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Low-temperature photoluminescence (PL) spectroscopy, in conjunction with transmission electron microscopy (TEM) and optical microscopy (OM) have been carried out to investigate the origin of radiative recombination from various extended defects that evolve during high-temperature processing of ion-implanted epitaxial silicon. From PL studies on N2-annealed samples, we provide spectroscopic evidence of precipitation of the implanted impurities well below the solid-solubility limit. This result is being supported by observations from secondary ion mass spectrometry and spreading resistance profiling of the implanted ions. Cross sectional TEM analyses on these samples reveal 〈111〉-oriented precipitates located in a region containing a high dislocation density. Postimplantation annealing in oxygen ambient results in the formation of dislocations and oxidation-induced stacking faults (OISF). A systematic analysis of PL spectra on different-implanted and preannealed samples, in conjunction with TEM and OM analy...

The structural, electrical and optical properties of crystalline Si co-doped with Er and O by molecular beam epitaxy (MBE) and annealed at 900°C for 1 h have been investigated in detail. We observed clear constraints to the Er content that can be incorporated in a good quality single crystal. Moreover, we show that the O:Er ratio represents the main parameter in determining the properties of this system: Er electrical and optical activation increases with O:Er ratio until a saturation regime is achieved for a ratio higher than 6–8. We attribute this saturation regime to the full O coordinated first shell surrounding Er atoms in the Si host after the annealing at 900°C. In contrast, the most intense room temperature photoluminescence (PL) peak is obtained in samples having an O:Er ratio ∼2, for which PL temperature quenching is strongly reduced. Moreover, we investigated by X-ray photoelectron spectroscopy (XPS) the Er mobility for different temperatures and observed its penetration into the Si bulk from an Er/Si surface only after the annealing at 900°C. These phenomena are investigated in detail and discussed.

The kinetics of the C49–C54 phase transition was analysed in TiSi2 thin films obtained by reacting a Ti layer deposited on amorphous silicon. The C54 fraction was determined in the temperature range 680–720°C by electrical measurements and by micro-Raman spectroscopy. The Raman spectra were acquired by scanning large silicide areas (100×50 μm) and images showing the evolution of the C54 grains at different times and temperatures were obtained. The transformed fraction, the density and size distribution of the C54 grains were measured, and a detailed discussion of the errors associated with the micro-Raman technique is presented. The data indicate that the nucleation rate is not constant and the Johnson–Mehl–Avrami model cannot describe this transition.

We have investigated the crystalline quality of 0.6–1.2 μm poly-CoSi 2 lines, formed on (001) silicon by a standard salicide process. The microstructure of silicide grains has been investigated by TEM and HRTEM techniques and related to their location inside the strip. The grains at the centre of the line were randomly oriented with respect to the substrate unlike at the edges, where some interesting epitaxial relationships were detected. Selected area diffraction (SAD) analyses on the line section indicated the presence of both A- and B-type epitaxial regions even inside the same grain, whose interface to silicon lies along the (1, 1 ,1) planes. In these regions, high-resolution transmission electron microscopy (HRTEM) analyses have shown misfit dislocations inserted along the (111) planes to compensate the lattice mismatch. High temperature anneals mainly deteriorate the line edges with serious damage to their electrical performance.

The mechanism of bubble formation when He is implanted into silicon is described. Many experiments are reviewed and several techniques are considered. During implantation and subsequent annealing, complex Hen–Vm clusters are formed, trapping vacancies, while Si self-interstitials recombine directly at the surface. By increasing temperature He atoms out-diffuse, and the entire process produces a supersaturation of vacancies (void formation). Their evolution is studied during isothermal and isochronal annealing, describing the mechanisms involved; that is, direct coalescence or Ostwald ripening. The internal surface is an efficient trap for self-interstitials and for metals. The gettering mechanism is governed by a surface adsorption at low impurity concentration while at high value a silicide phase is observed. The high getter capability is ensured by the large number of traps introduced (1017–1019 cm−3). Finally, voids introduce mid gap energy levels that act as minority carrier recombination centers, providing a powerful method to control lifetime locally in silicon devices. The reviewed results demonstrate that the trap levels are due to the dangling bonds present on the void surface. This property can be used in many applications.

We have investigated the optical and structural characteristics of defect evolution during high-temperature annealing of keV-ion-implanted epitaxial silicon using optical microscopy (OM), photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Postimplantation annealing in oxygen ambient resulted in oxidation-induced stacking faults (OISFs) and dislocations. The PL spectrum of these samples is dominated primarily by a dislocation-related D1 line, which is particularly strong in Al-implanted samples as a consequence of the enhanced formation of dislocations with Al implantation. Comparative analysis of the PL signature and OM observations of defects for different implants suggests that D1 and D2 lines result from dislocations rather than in the OISFs. Indeed, it is found that OISFs act as a nonradiative recombination channel in the luminescence of Si. PL studies of N 2 -annealed samples indicate the formation of nonradiative defect centres. In the case of dopant implants, after rapid thermal annealing (RTA) for 2 min in N 2 ambient, the specific signature of extended defects was found from PL studies, while TEM analysis reveals the presence of precipitates located in a region with a high dislocation density. In comparison with other dopants, Al implants show an enhanced formation of extended defects, and they are found even at a depth beyond the end-of-ion range damage.

The mechanisms of He bubble and, after annealing, of void formation have been investigated for single and multiple ${\mathrm{He}}^{+}$ implants in Si. Several analytical techniques have been adopted: photoluminescence (PL), Rutherford backscattering of protons, transmission electron microscopy, and atomic force microscopy. When a second implant is performed a systematic enlargement of the bubble band reveals the importance of the interaction between He atoms and point defects generated during irradiation. Size effects of the implanted region protrusions indicated a He diffusion mechanism and an interaction with vacancies and divacancies for the bubble formation. PL spectra indicate the presence of complexes helium divacancies in the same temperature where self-interstitials annihilate at the sample surface. The interaction of helium atoms with divacancies allows the inversion in the vacancy-interstitial balance producing a supersaturation of vacancies in the silicon bulk. This vacancy supersaturation causes the observed annihilation of interstitial type defects after a suitable annealing.

The kinetic of the C49–C54 phase transformation at 730°C in TiSi 2 narrow strips for width in the 0.5–1.3-μm range was investigated by resistance measurements and μ-Raman spectroscopy. With this last technique a growth rate of 0.15 μm/s and a nucleation density of about 0.035 sites/μm 2 were obtained. The fraction of the transformed material as measured by resistance follows the Johnson–Mehl–Avrami equation, with an exponent equal to 1 for all of the analysed linewidths. Nucleation site saturation occurs and the growth is one-dimensional along the length of the strip. The characteristic time increases as 1/ W , W being the width of the strip, and, taking into account the growth rate obtained by μ-Raman spectroscopy, the nucleation density resulted 0.034 sites/μm 2 in excellent agreement with the μ-Raman results.

The effect of lateral dimensional scaling on the thermal stability of polycrystalline cobalt disilicide wires reacted on Si (001) has been studied down to 0.6 μm linewidth. An unpatterned silicide has been used as a reference sample. The annealing processes were performed in N2 environment, between 900 and 1050°C, on both blanket and patterned silicide. Transmission electron microscopy analyses in plan-view and cross-section allowed us to study the morphology of lines before and after high-temperature processes. Resistance measurements showed a better thermal stability in blanket silicide layer compared to narrow lines. The electrical behaviour of the lines has been explained in terms of both lateral roughness and hole formation in the silicide layer.

The effect of lateral scaling on the thermal stability of cobalt disilicide has been investigated on Si (001) substrates. Resistance measurements on four terminal resistors, with linewidth dimensions ranging from 1.3 to 0.5 μm, have been performed after annealing in the range between 900 and 1000 °C. The resistance increases faster in the stripes than in blanket regions. This degradation process has been correlated to the morphological change in the strip cross section, as analyzed by transmission electron microscopy and atomic force microscopy. Grain growth, degradation processes at the line edge, and surface and interface roughness have been observed. These analyses show that the lateral constraints of the silicide lines are mainly responsible for the lowering of the silicide thermal stability compared with blanket regions. Moreover, from measurements of agglomerated silicide grains in equilibrium with the substrate, the silicide surface free energy is 2.3 times the free energy of the CoSi2/Si interface.

He atoms were implanted in crystalline and pre-amorphized silicon wafers at doses in the 2×10 16 1×10 17 cm −2 range. Using transmission electron microscopy (TEM) we monitored the evolution of He bubbles into voids upon thermal annealing. Bubbles are formed in both crystalline and amorphous silicon. However, in amorphous material bubble interaction with the moving crystalline–amorphous interface during the epitaxial regrowth prevents their evolution into voids. By implanting He at different target temperatures in crystalline Si, thus by changing the structure of radiation damage, we found that the interaction between point defects and He atoms is essential for the generation of He bubbles and for their subsequent evolution into voids.

Formation and properties of voids in silicon obtained by high dose helium implants are described and discussed in view of their applications in localised lifetime engineering. Voids are stable even after huge thermal budget as observed by transmission electron microscopy analyses. Leakage measurements on p + n diodes as a function of temperature allowed us to determine the hole trap level ( ΔE =0.16 from the Fermi level above the valence band) and the generation and recombination lifetime values. To demonstrate the advantage of the method in power device applications, high-speed IGBTs were fabricated both with voids in the buffer layer or with unlocalised recombination centres. The devices with voids show a lower on-resistance and a fast turn-off behaviour. Map measurements on 150 mm silicon wafers demonstrate the good uniformity that can be reached by the method in an industrial environment.

The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen, oxygen or fluorine at different concentrations. Enhancement of the thermal stability has been observed in O and N amorphous doped Ge2Sb2Te5. Larger effects have been found in the case of nitrogen doping. On the contrary, doping with Fluorine produced a decrease in the crystallization temperature. The electrical properties have been related to the structural phase change through in situ transmission electron microscopy analysis. The comparison between undoped and doped Ge2Sb2Te5 shows that the introduction of oxygen or nitrogen modifies in a different way the kinetics of the amorphous-to-fcc transition and gives new insight on the effects of doping with light elements in GeSbTe alloys.

The behavior of ion-implanted As in (100) silicon wafers, following thermal oxidation, has been investigated by Rutherford backscattering spectroscopy, atomic force microscopy, transmission electron microscopy, and extended x-ray-absorption fine structure. The adopted fluences ($3\ifmmode\times\else\texttimes\fi{}{10}^{15}$ and $3\ifmmode\times\else\texttimes\fi{}{10}^{16}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$) and oxidation conditions (wet 920 \ifmmode^\circ\else\textdegree\fi{}C, dry 1100 \ifmmode^\circ\else\textdegree\fi{}C) span quite a broad range of phenomena, giving rise to As diffusion in the bulk, and/or segregation and precipitation at the ${\mathrm{SiO}}_{2}/\mathrm{S}\mathrm{i}$ interface. The surface roughness is correlated to that measured at the interface, although the oxide presence strongly reduces the value with respect to that present at the interface. Rough interfaces and surfaces are formed when the arsenic concentration exceeds the solid solubility and precipitation occurs. The SiAs precipitates are characterized by a monoclinic structure with low surface energy for the (100) facet, as determined by the Wulff plot. Residual roughness is left at the oxide surface even if precipitates initially formed dissolve during subsequent oxidation. The depth profile of the dopant has been quantitatively computed by the analytical solution of the diffusion equation, taking into account the interface movement, the As redistribution at the interface between oxide and bulk silicon, the formation, growth, and dissolution of precipitates, and, of course, the drive-in process. The dependence of the diffusion coefficient on the dopant concentration has been also considered and determined as a converging parameter, considering iteratively the differential equation solution. In all the investigated cases the agreement between experimental data and calculations has been found to be good.

The dependence of the hole mobility on the dopant concentration ranging from to was determined at room temperature in Al-implanted Si samples. The trend was obtained by the use of Hall effect and resistivity measurements on the van der Pauw pattern in combination with secondary-ion mass spectrometry and spreading resistance analysis. The mobility data are in a quite good agreement with the Wagner curve for boron in the high Al concentration region while they approach the Thurber boron curves at low concentrations. This result indicates that the neutral and ionized impurity scattering mechanisms are not critically different for Al- and B-doped samples. The mobility - dopant concentration curve can be employed to convert the resistivity profiles obtained by spreading resistance measurements into hole concentration distributions for Al-doped samples.

Ultra-shallow p/sup +//n and n/sup +//p junctions were fabricated using a Silicide-As-Diffusion-Source (SADS) process and a low thermal budget (800-900/spl deg/C). A thin layer (50 nm) of CoSi/sub 2/ was implanted with As or with BF/sub 2/ and subsequently annealed at different temperatures and times to form two ultra-shallow junctions with a distance between the silicide/silicon interface and the junction of 14 and 20 nm, respectively. These diodes were investigated by I-V and C-V measurements in the range of temperature between 80 and 500 K. The reverse leakage currents for the SADS diodes were as low as 9/spl times/10/sup -10/ A/cm/sup 2/ for p/sup +//n and 2.7/spl times/10/sup -9/ A/cm/sup 2/ for n/sup +//p, respectively. The temperature dependence of the reverse current in the p/sup +//n diode is characterized by a unique activation energy (1.1 eV) over all the investigated range, while in the n/sup +//p diode an activation energy of about 0.42 eV is obtained at 330 K. The analysis of the forward characteristic of the diodes indicate that the p/sup +//n junctions have an ideal behavior, while the n/sup +//p junctions have an ideality factor greater than one for all the temperature range of the measurements. TEM delineation results confirm that, in the case of As diffusion from CoSi/sub 2/, the junction depth is not uniform and in some regions a Schottky diode is observed in parallel to the n/sup +//p junction. Finally, from the C-V measurements, an increase of the diodes area of about a factor two is measured, and it is associated with the silicide/silicon interface roughness.

Electroless silver deposition (for 1–100s) has been simultaneously performed on (100) and (111) planes of macro and micro patterned silicon, fabricated using optical lithography and anisotropic etching with alkaline solution. Metal clusters formation occurs preferentially on the upper edge region separating the two main planes. Their density and mean size are higher on the (100) plane. Similar experiments performed on same patterned samples but with the surface amorphized by ion implantation elucidated the role played by the preferential mass transport caused by the pattern geometry. For the micro-sized pyramidal holes, the non uniform surface distribution of metal clusters is enhanced. The metal deposition occurs mainly on the (100) top strips surrounding the pyramids. The subsequent preferential oxidation of silicon under the metallic clusters gives rise to nanowires of (100) and (111) orientation in the macro and to nanopillars in the micro patterns respectively. Nanowire’s tips are preferentially sites for metal deposition as shown after re-immersion in the plating solution. Samples with contiguous one dimensional nanostructures of different orientation could be used for the study of transport properties’ anisotropy. The formation of metal tips on top of the nanostructures might be of relevance in the field of metal-semiconductor contacts. © 2013 The Electrochemical Society. [DOI: 10.1149/2.002311jss] All rights reserved.

The electrical properties of amorphous GeTe films deposited at room temperature, ion implanted, and melt-quenched have been studied. The activation energy for the mobility gap varies from 0.64, in the melt-quenched, to 0.74 eV, in the as deposited film. In all the types of amorphous, pre-annealing at temperatures below crystallization induces relaxation, increasing the resistance and the mobility gap. Pre-annealing also reduces the nucleation rate for crystallization by a factor up to 4. A model is proposed, describing the competing processes of structural relaxation and crystallization, as governed by a population of sub-critical nuclei formed by medium range ordered regions.

A nano-sized ion beam apparatus has been used as maskless lithography to implant 20 keV Ga+ ions into a 26 nm thick silicon crystalline film on insulator. The ion beam, with about 5 nm standard deviation, delivered few hundred ions during a single shot. Circular areas with nominal diameter of 20 or 50 nm were irradiated to a fluence of 5 x 10(14)/cm(2). Transmission electron microscopy evidenced that the damaged regions are characterized by an irregular contour with many disordered filaments. Damage extends across the layer thickness and fast Fourier transform analysis indicates that implantation causes the amorphization of a region which extends beyond the nominal diameter. In situ annealing experiments demonstrated that the disordered filamentary regions disappear in the 250-450 degrees C temperature range and the interfaces with the surrounding crystalline regions sharpen. A temperature as high as 600 degrees C is required to fully re-crystallize the amorphous core of the implanted dots. Reordering occurs by multi-orientation lateral solid-phase epitaxial growth and the breaking of (111) and (101) interfaces, due to the formation of twins, triggers a fast crystallization kinetics. Rapid thermal annealing (890 degrees C-10 s) completely crystallizes the amorphous regions, twins are absent and small cluster of defects remains instead. Preliminary scanning capacitance measurements indicate that the implanted atoms, after crystallization, are electrically active. The implant method is then a viable processing step for the doping of non-bulk fully depleted ultra-thin-body MOSFET.

Rutherford Backscattering (RBS) of lithium ions is investigated to study the near-surface region of different targets. Lithium beams, 8 MeV in energy, are produced by the tandem accelerator of the Laboratorio Nazionale del Sud of Catania (Italy). RBS is applied to monocrystalline silicon substrates to perform, in axial and planar ion channelling, ion implantation “in situ” of heavy ion species at high energy (∼0.5 MeV/amu). Arsenic ions, 40 MeV in energy and doses ranging between 1 and 8 × 1015 at/cm2, are implanted in silicon substrates to modify the electrical resistivity of deep layers. This paper presents the limitations of the technique, the mass sensitivity, the cross sections involved and the minimum detection amounts compared to the traditional RBS of helium beams.

The diffusion and segregation of ion implanted Al in SiO2 and Si layers were studied for several experimental conditions. Al ions were implanted into SiO2, Si and through a SiO2 layer into Si substrates at several energies (80, 300, 650 and 6000 keV) and doses (3.4 × 1014–1 × 1015 cm−2). The Al diffusion coefficient in SiO2 was measured at 1200°C for times up to 5 days, and it results five orders of magnitude lower than in Si. The experiments show that the Al atoms implanted into Si do not out-diffuse during thermal treatments from the SiO2 capping layer, but segregate at the SiO 2 Si interface. The high segregation coefficient gives rise to a trapping of Al into the oxide layer comparable to the out-diffusion of Al from uncapped Si substrates. The determined parameters for Al diffusion and segregation in the SiO 2 Si system were introduced in a simulation code to calculate the Al diffusion profiles which result in agreement with the experimental data.

The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen or oxygen. The dependence of the electrical resistivity and structure on the annealing temperature and time has been investigated in samples with different dopant concentrations. Enhancement of the thermal stability and increase of the mobility gap for conduction have been observed in O- and N-doped amorphous Ge2Sb2Te5. Larger effects have been found in the case of nitrogen doping.

The kinetics of the amorphous-to-crystal transition in Ge2Sb2Te5 thin films have been studied through in situ transmission electron microscopy analyses. By following the time evolution of the grain density and size, the growth velocity and the nucleation rate have been separately measured at different annealing temperatures. Activation energies of 2.9+/-0.5 eV and 2.3+/-0.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus DeltaG(*) has been evaluated, and the scalability of phase change nonvolatile memories has been estimated.

The diffusion from CoSi2 layers, implanted with As and B ions, into the underlying Si substrate has been studied by a high-resolution carrier delineation technique. In the early stages of diffusion the junction shape follows the silicide/silicon interface for B, while it is deeper near the CoSi2 grain boundaries for As. The different behaviour is related to the different diffusion mechanisms of As and B in the silicide layer. Using a two-step anneal or a thin silicide diffusion source a laterally uniform junction has also been obtained for As-implanted CoSi2. The diffusion coefficients of arsenic and boron in silicon have been measured by this technique. The measured diffusivity values for boron and arsenic are very close to the data reported in the literature.

Two-dimensional diffusion of aluminum implanted through a mask in silicon has been measured after furnace or rapid thermal annealings. Chemical staining on cross-sectioned samples was used to determine both the vertical and the lateral function depths. The spreading resistance standard procedure was adopted to measure the vertical profiles while a new procedure was developed for the determination of the lateral diffusion profiles. The difference in the measured profile by staining and spreading resistance is related to the spilling phenomenon that distorts the carrier concentration profile on beveled samples. Moreover, experimentally aluminum diffusion parameters and segregation coefficient at the Si/SiO 2 interface have been introduced in advanced one-dimensional (SUPREM III) and two-dimensional (SUPREM IV) process simulators. The good agreement between the simulated and the experimental data, for both the lateral and the vertical directions, indicates that these process simulators can reproduce with accuracy the aluminum diffusion

An oxygen precipitation phenomenon was evidenced on high energy implanted Czochralski silicon samples. Al, Si, P, O and C ions with nergies in the 1–6.8 MeV range and doses in the 4 × 10 14 −1 × 10 15 / cm 2 range were single or double implanted in CZSi. A strong interaction was evidenced between the implanted species, the damage and the oxygen present in the substrates after annealing at 1100 or 1200°C for 30 min. The oxygen precipitation is greatly enhanced by the presence of Al that interacting with O results almost completely electrically inactive.

Boron ions were implanted at 80 keV for a dose of 2 × 1015 cm−2 in crystalline silicon. The silicon crystal was recovered using different annealing processes to produce layers with different secondary defect densities. The quality and the characteristics of the silicon oxide grown on the different surfaces were found to depend on the defects present in the layer immediately under it. The oxide quality was improved by using implanted and annealed silicon with a defect free surface. Iron contaminations, introduced in the wafers at different concentrations (up to 1 × 1015 cm−2), do not affect the oxide layer grown on unimplanted silicon wafers, while it degrades the oxide characteristics of layers grown on implanted and annealed samples. This degradation decreases if the residual damage is reduced by annealing processes.

He bubbles were formed in Si substrates implanting He at doses ranging from 5 × 1015 / cm2 to 1 × 1017 / cm2 and energies in the range of 40–300 keV. Bubbles are formed only if a dose of 1 × 1016 /cm2 at 40 keV is exceeded, while at 300 keV a dose of 5 × 1016 /cm2 has to be reached. If bubbles are present in the as-implanted sample after annealing at 700°C voids are formed. The void evolution during subsequent thermal processing was studied in detail. The thermal stability is found to be excellent for long thermal treatments and an increase in the void diameter with increasing the annealing temperature was observed. The gettering reactivity of these voids is higher than for conventional gettering processes.

In this paper, we present a nanoscale morphological and structural characterization of few layers of graphene grown by thermal decomposition of off-axis 4H-SiC (0001) and by C segregation on Ni thin films from a solid carbon source. Transmission electron microscopy in different configurations, i.e. cross-section and plan view, was used to get information on the number of graphene layers as well as on the rotational order between the layers and with respect to the substrate. Atomic force microscopy was used to study the changes in the surface morphology produced by thermal annealing. In particular, the density and the height of peculiar corrugations (wrinkles) in the few layers of graphene, formed during the cool down in the thermal process, were investigated.

As an aid toward a better understanding of data retention of phase change memories we have analyzed in situ by Transmission Electron Microscopy the crystallization of amorphous Ge2Sb2Te5 dots of 100 nm and 20 nm diameter, embedded in the hexagonal crystalline phase. Amorphization was obtained by 40 keV Ge+ irradiation at LN2 through Electron Beam Lithography masked pattern. At 75 degrees C/90 degrees C, crystallization in 100 nm dots occurs by grain growth from the surrounding crystalline material, with an initial growth velocity of 0.6 (6.4) pm/s followed by a slower rate of 0.14 (1.7) pm/s. At 75 degrees C, the 20 nm amorphous regions disappear just after two hours of annealing.

Graphene deposited on silicon dioxide (DG-SiO 2 ) and high- κ dielectric strontium titanate (DG-STO) are investigated for electrostatic properties by local capacitance measurements carried out with Scanning Capacitance Spectroscopy (SCS). The quantum capacitance associated with 2DEG in graphene showed significant increase for DG-STO as a function of Fermi level ( E F ) as compared to that for DG-SiO 2 . The quantum capacitance, being a fundamental property of graphene 2DEG, is not expected to vary with substrate dielectric properties in the absence of any interaction. However, the observed increase in quantum capacitance in our case is predominantly due to the enhanced effectively biased area in DG-STO. We suggest that this effect is a consequence of better dielectric screening of commonly observed charged impurities, on graphene and/or at the graphene/substrate interface, by the use of high permittivity substrate.

The crystallization of amorphous GexTe1-x (x = 0.36,0.51, 0.63) films (50 nm) has been investigated by time resolved reflectivity, transmission electron microscopy, Raman spectroscopy and X-ray diffraction. The Ge-rich film has the highest crystallization temperature (354 degrees C) with respect to both GeTe (180 degrees C) and Te-rich samples(244 degrees C). In non-stoichiometric films, the precipitation of the excess atomic species is the first step during the crystallization process: amorphous Ge and crystalline Te precipitates were detected in Ge and Te rich alloys, respectively. The atomic interdiffusivity was estimated to be similar to 5x10(-15) cm(2)/s at 220 degrees C in the Te-rich alloy and similar to 4x(10-14) cm(2)/s in the Ge-rich film at 330 degrees C. In both cases Tellurium is likely to be the diffusing species. This description accounts for the presence of amorphous Ge precipitates at the initial stage of the crystallization of the Ge rich alloy. The GeTe crystalline grains subsequently act as a seed for Ge crystallization. Non stoichiometric crystalline alloys have been reamorphized by laser or ion irradiation. In laser irradiated samples, the crystallization is similar to that of as deposited film since the precipitates mix with GeTe during the melt duration. In ion implanted samples this mixing doesn't occur and GeTe crystallization temperature is close to that of stoichiometric film.

Our recent work on the poly/single crystal Si interface evolution and on the epitaxial realignment under high temperature (∼ 1000°C) rapid thermal annealing is reviewed. The roles of the mucrystalline morphology, of the interfacial native oxide film, of the doping level and of the processing temperature on the realignment kinetics are addressed. Two different realignment modes are observed. For undoped layers a quasi planar interface motion occurs, while in highly doped polycrystalline layers the realignment proceeds via the formation of epitaxial columns and their lateral growth. These two different modes arise from the doping enhancement of the interface kinetics. It is shown that these processes can be interpreted within an Avrami-Mehl-Johnson nucleation and growth scheme. In the early stages of interface realignment the process is controlled by oxide clustering, arising from the evolution of the native oxide layer, and by the density of grain boundaries intersecting the interface with the single crystal. Once nucleated at specific sites the epitaxial front can then proceed, the kinetics and mode of realignment depending on the density of nucleation sites and on the growth velocity. It is also demonstrated that when narrow (∼ 0.25 μm) polycrystalline strips defined by oxide layers (as in real devices) are used in place of infinite planar layers the realignment mode and kinetics change due to the presence of size effects. These data are presented and their implications for applications to bipolar devices are discussed.

The induced changes of the flatband voltage by the location of holes in a silicon-rich oxide (SRO) film sandwiched between two thin SiO 2 layers [used as gate dielectric in a metal-oxide-semiconductor (MOS) capacitor] can be used as the two states of a memory cell. The principle of operation is based on holes permanently trapped in the SRO layer and reversibly moved up and down, close to the metal and the semiconductor, in order to obtain the two logic states of the memory. The concept has been verified by suitable experiments on MOS structures. The device exhibits an excellent endurance behavior and, due to the low mobility of the holes at low field in the SRO layer, a much longer refresh time compared to conventional dynamic random access memory cells. © 2002 American Institute of Physics.

N-induced cavity nucleation at the CoSi2/Si interface has been investigated for different doses and its influence on improving the thermal stability of the silicide layer up to 1075 °C has been detailed. The N-implant energy and doses have been chosen in such a way that the projected range (Rp) was near the interface and the underlying polycrystalline silicon substrate was completely amorphized. After a thermal treatment of 975 °C, it has been found that the cavity density depends on the dose, but the cavity size is dose independent. The cavity density should be enough to saturate the silicide grain boundaries but not so high to neglect ripening and coalescence. A density of 2.5×1010 cavities/cm2 has been measured at a nitrogen dose of 7×1015/cm2 corresponding to a partial saturation of the silicide grain boundaries and to the higher stability gain (150 °C).

Recently, giant carrier mobility mu (>10(5) cm(2) V-1 s(-1)) and micrometer electron mean free path (1) have been measured in suspended gaphene or in graphene encapsulated between inert and ultraflat BN layers. Much lower mu values (10000-20000 cm(2) V-1 s(-1)) are typically reported in graphene on common substrates (SiO2, SiC) used for device fabricaticn. The debate on the factors limiting graphene electron mean free path is still open with charged impurities (CI) and resonant scatterers (RS) indicated as the most probable candidates. As a matter of fact, the inhomogeneous distribution of such scattering sources in graphene is responsible of nanoscale lateral inhomogeneities in the electronic properties, which could affect the behavior of graphene nanodevices. Hence, high resolution two-dimensional (2D) mapping of their density is very important. Here, we used scanning capacitance microscopy/spectroscopy to obtain 2D maps of l in graphene on substrates with different dielectric permittivities, that is, SiO2 (kappa(SiO2) = 3.9), 4H-SiC (0001) (kappa(SiC) = 9.7) and the very-high-kappa perovskite strontium titanate, SrTiO3 (001), briefly STO (kappa(STO) = 330). After measuring l versus the gate bias V-g on an array of points on graphene, maps of the CI density (N-CI) have been determined by the neutrality point shift from V-g = 0 V in each curve, whereas maps of the RS density (N-RS) have been extracted by fitting the dependence of l on the carrier density (n). Laterally inhomogeneous densities of CI and RS have been found. The RS distribution exhibits an average value similar to 3 x 10(10) cm(-2) independently on the substrate. For the first time, a clear correlation between the minima in the l map and the maxima in the N-CI map is obtained for graphene on SiO2 and 4H-SiC, indicating that CI are the main source of the lateral inhomogeneity of l. On the contrary, the l and N-CI maps are uncorrelated in graphene on STO, while a clear correlation is found between l and N-RS maps. This demonstrates a very efficient dielectric screening of CI in gaphene on STO and the role of RS as limiting factor for electron mean free path.

The crystallization dynamic of amorphous GeTe 50 nm thick films deposited on a SiO 2 /Si substrate by RF magnetron sputtering, either ion implanted by Ge + ions or not, has been analyzed in situ by optical microscopy during annealing in the 143–155 °C temperature range. Raman spectroscopy has been also performed in as deposited, ion implanted (i.i.) and melt quenched (m.q.) amorphous samples to compare the local order among the different amorphous structure. Nucleation and growth rates, for i.i. and as deposited samples, have been observed and directly compared by optical microscopy in a region of about 5 × 10 4 μm 2 . From these data, the activation energy and pre-exponential terms of each process have been calculated. The nucleation rate and growth velocity of the i.i. films increased by a factor thirteen and a factor three with respect to the as deposited samples. This evidence, in agreement with Raman spectroscopy data, suggests that implantation, providing kinetic energy by collision cascade, induces a local atomic rearrangement towards more relaxed amorphous states. As a result the crystallization kinetic is enhanced by the reduction of wrong bonds formed during sputter deposition, a process which occurs far from equilibrium conditions.

Ion irradiation with 130 keV Ge+ or 120 keV Sb+ has modified, by thermal spike effect, the local atomic arrangement in the structure of as-deposited sputtered amorphous GeTe and Ge2Sb2Te5 thin films. The changes in the local order have been analyzed by Raman and EXAFS spectroscopy. In addition the crystallization kinetic, measured by “in situ” time resolved reflectivity and optical microscope analysis, is found to be faster in the irradiated samples. The nucleation rate and the grain growth velocity are enhanced by a factor of about ten with respect to the unirradiated samples in the investigated temperature range (120°C –170°C).

The local order of amorphous Ge2Sb2Te5films (50 nm) prepared by sputtering (AD), melt quenching (MQ), or ion irradiation (II) hasbeen probed by EXAFS and Raman spectroscopy. The Ge K edge of the AD sample shows a stronger contribution from homopolarGe-Ge bonds with respect to irradiated films. Raman spectroscopy measurements indicate a greater abundance of homopolar Te-Tebonds in AD film with respect to MQ and II. Irradiation of deposited amorphous GST films results in a reduction of "wrong"homopolar bonds. This variation is probably the origin of the faster crystallization speed of MQ and II amorphous samples.

Graphene, a two-dimensional sheet of C atoms, is the object of many scientific studies, especially due to the outstanding electronic properties. The behavior of graphene based nano-devices or mesoscopic devices is ultimately influenced by the lateral homogeneity of the carrier density, electron mean free path, and mobility on the layer. This chapter reviews the main applications of scanning probe methods to the local (nanoscale) characterization of the electronic properties of graphene.

We have investigated the stability of nano-amorphous region of Ge2Sb2Te5 (GST), fabricated by Electron Beam Lithography (EBL), dry etching, and ion implantation. Nano-structures, less than 100 nm in diameter and 20 nm thick, were either embedded in a crystalline environment or just isolated. We have observed nano-structure crystallization by in situ Transmission Electron Microscopy (TEM) in the 75°C-150°C temperature range. Re-crystallization of amorphous dots embedded in a crystalline region (either in the cubic or hexagonal phase) occurs by the movement of the interface at relatively low temperature (about 90°C). Instead, in the isolated structures the transition occurs at about 145°C by nucleation and growth. These results might be of relevance for the data retention of sub-50nm devices. Indeed, the more stable amorphous phase in self-standing regions indicates the better retention properties of isolated cells with respect to the traditional mushroom cell configuration.

Arsenic ions were implanted into CoSi2 thin layers and subsequently diffused into the underlying silicon substrate. Junctions in the range between 30 and 400 nm depth were obtained with a high dopant concentration (1019-1020 cm-3) at the silicide-silicon interface. Coherent Si-As precipitates were found at the silicide-silicon interface near the CoSi2 grain boundaries. The precipitate formation has been associated with the high tensile stress induced by the silicide layer on the surface silicon region and to its influence on the dopant solid solubility. The precipitate density decreases if the silicide thickness is reduced, i.e. if the tensile stress produced by a silicide layer gets lower. These precipitates are easily dissolved during high temperature annealing after the silicide layer removal. A new delineation technique based on TEM analysis of selectively etched samples has evidenced that the intersections of silicide grain boundaries with a silicon surface act as diffusion sources.

The early stages of the thermally induced epitaxial realignment of undoped and As-doped polycrystalline Si films deposited onto crystalline Si substrates were monitored by transmission electron microscopy. Under the effect of the heat treatment, the native oxide film at the poly-Si/c-Si interface begins to agglomerate into spherical beads. The grain boundary terminations at the interface are the preferred sites for the triggering of the realignment transformation which starts by the formation of epitaxial protuberances at these sites. This feature, in conjunction with the microstructure of the films during the first instants of the heat treatment, explains the occurrence of two different realignment modes. In undoped films the epitaxial protuberances, due to the fine grain structure, are closely distributed and grow together forming a rough interface moving toward the film's surface. For As-doped films, the larger grain size leaves a reduced density of realignment sites. Due to As doping some of these sites grow fast and form epitaxial columns that further grow laterally at the expense of the surrounding polycrystalline grains.

P and B ions with energies of 400 keV and 1 MeV were implanted in a random direction and along the [100] axis of single‐crystal Si samples patterned with oxide stripes. The lateral spread of the implants was determined by using two‐dimensional spreading resistance measurements. The lateral distribution of ions implanted in a random direction is always broader than that of ions implanted with the same energy along the [100] axis. With increasing dose the lateral penetration for channeled implants increases too due to the disorder introduced in the samples. The experimental results are discussed and then compared with Monte Carlo simulations obtained by the marlowe code.

Al-based precipitate evolution for 80 keV Al ions implanted in Si has been investigated. Precipitates are formed during high temperature annealings of 1 [times] 10[sup 15]/cm[sup 2] implanted samples. They are located at two depths where Al concentration peaks are detected. Al atoms are gettered into the extended defects present in the crystal and/or precipitate when their concentration is higher than the solid solubility value at the annealing temperature. Increasing annealing time, precipitates dissolve out and only a small fraction of atoms diffuses into the sample, meanwhile the greater part evaporates from the sample. At 1 [times] 10[sup 13]/cm[sup 2] dose Al concentration is below the solid solubility limit. The secondary defects are not detected and the dopant profile does not display anomalous peaks. Moreover, all the implanted Al is electrically active and remains in the sample during the first instant of annealing. At higher annealing times it diffuses out of the sample reducing the residual dose.

The diffusion of aluminium in single-crystal silicon has been studied in the temperature range 1000-1290 degrees C. A low implantation dose (1*1014 Al cm-2) was used to avoid dopant precipitation and a high energy (6.0 MeV) to reduce the influence, if any, of the surface. The experimental profiles, measured by spreading resistance, have been fitted taking into account the escape of Al from the Si surface into the ambient atmosphere. A pre-exponential value of 8.88 cm2 s-1 and an activation energy of 3.44 eV have been found in this experiment. When aluminium is implanted through a capping layer, a reduction of the residual amount has been observed at medium energy (300 keV), while no difference has been measured at high energy (6 MeV).

The electrical behaviour of ion implanted aluminum into silicon was investigated by varying the beam energy in the 80 keV-6 MeV range, the dose in the 1 × 1013–1 × 1014/cm2 range and the annealing procedure. Aluminum atoms precipitate into exten defects at the end of range damage and where the concentration exceeds the solid solubility value (about 2 × 1019/cm3 at 1200°C Escape of Al atoms occurs very easily as soon as they reach the external surface during the thermal diffusion. Using high energy implants, 6 MeV, it was possible to follow in detail the broadening of the diffused profiles. The measured trends between the retained dose and the junction depth and between the outdiffused dose and the annealing time are quite well predicted by the solution of the diffusion equation with the surface acting as a perfect sink for the dopant.