Specimen Preparation Process Research Articles

Characterization of Thin Films on Oxide Using a Unique Tem Specimen Preparation Process

Transmission Electron Microscopy technique is a powerful tool to examine microstructures. However, the specimen preparation process usually requires tedious and careful cutting and lapping. In this paper, we present a TEM specimen preparation process which is simple, requires about one hour, and allows specific areas of patterned films deposited on silicon dioxide to be examined. The sample consisted of three thin film layers deposited on a Corning 1737 glass substrate. The top layer was 1000 A thick, low temperature oxide; the middle layer, 1000 A thick; amorphous silicon; the bottom layer, 1000 A thick, low temperature oxide. The top oxide layer was patterned to contain a square array of 10 × l0um openings, with a 100 um center to center spacing. A thin nickel layer was the evaporated, and the specimen was heated to form nickel silicide in the 10 × 10 um areas where Ni and Si were in contact.

Transmission Electron Microscopy of Semiconductor Based Products

AbstractThe demand for increasingly higher performance semiconductor products has stimulated the semiconductor industry to respond by producing devices with increasingly complex circuitry, more transistors in less space, more layers of metal, dielectric and interconnects, more interfaces, and a manufacturing process with nearly 1,000 steps. As all device features are shrunk in the quest for higher performance, the role of Transmission Electron Microscopy as a characterization tool takes on a continually increasing importance over older, lower-resolution characterization tools, such as SEM. The Ångstrom scale imaging resolution and nanometer scale chemical analysis and diffraction resolution provided by modem TEM's are particularly well suited for solving materials problems encountered during research, development, production engineering, reliability testing, and failure analysis. A critical enabling technology for the application of TEM to semiconductor based products as the feature size shrinks below a quarter micron is advances in specimen preparation. The traditional 1,000Å thick specimen will be unsatisfactory in a growing number of applications. It can be shown using a simple geometrical model, that the thickness of TEM specimens must shrink as the square root of the feature size reduction. Moreover, the center-targeting of these specimens must improve so that the centertargeting error shrinks linearly with the feature size reduction. To meet these challenges, control of the specimen preparation process will require a new generation of polishing and ion milling tools that make use of high resolution imaging to control the ion milling process. In addition, as the TEM specimen thickness shrinks, the thickness of surface amorphization produced must also be reduced. Gallium focused ion beam systems can produce hundreds of Ångstroms of amorphised surface silicon, an amount which can consume an entire thin specimen. This limitation to FIB milling requires a method of removal of amorphised material that leaves no artifact in the remaining material.

A standard method for the preparation of polymers and plastics for microstructural examination by grinding and polishing techniques

One of the fundamental objectives of microstructural examination of manufactured materials is to gain a more complete understanding of the relationships between the manufacturing processes, the microstructure and texture of the material, and the product's performance. This objective, however, can only be achieved if the examination specimens are repeatably produced and are free of thermal, mechanical and chemical alterations, as well as artifacts, damage, or defects resulting from the specimen preparation process. It is also imperative that surface finish of the specimen be appropriate for the microscopical techniques to be used. The preparation process must provide specimens in a timely fashion, generally within a few tens of minutes or at most a few hours for typical industrial/manufacturing situations. Although designed for much harder more rigid materials, the general grinding and polishing techniques used in petrographic and metallographic specimen preparation can also be used for plastics and polymers. ASTM Committee E-4 on Metallography has a task group (TG-E04.01.05) which is preparing a standard guide for the preparation of polymeric specimens based on the ASTM E3-95 standard.

In Z-contrast, not all that glistens is high-Z

It is by now a given that high resolution Z-contrast is a useful imaging technique for detecting high atomic number (Z) domains in nanophase materials. However, image intensity also depends on specimen orientation, electron-optical geometry, thickness and local strain fields, as well as local structural ordering. In this paper we will present examples from our materials studies where contrasts from strain and short-range order in hollow-cone dark-field images provide important structural insights. Strain fields were found to be responsible for the unusual "blister' contrasts observed in hollow-cone dark field images of delaminated sheets of calcium sodium niobate layered materials. Wherever two sheets overlap, the average intensity increases and dark disks of diameter ~20 nm, with bright central spots, appear (Fig. 1). For large hollow-cone angles, q1 > 20 nm-1, the blisters vanish, although faint fine-scale features persist. Elasticity analysis and image simulations (Fig. 2) reveal that the blisters are pockets of gas or liquid that became trapped between sheets during the drying stage of the specimen preparation process, when individual sheets come into contact at random mutual angles and reseal (Fig. 3).

Analysis of shear stress distribution in pushout process of fiber-reinforced ceramics

The interfacial shear stress distribution of a thin specimen of SiC fiber-reinforced glass matrix composite (fiber volume fraction of 0.1, 0.5 and 0.7) during a fiber pushout process was subjected to finite element analysis using a three concentric axisymmetrical model which consisted of fiber, matrix, and composite. A stress criterion was used to determine interface debonding. Effects of thermally-induced stress and a post debond sliding process at the interface were also included in the analysis. The analytical result showed that shear stress near the specimen surface was introduced during the specimen preparation process. Before the interfacial debonding, the distribution of shear stress during the pushout test was affected by the existence of thermally-induced stress in the specimen. The interfacial shear debonding initiated ≈ 30 μm below the pushing surface and the sliding at the debonded interface proceeded in the direction of both the pushing surface and back surface from the peak shear position; the debonding from the back surface initiated just before the complete debonding of the interface. The pushout load-displacement curve near the origin was straight, however, after the existence of interface sliding at the debonded interface, the curve exhibited non-linearity with the increase in applied load up to the complete debonding at the interface. This debonding process was essentially independent of the fiber volume fraction. The results indicate that the total of thermally-induced stress in the specimen and shear stress distribution generated by applied load are important for the initiation of debonding and the frictional sliding process of the thin specimen pushout test.

Transmission Electron Microscopy of polysilicon microresistor

The electrical properties of electronic materials are greatly affected by their microstructure, which in turn is determined by the processes used for fabrication. Transmission Electron Microscopy (TEM) is one of the most powerful analytical techniques to provide localized information about microstructure as it relates to process control parameters. This information is used for process development and failure diagnoses as well as QA/QC control. In this study, the microstructures within the devicesof polysilicon microresistors were analyzed using TEM to understand different resistances.The TEM samples were prepared from the devices to be analyzed by the mechanical polishing method using the tripod polisherTM. The selected area polishing technique was used to find the area of interest within one micron range. Figure 1 shows the specimen preparation process. The low and high magnification optical micrographs in Figures 1a and 1b indicate the region of interest within the die. Figure 1c is the optical image of the cross section along the line A-A in Figure lb.

Cracking behavior of FeAl (40 at % Al) alloys during cutting operations

The intermetallic iron aluminides have long been studied for their great potential as engineering materials due to their excellent oxidation and corrosion resistance coupled with low density and low material cost. Yet, in addition to its brittle behavior at low temperatures and its poor high-temperature strength, a newly discovered problem of FeAl is the introduction of surface microcracks during the fabrication process of the material. These microcracks may affect the fracture strength and ductility of the alloy, causing some concern for its use as an engineering material. The understanding and prevention of these microcracks during fabrication are necessary for engineering uses of FeAl alloys. Cracking has been a major problem during sample preparation for the microstructural analysis and mechanical property evaluation of the alloy. Poor mechanical properties and inconsistency of data can many times be attributed to these microcracks. For this reason, the cracking behavior of these alloys must be investigated. The cracking of FeAl alloys has been most frequently noticed during microstructural analysis, but in a survey of all the various compositions and grain sizes of the FeAl alloys cut for microstructural analysis, the approximately 20% frequency of the existence of microcracks seemed to be completely random. The objectivemore » of this study is to determine in which step of the specimen preparation process the cracking is occurring and to investigate the mechanisms causing this cracking. The main results of this study show that the cracking can be attributed to environmental conditions during cutting of the alloy specimens.« less

Glycation alters collagen fibril organization.

Incubation of rat tail tendon in 0.2M ribose results in accelerated non-enzymatic glycosylation of collagen, with the formation of fluorescent cross-links between molecules and decreased solubility. Electron micrographs of tendon cross-sections show an increased fibril packing density with increasing degrees of glycation. After a one-week incubation in ribose, every fibril appears in close contact with all of its neighbors, and the packing density has increased to 76%, from a value of 62% in controls. Irregular diameters and fusion of fibrils also are seen. All of the fibrils in a bundle appear to become cross-linked together, creating a larger stress bearing unit. This model is consistent with stress-strain curves showing a large increase in tensile stress and stiffness after a one-week incubation period in ribose. The diameters of the collagen fibrils increase in size in glycated tendon. We hypothesize larger diameters result from an increased resistance to shrinkage during the specimen preparation process, as a result of the rigid sugar derived cross-links. Closer fibril packing, increased fibril diameters, and irregular diameters have been reported in diabetic tissues, and may result from decades of glycation induced cross-link accumulation.

A Biological Cryosystem for the Scanning Electron Microscope

Since early 1970's the use of cold stage on SEM for observation of hydrated samples in their natural state has become more and more popular despite its high cost. Experiences gained from earlier experiments indicate that a successful design should incorporate thefollowing features:1. The specimen temperature should be below −135°C (the recrystallization point of water), lower the temperature, better the results.2. The frozen specimen, the cold block in the specimen preparation chamber, as well as the cold stage should be kept under vacuum at all times to keep them frost free.3. Different specimen preparation processes such as fracturing, coating and sublimation should be possible in one compact preparation chamber .

Contrast effects at grooved interfaces

Recent studies have shown that the characterization of the microstructure of ceramics such as polycrystalline alumina is complicated by the surface grooving of the grain boundary (thermal grooving and preferential mechanical damage produced by specimen preparation processes). Many of the TEM techniques, such as the Fresnel-fringe technique and the dark-field diffuse scattering technique, that are used to test for the presence of a glassy phase at grain boundaries do not give unambiguous results due to this grooving effect. Fig. 1 shows an example of such a grain boundary in alumina: the grain boundary has been inclined to show grooving at both surfaces, see fig. 2a. It is the aim of this investigation to study the effect of grooving on the Fresnel-fringe contrast and on high resolution images of grain boundaries by computer simulations.The simulations were performed using the multislice program TEMPAS installed on a CONVEX computer.

Internal Standards for Quantitative X-Ray Phase Analysis: Crystallinity and Solid Solution

Quantitative phase analysis by X-ray diffraction (QTXRD) has been an established tool of analytical chemistry for more than four decades. Despite its age, this tool remains ascendant as the only universally applicable method for determining the manner in which elements are combined into crystalline phases in multiphase solids. QTXRD is entering its second renaissance. The first came with the introduction of the counter diffractometer in the late 1940's. The specimen preparation and data collection processes were exacting and tedious, but reasonably accurate analyses could be obtained. The second came with the introduction of computer controlled diffractometers, whose software packages include QTXRD routines, in the late 1970's. With the tedium of data collection and analysis greatly reduced, we can expect even more widespread adoption of this tool in the general analytical laboratory.

A computer model in the selection of multiple channel analysers

1. A simple computer model is described which was used to study possible test combinations on automated multichannel analysers. Specific objectives were minimisation of manpower and maximisation of throughput of the specimen preparation process. 2. In our case, by appropriate test combination selection, a staff saving of 50% in the aliquotting process is predicted. For tests that are available on multichannel analysers, a reduction from 198 to 121 aliquots per 100 patient specimens is expected on an 18 channel machine. With the use of filter separation systems, manual aliquotting would be required for 21 specimens per 100.