The epitaxial growth of CdTe on Si is currently being investigated as a means of generating an alternative substrate for the subsequent growth and processing of HgCdTe based infrared detecting devices. The most favorable orientation for the growth of high-quality HgCdTe is CdTe (111)B, which has been demonstrated to be grown on miscut Si (001) substrates with very high quality . However, twinning islands and multiple domains are present at the nucleation stage, which has a detrimental effect on the device properties.

An alternative approach, which has the potential to overcome the multiple domain problems in the nucleation stage, is to grow CdTe (111) B on Si (111) substrates. However, previous reports have shown that the direct growth of CdTe onto Si (111) results in an A-polarity for the films . In an attempt to overcome this limitation, passivation of the substrate surface has been investigated.

Narrow band gap semiconductors such as ReSi2-x (Eg ∽0.12 eV) are potential materials for infrared detectors [1]. Further, ReSi2-x is in thermodynamic equilibrium and has a very small lattice mismatch with Si offering the potential of developing ReSi2-x /Si heterojunction devices where the detector element and the signal processing circuitry can be integrated on one Si chip. In a previous study, strong crystallographic alignment between ReSi2-x film and (001)Si substrate was observed by ion channeling [1]. In this study, a transmission electron microscopy (TEM) study has been performed on ReSi2-x epitaxial films on (001) Si. Comparisons are made to our previous microscopy study [2] on the defect structures in bulk single crystals of ReSi2-x.

ReSi2-x films were prepared by reactive deposition epitaxy (RDE) technique by evaporating Re onto (001) Si wafer at 650 °C. A cap layer of Cr was evaporated at room temperature. A bright field (BF) TEM image of the interface in cross-section is shown in Fig. 1 with the corresponding selected area diffraction pattern (SADP) shown in Fig. 2.

The rate of heteroepitaxial strain relaxation via misfit dislocation introduction is strongly limited by the kinetics of dislocation nucleation, propagation and interaction. Here we describe real-time observations of the interaction between moving threading dislocations and pre-existing interfacial misfit dislocations using in-situ transmission electron microscopy. This was accomplished both during in-situ observations of the heteroepitaxial growth process using a modified ultrahigh vacuum TEM (UHV-TEM) equipped with chemical vapor deposition capabilities, as well as during in-situ anneals of metastable structures grown by molecular beam epitaxy.

In Figure 1, we present our UHV-TEM observations of the epilayer thicknesses and compositions at which dislocation interactions result in blocking of the propagating threading segment, and compare these with the theoretical predictions of Freund and those of Schwarz and Tersoff. Our results show that dislocation blocking can significantly affect the overall rate of strain relaxation in these structures. This is important, as blocked threading segments introduce undesired band gap states into electronic devices and can act as easy diffusion paths for impurities and dopants.

Nowadays, High Resolution Electron Microscopes are capable to resolve structures on a scale below 100 pm. They can be equipped for Electron Holography in order to detect electric / magnetic fields and for chemical analyses (Electron Energy Loss Spectroscopy & Energy Dispersed X-ray's) that can be performed with a lateral resolution of 0.5 to 1 nm [1]. With the aid of computer sciences it became also possible to quantify local strain. We utilize Philips CM200 and CM300 field emission instruments with attached image filters, the JEOL Atomic Resolution Microscope and specialized software [2] to perform these tasks. On the other hand, a recent highlight in materials sciences is the development a GaN technology that is driven by a fast trial and error approach and aims to revolutionize lighting [3]. It was unavoidable that basic materials properties of the nano-structured thin films are barely understood because of the rapid progress [4].

Cathodoluminescence (CL) microanalysis (spectroscopy and microscopy) enables both pre-existing and irradiation induced defects in the bulk and surface defect structure of wide band gap materials (i.e. semiconductors and insulators) to be monitored and characterized with high spatial resolution and sensitivity. The local micro-volume of specimen may be selected for investigation by varying the electron beam parameters. CL micro analytical techniques allow the in situ monitoring of electron irradiation induced defects and the investigation of irradiation induced electromigration of mobile charged defect species. Irradiation can result in the formation of defects and /or the transformation of existing defect precursors. CL emissions from a material are usually associated with native and impurity defects of the host lattice, however in special cases CL microanalysis can provide direct or indirect evidence for the presence of interstitial molecular species in a material. Atomic displacements from the normal bonding (i.e. defect free) sites induced by an electron beam can result from either knock-on, or radiolytic processes, depending on the incident electron beam energy.

The performance of III-V nitride-based microelectronic and optoelectronic devices relates directly to the micro structure of these materials. Selective lateral overgrowth has been exploited to produce GaN heteroepitaxial films with low defect density [1]. Si is a promising substrate due to its low cost, large size, and the potential for the intergration of GaN-based optoelectronic devices with Si-based electronics. It is also possible to produce high-quality GaN material for devices using lateral overgrowth on a Si substrate [2]. At present, only limited information on the defect structure in GaN heteroepitaxial films grown by selective lateral growth is available, especially those grown on Si substrate. Recent work [3] on GaN pyramids grown on (111) Si substrates by this method has shown that in the center, or core, of the GaN pyramid (at and above the window area) dislocations thread through the pyramid nearly perpendicular to the substrate surface and the dislocation density is quite high.

The possible dislocations and slip systems in the wurtzite structure are the same as in hcp structure [1]. The Burgers vectors of these dislocations are . The dislocations can lie on either the (0001) basal plane or prism planes. The dislocations lie on pyramidal planes. TEM studies have revealed that there are predominately three types of dislocations in a wurtzite GaN epilayer which has not been grown by selective overgrowth (e. g. [2, 3]). The majority of the dislocations are threading dislocations with Burgers vector which appear randomly in the epilayer, they result from the growth errors during the growth process. The other two types of dislocation are halflpops with a [0001] or Burgers vector. The [0001] dislocation half-loop lies on the prism plane and the dislocation half-loop lies on the (0001) basal plane which usually appears near the epilayer/substrate interface.

This report provides analysis data on black deposits observed on gold-plated test socket pads. The socket pads are an integral part of a burn-in test where the test simulates an accelerated aging process and is routinely performed on new products. The test consists of placing a device, as shown in Figure 1, with lead/tin plated copper leads in a test socket then placing that assembly into a “burn-in” oven set to a specific elevated temperature, 150° C in this case, for a specific time. Typically, a bias voltage is applied through the pads on the socket during the test. Historically, during extended burn-in tests of Quad Flat Pack (QFP) devices, problems arose when several devices unexpectedly exhibited open socket-to-device contacts. The “opens” problem repeated itself when new QFP devices were installed in the sockets . Upon visual inspection of the sockets, black deposits were observed in the contact regions, as shown in Figure 2.

Focused ion beam (FIB) instruments are useful for high spatial resolution milling, deposition, and imaging capabilities. As a result, FIB specimen preparation techniques have been widely accepted within the semiconductor community as a means to rapidly prepare high quality, site-specific specimens for transmission electron microscopy (TEM) [1]. In spite of the excellent results that have been observed for both high resolution (HREM) and standard TEM specimen preparation applications, a degree of structural modification is inherent to FIB milled surfaces [2,3]. The magnitude of the damage region that results from Ga+ ion bombardment is dependent on the operating parameters of the FIB (e.g., beam current, beam voltage, milling time, and the use of reactive gas assisted etching).

Lattice defects occur as a consequence of FIB milling because the incident ions transfer energy to the atoms of the target material. Momentum transferred from the incident ions to the target atoms can result in the creation of point defects (e.g., vacancies, self interstitials, and interstitial and substitutional ion implantation), the generation of phonons, and plasmon excitation in the case of metal targets.

Development of future semiconductor processes and improving existing ones requires a strong capability to identify and eliminate the sources of particle defects. The current industry approach for accomplishing this task is to analyze the particles on the wafer surface. The most commonly used technique for this purpose is SEM with EDX (SEM/EDX). This approach provides information about defect chemistry and morphology, which in turn provides a direct path to the reevaluation of processes and hardware parts needed to determine the root cause of a problem. However, the SEM/EDX has three fundamental limitations: (a) it is a large volume technique and therefore, the sensitivity can be insufficient for sub micron particles and thin patches; (b) there is no chemical bonding information due to poor energy resolution; (c) charging problem for dielectrics. In some cases there is a need to use other techniques to support or substitute the EDX results.

Devices for character recognition as well as cellular phones require computational elements that work at higher speeds with lower current requirements. Separation by IMplanted Oxygen (SIMOX) is one type of Silicon On Insulator (SOI) technology that shows great promise in meeting the future demands for faster and more efficient applications. The ultra-thin SIMOX substrates produced by low energy/low dose implant methods make possible the construction of large scale integrated circuits with fully depleted CMOS devices. One of the great challenges in the production of SIMOX technology is achieving high quality Si and Si02 layers. High energy implantation of 0+ ions causes damage to the Si crystal and therefore requires a high temperature annealing step to repair it. Annealing of SIMOX takes place in a mixed atmosphere of argon and oxygen. Having oxygen in the ambient creates a superficial Si02 layer. This reduces the thickness of the SOI layer but also protects the surface from pitting.

To serve the needs of future submicron electronic applications such as cellular communications and character recognition, the computational elements have to be drastically reduced in size as well as power consumption. A promising approach is based on implantation of oxygen ions into a silicon substrate and subsequent high temperature annealing. The process when properly done, results in a very thin silicon layer separated from the bulk silicon substrate by a thin layer of silicon oxide. In these SIMOX elements the top silicon layer is seriously degraded by defects introduced by the ion implantation process, consequently affecting the performance of devices built on them. A careful selection of processing parameters such as implant energy and dose is essential in order to minimize the defect densities. It is believed that Si interstitials are the main reason for the formation of most defects in SIMOX [1]. Consequently, the reduction of the implant oxygen dose minimizes the Si interstitials, and finally lowers the defect densities in both the top Si and buried oxide layers.

Wafer bonding allows the production of Compliant Universal substrates that are made by bonding a thin (< 10 nm) layer twisted ∼45 degrees to the underlying substrate. Subsequent growth on this twisted layer results in defect free films even when the growth material has a significant lattice mismatch with the substrate. Defects on the bonding interface are a common observation when bonding GaAs to many substrates, but the exact nature of these defects has not been clear. We have studied this bonding layer in GaAs-GaAs twist bonded structures by Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy and established that the defects are voids with a portion being partially filled with gallium. Two general sizes of voids are seen. The larger voids are approximately 45 nm in diameter and 22 nm in the wafer normal direction and are distributed in an approximately linear relationship.

The nano-scale dimensions of next generation VLSI and ULSI devices will drive the development of a variety of new processing requirements. Currently device processing conditions from substrate cleaning to thin film deposition require temperatures in the range of 600°C to 1200°C. In order to realize a Si device circuit architecture which integrates Si/Ge structures or the needed super abrupt junctions of buried channel CMOS, low temperature processes must replace those in current production lines. For these processes to be successfully developed and implemented, proper characterization techniques must be used. In the case of epitaxy, cross-sectional TEM is the tool of choice. We will discuss the prominent role that TEM has played in the development of a new Si epitaxy technology. Recently, at the National Renewable Energy Laboratory (NREL), we have shown low temperature, 195°C to 400°C, Si epitaxy via hot-wire chemical vapor deposition- HWCVD. In the past HWCVD has been used to produce amorphous, micro-crystalline, and polycrystalline Si thin films.

Nanosized semiconductors have been highly desirable as optoelectronic materials since the discovery of photoluminescence from porous nanostructured silicon. There are many investigations about visible light emission from nanostructured semiconductors, and several studies showed the size dependence of the photoluminescent and electronic property [1], [2]. In order to investigate the size effect of those optical properties of nanoparticles, the size-selection technique is important.

Size-selection of silicon nanoclusters has been carried out by crossing, an Ar molecular beam perpendicularly to the silicon cluster beam. The laser ablation in inert gas method was used for fabricating nanometer-sized silicon. Large size silicon clusters are produced by Nd:YAG laser irradiation of a silicon wafer which was rotating in ablation chamber under He-gas flow. Produced nanoparticles were extracted through a nozzle ( ϕ = 0.6 mm) to a differentially pumped chamber and then skimmed into a high vacuum chamber for size selection and deposition.

Recently there has been increasing interest in nickel induced lateral recrystallization of amorphous silicon because of its potential to improve device performance and to lower the thermal budget during processing. The hypothesis is that the formation of nickel silicide provides a low energy nucleus for the recrystallization of amorphous silicon. The silicide, moving into a-Si, leaves crystalline silicon behind.1 The grains formed, therefore, tend to elongated. In this paper, we attempt to use TEM to investigate in detail the nickel assisted lateral crystallization of amorphous silicon. The sample was prepared by first depositing a 1000A thick low temperature, oxide layer, LTO, on Corning 1737 glass. A 1000A thick amorphous silicon layer, a-Si, and 1000A thick a-Si were deposited subsequently. The sample was pattern and etched with hydrofluoric acid to form lOum x lOum holes in the oxide layer. Next, 200A of nickel was evaporated onto the sample, followed by a 600°C, 6 hours anneal to induce lateral recrystallization.

Zirconolite (CaZrTi207) is an important phase proposed for high level nuclear waste immobilization. Zirconolite was irradiated by 1 MeV Kr+ at various temperatures. At room temperature, zirconolite became amorphous after a dose of 7x1014 ions/cm2.1 Amorphization dose increased with temperature due to thermal annealing. The critical temperature, above which amorphization does not occur, was estimated to be 654 K. During the low temperature irradiation (<654 K), concurrent with amorphization, zirconolite transformed from a monoclinic structure to the cubic pyrochlore structure and then to the fluorite substructure. The structural change is due to the disordering between cations and between oxygen and oxygen vacancies.

After an irradiation at 673 K to a dose of 3.6x1015 ions/cm, the zirconolite samples remained crystalline. The diffraction pattern consists of strong maxima from the fluorite structure and diffuse maxima surrounding the Bragg positions of the pyrochlore superlattice (FIG. 1). Diffuse scattering patterns have been reported in other phases, and were generally attributed to the shortrange- order (SRO) domains.

Artificial defects generated by ion irradiation have been considered an efficient method to enhance the critical current density in superconducting materials. The mechanism of producing defects as flux pining centers is still an important issue since the efficiency of irradiation-induced defects in flux pinning strongly depends on their microstructures. Different types of defects have been found in heavy ion irradiation. However, there are few results that show light ion irradiation due to the target material selected, the type of light ion and energy, and the incident ion angle. Another factor is the difficulty of cross-sectional sample preparation. In this paper, a single crystal Bi2Sr2CaCu2O7-x with 11 MeV B5+ ion irradiation was observed by transmission electron microscope (TEM) from both plan and cross-sectional view.

The Bi2Sr2CaCu2O7-x single crystals used for ion irradiation were prepared using the floating-zone melting method. The crystals were cleaved into thin sheets of about 20 μm thickness along the a-b plane and cut to about 2mmx2mm size.

Irradiation-assisted stress corrosion cracking (IASCC) of irradiated austenitic stainless steels has been attributed to both microchemical (radiation-induced segregation (RIS)) and microstructural (radiation hardening) effects. The flux of radiation-induced point defects to grain boundaries results in the depletion of Cr and Mo and the enrichment of Ni, Si, and P at the boundaries. Similar to the association of stress corrosion cracking with the depletion of Cr and Mo in thermally sensitized stainless steels, IASCC is attributed in part to similar depletion by RIS. However, in specific heats of irradiated stainless steel, “W-shaped” Cr profiles have been observed with localized enrichment of Cr, Mo and P at grain boundaries. It has been show that such profiles arise from pre-existing segregation associated with intermediate rate cooling from elevated temperatures. However, the exact mechanism responsible for the pre-existing segregation has not been identified.

Two commercial heats of stainless steel (304CP and 316CP) were forced air cooled from elevated temperatures (∽1100°C) to produce pre-existing segregation.

TEM analyses of Si implanted with immiscible elements have shown that the implanted species characteristically segregate to form nanoscale inclusions in the amorphous Si matrix. Subsequen annealing induced recrystallization was found to lead to simultaneous removal of nearly all of the implanted species, explained in terms of stress-induced trapping of the implanted atoms at the amc phous/crystalline interface as it progresses towards the surface.

The solubility of Pb in Si is negligible, and it has previously been shown-that elemental nanoscale inclusions can be formed in Si either by ion implantation at elevated temperature or by rapid solidi cation. In the present work single crystals of <110> Si have been implanted with 80 keV Pb+ k at 300K, 625K and 925K respectively. The implanted fluence was 8-1019 m−2 corresponding to an average concentration of about 3 at.%. Combined TEM and RBS/channeling analysis showed that implantations at 300 K and 625 K induced amorphization of the implanted layer with dense distributions of nanoscale lead inclusions embedded in the amorphous silicon matrix (fig. 1).