Introduction

SiGe epitaxy on Si has been extensively studied, for semiconductor gap modeling and band structure engineering. Quantitative measurement of the Ge concentration is not a trivial exercise at the microscopic level, where classical tools such as X-Ray diffraction, ellipsometry and SIMS cannot be used. A new quantitative microanalytical technique is proposed based on extinction distance measurements using Convergent Beam Electron Diffraction (CBED) combined with dynamical diffraction simulations. A Ge concentration accuracy of less than 2% is demonstrated on strain relaxed SiGe epitaxial layers.

Experiment

Unstrained SiGe epitaxial layers are analyzed for different Ge concentrations, with two-beam CBED, using the transmitted and the 004 diffracted disc. Energy filtered CBED patterns are acquired at 197 keV with a Philips CM 200 FEG transmission electron microscope, using the Ik x Ik CCD camera of the Gatan GIF energy filter. A liquid nitrogen cryo-holder is used, to sharpen up the CBED patterns and to avoid contamination and degradation of the samples.

Advanced semiconductor devices on the SIMOX (Separation by IMplanted OXygen) substrate have many advantages including high-speed, large packing density and low power consumption. SIMOX consists of a layer structure generated by oxygen ion implantation into silicon wafers. The implantation process introduces a high density of defects that can be reduced by post-implantation annealing. Decreasing the oxygen dose not only reduces the cost but also decreases the damage to the top Si layers. Low-dose implantation results in thinner buried oxide (BOX) layer, in contrast to traditional high-dose SIMOX. The BOX layer formation mechanism is different for low-dose SIMOX from that of high-dose. For a high-dose SIMOX, the BOX layer is already formed by implantation. However, for a low-dose, a number of oxide precipitates are formed during implantation. The larger precipitates grow at the expense of smaller ones until they coalesce to the BOX layer during annealing. This step is known as Ostwald ripening, which is responsible for the thin BOX formation.

Atomic force microscopy (AFM) has been used extensively in recent years to study the topographic nature of surfaces in the nanometer range. Its high resolution and ability to be automated have made it an indispensable tool in semiconductor fabrication. Traditionally, AFM has been used to monitor the surface roughness of substrates fabricated by separation by implanted oxygen (SIMOX) processes. It was during such monitoring that a novel use of AFM was uncovered.

A SIMOX process requires two basic steps - a high dose oxygen ion implantation (1017 to 1018 cm-3) followed by a high temperature anneal (>1200°C). The result of these processes is to form a buried oxide layer which isolates a top single crystal silicon layer from the underlying substrate. Pairs of threading dislocations can form in the top silicon layer during the high temperature anneal as a result of damage caused during the high dose oxygen implant.

Ultra-thin Silicon-On-Insulator (SOI) materials are becoming increasingly attractive for fabrication of ultra-large scale integrated (ULSI) devices due to their performance, speed, and power reduction advantages [1]. In SIMOX (Separation by IMplanted OXygen) materials, extensive damage can be repaired by high-temperature annealing in an argon ambient. A small percentage of oxygen is added to give a sufficient oxygen partial pressure to prevent formation of silicon monoxide lumps and subsequent pits [2]. Capping the sample surface to prevent external thermal oxidation during annealing is important to preserve the thickness of the top silicon layer. This is particularly critical for the ultra-thin SIMOX produced by the low-dose low-energy process. However, the surface capping also affects the formation of the buried oxide (BOX). To study this effect, two sets of samples implanted at the same doses of 1.5, 2.0, 2.5, and 3.0x 1017O+ /cm2 at 65keV were annealed with or without protective cap on the sample surface.

To study the nature of metal-semiconductor junction, metal-clad InAs quantum wells with aluminum deposited on 15-nm thick InAs grown on (100) GaAs with AlSb barrier were prepared by an in-situ method (aluminum was grown immediately by molecular beam epitaxy) and by an ex-situ method (aluminum was deposited after exposing InAs surface in ambient condition by selective etching). Cross sectional TEM studies indicated that the Al grains in the clad aluminum layer were randomly arranged in the ex-situ grown junctions, while, in the in-situ samples, the aluminum grains were found to be well oriented to the underlying InAs.

When the interface is viewed along [Oil], three observed crystallographic relationships for in-situ Al growth are

1. 1. [011]AI // [011]InAs and (100)AI // (100)InAs as shown in Fig. 1(a): the aluminum grains of facecentered cubic (fee) structure are perfectly aligned with the fee InAs lattice when they grow;

Advancing technology continues to place greater and greater demands on semiconductor devices. It is clear that Si technology alone will not be able to meet all of these demands. Silicon Carbide (SiC) is a promising material for highpower and high-temperature applications, such as SiC devices for controlling power in a more electric vehicle in which the SiC device is cooled by the engine oil (200 C.) SiC is well suited for high-power/temperature applications due to its large bandgap of 3.03 eV (for 6H), high breakdown electric field of 2.4 x 106 V/cm (again for 6H), thermal stability, and chemical inertness. These properties hold the promise of reliable and robust performance, but the latter two also present challenges to fabricating such devices. For instance, a key part of making devices involves selected area doping. This is typically accomplished with ion implantation, because the rate of diffusion is so low, followed with an anneal to remove the implant damage and electrically activate the dopant.

GaN and related wide band gap semiconductor alloys have received considerable attention over the past several years because of their utility in short wavelength opto-electronic and high power / high frequency devices. In most cases, GaN alloys are grown heteroepitaxially on (0001) single crystal sapphire. Due to the high lattice mismatch between GaN and sapphire, typical dislocation densities in these films vary from as high as 1010 cm-2 to, at best, 108 cm-2. Hollow core dislocations - also known as nanopipes - are also frequently observed. The presence of high defect densities is widely believed to limit the performance of GaN based electronic devices, especially the lifetime of commercially important blue and green laser diodes.

In this work, we present real time, in-situ TEM observations of the formation mechanism of nanopipes in single crystal GaN.

Lateral epitaxial overgrowth (LEO) technique has recently been used to improve the quality of semiconductor layers grown on a substrate. Previous studies with GaN grown on sapphire showed a significant reduction in dislocation density in LEO layers. The LEO technique uses a thin mask layer to achieve selective epitaxy, allowing vertical and lateral growth through patterned windows. Reduced defect density is expected in laterally grown materials, since no lattice mismatch is involved. In practice, however, the thermal and mismatch stresses often cause dislocations to propagate laterally during LEO, and excessive dislocation activities induced by the stresses also tilt the LEO regions. GaSb-based semiconductors, which are of interest for infrared optoelectronic device applications, have much larger (∼8%) lattice constants than the commonly used GaAs substrate. The LEO technique is therefore of particular interest for its potential to significantly reduce the defect density in GaSb films grown on GaAs substrates.

Copper alloys are widely used as a leadframe (chip carrier) material in plastic packaged semiconductor devices. The oxidation of Cu leadframes during the assembly process can result in poor adhesion between the moulding compound and the die-pad. This often leads to interfacial delamination and contributes to popcorn cracking during the component-board attachment process. The main cause of poor adhesion has been attributed to the weak Cu oxide(s) layer on the leadframe surface. Studies have shown that the moulding compound/leadframe adhesion decreases with increasing oxide thickness.

The aim of this investigation is to give a detailed analysis of the phase formation of a CuNiSi alloy during oxidation and to identify the locus of failure for the interfacial delamination. The Cu leadframes were oxidized in an air oven at 240° C for up to 200 min exposures before encapsulation. A scanning acoustic microscope was used to locate delamination regions along the moulding compound/leadframe interface.

There is currently an increasing interest in the growth and characterisation of semiconductor quantum dots (QDs) for potential use in opto-electronic devices. Heteroepitaxy in the Stranski-Krastanow growth mode is thought to be one of the most promising routes towards the fabrication of such QDs. Little work has been done so far to extend the range of wavelength at which potential QD based opto-electronic devises might work into the middle infrared region of the electromagnetic spectrum. The aim of this paper is to expand on our previous reports on such work and to present new experimental observations concerning the formation of InSb rich QDs in GaSb and InAs matrices. Preliminary results on GaSb rich islands on GaAs are also given for comparison purposes. All samples were grown by metal-organic vapour phase epitaxy on nominal (001) GaAs and GaSb substrates at susceptor temperatures ranging from 460 to 545 °C.

It is well known that heat treatment induced plastic deformation of GaAs substrates is a key factor that reduces the yield of electronic devices in manufacturing processes on an industrial scale. Our recent X-ray topographic survey showed that a quite common, radiatively heated, non In-bonded sample holder design can cause severe plastic deformation in two-inch diameter GaAs (001) substrates when they are heated up to about 650 °C in a molecular beam epitaxy (MBE) growth chamber. Unintentional plastic deformation occurred for all three investigated MBE machines, which were of different make, but we overcame the technical problem by modifications to the sample holder of a user built MBE machine. At present, however, there is no theoretical model available that can satisfactorily describe the experimental observations including the spatial distribution of the majority of the dislocation bundles.

The plastic deformation up to about 98 % is realised by bundles of dislocations which start at the sample edges around the four <100> peripheral areas,

The performance of III-Nitride based Light Emitting Diodes (LEDs), LASERs, GaN/AlGaN MODFETs (Modulation-doped Field Effect Transistors) and HEMTs (High Electron Mobility Transistors) have been improved dramatically over the past few years [1,2], despite the relatively poor material quality of GaN, as compared to GaAs, for example. The intrinsic properties of the materials system make it extremely well suited to both optoelectronic and microwave power transistor applications. Typically, GaN is grown on substrates such as GaAs, Al2O3 (sapphire) or SiC with large lattice mismatch. This has usually resulted in an extremely high defect density in the GaN layer. The growth of GaN on lithium gallate LiGaO2 (LGO) affords many advantages compared to all other available substrates. LGO offers the smallest average lattice mismatch of any available substrate for the Ill-nitrides. This facilitates the growth of high quality GaN directly on Lithium Gallate without the need for a defective buffer to decouple the strain associated with the large lattice mismatch of other substrates [3].

The ultimate objective of instrumented indentation testing is to obtain absolute measurements of material properties and behavior. To achieve this goal, accurate knowledge of the shape of the indenter tip is required. For indentation measurements involving sub-micrometer scale contacts, accurate knowledge of the tip shape can be difficult to achieve. In this presentation, a technique referred to as blind reconstruction is applied to the measurement of tip shapes of indenters used with the atomic force microscope (AFM) to indent polymeric materials.

The AFM has been used recently to make nanoscale indentation measurements and is particularly useful for evaluating the mechanical response of polymeric materials. These measurements can be made using AFM cantilever probes and operating the AFM in force mode with some modifications to account for lateral tip motion. Because the AFM was not specifically designed as an indentation device, other complications can arise due to instrumental uncertainties such as piezo hysteresis, piezo creep, and photodiode nonlinearities.

Semicrystalline ionomers are industrially important materials in adhesives, packaging, engineering thermoplastics, coatings, and more. The most common of these are based on poly(ethylene-ran-methacrylic acid), E/MAA random copolymers partially neutralized with various cations and produced by DuPont under the tradename Surlyn®. In 1990, Register and Cooper described the morphology of semicrystalline ionomers as crystalline lamellae separated by an amorphous polymeric matrix that contains isolated cation-rich domains. Their anomalous small angle X-ray scattering experiments are consistent with the relative electron densities associated with this “three-phase” morphological model. Despite this agreement and the commercial importance of semicrystalline ionomers, a number of fundamental issues have remained unresolved regarding both the morphology of the ionic nanoaggregates and the efficiency of aggregation.

Recently, we have imaged the ionic aggregates using a scanning transmission electron microscope equipped with a field emission electron gun. This microscopy method offers the advantages of reduced phase contrast, high spatial resolution, and enhanced atomic number contrast relative to transmission electron microscopy.

Ionomers are ionically-associating copolymers whose distinctive rheological and mechanical properties arise from the formation of ionic aggregates. The ionic aggregates form when dipoles of minority anionic polymer backbone segments and cationic neutralizing species locally associate and dissociate among each other. Specific ionomer properties depend upon the base copolymer, the minority constituent and the neutralizing agent. One system that has been studied extensively is sulfonated polystyrene ionomer neutralized with Zn (Zn-SPS). The most common technique to date for studying ionomer morphology is small-angle x-ray scattering (SAXS). This technique has provided quantitative information about the aggregate morphology by imposing morphology models that have not been independently confirmed.

In the present study, we demonstrate the capability to directly image the ionic aggregates of Zn-SPS ionomers using scanning transmission electron microscopy (STEM). This method will allow us to confirm or deny the competing morphological models applied to SAXS data. We have applied similar methods to polyethylene-based ionomers.

Arborescent graft polymers are highly branched materials synthesized by grafting multiple generations of macromolecular precursors on a central core [1,2]. They can be synthesized with controllable size and molecular weight depending on the number of generations and the precursor molecular weight. They possess many of the unique structural [3], thermodynamic, and rheological [4] properties of dendrimers but do so on a length scale roughly one order of magnitude higher. This research describes the effect of confinement on the shape of arborescent graft polystyrene (PS).

This work used 3rd generation arborescent graft PS synthesized with 5kg/mole linear polystyrene precursor (G3- 5K). The G3-5K PS sample was mixed to a dilution of approximately 0.005 wt% in toluene. A single drop of solution was placed on either a holey-carbon film or an ultrathin continuous carbon film. The solvent was evaporated under ambient conditions. A Philips CM20 FEG TEM/STEM equipped with a Gatan 666 PEELS and a 679 multiscan CCD camera was used to study the structure of these specimens.

Chemical imaging of polymeric materials is attractive, because of the inherently poor contrast typically afforded by multiphase amorphous polymers in bright-field imaging techniques. Spectrum imaging and energy-filtering approaches are being increasing applied to polymeric materials (1,2, 3).

One recent example from the Stevens group using a Philips CM20 FEG TEM/STEM interfaced to an EmiSpec Vision data acquisition/control system and a Gatan 666 PEELS spectrometer is presented in figure 1. The specimen is a PVP sphere on a holey-carbon TEM grid. The specimen was cooled to approximately -125 °C in a single-tilt cryo stage. Drift correction was implemented by collecting HAADF STEM images from the sub-image region indicated by the dashed white box at periodic intervals. Based on an autocorrelation with the initial image, electronic shifts where imposed to correct for drift. A 3-D spectrum dataset was generated from the 70 x 70 pixel box around the polymer particle at an interpixel spacing of 5 nm and a pixel dwell time of 1.5 sec.

Poly(m-phenylene diisophthalamide) (MPDI) is an all-aromatic polyamide used to manufacture thermally stable high strength fibers (Nomex® by DuPont). The X-ray diffraction data of the commercial solution-spun fiber is in good agreement with a triclinic unit cell structure proposed by Kakida et al. with hydrogen bonds forming a two dimensional network approximately orthogonal to the polymer main chain. When MPDI dissolved in N,N-dimethylacetamide (DMAc) is crystallized over several weeks by exposure to a non-solvent (water) in a diffusion vessel, the polymer precipitates into uniform, regularly twisted crystalline bundles (Figure 1).

TEM images show that the bundles consist of 1-8 individual strands and can reach a length of 20 microns. The pitch and the diameter of these bundles are uniform along the visible length for each bundle but depend on the number of strands per bundle. The diameter of an individual strand is 20-50 nm resulting in a diameter of 20-300 nm for a bundle and a “macroscopic” pitch of 200-1000 nm (Figure 2).

Multi-component polymer films are important for numerous technological applications such as paint systems, adhesives, photographic material, and index-matched optical coatings. Unfortunately, different polymer components are often incompatible so they will phase-separate and create large agglomerations of like phases, which has adverse effects on the structural integrity of thin films. Stabilizing polymer blends usually requires the addition of a third component which is often an expensive emulsifying agent such as a block copolymer. Recent studies have shown the emulsifying benefits of less expensive clay additives in oil-water mixtures [1] but the effect on stabilizing polymer blends is not entirely understood.

We are systematically examining the effects of clay additives on polymer thin film blends using Near Edge Xray Absorption Fine Structure (NEXAFS) Microscopy. We present results from films composed of a 50/50 weight percent blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) (Mw=62k, 25k, respectively) spun cast from toluene onto Si3N4 membranes.

Innovations in the processing of polymers and polymer mixtures can have unintended consequences for microstructure. Microscopic investigations have been motivated in some cases by acquisition of new processing machinery which is larger, such as the supercompounding extruders. Strategies to expand the capacity of existing machines also necessitate detailed property and morphology comparisons between old and new batches of commercially important blends.

Other types of innovations use a temporary processing aid. Dispersed phase size reduction in melt blends on addition of supercritical carbon dioxide has been reported for PMMA/PS blends. TEM images showed smaller, more uniform domains attributed to reduction in melt viscosity. Blends are also under investigation now in flash spun plexifilament fibers to extend the range of end-use properties, but the need for a common solvent limits the possible pairs of polymers. A two-step R.UO4 vapor staining procedure, in which the bulk and sectioned material are exposed, has been used to examine non-equilibrium morphologies frozen in from flash spinning.