Search

In the previous chapters silicon was considered as the only substrate in which to perform the implants. More than 99% of the total production of solid state devices is based on silicon wafers and this might justify the choice. Regardless of the small quantity in which are produced devices based on compound semiconductors, e.g.. GaAs and InP, are of extremely relevance in optoelectronics, in high frequency applications and in the photon-electrical carrier conversion.[8.1]

Ion implantation is now routinely adopted for the doping of almost all-silicon-based devices. The key advantage of ion implantation is the precise control in the number of introduced ions. The most complex memory and microprocessor chips require during their fabrication from 10 to 15 implant steps. With the development of new structures other implants are added to improve the electrical behavior of devices. Implants are used to form source and drain regions, but also to control the threshold voltage of the MOSFET, to improve the latch-up immunity and to decrease the hot carrier production. New designs and new integrated circuits require also an accurate control of the dopant concentration gradients and profiles. The precise control of the dose is not any more enough and the other degrees of freedom offered by ion implantation, such as the independent control of the beam energy and of the incident angle, are employed with success. In the well of MOSFET the dopant profile is not that determined by the diffusion law with a maximum at the surface and a steadily decreasing concentration with depth. Several implants at different doses and energies are performed and the resulting profile looks like that shown in Fig. 7.1 [7.1]. Each peak has a specific aim in the optimization of the device electrical behaviour.

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.

Boron and phosphorus channeling implants in silicon at medium and high energies are reviewed. A wide range of doses has been investigated from low doses (1012/cm2), where the radiation damage can be neglected, to high doses (1015/cm2) where the damage influences the depth distribution. At low doses the profile results from the superimposition of the channeled and of the random component. So the maximum penetration of the channeled particles along the different channels can be easily experimentally determined. The maximum penetration of ions and the extracted electronic stopping are reported for [100], [110] axial channeling and for implants in thick amorphous Si targets. Increasing the dose a third component is necessary to describe the dopant profile. This contribution is related to the fraction of dechanneled particles that depends on the number of displaced silicon atoms. In this case the profiles can be determined as a convolution of three gaussian curves. Channeling tails are present also for implants performed in a random equivalent direction. These tails can be reduced but cannot be avoided. Monte Carlo simulations, based on a simple treatment of the electronic energy loss within different channels, describe quite well the profiles at low doses. The lateral spread of channeled implants under the mask is quite small also at relatively high doses. This lateral spread has been studied by means of two dimensional spreading resistance and a comparison with random implant is presented. In channeling implants the radiation damage is also reduced and the amount of extended defects generated after thermal annealing is reduced too. All these effects are presented and discussed.

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.

The process of ion beam amorphization of crystalline silicon is reviewed in order to elucidate the underlying mechanisms. The role of dopants on this process is also explored studying amorphization of undoped and highly doped crystalline Si in the temperature range 77–423 K and by using Ge ion irradiation at an energy of 400 keV or 1 MeV. At each temperature the amorphous fraction increases more than linearly with the fluence and, at temperatures higher than 300 K, is strongly dependent on dopants. In particular amorphization is retarded by B and enhanced by As doping at concentrations of ∼ 1020/cm3. These processes are shown to mirror closely ion beam induced amorphization of pre-existing amorphous clusters. The amorphization is modelled in terms of three dimensional nucleation and growth of amorphous Si clusters under ion irradiation. The defects which are not quenched into amorphous regions during the early stages following the collision cascade are long living and interact with the existing amorphous islands inducing their growth. In the presence of B the amorphization rate is reduced while the nucleation rate is unaffected. The As effect is discussed in terms of its strong interaction with point defects.

The phase transition of amorphous to single-crystal silicon has been investigated not only by conventional heating in a furnace but under direct-energy processes like pulsed-laser and ion beam irradiation. The first method allows the experimental determination of the free-energy-temperature diagram for amorphous, liquid and crystalline silicon. Due to the very fast heating and cooling the amorphous-to-liquid transition can be investigated in both directions. Ion beam irradiation induces either a layer-by-layer amorphization or crystallization by the movement of the initial α-Si/c-Si interface according to the substrate temperature. The two processes are governed by different types of defects created by the beam in the amorphous and in the crystalline side of the interface. The existence of a native-oxide layer at the interface between single crystal and deposited layer retards the ion beam crystallization until oxygen atoms are dispersed by beam mixing in the matrix. A recent alternative way of crystallizing deposited layers is by short high-temperature anneals obtained by incoherent-light irradiations. In this case the rupture of the native-oxide layer is achieved by the agglomeration of oxide into beads, thus allowing the realignment. This technique appears to be particularly promising for several technological applications.

In this work the interface between transition metals (Fe, Co) and Si has been investigated by soft X-ray photoemission spectroscopy. Synchrotron radiation has been used as photon source, measuring valence bands, Si2p and metal 3p core levels with high surface sensitivity. CoSi2 and beta-FeSi2 chemical phases have been obtained by thermal annealing (500-800-degrees-C) of thin films deposited onto room temperature Si and oriented wafers. Moreover, for the first time to our knowledge, a mixed (Fe0.785-Co0.25)/Si multilayered interface has been studied, showing remarkable differences with respect to single-metal deposition.

Channeling boron implants were performed into (100) and (110) silicon substrates in the energy range 80–700 keV. The dose ranged between 3.5 × 1011 and 1 × 1015 atoms/cm2. The axial channeling concentration profiles of implanted B+ were compared with that obtained for incidence along the random direction of the crystal and with that obtained by implantation in amorphous silicon. The electrical and chemical boron distributions were obtained by spreading resistance and secondary ion mass spectrometry measurements, respectively. The inelastic stopping power, Sc, was extracted from the experimental maximum ranges for the [100] and [110] axis. The energ dependence of the electronic stopping power is given by Sc = KEp with p[100] = 0.469±0.010 and p[110] = 0.554±0.004. Simulations obtained by the MARLOWE code, using the Oen-Robinson impact parameter dependent formula, for the electronic energy loss reproduce quite well the experimental depth profiles.

Using a method based on scanning capacitance spectroscopy, local measurements of the electron mean free path (l) and mobility (mu) have been carried out on single layers of graphene (SLG) mechanically exfoliated from highly oriented pyrolytic graphite and deposited on SiO2/Si. Lateral inhomogeneity of l and mu was found both on pristine and ion irradiated SLG with different C ion fluences (from 10(13) to 10(14) cm(-2)), with an increasing spread in the distribution of l and mu for larger fluences. Before irradiation, the spread was explained by the inhomogeneous distribution of charged impurities on SLG surface and/or at the interface with SiO2. After irradiation, lattice vacancies cause a local reduction of mu in the damaged regions.

We describe an experiment achieving radiation pressure excitation and cooling of a mechanical mode in a cryogenic Fabry-Perot cavity with a micromechanical oscillator [micro-electro-mechanical systems (MEMS)] as end mirror. The response function to periodic modulations of the intracavity power provides an independent measurement of the effective modal mass allowing an accurate estimate of the mode temperature from the corresponding displacement noise spectrum. We also obtained optical cooling of the MEMS fundamental mode at 110 kHz from 11 to 4.4 K, limited only by the optical Finesse and the mechanical quality of the system. These results represent a step toward the observation of quantum optomechanical effects and motivate further experiments with improved performances of the MEMS samples.

Scanning capacitance microscopy (SCM) is used to probe on nanoscale the capacitive behavior of graphene deposited on a SiO2/Si n(+) substrate (with SiO2 thickness of 300 or 100 nm). The SCM tip provides the contact on graphene, while the Si n(+) substrate acts as the backgate contact in the graphene/SiO2/Si capacitor. The authors studied the screening by the graphene two-dimensional electron gas on the modulating potential applied between the backgate and the SCM tip. In particular, they determined the effect of the oxide thickness on the lateral distribution (i.e., screening length) and the density of the screening charge in graphene. Experimental results indicate that thinner oxide leads to higher screening charge density in the graphene sheet and to higher effectively biased area on graphene. This correspondingly increases the total capacitance (C-tot) of the graphene/SiO2/Si capacitor. We evaluated the dependence on the dielectric thickness of the classical metal-oxide-semiconductor (MOS) capacitance (C-MOS) and of the quantum capacitance (C-q) contributions to C-tot.

80 keV B+ ions were implanted in 〈100〉 Si with a high-current implanter. The wafers were irradiated at 0° and 7°. The feasibility of the 0° implants was checked testing the influence of several geometrical parameters, such as the twist angle and the flex angle, on the shape and uniformity of the ion depth distributions. The damage generated by a high-fluence B+ implant was lower for the 0° implanted samples and the disorder evolution was analyzed after different annealing processes were performed in the 600-120°C temperature range. Agglomeration and dissolution of extended defects in the 0° implanted samples occurs at temperatures 100° C lower than those in the 7° implanted samples.

Phosphorus ions in the energy range 0.25\char21{}1 MeV and in the dose range 2\ifmmode\times\else\texttimes\fi{}${10}^{12\char21{}}$1\ifmmode\times\else\texttimes\fi{}${10}^{15}$ P/${\mathrm{cm}}^{2}$ were implanted along the [100] and [110] directions on Si single crystals or along a random direction (7\ifmmode^\circ\else\textdegree\fi{} tilt and 23\ifmmode^\circ\else\textdegree\fi{} twist angles). Some implants were performed also on Si samples with a 2-\ensuremath{\mu}m-thick surface amorphous layer to obtain truly random conditions. Profiles were obtained either by secondary-ion mass spectrometry or by spreading-resistance analyses after a rapid-thermal-annealing procedure. The presence of channeling tails in the so-called random implants in Si single crystals, due to feeding-in effects, is demonstrated and studied. In the channeling implants, the maximum penetration and the electronic stopping were determined as a function of the beam energy and axial direction. Furthermore, by increasing the implanted dose the dechanneled fraction was correlated with the number of displaced silicon atoms. All the obtained profiles were compared with Monte Carlo simulations using the marlowe code. A simple description of the electronic energy loss within different channels by a modified Oen-Robinson formula provided an excellent agreement between the calculated and the experimental profiles.

The epitaxial realignment induced by high temperature rapid thermal annealing of ion implanted polycrystalline and amorphous layers deposited on to oriented Si substrates has been studied. The As doses ranged from 2*1015 to 2*1016 cm-2 and the annealing temperature from 1000 to 1150 degrees C for annealing times ranging from 5 to 100 s. The characterization of the processed layers has been performed by means of Rutherford backscattering and channeling spectroscopy, sheet resistance measurements and transmission electron microscopy. The authors show that in the temperature and time ranges used here, an As concentration larger than 1*1020 cm-3 is necessary to induce the epitaxial realignment of the polycrystalline layer. However, for the amorphous layers a higher As concentration is needed. The difference is related to the way in which the As atoms redistribute in the two layers. It is found that the heavily doped amorphous layers can be realigned with limited As redistribution, thus giving them the potential of being used in the microelectronics technology for the formation of shallow junctions.

The annealing of low-fluence heavy-ion damaged Si crystals induced by ion-assisted treatments is reported. Damage was produced by 150 keV Au implantations at a dose of 2 × 10 13 ions/cm 2 onto 〈100〉 oriented Si single crystals and resulted in small amorphous-like regions surrounded by crystal material. The interaction of these damaged structures with defects induced by energetic ions (600 keV Kr 2+ ) was investigated. Kr post-irradiation resulted in either damage accumulation or annealing, depending on the substrate temperature. A transition temperature of about 420 K was found between these two different regimes. Ion-assisted processes are discussed and explained on the basis of the damage morphology.

We investigated the feasibility of electron programing and hole erasing in silicon nanocrystal Flash memory cells with fin field-effect transistor architecture having ultrashort channels (90 nm). Experiments show that, by choosing a proper program/erase condition, very large threshold voltage windows can be achieved, compatible with the needs of multilevel cells. These performances are coupled to excellent retention at high temperature. The obtained results evidence that hole trapping is less affected by electric field and temperature stress compared to electron trapping. Qualitative explanations for this behavior are given. (C) 2008 American Institute of Physics.

The interaction between high‐energy ion irradiation and pre‐existing damage clusters dispersed in single‐crystal Si is discussed. Silicon substrates were predamaged by low‐dose 150 keV Au ions. Post‐irradiation by 600 keV Kr2+ ions resulted in either damage annealing or damage accumulation, depending on the substrate temperature. The transition temperature between these two different regimes is 420 K. These data are discussed and compared with the ion beam induced epitaxy and amorphization of continuous surface amorphous layers.

The low temperature epitaxial crystallization of chemical vapor deposited silicon layers obtained by means of high energy ion irradiation is studied. Both the kinetics of the process and the morphology of the regrown layers are characterized. This novel procedure, in view of the small thermal budgets involved, can result interesting for possible application to the bipolar technology.

Ion beam induced epitaxy of amorphous Si layers onto 〈100〉 substrates has been investigated by varying the As concentration. At As concentrations below 4×1018/cm3 no rate effect is observed. In the intermediate regime, between 4×1018/cm3 and 2×1021/cm3, the growth rate increases linearly with the logarithm of As concentration and reaches a value about a factor of 2 higher than that of intrinsic Si. At concentrations above 2×1021/cm3, the epitaxy experiences a sudden, severe retardation. Finally, at a concentration of ∼6×1021/cm3, twins are observed to form.

The annealing behavior of the damage produced in Si single crystals by 150 keV Au implants at ∼2×1013 ions/cm2 and at substrate temperatures of 77 K (LN2T) and 300 K, room temperature (RT), has been investigated. The annealing kinetics has been studied in the temperature range between 493 and 623 K and for times up to 2 h. Data have demonstrated that, at a fixed temperature some damage anneals out fast and then a saturation occurs for both the LN2T and RT‐damaged samples. This behavior has been tentatively interpreted assuming that the damage is mainly composed by amorphous‐like material and that reordering is initiated at preferential growth sites present at nonplanar crystal‐amorphous interfaces.

The evolution of pre-existing damage structures in Si under high energy ion irradiation is discussed. Different initial morphologies are investigated: a sample partially pre-damaged with heavy ions and a sample partially pre-damaged with light ions are compared within them and with an undamaged single crystal. It is shown that ion irradiation can produce either damage accumulation, in the form of amorphous regions, or damage annealing depending on the pre-existing damage morphology, on the substrate temperature, and on the doping content in the irradiated layer. These data are discussed and interpreted on the basis of the existing models on ion induced amorphization and crystallization.

We study the phase transition from amorphous to face-centered-cubic (fcc) polycrystalline Ge2Sb2Te5 thin films. The transformation has the peculiar characteristic, still not well understood, of coexisting high transition rates at low annealing temperature (with grain growth velocities of the order of 1 nm/min at 140 degrees C) and large activation energies (about 2-2.5 eV). In this work all kinetic parameters governing the transition have been determined by in situ transmission electron microscopy analysis. They are thermally activated and consistently show large anomalies in the preexponential terms of transient and steady-state nucleation rates and grain growth rate. A possible explanation for these observations is described, based on a recently proposed atomic structure of the fcc Ge2Sb2Te5, characterized by a high level of disorder and distortion at the short range.

In this work we report an in situ transmission electron microscopy investigation of hole nucleation and growth under thermal processes. Two different systems are considered: a NiSi layer on poly-Si substrate without any interlayer and a NiSi+Mo (as metallic interlayer) system. This approach allows us to follow in situ hole formation and growth and to determine hole growth rate until the coalescence occurs. Furthermore, R-s measurements were performed for both systems to evaluate the effect of hole formation on electrical properties. The time and temperature dependences of the sheet resistance provide a relationship between the electrical properties and the morphological changes of the thin NiSi film during a thermal process. This dual characterization of nickel silicide with and without Mo ensures us on the key role of the interlayer in stabilizing the system when temperature is raised, causing a 60 degrees C shift of the temperature at which degradation occurs. Moreover, the energetics of such systems have been discussed by means of a theoretical approach based on an extended Srolovitz model of the thin film instability. This analysis shows the importance of the inclusion of the polycrystalline nature of NiSi films in the theory in order to obtain a reliable classification of the experimental data.

The lattice location of B in Si has been investigated by channelling analyses using nuclear reactions (650 keV proton beam, B-11(p,alpha)Be-8). The formation at room temperature of a specific, small B complex in presence of an excess of point defects has been inferred. In particular, B implanted in Si or B substitutional dissolved in Si and irradiated with proton beam form a unique B complex with B atoms not randomly located. The angular scans along the < 100 > and < 110 > axes are compatible with B-B pairs aligned along the < 100 > axis. The thermal annealing in the 200-950 degrees C range of the B complexes, analyzed by lattice location and carrier concentration measurements, depends on the residual defect density in the lattice. The B complexes dissolve at low temperature if no excess of Si self-interstitials (Is) exists or they evolve into large B clusters and then dissolve at high temperature if Is supersaturation holds.

Design and fabrication of single photon avalanche detector (SPAD) in planar technology is reported. Device design and critical issues in the technology are discussed. Experimental test procedures are described for dark-counting rate, afterpulsing probability, photon timing resolution, and quantum detection efficiency. Low-noise detectors are obtained, with dark counting rates down to 10 c/s for devices with 10 m diameter, down to 1 kc/s for 50 m diameter. The technology is suitable for monolithic integration of SPAD detectors and associated circuits.

The behavior of Al implanted in silicon has been investigated during thermal oxidation. It has been found that precipitation of Al into Al–O-defect complexes depends on the implant energy, i.e., on the distance of the dopant from the surface. It occurs at 650 keV, but it does not at 2.0 MeV or higher energies. This phenomenon has been explained taking into account the diffusivity of self-interstitials introduced during oxidation, the oxygen present in the Si, the Al concentration, and the annealing out of defects.

The thermal stability of thin cobalt silicide layers grown on preamorphized chemical vapor deposited silicon layers has been studied in the temperature range between 950 and 1100 °C. The morphology of the starting layers and their evolution during the thermal processes was analyzed by transmission electron microscopy, atomic force microscopy and Rutherford backscattering spectroscopy. The observed increase in sheet resistance with the annealing time has been correlated to the agglomeration process taking into account the dependence of the resistivity on film thickness and carrier mean free path. Sheet resistance measurements have been used to study the agglomeration process of CoSi2 by varying temperature and substrate doping (As, BF2, and Si implants). The process is thermally activated with an activation energy of 4.3 eV for the Si implanted samples. The BF2 implanted substrate show a higher activation energy (∼5.4 eV), while the arsenic implanted a lower one (∼3.6 eV). This difference is attributed to ...

We have studied by atomic force microscopy (AFM) the surface morphology of SiO2 layers grown by thermal oxidation of silicon wafers implanted with As, B, Ge, or Si ions. In order to grow oxides having comparable thickness at different temperatures, we have employed both dry and wet processes. Roughness values up to 0.4 nm have been measured on the surface of these oxides. Surface morphology is not influenced by the oxidation ambient, while temperature-related effects are predominant. For low temperature oxidation (920 °C), the predominating effects are due to the behavior of the implanted species, and mainly consist in segregation phenomena, that are the result of a complex competition among different factors, including the segregation coefficient, the relative diffusion rates in the oxide and silicon, and the oxidation rate. At higher temperature (1100 °C), impurity segregation is inhibited or considerably reduced by the increased diffusivity, and defects formation, due to the evolution of the radiation ...

Single-crystal heteroepitaxial growth of Pb x Sn 1− x Te films was achieved by r.f. sputtering deposition onto single crystals of germanium (both 〈100〉 and 〈111〉 orientations), although there is a large mismatch (∼12%) in the lattice parameters between the grown film and the substrate. The structures of the r.f. sputtered films were investigated by high energy electron diffraction microscopy, electron surface replicas and scanning electron microscopy. Differences in the substrate temperature needed for the epitaxial growth on 〈100〉 or 〈111〉 orientations are attributed to the tendency of Pb x Sn 1− x Te films to grow parallel to the (100) plane, which is the cleavage plane of the NaCl structure. This causes a mixed (100)-oriented phase in addition to the (111) orientation expected from the symmetry of the substrate surface in the case of (111) germanium substrates. Examples of the effects on the heterogeneous nucleation of the substrate temperature and deposition rate are shown for both orientations. The first stages of growth (initial reactions with the substrates) and the thickness and concentration profiles were investigated by ion beam backscattering analysis. Channelling techniques confirmed the high degree of order in the single- crystal structure of films deposited on large areas (∼1 cm 2 ).

An amorphous to a polycrystal or a single‐crystal transition by ruby‐laser irradiation of amorphous Si, obtained through ion implantation, is discussed. Both free‐generation and Q‐switched laser mode operation are used. Under a free‐generation operation only the amorphous to polycrystal transition is obtained, which is attributed to nonthermal effects. In the Q‐switched mode both transitions are obtained. The single‐crystal transition is interpreted as due mainly to the melting of the amorphous layer.

Au‐Al and Cu‐Al thin film bilayers were bombarded at 80 K with Kr+ ions of 60–240 keV energy. The Au2Al+AuAl2 and Al4Cu9 phases formed during bombardment and they were investigated by backscattering and x‐ray diffraction techniques. In all the cases the growth kinetics is linear with the parameter (fluence × interfacial deposited energy density)1/2 suggesting a correlation with a diffusion‐like process. Comparison with calculations of diffusion enhanced within the collision cascade gives good agreement with the experimental results.

The effect of irradiation with a Q-switched ruby laser pulse of 50 ns duration on Pb-implanted Si〈111〉 substrates is investigated by MeV He Rutherford backscattering in glancing geometry. The amount of implanted Pb atoms accumulated at the crystal surface after laser irradiation increases with laser power density in the range 15 to 100 MW/cm2. Reordering of the implanted layer takes place simultaneously with Pb accumulation on surface for all the investigated fluences. This behavious differs from thermal aging where the Pb profile is independent of temperature in the range 600 to 800°C and the substrate reordering is inhibited mainly at fluences higher than 1015 cm−2. The differences between thermal and laser annealing could be ascribed to a quasi liquid transition of the as-implanted amorphous layer during laser irradiation. An interpretation along this line is presented. Der Einflus der Bestrahlung mit Laserimpulsen von 50 ns Dauer von einem gutegeschalteten Rubinlaser auf Pb-implantierte Si-〈111〉-Substrate wird mit MeV-He-Rutherford-Ruckstreuung in Spiegelgeometrie untersucht. Der Anteil der implantierten Pb-Atome, der sich an der Kristalloberflache nach Laserbestrahlung ansammelt, nimmt mit der Leistungsdichte im Bereich von 15 bis 100 MW/cm2 zu. Die Wiederherstellung der Ordnung der implantierten Schichten erfolgt gleichzeitig mit der Pb-Ansammlung an der Oberflache fur alle untersuchten Flusse. Dies Verhalten unterscheidet sich von der thermischen Alterung, wo das Pb-Profil unabhangig von der Temperatur im Bereich von 600 bis 800°C ist und die Wiederherstellung der Ordnung des Substrats bei Flussen, die groser als 1015 cm−2 sind, nicht auftritt. Die Unterschiede zwischen thermischer und Lasertemperung lassen sich durch einen Quasiflussigkeitsubergang der ursprunglichen, implantierten amorphen Schicht wahrend der Laserbestrahlung beschreiben. Entsprechend dieser Vorstellung wird eine Interpretation gegeben.

The channeling effect technique has been applied to investigate dechanneling by stacking defects in heteroepitaxially grown silicon. Ion backscattering was performed on 0.9 μm Si layers grown on sapphire as a function of beam energy (1.1–2.5 MeV He + ), projectile ion (He + , D + ) and crystal direction (〈100〉, 〈111〉, 〈112〉,〈113〉). Transmission electron muscopy analysis revealed the presence of a high density of stacking faults and twin lamellae. A model based on the new interior surfaces presented by such stacking defects is used to calculate the dechanneling cross section, and the disorder profiles are obtained from the experimental dechanneled fractions in terms of displaced rows per unit volume. Direct backscattering of channeled particles from the defects is neglected since the dechanneling cross section per row is about one order of magnitude larger than that per displaced atom. The resulting defect depth distributions are independent of beam energy and projectile ion, and give improved quantitative agreement with previous studies. The application of channeling to stackingdefect measurements requires a minimum density of ∼10 15 displaced rows/cm 2 .

Energy dispersion spectroscopy has been used to measure the amount of titanium silicide formed on wedged SiO2 layers. The best experimental conditions for the measurements were determined using a Monte Carlo calculation for the x‐ray yields and for the evaluation of the lateral resolution. On the basis of these calculations we have chosen during measurements a step displacement of the electron beam of ∼40 nm. With this technique lateral extension of titanium silicide ranging from 120 to 520 nm was measured. The method has been applied to the analysis of lateral diffusion in titanium silicide obtained by annealing either in a furnace or in a rapid thermal apparatus.

The regrowth of amorphous layers in and Si substrates has been studied under irradiation with 600 keV Kr+ at target temperature in the 250–400°C range. The amorphous layers were obtained by P+ or Si+ implants. 2.0 MeV He+ backscattering in combination with channeling effect technique was adopted as the analytical technique. The regrown thickness increases linearly with fluence and with the energy density deposited into nuclear collisions at the amorphous-single crystal interface in all the investigated cases. The rate of regrowth for the orientation is two times that for the orientation. The measured activation energy of 0.22–0.05 eV is equal within the experimental accuracy for both orientations. The influence of impurities has been investigated in Si substrates preamorphized with P+ or Si+ ions. The regrowth is enhanced in the presence of phosphorus by a factor of ≈- 4 with respect to the Si self-ion implantation. The results are discussed in terms of the existing models of thermal and ion assisted epitaxial regrowth.

The transition to single crystal of ion‐implanted amorphous Si and Ge layers is described in terms of a liquid‐phase epitaxy occurring during pulsing‐laser irradiation. A standard heat equations including laser light absorption was solved numerically to give the time evolution of temperature and melting as a function of the pulse energy density and its duration. The structure dependence of the absorption coefficient and the temperature dependence of the thermal conductivity were accounted for in the calculations. In this model the transition to single crystal occurs above a well‐defined threshold energy density at which the liquid layer wets the underlying single‐crystal substrate. Experiments were performed in ion‐implanted amorphous layers of thicknesses ranging between 500 and 9000 A. The energy densities of the Q‐switched ruby laser ranged between 0.2 and 3.5 J/cm2; time durations of 20 and 50 ns were used. The experimental data are in good agreement with the calculated values for the amorphous thickness–energy−density threshold. The model deals mainly with plausibility arguments and does not account for processes occuring in the near‐threshold region or below the melting temperature.

Q-switched ruby laser is used to anneal nitrogen and oxygen heavily implanted 〈100〉 silicon wafers. The atomic concentration of nitrogen and oxygen in the implanted layer is about 4%, which is a value higher than the solid solubility of these elements in silicon. The thermal epitaxial regrowth of a-no morphized Si-layers on Si substrate is inhibited at these high nitrogen and oxygen concentration, whereas a very good crystallinity is ibtained after laser irradiation.

Backscattering of energetic He+ ions has been applied to study the thermal behavior of metallic thin film couples. A description of the methods used to determine the surface concentration and concentration profiles of interdiffusing species is given. As applications, the activation energy and diffusion coefficient of Cu dissolved in Au thin films have been measured. The Matano surface for interdiffusing Au and Cu has been determined. This surface practically coincides with the initial Au-Cu interface. Errors in the determination of the surface concentration of mixed metallic couples have been evaluated from both a theoretical and an experimental point of view. An example of the limitations of backscattering is given in the analysis of a laterally non-uniform target.

The angular dependence of MeV He + backscattering yield in glancing geometry has been used to obtain experimental information on surface structure in thin films and implanted crystals. Uniform layer yields are characterized by the (cos φ) −1 dependence as a function of the target tilting angle φ. Deviations from this simple law found in annealed Pb layers deposited on Si substrate have been attributed to the shadowing effect produced by the hill-like structure observed also with SEM.

Reflectance and electroreflectance measurements from 2.5 to 5.5 eV, performed on arsenic heavily doped silicon samples, are reported and discussed. Silicon crystals implanted with arsenic up to a fluence of 1017 cm−2 were laser irradiated and a free-carrier concentration of the order of 1021cm−3 was reached. The reordering of the system is studied in detail at different initial conditions. A comparison between reflectance and electro-reflectance appears to be quite useful to determine the behaviour of the heavily doped semiconductor.

The amount of damage present in germanium (and silicon) following : mplants of 200 keV H+ or 300 keV D+ at temperatures between 40–300°K has been measured using the channeling technique. The damage level is observed to increase strongly with decreasing implantation temperature. Damage profiles were obtained from the data by considering various scattering mechanisms, including single and plural scattering and a steady increase approximation treatment. For equal dose implants, deuterons create considerably more damage in germanium than protons. The ratio of deuteron damage to proton damage is significantly greater than the ratio of energy deposited in nuclear events for the two ions. The results of isochronal anneals at temperatures from 40 to 325°K on Ge crystals implanted at 40°K are also reported. A strong annealing stage is observed around 175°K; this is in good agreement with previous optical absorption studies of proton damage in germanium.

The effects of single-pulse ruby laser irradiation have been investigated in Si samples with disorder layers located at a depth of 2000 A from the crystal surface and extending up to 8000 A. This disorder was obtained by implantation with 350 keV N+ to a fluence of 2×1016/cm2. Channeling, diffraction and transmission electron microscopy were used to characterize the structure of the irradiated layers. After 1.5 J/cm2 irradiation the damaged layer reorders partially, while for about 2.0J/cm2 the surface single crystal becomes polycrystalline. At a higher energy density all the material undergoes the transition to single crystal. Calculations based on the liquid model accounts in part for the experimental results.

Channeling effect techniques with a 2.0 MeV He+ Rutherford backscattering and transmission electron microscopy were used to characterize the crystallized layers after Q-switched ruby laser irradiation of 4000 A thick amorphous layer on 〈100〉 and 〈111〉 underlined crystal substrates. At a laser energy density of 2.5 J/cm2 the crystal layer on the 〈111〉 specimen contains a large density of stacking-faults, that on 〈100〉 specimen contains a very small amount of screw dislocation lines. High quality single-crystal layers have been obtained after irradiation at 3.5 J/cm2. From a comparison with the growth rate and defect structure observed in thermally annealed implanted-amorphous layers, we propose that crystal growth by 50 ns pulse laser annealing occurs by melting the amorphous layer.