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Materials and processes for ULSI
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The microelectronic revolution has been driven for decades by Moore’s law with a tremendous scaling down of device dimensions. The smallest feature in silicon devices is rapidly approaching the order of atomic dimensions with 1 billion transistors integrated in a single chip. This trend imposes enormous challenges not only for technology but also for the physical understanding and for the characterization techniques. A measurement, understanding and control of the phenomena at an atomic level are in fact required. It might seem weird but, to make an example, the exact atomistic mechanism of B diffusion in Si (the most common p-type dopant in the most common semiconductor) is still unknown. Similarly, the trend of carrier mobility with dopant concentration presents enormous lacks in terms of understanding the role of lattice strain. For logic applications, crucial aspects relative to the device size scaling are the severe reduction of the source and drain junction depths, with the concurrent need for extremely high and confined doping concentrations. Understanding and control of phenomena such as transient enhanced diffusion and dopant clustering are hence needed. SiGe and high-k dielectrics are introduced in silicon technology and an understanding of their properties and performances is required. Germanium is today considered a new promising material able to substitute silicon for more performing devices. Main doping issues (dopant introduction, electrical activation and diffusion processes) in Ge, as well as structural properties of the Ge matrix subjected to typical industrial processing steps are investigated. To meet the continuous device size scaling and the high data transfer rate requested novel Phase Change Materials are investigated, in particular those lying on the GeTe-Sb2Te3 pseudobinary line (GST). The logical information is stored in the different phases of GST materials and the comprehension of the mechanism ruling the stability of the phases in (GeTe)1-x -(Sb2Te3)x is still to be assessed. |
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RECENT HIGHLIGHTS by MATIS: |
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| The mechanism of B diffusion in crystalline Ge was investigated under light ions irradiation in thin layers with B delta doping. This original approach allowed us to overcome the experimental limits related to the small B diffusivity and evidenced the mechanism of B diffusion in Ge. Indeed, the observed strong enhancement of B diffusivity under ion-beam irradiation and the peculiar shape of the diffused B profiles demonstrated the presence of a point-defect-mediated diffusion, likely assisted by self-interstitials. Bruno E., Mirabella S., Scapellato G., Impellizzeri G., Terrasi A., Priolo F., Napolitani E., De Salvador D., Mastromatteo M., Carnera A. Mechanism of B diffusion in crystalline Ge under proton irradiation Phys. Rev. B 80, 033204 (2009) - DOI: 10.1103/PhysRevB.80.033204 |
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| The migration of B atoms within amorphous matrix of Si has been shown to be far cry from a standard diffusion regulated by the Fick law, being an indirect process mediated by the unsaturated Si bonds present in the matrix. Mirabella S., De Salvador D., Bruno E., Napolitani E., Pecora E.F., Boninelli S., Priolo F. Mechanism of Boron Diffusion in Amorphous Silicon Phys. Rev. Lett. 100, 155901 (2008) - DOI: 10.1103/PhysRevLett.100.155901 |
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| A new route has been opened towards the study of the diffusion mechanisms in silicon, fixing the charge states and the reaction details that bring to B motion in crystalline Si. De Salvador D., Napolitani E., Mirabella S., Bisognin G., Impellizzeri G., Carnera A., Priolo F. Atomistic mechanism of B diffusion in Si Phys. Rev. Lett. 97, 255902 (2006) - DOI: 10.1103/PhysRevLett.97.255902 |
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| The relationships between i) self-induced strain and doping species and ii) carrier mobility and doping species, in silicon give new tools to dismantle bit by bit the issue of the carrier mobility in Si at high doping concentration. Romano L., Piro A. M., Grimaldi M. G., Bisognin G., Napolitani E., De Salvador D. Effect of Strain on the Carrier Mobility in Heavily Doped p-Type Si Phys. Rev. Lett. 97, 136605 (2006) - DOI: 10.1103/PhysRevLett.97.136605 |
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PARTICIPANTS |
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| BERTI Marina | 049 8277038 | |
| BISOGNIN Gabriele | 049 8277004 | |
| BONINELLI Simona | 095 3785289 | |
| BRUNO Elena | 095 3785509 | |
| CARNERA Alberto | 049 8277038 | |
| CARRIA Egidio | 095 3785289 | |
| CRUPI Isodiana | 095 3785396 | |
| DE SALVADOR Davide | 049 8277004 | |
| GRIMALDI Maria Grazia | 095 3785352 | |
| IMPELLIZZERI Giuliana | 095 3785509 | |
| MIRABELLA Salvo | 095 3785510 | |
| NAPOLITANI Enrico | 049 8277001 | |
| PRIOLO Francesco | 095 3785401 | |
| ROMANO Lucia | 095 3785289 | |
| SCAPELLATO Giorgia | 095 3785509 | |
| TERRASI Antonio | 095 3785431 | |