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The morphology of gold nanoparticles (AuNPs) deposited on a (100) silicon wafer by simple immersion in a solution containing a metal salt and hydrofluoric acid (HF) is altered by HF treatment both before and after deposition. The gold clusters are characterized by the presence of flat regions and quasispherical particles consistent with the layer-by-layer or island growth modes, respectively. The cleaning procedure, including HF immersion prior to deposition, affects the predominantly occurring gold structures. Flat regions, which are of a few tens of nanometers long, are present after immersion for 10 s. The three-dimensional (3D) clusters are formed after a cleaning procedure of 4 min, which results in a large amount of spherical particles with a diameter of ≈15 nm and in a small percentage of residual square layers of a few nanometers in length. The samples were also treated with HF after the deposition and we found out a general thickening of flat regions, as revealed by TEM and AFM analysis. This result is in contrast to the coalescence observed in similar experiments performed with Ag. It is suggested that the HF dissolves the silicon oxide layer formed on top of the thin flat clusters and promotes the partial atomic rearrangement of the layered gold atoms, driven by a reduction of the surface energy. The X-ray diffraction investigation indicated changes in the crystalline orientation of the flat regions, which partially lose their initially heteroepitaxial relationship with the substrate. A postdeposition HF treatment for almost 70 s has nearly the same effect of long duration, high temperature annealing. The process presented herein could be beneficial to change the spectral response of nanoparticle arrays and to improve the conversion efficiency of hybrid photovoltaic devices.

The damaging process of GeTe up to amorphization has been studied by introducing controlled levels of disorder by irradiation with 150 keV Ar+ ions. In situ reflectivity measurements and ex-situ resistance and Raman spectroscopy analysis have been employed to study the impact of ion bombardment on the electrical conduction properties and on the bonding. The results obtained are indicative for three different stages of film damage. The first step appears to be dominated by point defects, affecting the temperature coefficient of resistance (TCR) and inducing a transition from positive (metallic conduction) to negative TCR values (conduction dominated by localized states), whilst the material still remains crystalline. The second step is characterized by the annealing of the defects induced, presumably, by the formation of complex defects that act as sinks for point defect recombination. This process is facilitated by the high atomic mobility. The third phase of damage starts at a fluence of 3.5 × 1014 cm−2 and finally converts the material to the amorphous state, characterized by higher resistance and decreased optical reflectivity. The modifications observed upon ion irradiation provide important insights into the possible states that can be achieved in crystalline GeTe through different local atomic arrangements towards amorphization.

The electrical properties and the structure of isothermally annealed thin films of Ge2+xSb2Te5 (x=0 and 0.5) have been studied by in situ electrical measurements, x-ray diffraction, and transmission electron microscopy analyses. Phase separation has been observed in samples with an excess of Ge; by annealing amorphous Ge2.5Sb2Te5 films at temperatures in the range 130–160 °C, the material cannot be completely converted into the metastable face-centered-cubic (fcc) structure. At temperatures higher than 160 °C, the residual amorphous material may be converted into a fcc structure with a lower lattice parameter.

Crystallization of amorphised thin silicon layer on insulator (SOI), and subsequently doped by As implantation has been investigated after furnace annealing at 680 degrees C or laser irradiation in the milliseconds regime. In partly crystallized intrinsic amorphous SOI grains are 3 times larger than the ones observed in implanted layers produced by chemical vapor deposition. In the As implanted SOI, the density of grains is reduced whilst their size increases up to a factor 8 at 3 x 10(15) As/cm(2). The presence of As increases both the nucleation barrier and the grain growth velocity. Similar effects were observed after laser annealing. (C) 2014 Elsevier B.V. All rights reserved.

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 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 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.

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.

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.

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.

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.

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.

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 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.

We have investigated the origin of the photoluminescence (PL) W band in ion-implanted Si by studying the temperature evolution and depth profile of the related defects. Evolution of the PL spectra induced by postimplant annealing is correlated to a transition of small interstitial clusters to extended {311} defects in self-ion-implanted Si. Growth of W band intensity after step-by-step removal of the damaged layer rules out the involvement of vacancy-related defects in the formation of the W center and establishes that migrated and clustered interstitials give rise to an intense W band. The annealing behavior and the thermally activated growth of the W center suggest the involvement of small interstitial clusters, larger than di-interstitial. In accordance with recent results based on simulational studies, we argue that the W center consists of tri-interstitial clusters of silicon.

The epitaxial realignment of undoped and As doped polysilicon films onto crystalline silicon substrates induced by high‐temperature rapid‐thermal annealing has been investigated. It is shown that the realignment mode and the kinetics of the process are intimately related to the microcrystalline structure of the layers under investigation, to the morphology of the native oxide film present at the interface, and to the presence of As atoms dispersed in the deposited layers. For layers having fine grain dimensions, compared to the film thickness, the realignment takes place via the motion of the crystal‐polysilicon interface towards the surface. This is observed in undoped layers and in layers which have been subjected to a high‐temperature anneal before As doping. The preimplant anneal disrupts the interfacial oxide film and reduces the thermal cycle needed to complete the realignment of the polysilicon layers. In layers which have not experienced any thermal treatment before As doping, it is seen that the grain size first increases to dimensions on the order of the film thickness, and the realignment transformation then proceeds by lateral growth of epitaxial columns in a manner similar to secondary grain growth. The kinetics of both realignment modes are thermally activated and the atomic limiting processes have been tentatively identified to be As diffusion in bulk Si for As doped layers and Si self diffusion for undoped films. The effect of the microcrystalline structure on the realignment kinetics is attributed to its relationship with the driving force governing the realignment transformation.

We investigated low temperature formation of a 10 nm thick amorphous Ni–Si layer after room temperature deposition of a 7 nm Ni layer on [001] Si, by in situ transmission electron microscopy analyses. Instead of a conventional time sequence of phases or an immediate formation of NiSi2 domains, annealing at 220 °C promotes Ni diffusion through a thin interfacial amorphous layer, formed during deposition, into the Si lattice until the entire supply of pure Ni atoms is consumed. High concentration nickel diffusion induces a crystalline-to-amorphous transformation of the original silicon lattice. Further increasing the temperature, in the range between 300 and 350 °C, causes crystalline NiSi2 domains to nucleate and grow within the amorphous matrix.

A systematic study on the synthesis of silicon nanoclusters formed in plasma-enhanced chemical vapor deposited substoichiometric silicon oxide films by annealing at 1100 °C for 1/2 h as a function of different deposition parameters, has been performed. The clustered Si volume fraction is deduced from a fit to the experimental electron energy loss spectrum. At any deposition condition, the clustered silicon concentration is significantly lower than the initial silicon excess concentration, demonstrating that high temperature anneal of SiO x films induces only partially the phase separation between Si and SiO 2 . This effect, explained by taking into account the strain energy associated with the different atomic densities of Si and SiO 2 , has been confirmed through a detailed study of the host material by scanning a 2 A electron beam among agglomerated silicon dots, showing that the matrix it is not a stoichiometric SiO 2 but still a substoichiometric silicon oxide film whose excess of silicon is the one after to be subtracted by the agglomerated one. This stress the evidence that the phase separation between Si and SiO 2 , in PECVD deposited films, is not complete even after high temperature annealing for relatively long time.

The diffusion into a p-type silicon substrate of phosphorus ions implanted in TiSi2 layers has been investigated for several thermal treatments in the 950–1150 ° C temperature range. The drive-in was performed using either a rapid thermal annealing system or a traditional furnace. Shallow junctions, lower than 100 nm, were obtained with high dopant concentration at the silicide/silicon interface. The amount of diffused active phosphorus increases linearly with the square root of the annealing time, as measured by Hall technique in a layer-by-layer removal procedure. Precipitate particles are observed by transmission electron microscopy. The agglomeration and precipitation of impurities might be associated to the high tensile stress induced by the silicide layer on the surface silicon region and to its influence on the solid solubility and clustering of phosphorus atoms. Precipitates are easily dissolved after thermal annealing in absence of the TiSi2 layer.

The diffusion into a p‐type Si substrate of arsenic ions implanted into TiSi2 layers has been investigated for several thermal diffusion treatments in the 900–1100 °C temperature range. The drive‐in was performed using either a rapid thermal annealing system or a traditional furnace. Shallow (20–80‐nm depth) junctions were obtained with a high (1019–1020/cm3) dopant concentration at the silicide‐silicon interface. The amount of diffused arsenic atoms measured by Rutherford backscattering spectrometry increases linearly with the square root of the annealing time. A similar relation was found for the amount of electrically active arsenic, as measured by Van der Pauw structure in combination with anodic oxidation. The two quantities differ and the inactive dopants precipitate in the diffused layer as seen by transmission electron microscopy. This behavior might be associated to the high tensile stress induced by the silicide layer on the surface silicon region and to its influence on the solid solubility and...

Germanium, arsenic and krypton ions of 600 keV energy were implanted in silicon substrate at 250°C. The hot implantation results in the formation of extended defects (dislocation loops and cluster of point defects) as residual damage. Rapid thermal annealing process at a temperature above 1000°C was used to remove the damage. Rutherford-backscattering channelling technique was used to measure the amount of defects and their annealing. In some cases the channelling results were correlated to transmission electron microscopy (TEM) analysis. The annealing process of the damage is governed by an activation energy of (4.4±0.2) eV for both germanium and arsenic implants. During RTA processes broadening of the As and Ge distributions is quite negligible. The Kr atoms interact instead with defects and the annealing even after a prolonged time at 1100°C is not complete, bubbles surrounded by extended defects are left

The influence of both titanium silicide formation and a subsequent high-temperature treatment in the range 900-1100 degrees C on the arsenic profile in silicon has been investigated. As a result of the two-step process used for the silicide formation, the dopant contained in the reached silicon layer redistributes and segregates both at the sample free surface and at TiSi2-Si interface. The arsenic profile in the unreacted silicon is not modified. Subsequent rapid high-temperature annealing (900-1100 degrees C) induces a migration of arsenic atoms from the silicon into the silicide. The transport occurs for samples either capped with SiO2 or uncapped. In the latter, in addition, arsenic out-diffusion is also observed. The residual arsenic dose in silicon decreases linearly with the square root of time during the high-temperature anneal. The process is governed by a diffusion coefficient whose measured value, 6*10-14 cm2 s-1, is comparable to that of arsenic in silicon, thus indicating that diffusion is the limiting mechanism for the arsenic loss in uncapped samples.

The Rutherford backscattering/channeling and transmission electron microscopy techniques have been used to investigate the annealing of extended defects in silicon. The damage has been created by implantation of 600 keV Ge ions at a substrate temperature of 250°C. Rapid thermal processes at temperatures above 1000°C have been used for defect removal. The channeling data indicate that the annealing of extended defects is governed by a process with an activation energy of 4.3 ± 0.2 eV.

The phase transition from pure Ni to Ni2Si and NiSi was studied by in situ Transmission Electron Microscopy analyses from room temperature to 260degC. The reaction starts at 180degC with the formation of small Ni2Si transrotational domains. Their density and size increase by increasing the annealing temperature to 260degC. After 50 min, a uniform transrotational NiSi layer is formed by a grain by grain transition process. A polycrystalline NiSi layer was instead obtained at 550degC. It was concluded that the final layer structure is the result of a competition: at low temperature (260degC) transrotational domains prevails since slow structural modifications allow the match between silicide and silicon during the Ni2Si -NiSi phase transition ; at high temperature (550deg), the growth of randomly oriented silicide grains is favoured.

Silicon nanoclusters were formed in plasma-enhanced chemical vapor deposited substoichiometric silicon oxide films by annealing at 1100 C for 1/2 h as a function of different deposition parameters. The samples were analyzed by energy filtered transmission electron microscopy and Rutherford backscattering. At any deposition condition, the clustered silicon concentration is significantly lower than the initial silicon excess concentration. This behavior is explained by taking into account the free energy difference between the metastable SiO and stable SiO2 phase and the strain energy associated with the different atomic densities of Si and SiO2.

It is known that B deactivation and clustering occur in the presence of an excess of Si self-interstitials (Is). First principle calculations predicted the path of clusters growth, but the precursor complexes are too small to be visible even by the highest resolution microscopy. Channeling with nuclear reaction analyses allowed to detect the location of small B-Is complexes into the lattice formed as a consequence of the B interaction with the Is. In this work we extend this method to determine the complexes formed during the initial stage of B precipitation in Si doped at extremely high concentration (4 at%) and subjected to thermal treatment. The samples were prepared by excimer laser annealing (ELA) of Si implanted with I keV B. The thickness of the molten layer was 100 nm and the B profile was boxlike with a maximum hole concentration of similar to 2 x 10(21) cm(-3). The electrical deactivation and carrier mobility of this metastable system has been studied as a function of subsequent annealing in the temperature range between 200 and 850 degrees C. Channeling analyses have been performed to investigate the B lattice location at the initial stage of precipitation. The difference, with respect to previous investigations, is the very small distance (< 1 nm) between adjacent B atoms substitutional located in the lattice and the absence of Is that can be released during annealing, since the end of range defects were completely dissolved by ELA. In this way, information on the B complex evolution in a free-of-defects sample have been obtained. (c) 2006 Elsevier B.V. All rights reserved.

Liquid phase epitaxial regrowth following laser melting significantly modifies the concentration of point defects in Si, such that peculiar depth distribution of subsequently implanted B arises. At room temperature, a large fraction of B atoms, similar to15%, implanted in laser preirradiated Si, migrate up to the original melt depth. During high temperature annealing, the nonequilibrium diffusion of B is reduced to similar to25% of that measured in unirradiated Si. Both these phenomena are conclusively attributed to an excess of vacancies, induced in the lattice during solidification and to their interaction with impurities and dopant.

In a system consisting of two different lattices, structural stability is ensured when an epitaxial relationship occurs between them and allows the system to retain the stress whilst avoiding the formation of a polycrystalline film. The phenomenon occurs if the film thickness does not exceed a critical value. Here we show that in spite of its orthorhombic structure, a 14 nm-thick NiSi layer can three-dimensionally adapt to the cubic Si lattice by forming transrotational domains. Each domain arises by the continuous bending of the NiSi lattice, maintaining a close relationship with the substrate structure. The presence of transrotational domains does not cause a roughening of the layer, but instead it improves the structural and electrical stability of the silicide in comparison with a 24 nm-thick layer formed using the same annealing process. These results have relevant implications for the thickness scaling of NiSi layers which are currently used as metallizations of electronic devices.

Silicide formation in thin cobalt/poly-Si layers capped with Ti during annealing in the temperature range between 420 and 510°C was investigated by time-resolved sheet resistance measurements. We found that CoSi 2 nucleation is a fast process while Co diffusion through CoSi 2 grain boundaries is a slow process. Simulations of the resistance curves vs. time have shown that the pre-exponential factor of cobalt diffusivity is reduced by the presence of Ti contamination at the CoSi 2 grain boundaries, as it was shown by energy-filtered transmission electron microscopy analyses, whilst the activation energy does not change with respect to a reference.

In this work we study the phase transition of Co/poly-Si layers capped with Ti or TiN films. Silicide reaction has been performed by isothermal annealing in the temperature range between 420 and 510 °C and studied by measuring the sheet resistance during time. The time interval associated to the CoSi–CoSi 2 phase transition has been extracted as a function of the cap layer and the annealing temperature. The presence of the Ti cap systematically reduces the rate of CoSi 2 formation with respect to the sample with TiN. It has been found that the cap type has an impact on the pre-exponential factor of the growth time but it does not affect the activation energy. As an effect, the silicide capped with Ti has a flat interface with the substrate.

We report an accurate characterization (by RBS and XRD) of the stoichiometry and the phase formed in a multilayer sample (20 layers), constituted by the repetition of the stack 1.5 nm Co/27 nm Si. The samples were prepared by physical vapor deposition at a pressure of similar to10(-8) Torr. The multilayer structure is amorphous and a limited amount of mixing at the Si/Co interface occurs during deposition. Annealing at 600 degreesC resulted in the formation of a multilayer constituted by CoSi2/Si layers. Resonant backscattering spectrometry using a 3.036 MeV He+ has been used to quantify the oxygen contamination occurring during the deposition process.

The non equilibrium diffusion of ultra-low energy B ions implanted into Si is characterized by an ultra-fast process, occurring during the ramp-up of the thermal process and by a transient enhancement of the diffusion with an activation energy of 1.7 eV. We have also investigated the location of the defects causing the transient enhanced diffusion. The fast and ultrafast processes are found to be generated by defects located at different depths. The defects responsible for the fast tail shift are located closer to the surface than the defects leading to the ultrafast tail shift.

An extensive characterization by Spreading Resistance Profiling of the electrical activation of ultra-low energy implanted boron in silicon is reported. The study of the dependence on the implant energy, dose and annealing temperature throws light on the mechanisms responsible for the electrical activation at implant energies below 1 keV. The thermal activation energy for the electrical activation of boron slightly depends on the implant dose and is in the range of 2-3 eV. The implication of these data for the fabrication of future generation devices is discussed.

The amorphous-to-polycrystal transition has been studied in Ge2+xSb2Te5 (x = 0.0 and 0.5) films through X ray diffraction analysis and in situ electrical measurements. Phase separation has been observed in samples with excess of Ge, which cannot be completely converted into thence phase at temperatures lower than 170 °C.By using in situ transmission electron microscopy, the growth velocity and the nucleation rate in Ge2Sb2Te5 films have been measured at different annealing temperatures. Activation energies of 2.8 eV and 2.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus ΔG* has been evaluated.

Al, the fastest p-type diffuser in silicon, interacts strongly with oxygen, defects, and precipitates, with a detrimental effect on the electrical activity. Although, substrates with low oxygen content, such as epitaxial layers on FZ grown crystals, can be used, it is practically impossible to avoid oxidation steps and then the amount of oxygen that is introduced into the wafer depends on the oxidation temperature. The present work deals with the behaviour of Al implanted at high energies either in bare epitaxial Si or in pre-oxidized epitaxial Si with a 300 nm thick thermal oxide layer. The subsequent annealings were performed under oxygen or nitrogen atmosphere. The SIMS and the spreading resistance analyses indicate that even the oxygen present in the silicon substrates after the thermal oxidation at temperatures above 1000/spl deg/C causes the precipitation of Al at the depth of the damage peak. The effect has been quantitatively analysed by comparison with thermal processes in nitrogen atmosphere. For the Al implant through the oxide layer, the growth and dissolution of Al-O precipitates has been studied.

Aluminum ions at 100 MeV were implanted into floating‐zone (FZ) and Czochralski (CZ) grown Si substrates. At this energy the influence of the surface on the subsequent thermal treatment is negligible. In FZ samples the electrical active dose, as measured by spreading resistance profilometry, is independent of the annealing time at 1200 °C. In the CZ samples instead it considerably decreases with time. Secondary ion mass spectrometry analysis in CZ samples have revealed the presence of a multipeak structure around the projected range region for both Al and O signals. In FZ the structure is just detectable. The results imply that the Al‐O complex formation is enhanced by the presence of oxygen but that it is catalyzed by the damage created during the implant. The carrier profiles coincide in both CZ and FZ diffused substrates by predeposition of Al from a solid source, i.e., in damage‐free samples.

The realignment by rapid thermal annealing of polycrystalline silicon layers deposited onto 〈100〉 Si substrates can occur either through the planar movement of the interface towards the surface or through the lateral growth of columnar epitaxial islands. An anneal at 1075 °C for 15 s, followed by As implantation, is shown to cause planar growth even at subsequent anneal temperatures as low as 900 °C. In contrast, the direct annealing of As implanted samples induces columnar realignment. Further, the As redistribution throughout the polycrystalline layers and its diffusion in the crystalline substrate is considerably reduced in the case of the double step annealing. The different regrowth modes are related to the morphology of the interfacial oxide layer and to the microcrystalline structure of the polycrystalline layers during the initial stages of the realignment process.

The matter transport of arsenic ions implanted into titanium silicide layers has been investigated after thermal diffusion treatment in the 800 °C–1100 °C temperature range. The arsenic atoms redistribute between TiSi2 and Si with a segregation coefficient depending on temperature. The diffused amount increases linearly with the square root of annealing time at 1100 °C. The n‐doped shallow Si layer has a quite good electrical activity with a mean resistivity of about 1.2 MΩ cm. The leakage current of the reverse‐biased n+/p junction is instead quite high. Stacking faults are observed in the diffused layer.

The major drawbacks of the ion implantation process are the secondary defects that form during the thermal treatment required to activate electrically the dopant and to restore the crystalline order. Defects are detrimental for the electrical behaviour of the devices if located in the active regions and limit drastically the yield as shown in Fig. 1.14. Annealing is the key step of the implant and most of the work has been performed in this field to understand the evolution of defects, their aggregation, the influence of the ambient in which the annealing is performed, of the thermal procedure etc. Prolonged anneal at high temperature could result in a perfect crystal, but other related effects such as the diffusion of dopant may not be compatible with the device characteristics.

MeV boron implants were performed on silicon substrates patterned with an oxide mask. Secondary defects, generated after annealing under the mask edge, were studied by cross sectional transmission electron microscopy. The relative doped regions formed by these implants were investigated by one- and two-dimensional spreading resistance profiling and compared with analytical and Monte Carlo calculations provided by SUPREM IV and STORM, the most used 2D process simulators in microelectronic technology. The density of defects and the two-dimensional profiles of B were related to the slope of the oxide mask edge. The increase of lateral spread is simply due to the ion penetration through the edge of the oxide mask. The formation of defects is instead explained in terms of the amount of displaced Si atoms under the oxide mask.

The heterogeneous precipitation of oxygen in Cz silicon wafers has been investigated for the following implanted ions: Al, C, Si, P, and As, after anneal in the 800–1200 °C temperature range. The amount of precipitated oxygen, as measured by secondary ion mass spectrometry, ranges from 7 × 1013 (As implant) to 3 × 1014 cm−2 (Al implant) after an anneal at 1000°C for 20 min. The residual damage, as detected by transmission electron microscopy, does not show a significant dependence on the amount of precipitated oxygen as demonstrated by the analysis of Cz and epitaxial silicon wafers. The results are explained in terms of the interstitial trapping by species like C and Al, that enhances the heterogeneous formation of SixOy clusters. The subsequent growth of precipitates has been modelled for Al and C implants and for several annealing temperatures and times.

The formation and dissolution of Si‐O‐Al precipitates have been investigated in Czochralski silicon wafers implanted with 6 MeV Al ions and thermally processed. The data have been compared to the O precipitation in samples implanted with 6 MeV Si or P ions. The amount of precipitated O atoms is about one order of magnitude higher for Al than for Si or P implanted samples. Moreover, a strong gettering of the Al atoms by the silicon dioxide precipitates has been observed. The precipitate evolution has been studied for different annealing times and temperatures. The oxygen precipitation has been simulated by the classical theory of nucleation and growth, with the introduction of new factors that take into account the implant damage distribution, the agglomeration of point defects during the initial stages of the annealing and the oxygen outdiffusion from the sample surface.

Aluminum ions at 100 MeV were implanted into floating zone (FZ) and Czochralski (CZ) grown Si substrates. At this energy the implanted ions are located at a depth of about 40 μm so to minimize the influence of the surface on the subsequent thermal treatment. In FZ samples the electrically active dose, as measured by spreading resistance profilometry, is independent of the annealing time at 1200°C, but in the CZ samples it decreases considerably with time. Secondary ion mass spectrometry analysis in CZ samples has revealed the presence of a multipeak structure around the projected range region for both Al and O signals. In the FZ the structure is just detectable. The results imply that the Al-O complex formation is, of course, enhanced by the large content of oxygen but that it is catalyzed by the damage created during the implant. In contrast the carrier profiles coincide in both CZ and FZ substrates doped by predeposition of Al from a solid source and subsequent diffusion; i.e. in damage free samples.