To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Total reflection X-ray Fluorescence (TXRF) has been applied to the detection and quantification of metal contamination on the surface and near-surface regions of silicon wafers in the semiconductor industry The need for improving the sensitivity and detection limit of the TXRF technique is driven by the progress in producing thinner films and finer features in the development of larger Mbit DRAMS.
X-ray fluorescence spectrometry has been used in a broad spectrum of applications. These include elemental analysis, both qualitative and quantitative, based on wavelength dispersive (WDXRF) or energy dispersive (EDXRF) methods. In these methods the detection limit of analyte elements is mainly in the one to ten ppm range in solid samples. Therefore, improvement of these limits is desirable for many useful applications. In this context it is essential to remember that the excitation efficiency for fluorescent X-rays is very low when compared with electron or proton excitation. In the case of WDXRF, the dominant factor is the low reflectivity from the analyzing crystal.
Total reflection X-ray fluorescence (TXRF) analysis of “low Z” elements, Ti, Fe, Ni, Cu, Zn and “high Z” elements, Zr, W, Au, Pb, are required for micro scale semiconductor device production processes. In the past, the W–Lβ X-rays have been used for the analysis of S to Zn.
This paper describes a new three crystal monochromator coupled with a gold direct-drive rotating anode target. This development has produced significant improvements in the sensitivities and LLD's for all measured elements. The monochromator makes the Au Lα (9.71 keV), Au Lβ (11.44 keV) and Au Lγ (13.33 keV) available for routine use in TXRF analyses. The Au Lα X-ray is best used for the lower Z elements, Na to Cu. The best result for W, Cu and Zn are obtained with the Au Lβ X-ray. This is the result of both increased peak intensity and lower background. For the heavier elements, such as Au and Pb, the Au L X-ray yields intensities 100 times higher than what has been achieved in the past.
Over the past few years there has been substantial progress in the TXRF analysis of heavy element surface contamination on silicon wafers. Further advances and improvements are desired in the analytical performance and hardware. Extension of the analytical range to include the light elements is particularly desirable.
In the case of light element analysis, sodium and aluminum impurities have been monitored in the IC production process. The increase of the sodium impurity in a silicon wafer gives rise to a decrease in the insulation in IC devices and the growth of the SiO2 film is disturbed by the prsence of aluminum impurity on the silicon wafer surface.
Many light and ultra-light element analysis problems have been addressed by X-ray fluorescence. Recent innovative features of X-ray spectrometers have extended the applicability of X-ray fluorescence to ultra-light element analysis. Sensitivities have improved through the use of a newly developed end window X-ray tube. Selection of analyzing optics conditions optimize to some degree the sensitivity/resolution/intensity problems. Instrument stability is greatly improved by simply monitoring and controlling the vacuum within the analyzing chamber. Data are presented to illustrate the effects of these novel instrument components as well as describing several new application techniques for ultra-light element analysis.
Advancements in trace clement analysis require improvements in both the signal-to-noise ratio and accurate background correction. With a sequential spectrometer, one can obtain detection limits of around 0.1 ppm for medium to heavy Z elements. Conditions can be individually optimized for each element, for example, selection of filters, collimators, crystals and background subtraction. The disadvantage is that the analysis time may become “long” if many elements are to be analyzed. This long exposure time can lead to the deterioration of some samples.
The principles and techniques for performing coating thickness measurements in the laboratory and on-line using nuclear radiation have been established for tin or zinc coated steels. Recently, additional engineering efforts have been made toward the development of new coating substances consisting of complex layered materials. For example, zinc-iron alloy metal has higher corrosion resistance than pure zinc-coated steel sheets and evaluations have been made of beneficial characteristics in automobile production processes, such as easy welding, good paintability, high efficiency for press plastics forming, etc.
The problem of background radiation in X-ray fluorescence trace element analysis of fused-glass iron ore samples is addressed. A first-order model of coherent and Comptcn scattering with primary absorption is presented and used to correct measurements. Overlap coefficients for elements in iron ores are presented. The importance of these corrections is demonstrated. The accuracy achieved with X-ray measurements after background corrections compares well with the accuracy of chemical analysis.
The fundamental parameter method for x-ray spectrometry has been used most commonly for bulk samples, because it permits an analysis utilizing a minimum number of standards, even for samples with complicated matrices. The need for the analysis of thin film materials, which includes multi-layer films, has been increasing in recent years along with the rapid progress of high technologies. However, there have been few reports that deal with the application of fundamental parameter methods to multi-layer thin films. There may be two situations in the analysis of thin films. In routine analysis of quality control applications, they usually require precise analysis. Fortunately, it is possible to prepare well characterized standards similar to the unknowns.
In the spectroscopic analysis of minor and trace elements by fluorescent X-rays, many improvements in the analytical performance of trace element measurements have been made. For the analysis of trace elements, the background intensity governs the analytical accuracy and the lowest detection limit in a sample. A comparison is made between experimental and theoretically calculated background X-ray intensities in a previous paper. It is based on the formula for scattered X-ray intensity, from the estimation of Thomson and Compton scattered X-rays. Also, the asymmetrical peak profiles at the base of the giant intensity peak are discussed and are clearly shown in the skirt part of K beta X-rays, e.g. , Ni-K beta or Fe-K beta X-rays. The purpose of this report is to investigate the intensity of background X-rays, using glass beads and powder samples of iron oxide and quartz, based on the previous fundamental studies and the overlapping correction procedure for cobalt determination in low-alloy and stainless steel.
Several interesting phenomena involving ultra-soft X-rays and synthetic multilayer crystals were studied as a result of the on-going process of improving the Rigaku Mode] 3630 Wafer Analyzer for the measurement of BPSG (1000-2500 Å) and other thin films.1-3 These phenomena can be divided into four categories; “ghost” peaks, diffraction from the substrate, fluorescence from the multilayer and higher order lines from the multilayer. Each of these is a potential snurce nf error in the measurement of ultra-soft X-rays, Fortunately, as will be shown, each can be readily dealt with.
In the last few years, at the Denver X-Ray Analytical Conference, the author and co-workers presented two papers which described the principle and applications of carbon analysis by X-ray fluorescence based upon a monochromatization technique consisting of total reflection and filtering. Instead of the wavelength dispersive method based on Bragg reflection, this monochromatization, combining total reflection by a selected mirror and an appropriate filter, offered an alternative approach for the purpose of increasing measured X-ray intensity. The analytical performance of quantitative determination of carbon content in steel, cast iron and coal were reported.
Spectrographic analysis for carbon and boron using fluorescent x-rays has been studied over the past few years; principles and applications for using those ultra-soft x-rays were described, based on the combination of total reflection and filtering rather than on the wavelength dispersive method of Bragg reflection (1, 2). However, oxygen and nitrogen, with x-ray wavelengths of 23.7lÅ and 31.60Å, respectively, cannot be detected as easily because of their high absorption by the detector window materials such as polypropylene, polyester or formvar films.
The wafer analyzer has been used to fulfil many applications needs in the semiconductor industry. The prominent features of the XRF method for the semiconductor industry are:analysis of many types of films, e.g., oxides, silicides and metallic alloys, and simultaneous analysis of film thickness and compositions.
In the past, the analysis results of BPSG (Boron-doped Phospho-Silicate Glass) films, with thicknesses greater than 4000 Å, were reported. With the recent increased demand for larger scale and higher quality semiconductor devices (larger than 64 Mbit), more accurate analysis with high precision has been required.
X-ray fluorescence analysis is the most suitable method, for the characterization of the thickness and the chemical composition of thin film samples. It is non-destructive, rapid, precise, and accurate for both metal and oxide samples.
Recent studies have shown that anguillid eel populations in habitats spanning the marine–freshwater ecotone can display extreme plasticity in the range of catadromy expressed by individual fish. The apparent use of marine and freshwater habitats by the European eel Anguilla anguilla was examined by analysing the strontium (Sr) and calcium (Ca) concentrations in otoliths of eels collected from a tidal Atlantic lake system in Ireland. Variations of the Sr:Ca ratio in the otoliths indicated that a variety of environmental salinities had been experienced in the habitats that were occupied during the growth phase of these individuals in the tidal Atlantic lake system. The otolith microchemistry of these eels indicated that most of the eels had entered each salinity environment (freshwater (FW); brackish water (BW); marine-dominated water (MW) and full seawater (SW)) from fresh water to full seawater just after recruitment and had stayed in each environment until maturation without movement to other salinity environments. Only 2 of 93 (2%) eels had shifted their habitat once in their lives. This result suggests that each individual might have an environmental habitat preference, although each individual could move along a short (<2 km) salinity gradient.
Recently, an epoch-making printing technology called “SuPR-NaP (Surface Photo-Reactive Nanometal Printing)” that allows easy, high-speed, and large-area manufacturing of ultrafine silver wiring patterns has been developed. Here we demonstrate low-voltage operation of organic thin-film transistors (OTFTs) composed of printed source/drain electrodes that are produced by the SuPR-NaP technique. We utilize an ultrathin layer of perfluoropolymer, Cytop, that functions not only as a base layer for producing patterned reactive surface in the SuPR-NaP technique but also as an ultrathin gate dielectric layer of OTFTs. By the use of 22 nm-thick Cytop gate dielectric layer, we successfully operate polycrystalline pentacene OTFTs below 2 V with negligible hysteresis. We also observe the improvement of carrier injection by the surface modification of printed silver electrodes. We discuss that the SuPR-NaP technique allows the production of high-capacitance gate dielectric layers as well as high-resolution printed silver electrodes, which provides promising bases for producing practical active-matrix OTFT backplanes.
Here we discuss requirements for high performance and solution processable organic semiconductors, by presenting a systematic investigation of 7-alkyl-2-phenylbenzothieno[3,2-b]benzothiophenes (Ph-BTBT-Cn’s). We found that the solubility and thermal properties of Ph-BTBT-Cn’s depend systematically on the substituted alkyl-chain length n. The observed features are well understood in terms of the change of molecular packing motif with n: The compounds with n ≤ 4 do not form independent alkyl chain layers, whereas those with n ≥ 5 form isolated alkyl chain layers. The latter compounds afford a series of isomorphous bilayer-type crystal structures that form two-dimensional carrier transport layers within the crystals. We also show that the Ph-BTBT-C10 afford high performance single-crystalline field-effect transistors the mobility of which reaches as high as 15.9 cm2/Vs. These results demonstrate a crucial role of the substituted alkyl chain length for obtaining high performance organic semiconductors and field-effect transistors.
We report photometric results from 44 runs at 11 observatories during the international campaign ‘TT Ari–94’. No coherent oscillations in the frequency range 10… 900 cycle d−1 are found. The highest peaks in the power spectrum cover the wide range of 28… 139 cycle d−1. Variations occur at a few preferred time-scales rather than at one cycle length, with a possible secular decrease. In the frequency range 90… 900 cycle d−1 the power spectrum obeys a power law with slope γ ranging from 0.8 to 2.6 for different runs.
TT Ari is one of the brightest cataclysmic variables and remains one of the most interesting objects of this class. It exhibits a variety of phenomena observed at time-scales from seconds to months. A recent detailed photometric study of this object and a bibliographical overview may be found in Tremko et al. (1996). Tremko et al. (1992, 1993, 1994) discuss aspects of the TT Ari–88 campaign. Our campaign TT Ari–94 was unprecedented, as the observations were longitude-dispersed, from Japan through Turkmenia, to Europe and the American continent. Moreover, our optical data on October 7 partially overlap with the HST observations obtained by Home & Welsh (1995, private communication). The numerical results of observations obtained during these nights are shown in Table 1.