Sandro Solmi

Bio: Sandro Solmi is an academic researcher from National Research Council. The author has contributed to research in topics: Ion implantation & Silicon. The author has an hindex of 28, co-authored 104 publications receiving 2300 citations.

Diffusion of boron in silicon during post-implantation annealing

Abstract: The diffusion of B implanted in Si has been investigated at different concentrations in a wide range of experimental conditions (temperature from 800 to 1000 °C and time from 10 s to 8 h) by using furnace and rapid thermal treatments. In particular, the transient enhanced diffusion induced by the implantation damage in the early phase of the annealing and the precipitation occurring in concomitance with the diffusion for dopant concentration exceeding the solid solubility have been extensively analyzed. A simulation program taking these phenomena into account has been developed by modifying the supreme iii code. A satisfactory agreement with experimental data has been obtained for all the investigated conditions. The model represents a significative improvement of the diffusion simulation of B implanted in crystalline Si. In fact, the more commonly used codes of process simulation do not evaluate adequately the effects of the above considered phenomena.

High‐concentration boron diffusion in silicon: Simulation of the precipitation phenomena

Abstract: An extensive investigation on the diffusion of boron implanted at high concentration in preamorphized silicon has been carried out for rapid thermal annealing and conventional furnace annealing. The rapid process of epitaxial regrowth of the amorphous layer brings B atoms into substitutional positions, and thus electrically active, up to a concentration threshold of about 3.5×1020 cm−3. This value is nearly independent of the annealing temperature and of the implanted dose. Since the concentration of dopant in solution is higher than the solubility value, precipitation phenomena occur in concomitance to diffusion during the annealing. The kinetics of precipitation has been investigated at 800, 900, and 1000 °C with isothermal treatments ranging between 10 s and 171 h. A simulation program taking into account precipitation phenomena has been developed modifying the suprem iii code. The density of nuclei of the new phase has been evaluated on the base of the models of classic nucleation theory, while the ra...

Precipitation as the phenomenon responsible for the electrically inactive phosphorus in silicon

Abstract: The physical nature of the electrically inactive phosphorus in silicon was investigated by annealing experiments performed on laser annealed specimens doped by ion implantation up to 5×1021 at/cm3. The hypothesis of point defects, which compensate or make the excess dopant electrically inactive, is contradicted by the experimental results. It was verified that phosphorus solubility corresponds to the electrically active concentration in equilibrium with the inactive dopant, and that the latter is precipitated phase. This was confirmed by transmission electron microscopy (TEM) examinations with the weak beam technique, which detected a high density of very small coherent precipitates. This method allowed us to observe particles of the same kind even on specimens thermally predeposited in conditions typical of device technology. In both cases the amount of precipitates was consistent with the inactive dopant concentration. In addition these experiments show that precipitation is associated with a high enhan...

Dopant and carrier concentration in Si in equilibrium with monoclinic SiP precipitates

Abstract: The behavior of silicon slices very heavily implanted (1.5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$) with phosphorus was investigated by transmission electron microscopy and secondary neutral mass spectrometry (SNMS) after annealing at 800, 850, 900, and 1000 \ifmmode^\circ\else\textdegree\fi{}C. Precipitation of large monoclinic, and partially orthorhombic, SiP particles takes place in the most heavily doped region. From the shape of the SNMS profiles in the dissolution stage of these precipitates, we determined the concentration ${\mathit{C}}_{\mathrm{sat}}$ of P in equilibrium with the conjugate phase: ${\mathit{C}}_{\mathrm{sat}}$=2.45\ifmmode\times\else\texttimes\fi{}${10}^{23}$exp(-0.62/kT) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. This concentration has to be compared with the equilibrium concentration ${\mathit{n}}_{\mathit{e}}$ of the electrically active dopant. To this end, more accurate determinations of ${\mathit{n}}_{\mathit{e}}$ were performed on heavily P-doped polysilicon films. It was found that ${\mathit{n}}_{\mathit{e}}$=1.3\ifmmode\times\else\texttimes\fi{}${10}^{22}$exp(-0.37/kT) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. Hence for T\ensuremath{\gtrsim}750 \ifmmode^\circ\else\textdegree\fi{}C, ${\mathit{C}}_{\mathrm{sat}}$ exceeds ${\mathit{n}}_{\mathit{e}}$ and the concentration (${\mathit{C}}_{\mathrm{sat}}$-${\mathit{n}}_{\mathit{e}}$) of inactive mobile P increases with temperature. The formation and the diffusion behavior of this inactive dopant are in keeping with a preprecipitation phenomenon. \textcopyright{} 1996 The American Physical Society.

Retarded and enhanced dopant diffusion in silicon related to implantation-induced excess vacancies and interstitials

Abstract: The influence of the lattice defects induced by silicon‐ion implantation on the B, P, As, and Sb diffusivities is investigated after annealing between 700 and 900 °C The nature and depth position of the residual implantation defects in undoped samples is determined by the analysis of the rocking curves obtained by triple‐crystal x‐ray diffraction and transmission electron microscopy In particular, besides the interstitial dislocation loops and clusters below the original amorphous‐crystal interface, the epitaxial regrowth of the amorphized silicon leaves a vacancy‐rich surface layer and a deeper region enriched in interstitials These regions correspond to those where Monte Carlo simulations of defect production foresee excess point defects Accordingly, as the dopant is located in correspondence with the vacancy or interstitial clusters, different behaviors of anomalous diffusion are observed In the deep region where an interstitial excess is present, B and P show marked enhanced diffusion, while only a small enhancement is exhibited by As and Sb On the contrary, retarded diffusivity for B and light enhancement for As and Sb are observed in the surface layer These different trends are consistent with the different accepted contributions of vacancies and interstitials to the diffusion mechanisms of the investigated dopants

Semiconductor device, and manufacturing method thereof

Abstract: An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Point defects and dopant diffusion in silicon

Abstract: Diffusion in silicon of elements from columns III and V of the Periodic Table is reviewed in theory and experiment. The emphasis is on the interactions of these substitutional dopants with point defects (vacancies and interstitials) as part of their diffusion mechanisms. The goal of this paper is to unify available experimental observations within the framework of a set of physical models that can be utilized in computer simulations to predict diffusion processes in silicon. The authors assess the present state of experimental data for basic parameters such as point-defect diffusivities and equilibrium concentrations and address a number of questions regarding the mechanisms of dopant diffusion. They offer illustrative examples of ways that diffusion may be modeled in one and two dimensions by solving continuity equations for point defects and dopants. Outstanding questions and inadequacies in existing formulations are identified by comparing computer simulations with experimental results. A summary of the progress made in this field in recent years and of directions future research may take is presented.

Modeling of carrier mobility against carrier concentration in arsenic-, phosphorus-, and boron-doped silicon

Abstract: New carrier mobility data for both arsenic- and boron-doped silicon are presented in the high doping range. The data definitely show that the electron mobility in As-doped silicon is significantly lower than in P-doped silicon for carrier concentrations higher than 1019cm-3. By integrating these data with those previously published, empirical relationships able to model the carrier mobility against carrier concentration in the whole experimental range examined to date (about eight decades in concentration) for As-, P-, and B-doped silicon are derived. Different parameters in the expression for the n-type dopants provide differentiation between the electron mobility in As-and in P-doped silicon. Finally, it is shown that these new expressions, once implemented in the SUPREM II process simulator, lead to reduced errors in the simulation of the sheet resistance values.

Physical mechanisms of transient enhanced dopant diffusion in ion-implanted silicon

Abstract: Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy (MBE). Damage from nonamorphizing Si implants at doses ranging from 5×1012 to 1×1014/cm2 evolves into a distribution of {311} interstitial agglomerates during the initial annealing stages at 670–815 °C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of interstitials from the damage region involves the dissolution of {311} defects during Ostwald ripening with an activation energy of 3.8±0.2 eV. The excess interstitials drive substitutional B into electric...

Implantation and transient B diffusion in Si: The source of the interstitials

Abstract: Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during initial annealing, due to Si interstitials being emitted from the region of the implant damage. The structural source of these interstitials has not previously been identified. Quantitative transmission electron microscopy measurements of extended defects are used to demonstrate that TED is caused by the emission of interstitials from specific defects. The defects are rodlike defects running along 〈110〉 directions, which consist of interstitials precipitating on {311} planes as a single monolayer of hexagonal Si. We correlate the evaporation of {311} defects during annealing at 670 and 815 °C with the length of the diffusion transient, and demonstrate a link between the number of interstitials emitted by the defects, and the flux of interstitials driving TED. Thus not only are {311} defects contributing to the interstitial flux, but the contribution attributable to {311} defect evaporation is sufficient to explain the whole ...