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In this work, we compare the results of different Cliff–Lorimer (Cliff & Lorimer 1975) based methods in the case of a quantitative energy dispersive spectrometry investigation of light elements in ternary C–O–Si thin films. To determine the Cliff–Lorimer (C–L) k-factors, we fabricated, by focused ion beam, a standard consisting of a wedge lamella with a truncated tip, composed of two parallel SiO2 and 4H-SiC stripes. In 4H-SiC, it was not possible to obtain reliable k-factors from standard extrapolation methods owing to the strong CK-photon absorption. To overcome this problem, an extrapolation method exploiting the shape of the truncated tip of the lamella is proposed herein. The k-factors thus determined, were then used in an application of the C–L quantification procedure to a defect found at the SiO2/4H-SiC interface in the channel region of a metal-oxide field-effect-transistor device. As in this procedure, the sample thickness is required, a method to determine this quantity from the averaged and normalized scanning transmission electron microscopy intensity is also detailed. Monte Carlo simulations were used to investigate the discrepancy between experimental and theoretical k-factors and to bridge the gap between the k-factor and the Watanabe and Williams ζ-factor methods (Watanabe & Williams, 2006).

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.

Test structures consisting of shallow trench isolation (STI) structures are fabricated using advanced silicon (Si) technology. Different process parameters and geometrical features are implemented to investigate the residual mechanical stress in the structures. A technology computer aided design homemade tool, IMPACT, is upgraded and optimized to yield strain fields in deep submicron complementary metal–oxide–semiconductor devices. Residual strain in the silicon substrate is measured with micro-Raman spectroscopy (m-RS) and/or convergent beam electron diffraction (CBED) for large (25 micron) and medium size (2 micron), while only CBED is used for deep submicron STI (0.22 micron). We propose a methodology combining CBED and technology computer aided design (TCAD) with m-RS to assess the accuracy of the CBED measurements and TCAD calculations on the widest structures. The method is extended to measure (by CBED) and calculate (by TCAD) the strain tensor in the smallest structures, out of the reach of the m-RS technique. The capability of determining, by both measurement and calculation, the strain field distribution in the active regions of deep submicron devices is demonstrated. In particular, it is found that for these structures an elastoplastic model for Si relaxation must be assumed.

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...

A method to perform nanobeam diffraction (NBD) in a transmission electron microscope with high spatial resolution and low convergence angle is proposed. It is based on the use of a properly fabricated condenser aperture of 1 mu m in diameter, which allows an electron beam about 10 nm in size to be focused on the sample, with a convergence angle in the 0.1 mrad range. Examples of NBD patterns taken in an untilted < 110 > cross section of a silicon device are shown. Their quality is adequate for spot position determination and hence to obtain, in principle, quantitative strain information. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3003581]

Summary A method to extract accurate information on the displacement field distribution from split high-order Laue zones lines in a convergent-beam electron diffraction pattern of nanostructures has been developed. Starting from two-dimensional many beam dynamical simulation of HOLZ patterns, we assembled a recursive procedure to reconstruct the displacement field in the investigated regions of the sample, based on the best fit of a parametrized model. This recursive procedure minimizes the differences between simulated and experimental patterns, taken in strained regions, by comparing the corresponding rocking curves of a number of high-order Laue zone reflections. Due to its sensitivity to small displacement variations along the electron beam direction, this method is able to discriminate between different models, and can be also used to map a strain field component in the specimen. We tested this method in a series of experimental convergent-beam electron diffraction patterns, taken in a shallow trench isolation structure. The method presented here is of general validity and, in principle, it can be applied to any sample where not negligible strain gradients along the beam direction are present.

A few recent applications of scanning transmission electron microscopy (STEM) methods to problems of interest for nanoelectronics are reported. They include nanometer-scaled dopant profiles by Z-contrast and strain mapping by convergent beam diffraction.

Using a combination of the CBED and the LACBED techniques in the transmission electron microscopy (TEM), we have investigated the strain field in the silicon active region of a shallow trench isolation structure, underlying a TiSi 2 layer. Starting from the analysis of the deformation in a sample, thinned for TEM analysis, we have reconstructed the displacement field, simulating the split HOLZ lines visible in the experimental CBED patterns. From the comparison between the experimental LACBED patterns, taken in a suitable sample orientation to evidence the stressors distribution in the polycrystalline silicide layer, and the corresponding dynamically simulated ones, we have reproduced the strain field in the unthinned, bulk sample.

Silicon-germanium thin films have been analyzed by EDS microanalysis in a field emission gun scanning transmission electron microscope (FEG-STEM) equipped with a high angular dark-field detector (STEM/HAADF). Several spectra have been acquired in the same homogeneous area of the cross-sectioned sample by drift-corrected linescan acquisitions. The Ge concentrations and the local film thickness have been obtained by using a previously described Monte Carlo based “two tilt angles” method. Although the concentrations are in excellent agreement with the known values, the resulting confidence intervals are not as good as expected from the precision in beam positioning and tilt angle position and readout offered by our state-of-the-art microscope. The Gaussian shape of the SiKα and GeKα X-ray intensities allows one to use the parametric bootstrap method of statistics, whereby it becomes possible to perform the same quantitative analysis in sample regions of different compositions and thicknesses, but by doing only one measurement at the two angles.

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.

Residual stresses can significantly affect the performances of silicon micro-structures. The understanding of the residual stress growth during their processing is of great importance. However, the experimental tracing of the stress at the various stages of the machining is still almost impossible. Quantitative modelling of these problems is the alternative to provide guidelines for the minimization of the residual stresses. In this paper, we describe a technology computer aided design homemade tool, IMPACT. The mechanical models and the numerical implementation are presented. We give details about our methodology to calibrate and validate our implementation. The originality of this study lies in (1) the capability to simulate almost all the sources of stress taking into account of the complex rheological behaviors of the materials, (2) the experimental determination of the mechanical properties of various thin film materials and (3) the validation of the calculations by direct comparisons with measured deformations in the micro-structures.

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.

Convergent beam electron diffraction is a technique available in any modern transmission electron microscope. It allows the determination of the strain tensor in crystals at the nanometer scale. The basic principles of the method and examples of application to microelectronic devices are given.

A method of obtaining quantitative two-dimensional (2D) maps of strain by the convergent beam electron diffraction technique in a transmission electron microscope is described. It is based on the automatic acquisition of a series of diffraction patterns generated from digital rastering the electron spot in a matrix of points within a selected area of the sample. These patterns are stored in a database and the corresponding strain tensor at each point is calculated, thus yielding a 2D strain map. An example of application of this method to cross-sectioned cells fabricated for the 0.15 μm technology of flash memories is reported.

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.

The convergent beam electron diffraction technique (CBED) of the transmission electron microscopy (TEM) has been employed to determine the strain distribution along a cutline parallel to the padoxide/Si interface in a 0.80 micron wide recessed-LOCOS structure. The values of the components of the strain tensor so obtained have been compared with those computed by two simulator codes. It has been found that both the LOCOS morphology and the strain distribution deduced from TEM images and TEM/CBED patterns, respectively, were in agreement with the simulation results, if some oxidation-related parameters were modified.

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 effect on spatial resolution of the spherical aberration of the objective prefield of a Philips CM30 (S)TEM has been investigated. For this purpose, the lattice mismatch of a 20 nm thick Si-Ge film in a cross-sectioned Si/Si0.9Ge0.1/Si heterostructure has been determined by convergent beam electron diffraction (CBED), performed at 100 kV with a spot size of 20 nm. It has been found that, if the disk of minimum confusion is focused onto the specimen plane, the measurement is not affected by a change in the size of the condenser-2 aperture. Therefore, the mismatch information is contained within the Gaussian part of the electron probe. In strain profile determinations by CBED, this allows one to use higher beam intensities (larger C2-apertures) with improved signal/noise ratios and reduced sample drift due to shorter acquisition times.

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.

An overview is given of transmission electron microscopy techniques to address strain with nm scale spatial resolution. In particular the possibilities and limitations of (large angle) convergent beam electron diffraction ((LA)CBED) and electron diffraction contrast imaging (EDCI) techniques are discussed in detail. It will be shown by a few case studies that unique and quantitative information on local strain distributions can be obtained by the combined use of both (LA)CBED and EDCI in correlation with three dimensional finite element simulations of the strain distributions in the thinned specimen.

Despite the use of nanometer-sized probes in field emission transmission electron microscopes, the spatial resolution in strain analysis performed by convergent beam electron diffraction is limited in one direction by the need for tilting the cross-sectional sample in the electron microscope off the vertical direction. We demonstrate that it is possible to improve this resolution by using the zone axis, instead of the one, which has recently become of common use in the analysis of silicon microdevices. Quantitative strain information with good sensitivity and accuracy can be obtained in the new axis. An example of application to the two-dimensional strain mapping in shallow trench isolation structures, obtained with a scanning attachment and a high-angle annular dark-field detector, is reported.

A reliable and reproducible technique for preparation of TEM cross-sections of microelectric devices, having features of interest about 5 μm in size, is reported. With respect to the method presently employed to thin homogeneous samples, a few modifications have been introduced, which have proved to be succesful. They include the fabrication of a suitable vise, the continuous use of a good-quality optical microscope to control the different steps of preparation and a proper choice of the ion-beam parameters. By this method it is also possible to render observable details of about 1 μm in a device in the electron microscope.

A Monte Carlo code previously used in modelling x-ray emission by incident electrons of several tens of kilo-electronvolts has been extended up to 300 keV, which is typical of the present medium-energy transmission electron microscopes. With the aid of a further numerical code, both the thickness and composition of thin self-supporting films can be simultaneously determined. This code exploits the bootstrap statistical method, which provides a realistic error analysis of the final results from the precision of the experimental data. The potential of the two codes is illustrated through a simulated example of a single self-supporting film. Such calculations can also be applied to two or more overlying films transparent to an electron beam.

SUMMARY The ability of an end-window variable geometry flow proportional counter to detect the ultrasoft BeK and SiL X-ray lines induced by the electron beam of a transmission electron microscope (TEM) has been demonstrated. This counter has been used in the current work in the energy dispersive mode, and has been equipped with a Formvar window about 400 nm thick, aluminized on both sides with a layer of 65 nm total thickness. X-ray peaks generated by specimens of other light elements such as boron, carbon, oxygen, fluorine and aluminium, and detected with this technique, are also reported. In the case of the BK line, the counting rate obtained with this detector has been evaluated and compared with that of a crystal spectrometer equipped with a conventional side-window flow proportional counter. Finally, a linear relationship between X-ray energy and detected pulse height was found for the lines examined, i.e. from the SiL up to the SiK X-rays.

Titanium nitride films have been prepared by implanting 3.4×1017 cm−2 N+2 ions in 600‐A‐thick titanium layers deposited on silicon single crystals. Unlike the films obtained by evaporation or sputtering, both low electrical resistivity and fairly good optical properties were found even in the as‐implanted samples. Moreover, thermal treatments up to 700 °C performed both in vacuum and H2 atmosphere resulted in a further improvement of the overall films characteristics. This opens interesting perspectives of applications for TiN as a transparent (antireflective) conducting material in photovoltaic field, which are presently being investigated.

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 basic features of the convergent beam electron diffraction technique (CBED) ina transmission electron microscope (TEM) for the quantitative strainan alysis of silicon nanoregions are described. Details on the procedure employed to obtain the components of the strainten sor from anexp erimental CBED patternare given. The CBED methodology has been recently applied to the analysis of straininthe field of microelectronics; as anexample, the investigationof 0.22 μm wide electrically active silicon regions, underlying silicon nitride stripes in shallow trench isolation structures for non volatile memories, is reported. It is found that the strain field can be related to the different technological steps.