Study on the electrical properties of ultrathin in situ Boron-doped strained Si0.7Ge0.3 layers annealed by nanosecond pulsed laser - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2023

Study on the electrical properties of ultrathin in situ Boron-doped strained Si0.7Ge0.3 layers annealed by nanosecond pulsed laser

Rémi Demoulin
Etienne Talbot

Résumé

The downscaling of CMOS transistors requires high active dopant concentrations in the source and drain terminals to minimize contact resistance. Pulsed laser annealing is an attractive option as it enables to locally reach, typically ~100 nm below the surface, high temperatures (e.g. above the melt threshold), with extremely fast temperature ramps (>109 °C/s). Structural investigations have already allowed to identify the best conditions to obtain fully strained and defect-free undoped SiGe layers by liquid phase epitaxial regrowth (LPER). In this work, we report on the electrical properties of laser annealed 30 nm-thick boron-doped strained-Si0.7Ge0.3 layers. These layers were CVD grown on p-type bulk Si (100), with three different boron concentrations probed at: 7.3x1019 (A), 1.4x1020 (B) and 2.3x1020 cm-3 (C). Electrical properties were evaluated thanks to an algorithm comparing Hall parameters calculated from boron and germanium SIMS profiles with the corresponding Hall effect measurements. Germanium redistribution occurring during laser annealing in melt conditions was taken into account through Hall scattering factor variations. For the as-grown layers, activations rates of ~100%, ~80% and ~60% were found, without any significant carrier mobility degradation. These layers were annealed in a SCREEN-LT3100 platform, equipped with a pulsed laser operating at 308 nm (XeCl laser), with a pulse duration around 160 ns and energy densities ranging from 1.20 to 2.40 J/cm2. The different laser regime transitions as well as the strain state were studied thanks to surface, structural and chemical characterizations, in addition to electrical measurements. In the three layers, the simultaneous variation of strain state and dopant activation had a definite impact on the electrical properties. Indeed, when reaching the beginning of the melt, crystal defects appeared, resulting in a partial relaxation of the compressive strain in the layers. When getting close to the complete melt of the layers, the compressive strain was recovered. The higher the dopant concentration, the earlier the strain was retrieved before reaching the full melt, certainly due to compressive strain compensation by boron atoms. Activation rates were evaluated, taking into account the relaxation phenomena by modifying the Hall scattering factor in accordance with the literature. It was found that the activation in the three layers was improved up to 100% when the energy density was increased, confirming the efficiency of the laser annealing technique. For device purposes, and as already discussed in the literature, shorter pulse laser anneals (308 nm, 25 ns) were performed on as-grown layers to circumvent the partial relaxation. Preliminary results showed a positive impact of such pulse duration reduction on the previously evidenced phenomena, although further investigations are still in progress.
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Dates et versions

hal-04442327 , version 1 (06-02-2024)

Identifiants

  • HAL Id : hal-04442327 , version 1

Citer

Richard Daubriac, Rémi Demoulin, Sébastien Kerdilès, P. Acosta-Alba, M. Opprecht, et al.. Study on the electrical properties of ultrathin in situ Boron-doped strained Si0.7Ge0.3 layers annealed by nanosecond pulsed laser. 2023 E-MRS Spring Meeting, May 2023, Strasbourg, France. ⟨hal-04442327⟩
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