G. Impellizzeri

Fluorine effect on As diffusion in Ge

The enhanced diffusion of donor atoms, via a vacancy (V)-mechanism, severely affects the realization of ultrahigh doped regions in miniaturized germanium (Ge) based devices. In this work, we report a study about the effect of fluorine (F) on the diffusion of arsenic (As) in Ge and give insights on the physical mechanisms involved. With these aims we employed experiments in Ge co-implanted with F and As and density functional theory calculations. We demonstrate that the implantation of F enriches the Ge matrix in V, causing an enhanced diffusion of As within the layer amorphized by F and As implantation and subsequently regrown by solid phase epitaxy. Next to the end-of-range damaged region F forms complexes with Ge interstitials, that act as sinks for V and induce an abrupt suppression of As diffusion. The interaction of Ge interstitials with fluorine interstitials is confirmed by theoretical calculations. Finally, we prove that a possible F-As chemical interaction does not play any significant role on do...

Activation and carrier mobility in high fluence B implanted germanium

High doping regimes of B implanted Ge have been accurately characterized combining Hall effect technique and nuclear reaction analysis. Preamorphized Ge was implanted with B at 35keV (spanning the 0.25–25×1020B∕cm3 concentration range) and recrystallized by solid phase epitaxy at 360°C. The Hall scattering factor and the maximum concentration of active B resulted rH=1.21 and ∼5.7×1020B∕cm3, respectively. The room-temperature carrier mobility was accurately measured, decreasing from ∼300to50cm2∕Vs in the investigated dopant density, and a fitting empirical law is given. These results allow reliable evaluation for Ge application in future microelectronic devices.

Role of fluorine in suppressing boron transient enhanced diffusion in preamorphized Si

We have explained the role of fluorine in the reduction of the self-interstitial population in a preamorphized Si layer under thermal treatment. For this purpose, we have employed a B spike layer grown by molecular-beam epitaxy as a marker for the self-interstitial local concentration. The amorphized samples were implanted with 7×1012, 7×1013, or 4×1014 F/cm2 at 100 keV, and afterwards recrystallized by solid phase epitaxy. Thermal anneals at 750 or 850 °C were performed in order to induce the release of self-interstitials from the end-of-range (EOR) defects and thus provoke the transient enhanced diffusion of B atoms. We have shown that the incorporation of F reduces the B enhanced diffusion in a controlled way, up to its complete suppression. It is seen that no direct interaction between B and F occurs, whereas the suppression of B enhanced diffusion is related to the F ability in reducing the excess of silicon self-interstitials emitted by the EOR source. These results are reported and discussed.

Phase separation and dilution in implanted MnxGe1-x alloys

The structural and electronic properties of MnxGe1−x alloys (x⩽0.15) fabricated by ion implantation are investigated by means of x-ray diffraction and synchrotron radiation photoemission spectroscopy. The diffraction patterns point to the presence of ferromagnetic Mn5Ge3 nanoparticles; however, valence band spectra, interpreted by means of accurate ab initio calculations including Hubbard-like correlations, show clear fingerprints of an effective substitutional Mn dilution in the Ge semiconducting host.

Nanostructuring in Ge by self-ion implantation

We report here a detailed study about the formation and self-organization of nanoscale structures during ion beam implantation at room temperature of 300 keV Ge+ in Ge as a function of the ion fluence in the range between 1×1014 to 4×1016 cm−2. “Microexplosions” characterize the morphology of the swelled material; a random cellular structure consisting of cells surrounded by amorphous Ge ripples has been observed and studied in details by combining atomic force microscopy, scanning electron microscopy, and transmission electron microscopy.

Ga-implantation in Ge: Electrical activation and clustering

The electrical activation and clustering of Ga implanted in crystalline Ge was investigated in the (0.3–1.2)×1021 Ga/cm3 concentration range. To this aim, Ge samples implanted with 50 keV gallium, and annealed at several temperatures up to 650 °C, have been subjected to a detailed structural and electrical characterization. The substrate was maintained at 77 K during implantation to avoid the formation of the honeycomb structure that occurs during implantation at room temperature of heavy ions at high fluence. Secondary ion mass spectrometry analyses indicated a negligible Ga diffusion and dopant loss during the thermal annealing. The carrier concentration in the recrystallized samples measured by Hall effect showed a maximum concentration of active Ga of ∼6.6×1020 Ga/cm3. A remarkable Ga deactivation occurred with increasing the annealing temperature from 450 to 650 °C although the sheet resistance did not change considerably in this temperature range. It turned out that the carrier concentration reducti...

B activation and clustering in ion-implanted Ge

Experimental studies about electrical activation and clustering of B implanted in crystalline Ge (c-Ge) are reported. To this aim, we structurally and electrically investigated c-Ge samples implanted at different temperatures with B at 35 keV in the high-concentration dopant regime (0.67–25×1020 B/cm3). We elucidated that a high level of damage, in the form of amorphous pockets, favors the electrical activation of the dopant, and a complete activation was achieved for properly chosen implant conditions. We found, by joining channeling measurements with the electrical ones, that the reason for incomplete B activation is the formation of B-Ge complexes with a well-defined stoichiometry of 1:8. The thermal stability of the B-doped samples, up to 550 °C, was also investigated. The tested stability demonstrates that the B clustering, responsible of B inactivity, is characterized by high binding energies and higher thermal budgets are needed to make them to dissolve. These studies, besides clarify the physical ...

Fluorine segregation and incorporation during solid-phase epitaxy of Si

We report on the F incorporation into Si during solid-phase epitaxy (SPE) at 580°C and with the presence of B and∕or As, clarifying the F incorporation mechanism into Si. A strong segregation of F at the moving amorphous–crystalline interface has been characterized, leading to a SPE rate retardation and to a significant loss of F atoms through the surface. In B- or As-doped samples, an enhanced, local F incorporation is observed, whereas in the case of B and As co-implantation (leading to compensating dopant effect), a much lower F incorporation is achieved at the dopant peak. The F enhanced incorporation with the presence of B or As is shown to be a kinetic effect related to the SPE rate modification by doping, whereas the hypothesis of a F–B or F–As chemical bonding is refused. These results shed new light on the application of F in the fabrication of ultrashallow junctions in future generation devices.

N-type doping of Ge by As implantation and excimer laser annealing

The diffusion and activation of arsenic implanted into germanium at 40 keV with maximum concentrations below and above the solid solubility (8 × 1019 cm−3) have been studied, both experimentally and theoretically, after excimer laser annealing (λ = 308 nm) in the melting regime with different laser energy densities and single or multiple pulses. Arsenic is observed to diffuse similarly for different fluences with no out-diffusion and no formation of pile-up at the maximum melt depth. The diffusion profiles have been satisfactorily simulated by assuming two diffusivity states of As in the molten Ge and a non-equilibrium segregation at the maximum melt depth. The electrical activation is partial and decreases with increasing the chemical concentration with a saturation of the active concentration at 1 × 1020 cm−3, which represents a new record for the As-doped Ge system.

Fluorine in preamorphized Si : Point defect engineering and control of dopant diffusion

While it is known that F modifies dopant diffusion in crystalline Si, the physical mechanisms behind this process are still unclear. In this work we report experimental studies about the F control of the point defect density in preamorphized Si layers. These studies put the basis for the understanding of the F behavior and for the realization of ultra-shallow junctions. We first investigated the F incorporation process during the solid phase epitaxy (SPE) of amorphous Si layers. We elucidated the role of the SPE temperature on the F incorporation and suggested a new route towards a F profile engineering. Moreover, we explained the role of F in modifying the point defect population (self-interstitials, Is, and vacancies, Vs), employing B and Sb spike layers as markers for Is and Vs, respectively. We clearly showed that F decreases the B diffusion while enhances the Sb one, pointing out the capacity to induce an Is undersaturation or a Vs supersaturation. These data rule out the hypothesis of a chemical bon...