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In this paper the electrical and structural characteristics of n-MOSFETs fabricated on 4H SiC with a process based on nitrogen (N) implantation in the channel region before the growth of the gate oxide are reported for low (5x1018 cm-3) and high (6x1019 cm-3) N concentration at the SiO2/SiC interface. The electron mobility and the free carrier concentration in the MOSFET channel were evaluated by Hall effect measurement. The MOSFETs with the higher N concentration had the best electrical characteristics in terms of threshold voltage and field effect mobility, in spite of a lowering of the electron mobility in the channel. The latter is a negative drawback of the fabrication process that probably can be ascribed to an incomplete recovery of the implantation damage or to a high density of interstitial N atoms present in the channel region. In fact, the MOSFETs with the superior electrical performances were fabricated with the higher N+ dose and the shorter thermal oxidation time. However, no evidence of extended defects, clusters or nano-particles in SiC at the interface with the gate oxide was found in every SiC MOSFETs devices observed by electron transmission microscopy

A technology computer aided design homemade tool, IMPACT, is described. The mechanical models and the numerical implementation are presented. Details are given about the methodology to calibrate and validate the implementation. This tool is used for the analysis of the processing of a micromachined cantilever. The originality of the study lies in (i) the capability to simulate almost all the sources of stress taking into account the complex rheological behaviours of the materials, (ii) the experimental determination of the mechanical properties of various thin film materials, and (iii) the validation of the calculations by direct comparisons with the measured deformations of the cantilever.

The use of TiSi 2 layers as ohmic contacts in complementary MOS (CMOS) devices is expected to introduce large distortions in the underlying silicon which may degrade the device performances. In this work, the TEM technique known as convergent beam electron diffraction (CBED) has been employed to map the strain distributions across 〈1 1 0〉 cross-sectional specimens of sub-quarter-micron CMOS structures. Different experimental set-ups in terms of energy filtering, liquid nitrogen cooling and zone axis have been explored and compared to each other by using three differently equipped microscopes. The strain induced on silicon by TiSi 2 layers has then been investigated, quantified and compared with that due to the presence of an oxide isolation trench. Also, the effects of depositing a TiN capping layer on TiSi 2 have been analysed. Our results show that its presence results in a more tensile strain without altering the strain distribution trend.

The Large Angle Convergent Beam Electron Diffraction (LACBED) technique has been applied to determination of the tetragonal mismatch in coherent Si/Si1−xGex/Si heterostructures. Two-dimensional (2D) dynamical simulation of the LACBED patterns has been performed and compared with the corresponding experimental ones. A good agreement is found in the whole simulated area, particularly as regards the splitting of the Bragg contours, due to the strain field present in the TEM cross-sections.

The relaxation which occurs along the thinning direction of transmission electron microscopy (TEM) cross-sections of heterostructures is still poorly known. This has so far prevented the accurate determination of the corresponding bulk mismatch values from convergent-beam electron diffraction (CBED) patterns. In this paper it is demonstrated that, by using elasticity theory, it is possible to deduce a simple relationship for (001) heterostructures which relates the latice mismatches along the different crystallographic directions of the TEM specimen, as deduced from a single CBED pattern, to the bulk value. Both 〈001〉 and 〈110〉 orientations of the TEM cross-sections are considered. However, to obtain accurate results, the validity of the kinematical approach used to deduce mismatches from high-order Laue zone line patterns must be critically checked; it depends on the crystallographic projection, on the beam voltage and, in the case of Si1−xGex heterostructures, on the Ge concentration. It is fou...

The convergent beam electron diffraction (CBED) technique has been applied to determine the lattice strain in Si1−xGex/Si heterostructures and in local isolation structures. Both plan and cross-sections have been investigated by transmission electron microscopy. In the heterostructures, the strain value obtained by CBED along the growth direction ɛCRED is affected by a relaxation induced by the thinning process in a direction normal to the cross-section plane, being generally smaller than the bulk tetragonal value ɛT This effect can be overcome using the large angle CBED technique on plan sections. In addition, in the heterostructures the Ge concentration has been determined by energy dispersive X-ray spectrometry, allowing the pseudomorphicity of the samples to be evaluated. All the values of strain and Ge concentration thus obtained are in good agreement with those deduced from Rutherford backscattering spectrometry. In isolation structures, the CBED technique has been applied to determine the d...

The tetrahedral heterobimetallic cluster (C 5 H 5 )NiRu 3 H 3 (CO) 9 , 1 , when decomposed on KOH-modified γ-alumina, produces an effective heterogeneous catalyst for ammonia synthesis. Bimetallic particles have been evidenced on the support surface by analytical electron microscopy; their main size is 4.0 nm and their Ni/Ru atomic ratio is practically the same as that of the starting cluster. The treatment of unsupported 1 with alcoholic KOH gives a black, conductive, amorphous alloy powder. In this case, the ultrafine and bimetallic nature of the individual particles was also revealed by analytical TEM investigations.

Silicon wafers have been implanted with As+ ions at an energy of 100 keV and a dose of 1 × 1017 cm−2 and subsequently annealed at 1050°for 15 min. This results in a peak As concentration of 7 × 1021 cm−3, which is far beyond the solid solubility value of arsenic in silicon at this annealing temperature. Rod-like precipitates, dislocations, and small precipitate-like defects have been observed by transmission electron microscopy. From the analysis of several diffraction patterns taken on a number of rod-like particles at different tilt angles, it has been unambiguously found that they have the structure of the monoclinic SiAs compound previously reported in literature. The stoichiometry of the precipitates has been confirmed by x-ray microanalysis. To our knowledge, this is the first time that this SiAs phase is detected in As+-implanted silicon.

High order Laue zone lines present in the central disk of convergent beam electron diffraction patterns have been used to determine the bulk mismatch in thinned, cross‐sectioned heterostructures, where a relaxation occurs along the thinning direction. The position of these lines is sensitive to lattice parameters along different crystallographic directions, so that information on the residual strain along the growth and the thinning directions can be extracted from a single diffraction pattern. This information has been properly combined using the isotropic elasticity theory to give the bulk mismatch. The results are in good agreement with independently obtained bulk measurements.

In this paper we discuss the physical mechanism and the critical factors for the dislocation generation in device processing. The mechanisms of the stress development are identified. Elastic stress is estimated from the convergent beam electron diffraction (CBED) measurements using transmission electron microscopy (TEM), and the defect generation is monitored by electrical measurements of a specific monitor structure. The implantation conditions and the implantation damage recovery is shown to be another key factor in the defect generation. Thermal oxidations of the STI structure are shown to be a major responsible of the stress increase. In addition to the process the pattern geometry strongly affects the mechanical stress. Minimum geometry structures with a complex layout are prone to defect generation.

The principles of the convergent beam electron diffraction technique, which is a point-to-point method for local strain analysis of thin crystals in the transmission electron microscope, are briefly outlined. The availability in modern instruments of scanning attachments coupled with high-angle annular dark-field detectors (STEM/HAADF) has recently enabled the automatic acquisition of diffraction patterns ill a large number of points, selected by digitally rastering the probe in a two dimensional region of the sample. As the components of the strain tensor can be calculated at each point, 2D strain mapping has thus become possible. An example of application of the technique to deep sub-micron shallow-trench isolation structures in silicon is reported.

Silicon on insulator (SOI) substrates, uniformly n doped with As or P at different concentrations in the range between 1.9 and 8 × 10 20 cm −3 , have been irradiated with increasing doses of high energy (2 MeV) Si + ions. The effects of irradiation and the subsequent recovery have been followed by electrical conductivity and carrier mobility measurements and transmission electron microscopy observations. Isothermal annealings have been performed at temperatures in the range 600–800 °C. It was found that recovery takes place in two distinct stages which have been evidenced by using rapid thermal annealing and furnace heating. Our results show a very similar behavior for the two donors and indicate that electron trapping is the responsible of the reduction of the carrier density upon irradiation both in As and P doped samples.

In this paper, three techniques are discussed that provide information on process-induced local mechanical stress in silicon: the convergent beam electron diffraction technique of transmission electron microscopy, X-ray micro-diffraction and micro-Raman spectroscopy. We discuss the principles of these techniques, their spatial resolution, the ease-of-use, the information that can be obtained, the required sample preparation, the measurement time, and the complementarities of these techniques. We demonstrate this for stress induced by shallow trench isolation and correlate the results to finite element analysis results.

The convergent beam electron diffraction (CBED) technique of transmission electron microscopy (TEM) has been applied to 〈1 1 0〉 cross-sections of shallow trench isolation structures in silicon, in order to evaluate the strain field distribution in 0.22 μm wide active areas. Different spot sizes (1 and 10 nm) and sample temperatures (room temperature with energy filtering, liquid nitrogen cooling without filtering) have been employed. It has been found that the regions of the active area closer than about 100 nm to the padoxide/substrate interface can be analysed only by using a 1 nm spot size. Moreover, the use of an energy filter to reduce the inelastic scattering improves the contrast of the diffraction lines in the CBED pattern, thus allowing the analysis to be performed at room temperature.

Large-angle convergent beam electron diffraction (LACBED) dynamical simulations have been applied to the investigation of the strain distribution in the silicon region underlying a local oxidation of silicon (LOCOS) structure. This distribution is revealed through the modification of the profile of the (0 0 8) Bragg contour in the [1 2 0] projection of a [1 1 0] TEM cross-sectioned structure. If one assumes a strain field independent on the direction normal to the cross section, a contrast in the LACBED pattern is obtained only if a rotation of the lattice planes in the silicon region under stress is taken into account. The experimental patterns, taken on a submicron recessed-LOCOS, are in fair agreement with those calculated assuming, for the strain field, an analytical model based on the planar stress approximation [J. Vanhellemont, Ph.D. Thesis, University of Antwerp, 1990; I. De Wolf, J. Vanhellemont, A. Romano-Rodriguez, H. Norstrom, H.E. Maes, J. Appl. Phys. 71 (1992) 898].

The LACBED technique has been applied to the determination of the tetragonal distortion in Si 1-x Ge x /Si heterostructures, which are of great interest in the device technology. The strain determination has been performed on plan sections in an analytical electron microscope. The agreement between this strain value and the tetragonal distortion is influenced mainly by the local sample flatness and the acceleration voltage.

Using isotropic elasticity theory it is possible to determine the bulk mismatch in thinned, cross-sectioned heterostructures, where a relaxation occurs along the thinning direction. This is accomplished by measuring, in the central disk of a single Convergent Beam Electron Diffraction (CBED) pattern, the position of the High Order Laue Zone lines, which are sensitive to lattice parameters along different crystallographic directions. The results obtained in both uniform and graded Sil-xGex/Si heterostructures are in good agreement with bulk values deduced from independent techniques.

It is now widely accepted that one of the major issues for the future deep sub-micron integrated circuit (IC) technologies regarding yield, device performance and stability and device and product reliability, is the mechanical stress built up in the layers and substrate. It is therefore important to give a quantitative account of these stresses and this can only be achieved by disposing of reliable, performant (as to spatial resolution) and quantitative techniques for the local stress determination in the substrate, of adequate and dedicated process simulation tools and of sensitive methods to analyse the stress effects on device performance.The only experimental technique presently available which allows the strain field distribution in sub-micron CMOS devices is the convergent beam electron diffraction technique of the transmission electron microscopy. Its sensitivity is of the order of 10-4 and its spatial resolution is of 1 nm if a TEM/FEG is employed.

Boron activation and carrier mobility were measured after low temperature furnace heat treatments, in silicon layers implanted with BF2+ ions at 60 keV and at fluence in the 1 − 5 × 1015 ions cm−2 range. These quantities were correlated with boron and fluorine chemical depth profiles obtained with secondary ion mass spectrometry (SIMS), and with the lattice defects revealed by transmission electron microscopy (TEM). High dopant activation, well above the extrapolated boron solid solubility, was found for all the fluences investigated after a thermal treatment of 20 min at 600‡ C. In the high fluence implanted samples, the solid phase epitaxial regrowth of the amorphous layer induces a severe fluorine redistribution which causes the formation of a defective band at the sample surface containing microtwins and small precipitates; a decrease in both the activated dopant concentration and carrier mobility was found in this region. The comparison with dopant activation data obtained in samples diffused at higher temperature (from 900 to 1000‡ C) shows that twins are electrically active only when they are decorated by isolated impurities and/or in presence of very small precipitates.

The composition of ternary Si-B-O films some tens of nm thick, which grow during the thermal pre-deposition of boron in silicon, has been determined by X-ray microanalysis. The X-ray intensity data have been obtained by using an automated ARL-SEMQ microprobe operated at 20 kV. The experimental k ratios have been converted into concentrations using a Monte Carlo computer program based on the single-scattering approach. In the case of a film with an underlying substrate, which includes an element of the compound film, an independent determination of thickness is necessary. A general computer analysis on the effect of the substrate on electron trajectories and X-ray yields is performed; the possible sources of error are discussed. The composition of the films so obtained is in satisfactory agreement with the data previously deduced from Rutherford backscattering experiments. This result allows us to solve a discrepancy between the two analytical techniques found before in the case of substrate removal; a variation in chemical composition of the films during the removal of the substrate may be suggested.

Doubly charged arsenic ions have been implanted into crystalline Si〈100〉 at an energy of 1.06 MeV and with doses of 1.2 and 2.4 × 10 15 cm−2. Both the chemical and the electrical profiles showed the presence of two peaks, which are attributed to channelling effects, as confirmed by Monte Carlo calculations. Corresponding to these peaks, two bands of lattice defects have been found by electron microscopy after an anneal at 750 °C for 30 min in a furnace. The evolution of these defects on increasing the annealing temperature up to 950 °C is presented. Good electrical activation and mobility values have been found for all the investigated temperatures.

The properties of boron-doped silicon layers obtained by ion implantation using BF/sub 2//sup +/ molecular ions are studied with Rutherford backscattering spectrometry, transmission electron microscopy, secondary ion mass spectrometry, and with incremental sheet resistance and sheet Hall coefficient measurements by the anodic sectioning method. The implantation step is responsible for the formation of interstitial aggregates at the amorphous/crystal interface. The size of these aggregates, and hence the total number of defects involved, depends on the implant conditions, and is different for samples implanted in the two systems used (a medium current and a high current implanter). During a high temperature (900-1000/sup 0/C) diffusion step in an inert atmosphere, the aggregates anneal out and induce an interstitial oversaturation. As a consequence diffusion enhancement is observed which was modeled simulating the creation of the excess of interstitials with a thermal treatment in a partially oxidizing atmosphere (oxidation-enhanced diffusion). The carrier concentration profiles are nearly identical for samples implanted in the two systems and show an incomplete dopant activation in the diffusion tail.

The equilibrium solid solubility of antimony in silicon was determined in the range 850°–1300°C by carrier density measurements on polysilicon films doped by ion implantation. Up to 1150°C this property follows very tightly the exponential dependence with and . The values at higher temperatures show a smaller increase, the figures at 1200°, 1250°, and 1300°C being , respectively. The attainment of the two‐phase equilibrium was confirmed by carrier profile measurements on isothermally annealed single‐crystal specimens doped in a wide range of concentrations, as well as by TEM examinations which detected a high density of particles having the hexagonal structure of antimony. It is shown that the new solubility values, unlike the previous ones, fully comply with the conditions for phase equilibrium. According to this treatment, the values of 0.58 eV and of are deduced for the partial molar enthalpy and, respectively, for the excess partial molar entropy of the dopant in silicon relative to the standard liquid state of antimony.

The characteristic fluorescence correction has been taken into account in the authors Monte Carlo program for the case of a film fluorescing under X-ray emission from the substrate. The effect is evaluated for Al on Si, at electron energies of 10, 20 and 30 keV and thicknesses ranging up to 0.6 mg cm-2. In the particular limit of zero thickness the correction is in agreement with the analytical model by Cox et al. (1979).

Phosphorus predepositions are performed at 920 and 1000 °C on (100) silicon wafers, previously implanted with chlorine doses ranging from 5 × 1013 to 1 × 1016 cm−2. From the comparison with unimplanted specimens, it is observed that chlorine reduces the concentration of silicon interstitials produced by the doping process. This reduction results in a shallowing of the high diffusivity tail of the carrier profile and in preventing the formation of interstitial-type dislocations. Bei 920 und 1000 °C werden an (100)-Siliziumwafer, die zuvor mit Chlor im Dosisbereich von 5 × 1013 bis 1 × 1016 cm−2 implantiert wurden, Phosphorvorbelegungen durchgefuhrt. Aus dem Vergleich mit nichtimplantierten Proben wird beobachtet, das Chlor die Konzentration von Si-Zwischengitterstorstellen verringert, die durch den Dotierungsprozes erzeugt werden. Diese Verringerung fuhrt zu einer Erniedrigung des hohen Diffusionsauslaufers im Ladungstragerprofil und zur Vermeidung von Zwischengitterversetzungsbildung.

The contrast in HREM images of small spherical coherent precipitates in silicon, having a hypothetical sphalerite structure and an SiX composition, is computed by the multislice method; X represents a dopant (or impurity) atom, ranging from boron up to platinum. The particles are assumed to have a diameter of 2 nm and to exert different amounts of in situ strain ϵ on the silicon matrix. The ideal case of no misfit (ϵ = 0) is also considered. For in situ strains 0 < ϵ < 2%, the maximum contrast, corresponding to the optimum defocus, depends mainly on the atomic number of the element X. For larger strains, which can occur in some cases if the SiX bond length in the SiX particle is determined by the covalent radius of the impurity atom X, the strain contrast dominates over the structure factor contrast. Der Kontrast in hochauflosenden, elektronenmikroskopischen Abbildungen kleiner, kugelformiger, koharenter Ausscheidungen in Silizium, die eine hypothetische Sphaleritstruktur und die Zusammensetzung SiX haben, wird mittels der Vielschichtmethode berechnet; X stellt hier ein Dotierungs- bzw. Verunreinigungsatom von Bor bis Platin dar. Es wird angenommen, das die Ausscheidungen einen Durchmesser von 2 nm haben und verschiedene in-situ-Dehnungen ϵ auf die Siliziummatrix ausuben. Der Idealfall, wo keine Fehlanpassung (ϵ = 0) vorhanden ist, wird auch betrachtet. Fur 0 < ϵ < 2% ist der maximale Kontrast, der der optimalen Defokussierung entspricht, hauptsachlich von der Atomzahl des X-Elementes abhangig. Fur grosere Dehnungen, die in einigen Fallen vorkommen konnen, wenn die SiX-Bindungslange im SiX-Teilchen vom kovalenten Radius des X-Verunreinigungsatoms bestimmt wird, uberwiegt der Dehnungskontrast den Strukturfaktorkontrast.

The apparent width of the SiO2Si interface was evaluated with Auger electron spectrometry, secondary ions mass spectrometry and transmission electron microscopy for thin silicon dioxide films grown at temperature ranging from 900 to 1100°C, both on single- and poly-crystalline silicon (polysilicon), with the aim of finding the meaning of this kind of measurement for this particular system. The width of the transition between SiO2 and polysilicon was found to depend on both the oxidation temperature and polysilicon doping method, being lower for ion implanted than for gas phase (POCl3) doped samples and for oxides grown at higher temperature. The possible causes for the differences in the interface width are discussed and attributed, in the present case, to the oxide thickness non-uniformity. This is due, in turn, to the lower oxide growth rate, particularly for the lower oxidation temperature, on the silicon grains protruding out of the surface.

The Convergent Beam Electron Diffraction technique (CBED) has been applied to determine the lattice strain in Si 1-x Ge x /Si heterostructures and below patterned films on silicon substrates. The well known problem of the stress relaxation which occurs in thinned TEM samples has been overcome, in the case of the heterostructures, by applying the isotropic elasticity theory to the lattice constants measured along different crystallographic directions through the shift of the High Order Laue Zone (HOLZ) lines in the central disk of the CBED patterns. In this way bulk strain values have been obtained, in good agreement with values deduced from independent techniques. In patterned structures, the high spatial resolution of the CBED technique has been applied to determine the distribution of the components of the strain tensor induced into oxidized silicon substrates by Si 3 N 4 stripes. A good agreement with the results obtained using numerical computations has been found.

The codiffusion of B and Sb implanted in Si with a dose of 2 × 1016 cm−2, corresponding to concentration far above the solid solubility, is investigated at 900 and 1000 °C on the basis of SIMS and carrier profile measurements and TEM observations. The comparison of the codiffusion data with the corresponding ones obtained by the diffusion of each element alone revealed several anomalous effects due to dopant interaction. In particular, our experimental results support the hypothesis of the formation of mobile donor-acceptor pairs and of the increase of the Sb solubility in the region where a high concentration of acceptors is present. On the basis of this feature, a diffusion model that takes pairing and precipitation into account is presented. A simulation program including this model allows us to foresee most of the anomalous phenomena occurring in the high concentration codiffusion experiments and shows in general a satisfactory agreement with experimental profiles.

High resolution electron microscopy images of small cubic SiP particles in silicon are computed by means of the programme SHRLI (Simulated High Resolution Lattice Images). A super cell consisting of 4 × 4 silicon unit cells (a = 2.172 nm; b = 1.536 nm), which includes three SiP molecules, is assumed in the multislice calculations. A contrast is evidenced in the image only if preferential etching of the sample at the particles is taken into account. The SiP precipitates result to be darker than the surrounding matrix in both, axial and tilted three beam illumination, in agreement with the experimental observations. Die im Hochauflosungselektronenmikroskop erhaltenen Abbildungen kubischer SiP-Ausscheidungen in -Silizium werden mit Hilfe des SHRLI (Simulated High Resolution Lattice Images)-Programms berechnet. Das „multislice”-Rechenverfahren wird auf eine aus 4 × 4 Si-Einheitszellen bestehenden Uberzelle angewandt, die drei SiP-Molekule enthalt. Ein Kontrast entsteht in den berechneten Abbildungen nur, wenn eine bevorzugte Atzung der Probe an den Teilchen in Betracht gezogen wird. Die SiP-Ausscheidungen treten im Bild dunkler auf als die Umgebung, sowohl in der axialen als auch in der gekippten Beleuchtung. Dieses Ergebnis ist mit den experimentellen Beobachtungen in Ubereinstimmung.