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Abstract

Monocrystalline silicon was implanted with boron (32 keV, 1.3×1015 at. cm-2), post-annealed (740°, 10 min, N2) and further analyzed at the atomic scale by atom probe tomography. A comparison between the as-implanted and annealed samples demonstrated the presence of large B-Si clusters after annealing which were associated with the well-known boron interstitial clusters. The cluster density (up to 5×1017 cm-3) and the number of B atoms per cluster (up to 50) were found to vary with the boron concentration. Only 8% of the B atoms were found trapped in those clusters, suggesting the presence of a majority of very small B-Si aggregates in correlation with simulations.

Abstract

The detailed knowledge of the effects of the buried interface on defect evolution in silicon-on-insulator wafers is mandatory to accurately control dopant diffusion and activation. To be able to study this phenomenon, quantitative data on end-of-range defect evolution must be obtained taking into account the several possible effects of the buried interface. In this work we report some transmission electron microscopy data acquired to study the effect of the Si top layer/buried oxide interface acting as an interstitial sink in silicon-on-insulator wafers. It is shown that this effect can explain the obtained data and that our results are compatible with a non-conservative Ostwald ripening mechanism describing defect evolution in silicon-on-insulator structures.

Mots-Clés / Keywords

Silicon-On-Insulator (SOI); End-of-range defects; Germanium implant; Transmission electron microscopy;

Abstract

Millisecond annealing as an equipment technology provides temperature profiles which favour dopant activation but nearly eliminate dopant diffusion to form extremely shallow, highly electrically activated junctions. For the 45-nm technology node and beyond, precisely controlled gate under-diffusion is required for optimum device performance. Therefore, on boron and arsenic beamline-implanted wafers, various annealing schemes were investigated for the formation of ultra-shallow and custom-shaped junctions. The main scheme consisted of flash annealing with peak temperatures ranging from 1250 to 1300 °C, combined with spike rapid thermal annealing with peak temperatures in the range from 900 to 1000 °C to achieve a desired junction depth. As alternative, to reduce the sheet resistance of pMOS and nMOS source-drain extensions, combinations of two or three flash anneals in succession were tested. Finally, the standard flash anneal condition of a 750 °C intermediate temperature followed by the flash anneal was changed to a high intermediate temperature of 950 °C followed by the flash anneal up to 1300 °C. The results of all these annealing schemes were analysed by four-point probe measurement. Selected samples were analysed by Hall-effect measurements for peak activation, and by secondary ion mass spectrometry for profile shape as well as diffusion effects. Transmission electron microscopy was used to study residual defects. Selected boron and arsenic dopant profiles were also compared to predictive simulation results which address the diffusion and activation at extrinsic concentrations.

Abstract

We have studied the Ge-Si interdiffusion from structures in which not, vert, similar300 nm-thick pure Ge(:B) layers were grown on Si 200 mm substrates by CVD at 450 °C. As-grown samples were capped with SiO2 and then annealed in the 750-900 °C range for various times. Using the secondary ion mass spectrometry (SIMS) MCs2+ methodology, we measures precisely the Ge diffused profiles. Boltzmann-Matano analysis was used to extract the interdiffusion coefficients. Si-Ge interdiffusion is found to be strongly dependent on the Ge concentration. Also, an effect of dislocations near the Ge/Si original interface is suggested by our results. A physical model including the various observed effects is proposed, that gives a very good agreement with experiments. Finally, we show that the effect of the in situ B doping of the pure Ge layer is to reduce the interdiffusion.

Mots-Clés / Keywords

Interdiffusion; Germanium; Silicon; CVD; SIMS; MCs2+; Boltzmann-Matano; Defects; Modeling;

Abstract

In this work, the evolution of boron trapping at End-of-Range (EOR) defects was investigated by secondary ion mass spectrometry (SIMS) and transmission electron microscope (TEM). Si wafers with a constant boron concentration of 2 × 1018 cm-3 were implanted with 30 keV germanium and with a dose of 1015 cm-2 and then annealed at 700, 800, or 900 °C in an N2 ambient for various times. The experimental results suggest that the evolution of boron-trapping peak is driven by the evolution of {3 1 1} defects and that the dislocation loops contribution to the trapping mechanism is less pronounced. An analytic model for the concurrent boron trapping at {3 1 1} defects and dislocation loops was developed by taking into account the geometry of the EOR defects. The trapped species is represented by neutral BI pairs which can be captured either by {3 1 1} defects or by dislocation loops. The model accurately reproduces the complex evolution of the trapping peak as a function of both the annealing time and temperature. These results confirm that the evolution of the boron-trapping peak is closely related to the evolution of the {3 1 1} defects, therefore suggesting that boron trapping is associated to the capture and release of boron atoms at the {3 1 1} defects formed in the EOR region.

Mots-Clés / Keywords

Boron; Germanium implant; End-of-range defects; SIMS; Transmission electron microscopy;