Scanning low energy electron loss microscopy (SLEELM): metals on semiconductors

Classified abstracts 6789-6796 structure in NbSe3 has been clearly resolved and the STM profiles are dominated by the heights and effective charges of the surface Se atoms. Improved sensitivity and resolution will be required to study any details of the C D W structure in both compounds. R V Coleman et al, J Vac Sci Technol, A6, 1988, 338-343. 54 6789. Energy-loss image formation in scanning transmission ion microscopy One contrast parameter which can be used to form images in scanning transmission ion microscopy (STIM) is the energy loss of individual transmitted ions. This paper explores three techniques which can be used if energies of several ions are measured at each incident beam location. The techniques are energy averaging, s u m m i n g of events within a preset energy window, and median filtering of energy values. Median filtering is the method of choice to reduce noise and to sharpen certain features. Examples of line scans of a sharp edge and of a ramp-like knife edge are presented. With median filtering localization of features to within 10% of beam size is demonstrated. A mechanism for identifying and mapping unresolved spatial structure is proposed. The other techniques are shown to be better tools for beam-profile diagnostics. J C Overley et al, Nucl Instrum Meth Phys Res, B20, 1988, 337 341. 54 6790. Mierostructure of Fe implanted yttria stabilized zirconia studied by M6ssbauer spectroscopy and T E M Single crystalline and ceramic solid solutions of (1-0.x)(ZrO2) -(0.x)(YO~.5) with x = 14--17 were implanted with high doses of Fe. Specific profile shapes were realised. The microstructure of the material before and after annealing was studied by conversion electron M6ssbauer spectroscopy (CEMS), ion channeling and transmission electron microscopy (TEM). Initially Fe is present as metallic particles Fe ° and as Fe 2÷ and Fe 3÷ ions. Their relative abundancy depends on the implantation conditions. Annealing leads to complete oxidation (Fe 3÷) at low temperature and to the formation of microprecipitates of Fe203 ( < 5 nm). A m a x i m u m of 4 . 5 x 10zl Fe cm 3 can be substitutionally incorporated for Zr. This Fe is present in a metastable state. Ion channeling and electron diffraction experiments revealed that high fluence Fe implantation does not result in amorphisation but in recrystallisation of the matrix. A J Burggraaf et al, Nucl lnstrum Meth Phys Res, B32, 1988, 3 ~ 3 6 . 54 6791. Fracturetestingofsiliconmicroelementsinsituinascanningelectron microscope Fracture testing of silicon cantilever beams (thickness 1(~ 20 /tm) was performed in situ in a scanning electron microscope by means of an equipment specially designed for this purpose. Beams of various sizes and orientations ((011 ) and (001)) were manufactured in Si (100) wafers by two different micromachining procedures. The beams were tested by simple bending to fracture, and a number of fundamental fracture parameters were determined from an analytical model of elastic fracture. To verify its validity, the model was utilized to evaluate an experimental E modulus, which was found to agree well with previous results. Fracture limits, fracture strains, and initiating flaw sizes were determined. The m a x i m u m fracture limit was very high; about 10 GPa. The strengths of different beams scattered from this value down to practically zero strength, with an average close to 4 GPa. The corresponding fracture strains and initiating flaw sizes were 6% and 3 nm, respectively (maximum strength), and 2% and 17 n m (average strength). Finally, a simple fractography study was performed on the fractured beams. Stefan Johansson et al, J appl Phys, 63, 1988, 4799M803. 54 6792. Structural investigation of helium ion-beam-irradiated glassy carbon R a m a n spectroscopy, high-resolution transmission electron microscopy, energy filtered electron diffraction, and electron energy loss spectroscopy were used to investigate the microstructural changes accompanying the observed ion-beam-induced enhancement of the abrasive wear properties of glassy carbon (GC). The R a m a n results suggested that doses of about I x 10 ~6 He + cm 2 at 600 keV were sufficient to seriously disrupt the structure. However, the electron-beam-based diagnostics failed to reveal any significant differences between "he as-grown and irradiated material. It is suggested that the defect concentrations created by the ion beam are sufficient to disrupt the medium to short-range order in the material but insufficient to alter the overall structure. However, ion-beam thinning

528

glassy carbon with 5-keV Ar ions was found to partially graphitize the material. S Prawer and C J Rossouw, Jappl Phys, 63, 1988, 4435M439. 54 6793. Transmission electron microscopy of elastic relaxation effects in S i Ge strained layer superlattice structures A series of Si/GexSil_~ (x-~ 0.2~0.4) strained layer superlattices have been grown by molecular-beam epitaxy on (I00) oriented substrates in order to study elastic relaxation effects. In the bulk of a Si~Ge strained layer system grown on a relatively massive substrate, the elastic misfit strain resulting from unit-cell expansions and contractions is accommodated in the GexSi~_~ alloy layers. However, it is known that these stresses can be significantly relaxed near surfaces o f the bulk or in thin foils prepared for cross-sectional transmission electron microscopy. It has been found that this stress relaxation introduces a n u m b e r of electron diffraction effects which are superimposed on structure factor or other contrast effects associated with layered structures. We derive equations describing the relaxation strain field for GexSi~ x alloy layers -~ 10 n m in thickness present on relatively massive substrates ( > 100 nm) based on the solution of a line force acting on an elastic half-space. This predicts a long-range stress relaxation. D D Perovic et al, J Vac Sci Technol, A6, 1988, 1333 1336. 54 6794. Transmission electron microscopy studies of brown and golden titanium nitride thin films as diffusion barriers in very large scale integrated circuits The usefulness of reactively sputtered TiN as a diffusion barrier in the A1TiN/Ti/Si metallization scheme in very large scale integration was reported in a previous publication. Two types of TiN thin films were studied in these experiments. Depending on the applied substrate bias voltage, the resulting TiN films can have different properties. Under nobias conditions, dark brown colored films (called B films) with low density (3.22 g/cm3), high electrical resistivity ( ~ 4 0 0 / ~ cm), and 5% 8% 02 are obtained. At --75 V dc substrate bias, bright golden colored films (called G films) with high density ( ~ 5 . 0 g/cm3), low resistivity ( ~ 2 0 # ~ cm), and negligible 02 are obtained. Even though the B films contain more 02 the G films were found to be better diffusion barriers for silicon. To investigate the effect of film microstructure on the diffusion barriers, cross-sectional and planar transmission electron microscopy samples were used. Both, brown and golden, types of films have columnar grain structure with approximately the same size ( ~ 4 0 0 - 5 0 0 / ~ ) , contrary to fine-grained structure observed for G films by some other groups. The columns in the G films increase in size with an increase in distance from the TiN/Si interface, while the grain size remains almost constant in the B films. The intergrain structure also differs considerably; the grains in G films are very closely packed while they are very loosely bound in the B films. The intergrain voids in the B films can act as an easy path for silicon diffusion. Also, these films were studied by Rutherford backscattering spectroscopy, Auger electron spectroscopy, and x-ray diffraction to understand the diffusion mechanisms. N Kamar et al, J Vac Sci Technol, A6, 1988, 1602 1608. 54 6795. Defining the fractal nature of thin-film top surfaces from microdensitometer analysis of electron micrographs of surface replicas In this paper, the very first results are reported about searching for the fractal nature of thin-film top surfaces from the surface relief reconstructed by microdensitometer analysis of an electron micrograph of a shadowed replica of the surface. It is found that such a reconstruction could be very helpful when dealing with the fractal nature of a surface. F Varnier et ai, J Vac Sci Technol, A6, 1988, 1627 1630. 54 6796. Scanning low energy electron loss microscopy (SLEELM): metals on semiconductors High resolution scanning low energy electron loss imaging of W and A u on Si is demonstrated in reflection geometry at a primary electron energy Ep of order 0.7 keV and spatial resolution of 3/~m. Characteristic losses below 60 eV are chosen to examine contrast between two regions (metal and silicon dominated) respectively. By differencing between a m a x i m u m in a loss intensity and an adjacent trough, high quality Si images are obtained with contrast superior to L23VV Auger electron images produced in comparable times. In contrast to scanning Auger microscopy (SAM), the spatial resolution of SLEELM is defined only by the profile

Classified abstracts 6797~5804

of the incident beam, but application of the technique is somewhat limited by the possibility of low energy characteristic losses overlapping in the different surface phases. SLEELM is shown to be complementary to SAM, and its future role in device characterization is outlined. M M El Gomati and J A D Matthew, Vacuum, 38, 1988, 209-211. 55. X-RAY A N D PHOTOELECTRON SPECTROSCOPY 55 6797. Electron stimulated desorption from GaAs(100) surface Measurements of electron stimulated desorption of CO +, CO +, C + and O + have been carried out for a sputter-cleaned and annealed GaAs(100) surface exposed to CO2, O2 and NO at room temperature. The dependence of the ion yields on the incident electron beam energy from 0 to 200 eV exhibits thresholds at the Ga 3d, 3p, and 3s and As 3d and 3p core level binding energies. The total desorption cross section for the ionic species is ~ 10 -~s cm 2. E C Ekwelunda and A Ignutiev, J Vac Sci Technol, A6, 1988, 51-56. 55 6798. Experimental comparison of micro-PIXE with other methods utilized for biomineralization studies The present study deals with the investigation of arterial wall mineralization i.e. of inorganic compound development within artery wall under normal or pathologic conditions. Autopsy samples of human aorta as well as fragments of aorta obtained from hypercholesterolemic rabbits were used for the experiments. The samples were investigated using microPIXE, PIXE, and PIGE technqiues, infrared and Raman spectroscopy, X-ray powder diffraction and a variety of histochemical methods in order to compare the techniques based on a proton microprobe with the other methods which aimed at the investigation of inorganic deposits. Proton microprobe measurements confirm the different composition of mineral deposits found in rabbit and human aorta samples. In the case of animal aorta the apatite crystals constitute the mineral form of deposits while for human samples we deal with a mixture of different compounds. Moreover, for rabbit aorta samples the deposits were found always in the atheromas, while in human aorta sections the mineral deposits were localized in the media of the aortic wall. The proton microprobe can be considered to be a valuable addition to the experimental methods that have been applied in the study of the biomineralization process. It permits a quantitative determination of mineral deposits in situ while infrared and Raman spectroscopy as well as X-ray powder diffraction measurements may be performed only for ashed aorta samples. The possibility of in situ measurements and high detection sensitivity seem to be the most significant advantages of a proton microprobe in the study of artery wall mineralization. T Cichocki et al, Nucl Instrum Meth Phys Res, B31, 1988, 44%455. 55 6799. Characterization of microcrystallinity in hydrogenated silicon thin films The characterization of microcrystallinity in undoped hydrogenated silicon thin films by means of X-ray diffraction and Raman spectroscopy is discussed in detail. We present experimental results for glow discharge films prepared under a wide range of conditions. Microcrystallinity is characterized in terms of crystalline volume fraction and crystallite size, and it is correlated with deposition rate and substrate temperature. A systematic discrepancy appears between the crystalline fractions determined from X-ray diffraction and Raman scattering and is discussed according to two possible origins: the different Raman cross-sections for the microcrystalline and amorphous phases, and the inhomogeneity of crystallinity as a function o f thickness. We show that the accuracy can be improved by using fully recrystallized samples as a reference. C Godet et al, Thin Solid Films, 155, 1987, 227-242. 55 6800. Characterization of epitaxial films by grazing-incidence X-ray diffraction Grazing-incidence X-ray diffraction, a recently developed, powerful, nondestructive and surface-sensitive technique, allows characterization of epitaxial films with thicknesses down to a few atomic layers. Lattice parameters, strains and crystallite sizes can be determined parallel to the interface, complementing results obtained for these parameters in other directions by conventional Bragg diffraction. Epitaxial relationships between substrate and film and their orientational spread can be determined uniquely, and minority domains with an orientation or strain state

different from that of the main mass of the film can frequently be detected with this technique while they are not observable with conventional diffraction. The power of this technique, as performed in our laboratory with a 12 kW rotating-anode X-ray generator, is demonstrated with various examples of epitaxial systems: Cu/A1203(0001), W/AI20 3 (1"[02), molybdenum and niobium on GaAs(001) and GaAs(ITi), GaAs/ A1203(0001) and InAs/GaAs(001). Armin Segmfiller, Thin Solid Films, 154, 1987, 33~42. 55 6801. An electron spectroscopy study of the growth and thermally activated diffusion of nickel thin films on AI(lll) and AI203/AI(111) High-resolution electron energy loss spectroscopy (EELS) and Auger electron spectroscopy have been used to study the interaction of nickel with clean and oxidized AI(111) surfaces. At about 200 K, nickel deposition on A1203 forms three-dimensional nickel clusters. The nickel clusters are bonded directly to surface A1 O moieties as determined from the preferential influence of nickel on the A1203 surface phonon modes. Two thermally induced processes compete for dominance for nickel thin films on A1203. Heating between 200 and 450 K results in conversion of the nickel clusters to a smoother nickel layer, whereas heating to higher temperatures (450-700 K) causes substantial inward diffusion of the nickel overlayer through defects in the A1203 thin film. Only one process occurs for nickel on clean AI(111), as the nickel overlayer simply diffuses steadily into the aluminum throughout the temperature range of about 300-700 K. The A1203 layer acts as a barrier to inward diffusion for nickel on AI203/AI(I 11), since the temperature at which inward diffusion starts increases with the thickness of the A1203 layer. For nickel deposited onto both clean AI(111) and A1203, we find that the metallic aluminum present provides a major driving force for inward diffusion from the nickel overlayer, resulting in Ni AI alloy formation and segregation of aluminum toward the surface. Our study demonstrates the utility of EELS as a new tool for investigation solid solid interfaces and thin film barriers. J E Crowell et al, Thin Solid Films, 153, 1987, 341-347. 55 6802. Large grain size CdTe films grown on glass substrates Polycrystalline films of CdTe (with grain size up to 100/zm) were grown by the hot wall close-spaced vapor transport technique in an Ar atmosphere. In most cases they grow on a zinc-blende type of structure with a preferential orientation of growth along the ( 111 ~ directions, as shown by x-ray diffraction studies. The grain size in the films presents a maximum around 3.5 Torr, as well as a minimum of preferential orientation. The grain size shows an exponential increase in the substrate temperature (T,) 450-650°C range. For T~ ~< 600°C, the films grow with a (111) preferential crystallographic orientation, whereas for T~ > 600 °C the preferential orientation changes to the (220) directions. For T, > 600°C, the films show a mixture of zinc-blende and wurtzite phases, according to the x-ray analysis. A Te crystalline phase is detected for Ts > 550°C. O Zelaya et al, Jappl Phys, 63, 1988, 410-413. 55 6803. Ultrahigh-vacuum system for surface studies using high-energy ion scattering and X-ray photoemission spectroscopy We describe a new ultrahigh-vacuum facility which is being used for studies of solid surfaces. The target chamber is attached via a differentially pumped beamline to a 2-MV Van de Graaff accelerator, and includes: (l) instrumentation for high-energy ion backscattering and channeling studies and nuclear reaction analysis, (2) a 100-ram radius hemispherical analyzer for photoemission studies, and (3) low-energy electron diffraction (LEED) optics. R J Smith et al, Rev Sci lnstrum, 58, 1987, 2284-2287. 55 6804. Multilayer PIXE analysis Thick target PIXE analysis has been extended to cases where there is a superposition of layers of different compositions. A computer program was developed for calculating the K~ X-ray yield of up to three layers containing up to five different elements each, when bombarded by protons of arbitrary energy. The enhancement of peaks due to secondary fluorescence is included, with the possibility of the primary and secondary emitters being in any of the three layers. The thickness of titanium films deposited on steel backings was measured using the Ti/Fe ratio method, and proton energies of 400 to 700 keV. J Rickards and E P Zironi, Nucl Instrum Meth Phys Res, B29, 1987, 527530. 529