Sectional TEM Research Articles

HREM study in Ti/6H-SiC interface

A semiconductor of Ti/6H-SiC with rectifying characteristics was reported recendy. That its electrical properties were degraded for 20 min. anneal at 700°C but improved again with subsequent 20 min. and longer anneal was considered to be caused by phase transformation during annealing. The purpose of this study is to identify those phases formed in the annealing process, and to identify those responsible for changing the electrical properties.A 100 nm Ti thin film was deposited on 6H-SiC by electron beam evaporation in UHV, and subsequent annealing was also done in UHV at 700°C. Cross section TEM specimens were prepared by bonding wafers with Ti-films face to face, grinding, polishing, and then ion milling in a Gatan 600. All TEM observations were performed in an ISI 002B with a 0.18nm resolution at 200KV. HREM images were analyzed by using die SEMPER program.

Early Stage in Polycrystalline Growth of Si by Fluoro-Oxidation of Silane

ABSTRACTWe have studied the polycrystalline growth of Si prepared by a reactive gas flow of SiH4 and F2. In a very early stage of the film growth on the amorphous substrates, a thin layer of the amorphous phase was deposited even in the favorable condition for the crystal growth, whose thickness was determined by the growth condition and reached to 200–300nm in a certain condition. The crystalline phase consisted of closely packed small grains perpendicular to the substrate, 200–500nm in diameter, each of which displayed a tooth-like shape with fine structures, indicating a formation of the crystal nuclei in the amorphous phase and their growth to the grains. The generation probability of the nuclei was not uniform in the amorphous phase, high at the region far from the substrate, and very sensitive to the growth temperature, judging from cross sectional TEM micrographs of the films. These suggest that the network propagation of Si in which fluorine, participates the chemical process in the vicinity of the growing surface enhances a formation of the long range ordering in the network, resulting in the generation of the crystal nuclei.

Production of Diamond-Like Carbon Films by Plasma Source Ion Implantation

ABSTRACTIn addition to being successfully used for ion implantation, the plasma source ion implantation (PSII) technique has been used to produce diamond-like carbon films. Homogeneous, adherent films were obtained on silicon and stainless steel substrates under 2 kV pulse bias voltages and 50 mtorr methane plasma pressure. Chemical composition analysis was made using Auger electron microscopy. Fretting wear tests and scratch tests were performed to study the tribological and adherent properties. Cross sectional TEM samples were prepared. The interfacial microstrucutres and chemical compositions were analyzed using transmission electron microscopy and scanning transmission electron microscopy.

A Particular Structure of B-doped μc-Si/a-Si:H Layers on Insulator

ABSTRACTMicrocrystalline films of thicknesses ranging from 0.3 to 1.1 μm have been deposited on oxidized silicon wafers by PECVD in a 50KHz capacitive discharge reactor at 450°C. Two series of films have been elaborated over a wide range of boron concentrations at the same H2:SiH4 ratio of 9:1. Cross section TEM micrographs showed the films to consist of two sublayers of distinct crystalline nature, whose relative thickness depends on the preparation conditions. With a strongly <220> textured microcrystalline structure, the overlayer snowed a columnar morphology, while the amorphous underlayer reached thicknesses of 350nm. Two additional striking features were observed by TEM: - The grains took two symmetrical orientations relative to the preferential [220] growth axis;- The interface between the amorphous and crystalline regions had a sawtooth pattern with a period around 300nm. In contrast to these microstructural results, the B-profile as measured by SIMS was found to be fiat accross the whole thickness. These local measurements are compared to the results of grazing X ray diffraction and Raman measurements. We observe and discuss a discrepancy between the X ray coherence length and the dimensions of the columns as observed by TEM. While optimized conditions lead to a vanishing amorphous sublayer, the more original features described above are tentatively interpreted taking into account the high compressive strains in the layers deposited at low plasma frequencies.

Nanocrystalline Ge Synthesis by Reduction of Si1-xGexO2 Formed by High Pressure Oxidation

ABSTRACTNanocrystalline Ge suitable for photoluminescence studies was synthesized from hydrothermally oxidized alloys of Si60Ge40 using steam at 25 MPa and 475°C. Annealing in either an inert atmosphere (UHP N2) or in flowing forming gas (80:20 N2:H2) results in Ge precipitation. In the first case the Ge precipitates are large and concentrated in the bottom portion of the oxide and result from Si reduction of GeO2. In the case of flowing forming gas the Ge precipitates are distributed diroughout die oxide and are formed by reaction between H2 and GeO2. The precipitated samples were analyzed using Raman spectroscopy and cross sectional TEM. Preliminary photoluminescence data reveal that oxide samples excited by the 325 nm line of a HeCd laser after annealing in H2 at both 750 and 800°C for 30 min show strong visible luminescence while unannealed samples do not.

Structural Characterization of GaP/GaAs/GaP Heterostructure by TEM

ABSTRACTThe defect structure in a GaP/GaAs/GaP heterostructure deposited on a (001) GaAs substrate with a GaAs buffer layer has been characterized by cross sectional TEM. The buffer layer presents dislocations and (α-δ)-fringe contrast parallel to (001) interface plane. HREM study reveals uniformly distributed amorphous capsules in the first GaP/GaAs buffer layer interface. The dominant defects are microtwins which are propagated into the overall heterostructure. Microtwin density is different in the GaP and GaAs layers.The different stress signs may explain the density difference.

Raman scattering and photoluminescence analysis of SOI/SIMOX structures obtained by sequential implantation and annealing correlated with cross sectional TEM

In this paper we describe the analysis by Raman scattering and photoluminescence spectroscopy of silicon-on-insulator (SOI) structures obtained by sequential implantation and annealing (SIA). TEM observations have allowed correlation of the tensile strain observed from the Raman spectra obtained with excitation wavelengths higher than 488 nm and the D bands from the photoluminescence spectra to the presence of a region with precipitates and dislocations close to the buried oxide. Likewise, the comparison between the Raman spectra obtained with lower wavelength (457.9 nm) from SIA samples and from equivalent ones obtained by a single implantation and anneal, has corroborated the higher quality of the surface silicon layer from the SIA structure.

Pulsed Laser Planarization of Metals for IC Interconnect

AbstractWe consider the feasibility of using an excimer laser to planarize copper deposited over polyimide. Even though the polyimide is thermally sensitive, a 2.8 µn thick copper film, deposited over polyimide, was planarized with 248 nm, 25 ns, laser fluences from 1.7 to 2.6 J/cm2. Although planar surfaces were readily produced, a variety of defects were observed in the underlying structures. The defects observed include stress induced fractures of the interconnect structure, polyimide surface roughening, and changes in the electrical characteristics of the polyimide. We also describe cross sectional TEM images of cavities formed in interlayer contacts during laser planarization that support recent descriptions of the surface tension driven flow.

Preparation of Cross Sectional and Plan View TEM Samples of Thin Films on Mgo Substrates with an Additional Chemical Thinning Step

ABSTRACTSingle crystal MgO is a common substrate for the deposition of oxide thin films. The conventional cross sectional transmission electron microscopy sample preparation procedure suffers the drawbacks of: 1)- extensive ion milling time; 2) a higher milling rate for the thin films than for the substrate; 3) introduction of artifacts and contamination during ion milling; and 4) generation of excess defects into the substrate during mechanical thinning. An additional chemical thinning step using hot orthophosphoric acid can reduce or eliminate these adverse effects.This technique can be applied generally to thin film samples deposited on substrates with a low ion milling rate. Furthermore, substrates which are sensitive to mechanical stress and ion beam damage are also suitable for this technique, provided an appropriate chemical polishing solution and compatible epoxy can be found. The unique features of this technique are briefly presented.

Preparation of Cross Sectional TEM Samples Using Lithographic Techniques and Reactive Ion Etching

ABSTRACTThis paper summarizes methods used to create cross-sectional samples for transmission electron microscopy and introduces another variant of the technique all of which rely upon some combination of lithographic patterning and reactive ion etching. The basic idea pursued in using these techniques was to form, from a preselected location, samples that had a large transparent area without use of mechanical polishing or ion milling. Samples were successfully prepared in this manner, but room for improvement remains due to the limited range of diffraction conditions available for imaging or diffraction pattern formation.

Structural Investigation of the Silver—Polyimide Interface by Cross—Sectional Ten and Ion—Beam Sputtering

ABSTRACTWhen metals are deposited on polymers at low rates and elevated temperatures extended and non—uniform interfaces may form, the structural investigation of which requiresspecial techniques. In this paper the morphology of the silver—PMDA—ODA boundary formed during vapor deposition of the metal at 360 ºC has been investigated by means of cross—section TEM and a radiotracer technique in combination with ion—beam sputtering (IBS) for depth profiling. Ag was found to form clusters at the interface, but nearly spherical Ag particles up to diameters as large as 28 nm were also observed within the bulk of the polymer. The formation of Ag clusters is also reflected in the depth profiles, which, in addition, provide direct evidence for the diffusion o; singel Ag atoms deep into the polyimide. Diffusivities in the range of 10–21 – 10–18 m/s were determined for 300 ºC< T < 400 ºC. The Arrhenius plot is curved in accordance with a free—volume mechanism of diffusion. Cross—sectional TEM and low—energyIBS—depth profiling turned out to be an ideal combination for the investigation of extended metal—polymer interfaces.

Delineation of p-n Junctions on Cross Sectional TEM Device Samples

ABSTRACTThe delineation of n-p junctions is one of the techniques routinely required in the analysis of electronic devices. The delineation of the junction profile is typically done either in a scanning electron microscope (SEM) or by angle lapping / staining/ optical microscopy. Recently TEM foils have been selectively etched to simultaneously provide an interface demarcation and an image of processed induced dislocations. A case study is presented in this report on concentration dependent delineation techniques with emphasis on the special problems associated with cross sectional transmission electron microscopy (XTEM) samples. The etchants used in delineating junctions for the SEM or with angle lapping / optical microscopy of transistors are too aggressive for the extremely thin TEM foils. This paper discusses etchants which deliver reproducible, high contrast delineations in XTEM samples with known concentration profiles.

Fabrication of a-Si:H/a-Al1−xOx Superlattice by Excimer Laser MOCVD and its Properties

Abstracta-Si:H/a-A11−xOx superlattice structures have been fabricated by ArF excimer laser MOCVD. Periodic variation of composed elements in multilayers with quite uniform layer thickness was clearly shown by SIMS analysis. Optical band gap was increased with the decrease of the well layer thickness, indicating the quantum size effect. With the advantage of the inherent digital process, very sharp interface was obtained, which was confirmed by both XPS and cross sectional TEM analyses.

The Influence of Substrate Patterning on Threading Dislocation Density and Residual Stress in GaAs/Si Heteroepitaxial Layers.

ABSTRACTThe growth of GaAs films by MBE on mesa-type patterned Si substrates has been investigated. Mesa widths were varied from 10 µm to 200 µm and were prepared using chemical etching with Si3N4 masks and reactive ion etching. The residual stress in the epitaxial layer was estimated using low temperature (7K) photoluminescence and the defect distribution was studied by cross sectional TEM, dislocation densities were in addition determined by etch pits. The residual stress and the dislocation density decreased monotonically with the reduction of growth area. By the incorporation of strained layers with the reduction of growth area, the etch pit density in GaAs layers on mesas was reduced further.

Microanalysis of a thin native oxide layer on silicon surfaces by parallel EELS

It is known that a thin layer of so-called “native oxide” is formed immediately on clean silicon surfaces upon exposure to air at room temperature. The composition of native oxide, SiOx, is uncertain. Various experimental methods have yielded values less than 2 for x. Parallel energy loss spectrometers fitted to analytical electron microscopes with field emission sources provide sufficient spatial resolution (≤4nm) for direct quantitative analysis of native oxide films. In this note we report the first EELS analysis of native oxide on silicon.CZ Si {001} wafers, HF etched at room temperature and rinsed in doubly deionized water, were exposed to air until placed in an UHV chamber. A thin layer of Au wasthen deposited on Si surfaces, so that the native oxide layer was preserved between Si substrate and deposited Au film. Cross section TEM specimens were made in the usual way.

Depth distribution analysis of martensitic transformations in Xe implanted austenitic stainless steel

In recent years the implantation of noble gases in metals has been found to induce some exciting phenomena such as formation of inclusions containing solid gas at extremely high pressures. In stainless steels these inclusions are the origin of a stress-induced martensitic fcc → bcc phase transformation in the implanted layer. In this work we present results from a depth distribution analysis of the martensitic phase change occurring in Xe implanted single crystals of austenitic stainless steel. Analysis was done by in situ RBS/channeling analysis, X-ray diffraction and cross-section transmission electron microscopy (XTEM) of the implanted surface. It is found that the martensitic transformation of the surface layer occurs for fluences above 1 × 10 20 m −2. The thickness of the transformed layer increases with fluence to ≈ 150 nm at 1 × 10 21 m −2, which far exceeds the range plus straggling of the implanted Xe as calculated by the TRIM computer simulation code. Simulations using the MARLOWE code indicate that the thickness of the transformed layer coincides with the range of the small fraction of ions channeled under random implantation conditions. Using cross sectional TEM on the Xe implanted crystals, the depth distribution of gas inclusions and defects can be directly observed. Besides microstructural details of the near surface region, this technique offers a well calibrated depth scale to be compared with that derived by RBS. Using X-ray diffraction on implanted single crystals, the solid epitaxial nature of the Xe inclusions, induced prior to the martensitic transformation, was established. The lattice constant obtained from the broad diffraction peak indicates that the pressure in the inclusions is ≈ 5 GPa.

High Resolution and Analytical Electron Microscopy of Multilayer Heteroepitaxial Semiconductors

ABSTRACTThin-film epitaxial layers on silicon substrates are being actively developed as an alternative to bulk substrates for infrared detectors. Success in this development is expected to yield improvements in size, strength, monolithic signal processing, and cost of the detector arrays. To provide feedback to the thin-film growth process, this study has investigated the structural and chemical properties of these films. CdTe or CdZnTe was grown on GaAs on Si wafers by metalorganic chemical vapor deposition (MOCVD) followed by the growth of HgCdTe by liquid-phase epitaxy (LPE). Development of TEM specimen preparation techniques permitted investigation of materials with up to four layers. Cross sectional TEM and AEM investigations resulted in the following observations: Selected area diffraction and CTEM show relations between the layers and structural defects. High resolution imaging of the multilayers reveals that most of the heteroepitaxial misfit is accomodated by misfit dislocations. Many, but not all, stacking faults and dislocations which propagate across the films appear to be related to structural interface defects. The evidence indicates that there is little, if any, contamination at MOCVD and LPE interfaces. Interface defects mainly appear to be extremely minute pits or hillocks. AEM investigations of interface regions have demonstrated a redistribution of material close to the CdZnTe / HgCdTe interface.

Tem Study of Defects In CdTe/CdMnTe Superlattices on (100) InSb

ABSTRACTCdTe/Cd1−xMnx Te superlattices with well/barrier thicknesses ranging from 20Å to 300Å were examined via plan and cross section TEM in analytical instruments capable of EDX and CL. Misfit dislocations, inclined dislocations and stacking faults were observed with a net density of around 109cm−2.It was observed that the dislocations originated near the substrate/epilayer interface and that stacking faults appeared preferrentially on the pair of {111}B (tellurium terminated) planes in the growth direction rather than on the {111}A planes.It is suggested that this is due to a difference in mobility between a and P dislocations originating at or near the substrate.

Synthesis and Properties of Ultra-Thin YBa2Cu3O7 and YBa2Cu3O7/La2-xSrxCuO4 Multilayers

AbstractUsing our standard single target off-axis sputter deposition procedure[1], ultra-thin YBa2Cu3O7 superconducting films were made in-situ. We have studied the thickness dependence of superconducting properties (Tc, Jc) from 20 to 5000Å. Tc starts degrading below 125Å and falls to 50 K for the 30 Å film. Jc drops linearly with decreasing thickness below l000Å. We have grown YBa2Cu3O7/La2-xSrxCuO4 superconducting thin film multilayers in-situ by the same process. The modulation wavelength of the multilayers ranged from 45Å to 2000Å. X-ray diffraction and cross sectional TEM confirm the superlattice periodicity. The superconducting transition temperature drops in much the same way as the single layer ultra-thin films. Both the critical current density and its magnetic field dependence decrease as the modulation wavelength decreases.

Raman scattering in-depth evaluation of recrystallized silicon-on-oxide using different wavelength excitation

Recrystallized silicon-on-oxide were analyzed by laser Raman scattering spectroscopy. By changing the excitation laser wavelength, the in-depth stress profile was obtained. The in-depth stress change was strongly dependent on recrystallization power. Recrystallized silicon structures were confirmed by cross sectional TEM observations. Dependent on recrystallization power, silicon film structures changed from small grain or small and large two grain layers to continuous large grain films.