity gettering. It has been proposed that the gettering does not occur via chemisorption or silicidation layering on the internal surface of the void walls, as in the well-known case of helium-induced cavities, but rather proceeds in a mode of metal–metal atom binding in the vicinity of the Rp/2 voids.
A rf wave resonance plasma (WARP) source has been used to plasma oxidize Si at temperatures below 100 °C. Oxidation under positive substrate bias in constant current mode gives an oxidation rate of 1–8 nm/min for current densities of 0.4–5.5 mA/cm2. This corresponds to an ionic (O−) current of about 10% of the total current, which is 2–5 times higher than previously reported, due to the high plasma density of 1012–1013 cm−3 achieved by the WARP source. The breakdown field of ∼10 MV/cm and the etch rate of 60 nm/min of the oxide are independent of the oxidation rate and similar to those of the thermal oxide. Results from capacitance–voltage measurements, Fourier transform infrared absorbance spectroscopy, null ellipsometry, and Rutherford backscattering spectroscopy suggest that the oxide grown at low rates (<2 nm/min) is very close to stoichiometric SiO2 while the oxide grown at high rates (>3 nm/min) is Si rich (35%–40% atomic Si).
The nature of amorphization and crystallization of Si brought about by 50 keV Zn ion implantation within the dose range 2×1017–1×1018 cm−2 is studied. The structures are evaluated in the as-implanted state by transmission electron microscopy, transmission electron diffraction, reflection high-energy electron diffraction, selected-area electron diffraction, x-ray energy-dispersive analysis, and Rutherford backscattering spectrometry. It is found that, contrary to the theoretical predictions, the Zn concentration profile does not reach saturation even at a dose as high as 1×1018 cm−2. A common feature of the microstructure of these high-dose implants is the formation of a continuous amorphous layer and concurrent crystallization of Zn and Si in small crystalline clusters. Microscopic beam-heating effects are also believed to play an appreciable role in the development of the specific morphologies observed. The results are interpreted in terms of two recent models proposed in the literature and the concept of critical dose ranges.
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