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The modeling of the atom-by-atom growth of extended defects is coupled to the diffusion equations of boron by transferring the free interstitial supersaturation calculated with a defect model into a process simulator. Two methods to achieve this coupling (equilibrium method and fully coupled method, respectively) are presented and tested against a variety of experimental conditions. They are first applied to a transient enhanced diffusion experiment carried out on a structure containing several B delta-doped layers, in which the amount of diffusion of the different layers is accurately predicted. The fully coupled method is then used to simulate the diffusion of ultrashallow B-implanted profiles. This work definitely demonstrates the relevance of accurate physical defect models for the successful design of ultrashallow junctions in future generations of integrated circuits. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

P-type ultrashallow junctions are widely fabricated using Ge preamorphization prior to ultralow-energy boron implantation. However, for future technology nodes, issues arise when bulk silicon is supplanted by silicon-on-insulator (SOI). An understanding of the effect of the buried Si/SiO2 interface on defect evolution, electrical activation, and diffusion is needed in order to optimize the preamorphization technique. In the present study, boron has been implanted in germanium preamorphized silicon and SOI wafers with different preamorphizing implant conditions. Subsequent to implantation an isothermal annealing study of the samples was carried out. Electrical and structural properties were measured by Hall-effect and secondary-ion-mass spectroscopy techniques. The results show a variety of interesting effects. For the case where the Ge preamorphization end-of-range defects are close to the buried oxide interface, there is less dopant deactivation and less transient-enhanced diffusion, due to a lower interstitial gradient towards the surface. [ABSTRACT FROM AUTHOR]

In this study we investigated the effect of position and dose of a separate fluorine coimplant on the activation and diffusion behavior of germanium preamorphized boron implants. Germanium preamorphized silicon was implanted with boron, and fluorine was subsequently implanted with different energies and doses to place it either at the projected range of the boron implant, or between the boron profile and the amorphous-crystalline interface, or at this interface. The wafers were spike annealed at temperatures ranging from 950 to 1050 °C. In terms of sheet resistance it was found that the superposition of B and F profiles leads to decreased activation compared to the wafers without any F implant. Increased boron activation is seen for all the other cases with the biggest effects for the highest fluorine dose. The positioning of F either between the boron projected range and the end of range (EOR) or at the EOR leads to more box-shaped boron profiles with shallower junction depth than the reference wafer. [ABSTRACT FROM AUTHOR]

Preamorphization of ultrashallow implanted boron in silicon on insulator is optimized to produce an abrupt boxlike doping profile with negligible electrical deactivation and significantly reduced transient enhanced diffusion. The effect is achieved by positioning the as-implanted amorphous/crystalline interface close to the buried oxide interface to minimize interstitials while leaving a single-crystal seed to support solid-phase epitaxy. Results support the idea that the interface between the Si overlayer and the buried oxide is an efficient interstitial sink. [ABSTRACT FROM AUTHOR]

Electrical activation and redistribution of 500 eV boron implants in preamorphized silicon after nonmelt laser annealing at 1150 °C and isochronal rapid thermal postannealing are reported. Under the thermal conditions used for a nonmelt laser at 1150 °C, a substantial residue of end-of-range defects remained after one laser scan but these were mainly dissolved within ten scans. The authors find dramatic boron deactivation and transient enhanced diffusion after postannealing the one-scan samples, but very little in the five- and ten-scan samples. The results show that end-of-range defect removal during nonmelt laser annealing is an achievable method for the stabilization of highly activated boron profiles in preamorphized silicon. [ABSTRACT FROM AUTHOR]

We investigate the impact of amorphization and C co-implantation on B diffusion and activation properties after conventional spike rapid thermal annealing (RTA). We observe that after complete recrystallization at 600 °C the B tail deepens by 5 nm (at 5×1018 at./cm3) due to B diffusion in a-Si. After spike RTA it becomes 12 nm deeper with respect to an as-implanted profile, which proves that both diffusion mechanisms in a-Si and c-Si are important. However, the B diffusion in c-Si is sensitive to the fraction of substitutional C incorporated into c-Si. The best junction depth is Xj=16.5 nm, with abruptness of 2 nm/decade and Rs=583 Ω/□. [ABSTRACT FROM AUTHOR]

Shallow fluorine-vacancy (FV) complexes in Si have been directly observed using variable-energy positron annihilation spectroscopy and secondary ion mass spectrometry. The FV complexes, introduced to combat the deactivation and transient-enhanced diffusion of ultrashallow boron, were observed in preamorphized Si wafers implanted with 0.5 keV B and 10 keV F ions at a dose of 1015 cm-2, and then annealed isothermally at 800 °C for times ranging from 1 to 2700 s. The results are in agreement with a model which predicts that the complexes are of the form F3nVn, with n most probably being 1 and/or 2. [ABSTRACT FROM AUTHOR]

The formation of boron interstitial clusters is a key limiting factor for the fabrication of highly conductive ultrashallow doped regions in future silicon-based device technology. Optimized vacancy engineering strongly reduces boron clustering, enabling low-temperature electrical activation to levels rivalling what can be achieved with conventional preamorphization and solid-phase epitaxial regrowth. An optimized 160 keV silicon implant in a 55/145 nm silicon-on-insulator structure enables stable activation of a 500 eV boron implant to a concentration ∼5×1020 cm-3. [ABSTRACT FROM AUTHOR]

We investigate the influence of thermal conditions during solid phase epitaxial regrowth (SPER) on the electrical activation level of boron in preamorphized silicon, both with respect to heating ramp rates and the use of low temperature preanneals. Enhancement of electrically active boron concentration by 36% is observed for activation with the fastest ramp rate (487 °C/s) compared to the slowest one (1 °C/s). An important clustering pathway occurs within the amorphous silicon phase (during low temperature preanneal) prior to completion of the SPER process. In these junctions boron deactivation during isochronal post-annealing is almost independent on the maximum boron activation level. [ABSTRACT FROM AUTHOR]

We investigate the thermal stability of boron-doped junctions formed by Ge preamorphization and solid phase epitaxial regrowth. Isochronal annealing and characterization by sheet resistance, secondary-ion mass spectrometry, and spreading-resistance measurement are used to extract detailed information on the thermal stability of the boron activation. Using a previously established model of self-interstitial defect evolution from clusters to dislocation loops, we perform simulations of the release of interstitials from the end-of-range region. The simulations indicate that the measured deactivation is driven by interstitials emerging from the end-of-range defect region. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The recently observed phenomenon of boron uphill diffusion during low-temperature annealing of ultrashallow ion-implanted junctions in silicon has been investigated. It is shown that the effect is enhanced by preamorphization, and that an increase in the depth of the preamorphized layer reduces uphill diffusion in the high-concentration portion of boron profile, while increasing transient enhanced diffusion in the tail. The data demonstrate that the magnitude of the uphill diffusion effect is determined by the proximity of boron and implant damage to the silicon surface. [ABSTRACT FROM AUTHOR]

We investigate the nucleation and evolution of boron-interstitial clusters (BIC), driven by high interstitial supersaturations, S(t), during Si implant damage annealing. The BICs are "fabricated" in a narrow band by overlapping the Si implant damage tail with a lightly doped B buried layer. The BIC band is found to be a net sink for interstitials at supersaturations S(t)>10[sup 4]. Our results suggest that silicon self-interstitial defects are the primary source of interstitials driving transient enhanced diffusion, and that BICs act as a secondary "buffer" for the interstitial supersaturation. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]