The diffusion and activation of low-energy implanted B in F preamorphized Si during rapid thermal annealing has been studied. Compared with low-energy B or BF2 implant into crystalline Si, low-energy B ion implantation into F preamorphized Si allows the formation of shallow junctions with reduced junction depth and increased B activation. F preamorphization suppresses the B transient enhanced diffusion in the low B concentration region resulting in a steep dopant profile which is necessary for shallow junction formation. Secondary ion mass spectroscopy and cross-sectional transmission electron micrograph results show F accumulation near the surface and at end-of-range defects. The interaction of F with defects is believed to reduce B diffusion in the low B concentration region. Low-energy B implant into F preamorphized Si followed by rapid thermal annealing has been demonstrated as a promising process for shallow junction formation.
The diffusion and activation of boron following the rapid thermal annealing (RTA) of ion-implanted boron and BF2 are investigated. The early stage of RTA is characterized by the enhancement of boron diffusion and the suppression of dopant activation throughout the impurity depth profile. This phenomenon is explained and modeled by considering the reaction kinetic between the electrically activated boron species and the inactive boron-silicon interstitialcy. The self-interstitial supersaturation created by ion implantation damage is believed to lower the boron activation during RTA by forming electrically inactive boron interstitialcies. A model that accurately predicts both the enhanced diffusion and the suppressed activation of boron during RTA is presented.
The effect of fluorine preamorphization on boron diffusion and activation during rapid thermal annealing (RTA) has been investigated. Compared with low energy B or BF2 implant into crystalline Si, F preamorphization suppressed the transient enhanced diffusion of B and increased dopant activation. Results show that the tail diffusion was absent, and thus the junction depth of the RTA annealed sample was established by the as-implanted B profile. Secondary ion mass spectroscopy and cross-sectional transmission electron micrograph results show F accumulation near the surface and at end-of-range defects. The interaction of F with defects is believed to reduce the B diffusion during RTA.
Pseudomorphic Ge0.12Si0.88 films 265 nm thick grown by molecular beam epitaxy on p- Si(100) substrates were implanted with 100 keV 31P at room temperature for a dose of 5 x 1013/cm2. The projected range of the implanted P is about half the epilayer thickness. The implanted layers, together with non-implanted virgin samples, were subsequently annealed by both rapid thermal annealing in nitrogen and by steady-state furnace annealing in vacuum. The damage and strain of the annealed layers were studied by 4He channeling and x-ray doublecrystal diffraction. For a dose of 5 x 1013 P /cm2, both the damage and strain introduced by implantation can be completely removed, within instrumental sensitivity, by rapid thermal annealing at 700 °C for 10 - 40 s. Furnace annealing at 550 °C for 30 min for this sample removes most of the damage and strain induced by implantation. Furnace annealing at 700 °C or higher worsens the crystallinity of the layer and the strain relaxes. Hall measurements were performed on the same samples. Furnace annealing cannot achieve good dopant activation without introducing significant strain relaxation to the heterostructure, while rapid thermal annealing can.
The mechanism of the enhanced diffusion of boron during rapid thermal annealing (RTA) of BF2-implanted Si has been investigated, and a diffusion model is accordingly developed for a wide range of implant and annealing conditions. Simulation results are in excellent agreement with experiments for BF2 implant doses from 2×1013 to 5×1015cm−2, implant energies from 6 to 45 keV, and annealing temperatures from 950 to 1100°C. This model not only accounts for the transient enhanced diffusion due to the annealing of point-defect clusters and dislocation loops, but also for the retarded diffusion due to dopant precipitation. All the parameters used in this model are analytically determined.
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