Surface Imaging Techniques Research Articles

Characterization of integrated circuit aluminium bonding pads by nanoindentation and scanning force microscopy

The mechanical properties of thin films and surface modified layers can be measured by a variety of different techniques, with nanoindentation being one of the most recent developments in this growing field. It is particularly suited to the characterization of bonding pads used to connect individual microcircuits and chips. Such pads are commonly made of aluminium and have a thickness of approximately 1 μm. By using a depth-sensing indentation method it is possible to obtain quantitative values for the hardness and modulus, and thus gain better insight into the response of a bonding pad material to controlled deformation at such small scales. The nano hardness tester (NHT) is a recently developed instrument using an already established method where an indenter tip with a known geometry is driven into a specific site of the material to be tested, by applying an increasing normal load. When reaching a preset maximum value, the normal load is reduced until partial or complete relaxation occurs. At each stage of the experiment the position of the indenter relative to the sample surface is precisely monitored with a differential capacitive sensor, giving a load/displacement curve characteristic of the sample material. By consequently measuring the topography of the residual indent using a surface imaging technique (e.g., scanning force microscopy) and combining this information with the indentation data, it is possible to gain a fuller understanding of the material response, as well as additional information on surface roughness and frictional properties, the latter being of particular importance in bonding applications. Experimental results are presented for a variety of integrated circuit bonding pads, these confirming the ability of the NHT to becoming a common test in quality assurance and process development of thin films and coatings for the microelectronics industry.

Tone control in dry development of photosensitive polyimides

A dry-developed photosensitive polyimide process has been widely studied as a top surface imaging technique for photoresist applications in microsystem technology. Photografting of photoimageable polyimides are obtained by using a silicon-based monomer having methacrylate sensitizer group, analogous to that contained into the polyamic precursor resist. For this purpose standard UV lithography exposure is employed. The modified surface is retarding the oxygen reactive ion etching process, while the resist pattern containing the Si-containing compound is remaining. Processing steps sequenced in different order are resulting in both positive- and negative-tone patterns after development by oxygen reactive ion etching.

Correlation between processing parameters and mechanical properties as a function of substrate polarisation and depth in a nitrided 316 L stainless steel using nanoindentation and scanning force microscopy

The effects of substrate polarisation in a nitrided 316 L stainless steel have been investigated in an attempt to accurately correlate processing parameters with surface mechanical properties. Nanoindentation allows the Vickers hardness to be measured at precise depths, meaning that the variation in properties with nitriding depth can be evaluated and correlated with the process parameters. By combining such measurements with surface imaging techniques (scanning force microscopy and scanning electron microscopy) and electron probe micro-analysis, it is possible to explain both the mechanical property and microstructural variations of such layers, having been produced in a low pressure arc plasma discharge at 680 K with a mixed Ar-N 2 gas. In this study the nanoindentation technique is presented as a new and valid method for the characterisation of nitrided layers, shown by hardness measurements on four nitrided layers produced with different substrate polarisation potentials. The net advantages of such an approach over conventional methods (e.g. microhardness testing) and the possibility of analysing microstructural phases previously not well detected by X-ray diffraction, make nanoindentation an attractive tool for a more complete understanding of the nitriding process.

Nuclear Pore Complex Structure in Birds

The nuclear envelope consists of two parallel membranes enclosing an aqueous lumen. In places there are pores in both membranes at which the two membranes are joined. Within these pores reside the nuclear pore complexes. The current structural models of the nuclear pore complex have been derived from a number of studies using different electron microscopical techniques. Recently, using surface imaging techniques such as field emission in-lens scanning electron microscopy, novel structures have been identified, particularly at the periphery of the structure, most notably the nucleoplasmic basket. One limitation of the current models is that they are based almost entirely on nuclear envelopes isolated from amphibian oocytes and a pressing question is whether this structure is the same in other organisms and tissues. Here we have studied the structure of nuclear envelopes isolated from bird oocytes. We show that the overall structure is remarkably conserved. In particular, recently discovered peripheral structures appear very similar. We see variations in basket conformation but believe that this is related to the functional states of individual pore complexes.

Noninterferometric differential confocal microscopy with 2-nm depth resolution

By utilizing the sharp slopes of the axial response curve of confocal imaging, we demonstrate a differential confocal technique for surface imaging with depth resolution as great as 2 nm. Neither servo feedback loop nor lock-in detection are used, hence measurements can be performed at high speed with long working distance. Because the technique uses no interferometric effects, it offers large open-loop dynamic range and is compatible with fluorescence microscopy.

Some microrheological aspects of wood-pulp fibres subjected to fatigue loading

Wood-pulp fibres are recognized as concentrically-layered, laminated composite tubes of structural reinforcing material, the cellulose microfibrils, embedded in a cementing matrix of hemicellulose and lignin. When the single fibres are subjected to cyclic mechanical action, their morphological behaviour is characterized by the fatigue growth of micro-voids and surface damage which individually and collectively give rise to stress concentrations, and eventually crack development. The progressive damage phenomena, evinced by the surface imaging and optical sectioning techniques through utilizing confocal laser scanning microscopy, are understood to be consequences of the cumulative material micromechanical degradation and subsequent microstructural breakdown of the cellulose microfibrillar framework. This structural breakdown is believed to effect the fibrillation and flexibilization of the fibres

Enhancement of the Annular Illumination Effect Using a Printing Process Resolvable with Low Image Contrast

Resolution enhancement by annular illumination is discussed. The image contrast of patterns on a wafer is improved by annular illumination in high spatial frequency regions. However, it is still less than 0.5, although the ordinary resist patterns can be resolved only when the image contrast is over about 0.6. Therefore, the actual resolution limit is hardly extended at all by the ordinary resist process. To utilize the small improvement of the image contrast and to realize a noticeable resolution enhancement, a special resist process, by which fine patterns can be printed with a low image contrast of less than 0.5, should be adopted. A large resolution enhancement is actually demonstrated by combining an extra-thin resist process with annular illumination. The optimum annular illumination conditions for low-image contrast printing are also investigated, and it is clarified that a large annular source radius is preferable. Since the resist process used is a matter of choice, various surface imaging techniques will also be applicable.

Technical Note:Application of Surface and Surface Imaging Techniques in the Study of Erosion-Corrosion in Stainless Steel

Abstract The surface analysis methods of x-ray photoelectron spectroscopy (XPS), x-ray spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS), secondary ion mass spectrometry (SIMS), field emission scanning electron microscopy (FE-SEM), and energy-dispersive x-ray spectroscopy (EDS) were used to study erosion-corrosion on a stainless steel (SS) impeller blade used in a pilot plant. The material, of type 304 SS (UNS S30400), was exposed to a humid environment and simultaneously subjected to or contaminated with Cl-containing compounds. The SS impeller blade was subjected simultaneously to high-speed rotation during use and to a sandblasting type of mechanism. Damage to the impeller blade was from a combination of erosion and corrosion. The SS surface of the corroded sample contained very high levels of Cl, C, and O (a portion of the O likely was due to H2O). Appearance of the aggressive chloride (Cl−) anions in the presence of H2O was shown to be a good reason for breakdown of the oxi...

Multivariate Fluorescence Imaging of Gel on Nylon 66 Production Pack Screens

Fluorescence microscopy is an established technique for qualitative and quantitative surface imaging. Because many “real world” surfaces of interest are optically rough (vertical variations on the order of 100 μm or more) it is of great interest to minimize the amount of spectral information lost because of depth-of-focus variations. Multivariate statistics on normalized spectra provide an ideal method for extracting information from such data. The following study examines nylon 66 gel on production pack screens via multivariate fluorescence imaging.

Atomic force microscopy observations of pitting corrosion and inhibition on 7075-T651 aluminum alloy in hydrochloric acid solutions

Atomic force microscopy, a unique surface imaging technique that enables the effects of an imposed environment on the substrate to be measured and assessed, was used to define the effects of a dilute aqueous hydrochloric acid solution (0.03 N) on a polished and etched surface of a peak aged aluminum-zinc-magnesium alloy (7075-T651). A multifunctional corrosion inhibitor with dichromate, nitrite, borate, and molybdate ions, especially solubilized in an organic medium, was introduced to the study and its corrosion retardation effects were observed in situ by the atomic force microscope.

Photochemistry and Surface Properties of Self-Assembled Monolayers of cis- and trans-4-Cyano-4'-(10-thiodecoxy)stilbene on Polycrystalline Gold

Herein we describe a self-assembled array in which a photochemical reaction within a monolayer results in modification of the surface properties. Irradiation of an ordered monolayer of cis-4-cyano-4'-(10-thiodecoxy)stilbene (1) on a gold surface with visible light ([ge] 350 nm) results in a decrease in the contact angle with water in the irradiated region. Significantly, irradiation of a monolayer of the trans isomer (2) under identical conditions does not result in any change in contact angle. When the sample is cooled so that atmospheric moisture condenses on the native and isomerized surfaces, these differences can easily be followed by the naked eye; thus, irradiation constitutes a new technique for surface imaging and for differentiation of surface composition. The results demonstrate that photoisomerization of 1 may be used to photopattern a self-assembled monolayer on a gold surface. Significantly, changes in the contact angle with water are achieved in the monolayer without any contacting reagent or solvent during the irradiation and without any treatment afterward. 22 refs., 3 figs.

Resist process to join electron beam lithography and photolithography

An advanced resist process will be introduced connecting the high resolution of electron beam lithography (EBL) and the high productivity of photolithography using a surface imaging technique. A method to overlay these two exposure processes will be discussed. In addition the process was analysed using simulation. A pattern transfer down to 0.2 μm was achieved.

Applications of scanning acoustic microscopy in analyzing wear and single-point abrasion damage

Wear science has historically relied heavily on observations of surface features to elucidate the fundamental nature of wear processes. A host of surface imaging techniques are currently available, each with its own set of strengths and limitations. This paper considers the application of scanning acoustic microscopy (SAM) for analysis of wear damage processes. Reflection-mode SAM images are produced by the interaction of focused, high-frequency (100 MHz-2 GHz) sound waves with solid surfaces, and contrast is produced by localized variations in near-surface elastic properties. A powerful advantage of SAM is its ability to probe subsurface regions where fractures and delaminations may be concealed from the view of traditional light-optical and electron-optical instruments. The current paper will describe the principles of SAM and illustrate several of its uses in wear surface analysis; specifically, as regards the imaging of elastic strain fields near single-point abrasion damage in silicon carbide, in elucidating the geometry of slip line fields produced during friction tests of an oriented single crystal of stainless steel, and in studying the highly deformed layers of a taper-sectioned intermetallic alloy of Ni 3Al. SAM images are compared with photomicrographs of the same worn areas to illustrate the strengths and limitations inherent in the technique.

Entrance surface and ovarian doses in hysterosalpingography.

A survey of entrance surface doses on 40 patients undergoing hysterosalpingography (HSG) has been undertaken. HSG is performed on women primarily of child-bearing age, with the dose to the gonads of these patients being of significant interest. Four lithium fluoride thermoluminescent dosimeters (TLDs) were attached to anatomical landmarks on the patient's skin to measure entrance surface doses. The results ranged from 0.5 mGy to 38.6 mGy with an average entrance surface dose of 13.3 mGy measured at the symphysis pubis. A correlation was observed between the entrance surface dose and imaging technique. Higher doses were measured when 24 x 30 cm film-screen radiography was used as opposed to fluoroscopy using 100 mm cut film for hard copy. Estimates of the organ dose to the ovaries were derived for both techniques yielding 2.8 mGy for 24 x 30 cm film-screen radiography and 1.7 mGy for 100 mm cut film.

Influence of chemical etching on metal contacts to II-VI compounds: CdTe and ZnSe

The chemical nature of CdTe and ZnSe surfaces prepared by various chemical treatments has been studied by X-ray photoelectron spectroscopy. It has been found that the stoichiometry of the surfaces is very sensitive to the chemical treatments and each surface shows a similar pattern. In general bromine-containing or acid-based solutions preferentially remove the semiconductor cation, leaving a semiconductor anion-rich surface. In contrast, alkaline-based systems preferentially remove the semiconductor anion to produce a semiconductor cation-rich surface. Metal contacts fabricated on these surfaces show considerable differences in current-transport properties. The stability of these metal-semiconductor contacts has also been investigated and the microscopic interactions at these interfaces studied with Auger depth profiling and secondary-ion mass spectroscopy surface imaging techniques. The influence of microscopic interactions on the macroscopic electrical properties is presented and discussed in detail

Detection of rotational modulation in the coronal extreme-ultraviolet emission from V711 Tauri?

The RS CVn binary V711 Tauri was observed by the Extreme Ultraviolet Explorer satellite (EUVE) twice during the latter half of 1992, for periods lasting several days. Light curves for the waveband 60-180 angstroms derived from the all-sky survey scanning in August and from a pointed calibration observation made in October both exhibit a modulation of about 40%. The modulation in both data sets is very similar, with minimum flux occurring near orbital phase phi=0.5. Analysis using a two-temperature optically thin plasma emission model reveals that most of the detected extreme ultraviolet (EUV) flux emanates from hot (approximately 10(7) K) coronal plasma. The modulation is probably mostly due to either flare-like activity or to rotational occultation of a long-lived, compact, and especially bright coronal structure on the more active star of the system. The phased data support the latter hypothesis. This coronal structure is then likely to be associated with the persistent spot patterns seen on V711 Tau when using Doppler and photometric surface imaging techniques. Comparison with contemporaneous Stromgren b-band photometry indicates that the optical minimum light leads the EUV maximum light by 90 degrees in phase.

The application of surface imaging techniques to the study of pitting corrosion initiation in stainless steels

AbstractA combined Auger, EDX and SEM surface imaging study of the initial stages of pitting corrosion is presented. Examples of different pitting initiation situations are shown and the importance of multi‐technique imaging to interpret the results is demonstrated. The information provided by the images is compared with theories established primarily from electrochemical results. The development of scanning probe microscopies presents the opportunity of directly studying pitting initiation using imaging. Initial atomic force microscopy images of the corrosion of sulphide inclusions in stainless steels are given and the possible capabilities of the technique for application in this field are considered.

0.35 μm rule device pattern fabrication using high absorption-type novolac photoresist in single layer deep ultraviolet lithography: Surface image transfer for contact hole fabrication

0.35 μm design rule device patterns were fabricated using high absorption-type positive and negative photoresist with a KrF excimer laser stepper. The main reason for using high absorption-type photoresist was to minimize the thin film interference effect caused by high reflectivity of the substrate in the deep ultraviolet region. The positive photoresist was FH-EX1 (Fuji-Hunt) and negative photoresist was SAL601. Both contain novolac resin as the base polymer. The positive photoresist was mainly used for poly-Si and W–Si layer pattern fabrication and the negative photoresist was used for the contact hole pattern fabrication. In the contact hole fabrication a surface image transfer technique was used. This technique relies on the direct transfer of the surface negative photoresist image to the insulating layer with highly anisotropic etching and is completely different from the so-called ‘‘surface imaging technique’’ using gas phase silylation and successive dry resist development (O2 reactive ion etching). Although the process was a tentative one, critical dimension controllability of this approach satisfied research and development level device fabrication requirements.

The use of field emission in-lens scanning electron microscopy to study the steps of assembly of the nuclear envelope in vitro

At mitosis the nuclear envelope (NE) is disassembled to allow chromosome separation. In telophase it is reassembled as the chromosomes decondense. Cell-free extracts of Xenopus eggs have been used extensively to study assembly of the NE and the nuclear pore complexes (NPCs), providing several models for the steps involved. The NE is a surface structure which in cell-free extracts is easily exposed. It is appropriate, therefore, to use a surface imaging technique to study NE dynamics. Field emission in-lens scanning electron microscopy (FEISEM) provides the opportunity to image surfaces, directly, and to visualise details of structures such as the NPC. Here we show the feasibility and value of FEISEM to study the steps of NE formation. Nuclei have been assembled in vitro and fixed at different time points during assembly, followed by conductive staining, platinum coating, and visualisation by FEISEM. Changes on the nuclear surface with time are shown. Details of the surface of chromatin and the cytoplasmic face of NPC structure are demonstrated without the need to isolate the structures from the nucleus.

Silylation Process for Quarter Micron Lithography.

Silylation process is one of the most attractive surface imaging techniques for deep-UV lithography. We demonstrate the quarter micron pattern fabrication by using KrF excimer laser (248nm) lithography with surface imaging such as silylation process. Furthermore, by combining silylation process with the phase-shifting mask, it can be expected that the excellent resolution and focus latitude are obtained. In fact, experimental results exhibit below quarter micron pattern resolution with large depth of focus. The developed surface imaging technology is very promising for the fabrication of 256MDRAM.