Ljubo Radic

Kinetics of boron reactivation in doped silicon from Hall effect and spreading resistance techniques

In this work, a series of 13 boron implants were performed into Czochralski silicon substrates with doses of 2×1014–1.6×1015 cm−2 at energies of 10–80 keV. The boron was deliberately clustered with a 750 °C anneal of 10 or 30 min and the electrical activation of the boron implants was determined following a second anneal at 750 or 850 °C with a Hall effect system with certain samples also being analyzed with a spreading resistance technique. Analysis of the reactivation rates allows for the determination of the net energy to boron reactivation to be approximately 3.0 eV assuming the reactivation process is mediated by release of a boron interstitial with a migrational energy of 0.3 eV. This results in a critical binding energy of approximately 2.7 eV from the process limiting the dissolution of the most stable boron-interstitial cluster.

Kinetics of the end of range damage dissolution in flash-assist rapid thermal processing

This study investigates the effectiveness of flash-assist rapid thermal processing in dissolving the end of range damage inherent to preamorphizing implants. A series of silicon wafers is preamorphized with a Ge implant and subsequently implanted with B. The wafers are then subjected to a flash anneal, a rapid thermal anneal, or both annealing processes. The flash anneal results in higher defect densities and trapped interstitials than the rapid thermal anneal. Defect dissolution has been previously reported to have an activation energy between 4 and 5eV. This work demonstrates that the defect dissolution during flash-assist rapid thermal processing is mediated by a 2.2±0.05eV activation energy.

Dependence of boron cluster dissolution on the annealing ambient

Boron is introduced into silicon via implantation to form p-type layers. This process creates damage in the crystal that upon annealing causes enhanced diffusion and clustering of the boron layer. Reactivation of the boron is not a well-understood process. In this letter we experimentally investigate the effect of the annealing ambient on boron reactivation kinetics. An oxidizing ambient which injects silicon interstitials is compared to an inert ambient. Contrary to published theory, an excess of interstitials does not accelerate the reactivation process.

Dislocation loops in silicon-germanium alloys: The source of interstitials

The relationships between extended defect evolution and boron diffusion in Si0.77Ge0.23 have been investigated. A SiGe structure was grown by molecular beam epitaxy with a 3×1018atoms∕cm3 boron marker layer positioned 0.50μm below the surface. Samples were ion implanted with 60 keV Si+ at a dose of 1×1014atoms∕cm2 and subsequently annealed at 750 °C for various times. The evolution of extended defects in the near surface region was monitored with plan-view transmission electron microscopy. Secondary ion mass spectroscopy concentration profiles facilitated the characterization of boron diffusion. Boron experiences transient enhanced diffusion regulated by the dissolution of dislocation loops. The maximum diffusion enhancement in Si0.77Ge0.23 is less than that observed in pure Si.

Modeling of B diffusion in the presence of Ge

In order to investigate the B and Ge interaction in silicon, an implant/anneal experiment is performed. The initial Si pre-amorphization step defines the amorphous layer depth and the end-of-range point defect distributions for all samples. The following Ge implant provides a low Ge content, thus minimizing the strain and the band gap narrowing effects on the diffusion of the subsequent B implant. The control sample received Si and B implants. The annealed profiles of the control samples show B profile broadening consistent with the transient enhanced diffusion. The B tail diffusion in the Ge implanted samples is almost identical to that of the control samples, indicating that Ge does not act as a trap for the BI pair. The GeB complex, suggested in literature, was used to explain the higher profile peak magnitude in Ge implanted samples.

Modeling B Uphill Diffusion in the Presence of Ge

Several models for B diffusion in Si1-x Gex have been proposed [1, 2]. In order to help discriminate between the models, an experiment was performed. Preamorphized Si wafers were implanted with varying doses of Ge, followed by a B implant. Samples were annealed at several temperatures. Ge implanted samples showed an increase in the B profile peak magnitude with anneal time, as well as its shift towards the surface. Control samples, receiving two Si implants, showed the expected enhanced B diffusion and none of the uphill diffusion behavior. Simulations accounting for the formation of GeB complex show qualitative fit to the measured profiles.

Modeling of Dopant Defect Interactions

This paper presents a model for {311} defects based on in-situ experiments. The model fits the 311 dependence on silicon implant energy and doses. The surface dependence of the model is described in detail, and compared to previous literature data. New data is presented on the surface effect on {311} dissolution and the model is compared to that data. In addition, the model is also used to explain the effects of doping on {311} defect behavior. Doping does not influence the dissolution of {311} defects, but only influences their nucleation behavior.