Application of the two-dimensional lateral microanalysis by SIMS and EPMA in materials research

Summary Possibilities of the measurement of elemental maps and their digital processing are demonstrated. Hardware and software developments and some applications for various material problems are discusses.     

SIMS: from research to production control

In 1958, when I joined the Philips Research Laboratories, there were a number of technological problems related to the analysis of solids within Philips that needed analytical support. Because the available (bulk) techniques did not give sufficient results, a new technique, later called secondary ion mass spectrometry (SIMS), was launched that involved the bombardment of a solid target with (primary) energetic ions, followed by mass analysis and ion detection of the sputtered (secondary) target ions. The restrictions of the available infrastructure for such an analytical technique were many: there was no PC for data handling, no internet or database for literature search, the photocopying machine was not yet invented, communication with other scientists had to be done by mail (there was no fax, no E‐mail, no mobile phones) and, what was worse, SIMS was not considered to be a useful analytical technique compared with established techniques! In the years that followed there were many advances:

• (1) The SIMS instrumentation was improved by better ion optics, advanced electronic equipment and was extended from sector type to quadrupole and finally to time‐of‐flight (TOF) mass spectrometers.
• (2) The methodology of SIMS was developed step by step (parameters such as lateral and depth resolution, detection limit and quantitative analysis were all optimized in turn).
• (3) The SIMS technique then made its entrance to solve problems in technology development.

In the last two decades SIMS has become an indispensable, reliable, quantitative analytical technique for production control in integrated circuit technology and the after‐sales care of integrated circuits. The philosophy of the provision of an analytical service at the Philips Research Laboratory (hereinafter referred to as ‘our laboratory’) is discussed. After the initial period, where every method (SIMS, AES, ESCA, RBS, etc.) was claimed to be ‘the only one’ (the panacea), we learned how to organize analytical service cost efficiently and for the optimum benefit of the ‘customer’. The core analytical techniques were concentrated in one department and the customer would profit from synergy by using several appropriate analytical techniques for the same problem. Today, the latest developments in SIMS instrumentation keep pace with the latest challenges of the ultra‐large‐scale integration (ULSI) roadmap for integrated circuits, which indicates the dimensions of the circuits that are predicted for the years to come. Copyright © 2003 John Wiley & Sons, Ltd.     

SIMS depth profiling of semiconductor interfaces: Experimental study of depth resolution function

Reconstruction of original element distribution at semiconductor interfaces using experimental SIMS profiles encounters considerable difficulties because of the matrix effect, sputtering rate change at the interface, and also a sputtering‐induced broadening of original distributions. We performed a detailed depth profiling analysis of the Al step‐function distribution in GaAs/Al_xGa_1?xAs heterostructures by using Cs⁺ primary ion beam sputtering and CsM⁺ cluster ion monitoring (where M is the element of interest) to suppress the matrix effect. The experimental Depth Resolution Function (DRF) was obtained by differentiation of the Al step‐function profile and compared with the ‘reference’ DRF found from depth profiling of an Al delta layer. The difference between two experimental DRFs was explained by the sputtering rate change during the interface profiling. We experimentally studied the sputtering rate dependence on the Al_xGa_1?xAs layer composition and applied it for a reconstruction of the DRF found by differentiating the Al step‐function distribution: the ‘reconstructed’ and ‘reference’ DRFs were found to be in good agreement. This confirmed the correctness of the treatment elaborated. Copyright © 2010 John Wiley & Sons, Ltd.     

Application of SIMS in patina studies on Bronze Age copper alloys

Summary The potential of secondary ion mass spectrometry for the patina studies on Bronze Age copper alloys is discussed. It is shown that the combined use of metallography, electron probe micro-analysis and ion microscopy can obtain very useful information concerning fabrication technology and corrosion mechanisms of ancient metals. Especially the convenience of measuring ion micrographs for relatively rapid qualitative indication of phases and inclusions, which are of interest for the investigation of different corroded surfaces found on ancient bronzes, is outlined. The results of investigations of two bronze objects with a specific patina appearance are presented.     

Application of ETV-ICPMS in semiconductor process control

Submicron semiconductor manufacturing requires ultra-clean processes and materials to achieve high product yields. It is demonstrated that electrothermal evaporation (ETV) in a graphite furnace coupled with ICPMS offers a new possibility for a fast simultaneous analysis of eight elements with detection limits below 0.2 ng/g in conc. hydrofluoric acid and buffered oxide etch (ammonium fluoride/hydrogen fluoride mixture). ETV-ICPMS also comprises significant improvements in the analysis of metal contamination on silicon wafer surfaces with respect to currently used methods. The contaminants on the surface are usually analyzed by total reflexion X-ray fluorescence spectrometry (TXRF) or dissolved by HF vapour (vapour phase decomposition; VPD) or a mixture of hydrofluoric acid and hydrogen peroxide (droplet surface etching, DSE) and analyzed by GFAA or TXRF. ETV-ICPMS combines the advantages of both analytical methods: the multielemental advantage of TXRF and the possibility to analyze light elements like Al, Mg, Na which may not be analyzed by TXRF. With VPD/DSE-ETV-ICPMS detection limits between 0.2 and 2×10⁹ atoms cm^?2 on a 6″ wafer have been achieved in a simultaneous analysis of eight elements. The main advantage of ETV-ICPMS versus conventional ICPMS in both applications — chemical and surface analysis — is its capability to analyze Fe in the sub-ng/g range. As Fe is one of the most important impurities in semiconductor manufacturing ETV-ICPMS is much more useful for semiconductor applications than low-resolution ICPMS. For the present application potassium iodide was used as a modifier. It enhances the sensitivity by a factor of 3–4 and improves the reproducibility significantly.     

Application of tandem analyser to SIMS studies of hydrocarbon polymers

The fragmentation of ions sputtered from the surface of low-density poly(ethylene) (LDPE) has been investigated by studying their collisionally activated dissociation (CAD) when incident upon a variety of target gases in the collision cell of a triple quadrupole SIMS instrument. It was found that heavier targets resulted in more extensive CAD than was observed with lighter targets but that sulphur hexafluoride is inefficient target because of the amount opf energy that is transferred to its vibrational modes of motion (rather than being available to induce fragmentation in the parent ion.) The behaviour observed for an oxygen target was quite different to that observed for other targets (at higher pressures). In general oxygen induced markedly greater fragmentation for the small parent ions but xenon was the preferred target for the larger parent ions. Fragmentation patterns could readily be assembled for all of the parent ions observed in the SIMS spectrum of LDPE using the CAD data. There are good indications that the data obtained may assist in indentification of ion structures and in elucidation of general rules governing the fragmentation of organic materials during SIMS. For example, LDPE fragment ions were found to obey quite strictly the Even Electron Rule, a well-known rule in mass spectrometry.     

Profile distortion in SIMS

A short survey is given of the relation between depth profile distortions observed in Secondary Ion Mass Spectrometry (SIMS) and the basic interaction process of energetic particles with a solid material. An experimental method proposed in the literature to determine the width of the cascade mixing layer is discussed and it is shown that for interpretation of the results matrix effects must be taken into account. The influence of primary ion implantation on shallow depth profiles is demonstrated and finally a mechanism is proposed which relates profile distortions to the existence of a chemically modified surface layer after oxygen ion bombardment.     

Application of ion chromatography in the semiconductor industry

This review discusses ion-chromatographic advances in the semiconductor industry during the past 5 years. Through the development of more selective and sensitive instruments and columns, plus better attention to contamination control, the detection limits for many analyses are now in the low-ppt (w/w) range. The primary area of interest continues to be anion analysis, since spectroscopy remains the industry's preferred technique for quantifying cationic species. Noteworthy ion-chromatographic methods for analyzing semiconductor chemicals, gases, and solid samples are discussed and evaluated critically. Thirty-eight references are included.     

Promising avenues of research in nanoscience: chemistry of semiconductor nanoparticles

The state-of-the-art in the field of research on semiconductor nanoparticles is analyzed; cadmium chalcogenide nanoparticles are considered in most detail. Emphasis is placed on the methods of synthesis and on control of the size, composition, and structure of semiconductor nanoparticles — “quantum dots”. The state of the surface plays a significant role in determining the properties of nanoparticles. Organized nanostructures comprised of quantum dots are considered. The properties of semiconductor nanoparticles are described. Prospects for applications of semiconductor nanomaterials are discussed. Dedicated to Academician V. I. Minkin on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 811–836, April, 2005.     

Reduction of matrix effects in TOF‐SIMS analysis by metal‐assisted SIMS (MetA‐SIMS)

We investigated reduction of the matrix effect in time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) analysis by the deposition of a small amount of metal on the sample surfaces (metal‐assisted SIMS or MetA‐SIMS). The metal used was silver, and the substrates used were silicon wafers as electroconductive substrates and polypropylene (PP) plates as nonelectroconductive substrates. Irganox 1010 and silicone oil on these substrates were analyzed by TOF‐SIMS before and after silver deposition. Before silver deposition, the secondary ion yields from the substances on the silicon wafer and PP plate were quite different due to the matrix effect from each substrate. After silver deposition, however, both ion yields were enhanced, particularly the sample on the PP plate, and little difference was seen between the two substrates. It was therefore found that the deposition of a small amount of metal on the sample surface is useful for reduction of the matrix effect. By reducing the matrix effect using this technique, it is possible to evaluate from the ion intensities the order of magnitude of the quantities of organic materials on different substrates. In addition, this reduction technique has clear utility for the imaging of organic materials on nonuniform substrates such as metals and polymers. MetA‐SIMS is thus a useful analysis tool for solving problems with real‐world samples. Copyright © 2005 John Wiley & Sons, Ltd.     

Metallurgical applications of SIMS

Summary This paper reviews the unique advantages provided by Secondary Ion Mass Spectrometry (SIMS) for the characterization of heterogeneous conducting metallurgical samples: detection and imaging of the lateral distribution of every element (H-U), even at very low concentration and excellent depth resolution in the nanometer range. The advantages brought by coupling SIMS with other conventional microscopical and microanalytical techniques (SEM, EPMA, TEM/STEM) are illustrated by examples taken from the author's laboratory: quantitative analysis of the solid solution and within phases, surface, thin film and interface analysis by depth profiles. Special attention will be brought to the advantages of Ion Microscopy and the importance of high mass resolution. The difficulties associated with the variations of sputtering rate and ionization probability in multiphase systems will also be discussed.

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Anwendungen von SIMS in der Metallurgie

     

Application of SIMS in Re-Technology Studies: Characterization of Trace-Element Distributions and Quantitative of Carbon-Determination

 The content and the three dimensional distribution of impurities play an important role in the production process of high purity rhenium powder (99.99% purity grade) and for its further use as alloying and coating agent in high temperature applications. In this paper the characterization of raw Re granulate, Re powder, cleaned by heat treatment, Re coatings, produced by most common preparation methods (PVD and VPS) and PM Re by means of SIMS is presented. The analysis of the three dimensional distribution of trace elements is performed by 3D SIMS. The quantification of carbon, which was not possible with other analytical techniques as a result of the high volatility of Re₂O₇ until now, has been carried out by SIMS depth profile analysis. It is discussed if internal standards, produced by introduction of defined amounts of carbon soot to the Re powder lead to useful results.     

SIMS investigation of CrN sputtercoatings

Chromium nitride layers produced by reactive sputtering with different process parameters were characterized with EPMA, SIMS depth profiling, and three-dimensional SIMS imaging. EPMA results are used to quantify the major components of the films while SIMS is used to gather information about the distribution of the elements chromium, silicon, nitrogen, and oxygen. For all measurements a Cs+ primary ion beam was applied to sputter the sample. Positive MCs+ (M represents the element to be analyzed) secondary ions were detected. SIMS depth profiling shows an even distribution of all major elements except oxygen, which shows significant differences in concentration and distribution depending on the process parameters. CrN layers produced at low sputter power have much higher concentration of oxygen than layers produced with high sputter power. Heating the silicon substrate during the process results in an enrichment of oxygen at the interface.     

Quantitative SIMS analysis of SiC

We performed a systematic study of ion‐implanted 6H‐SiC standards to find the optimal regimes for SIMS analysis. Relative sensitivity factors (RSFs) were acquired for operating conditions typical of practical SIMS applications. The experimental SiC RSFs were compared with those found for silicon: 1 the matrix effect was insignificant in most cases. It was found that the SiO^? cluster ion cannot represent correctly the real oxygen distribution in SiC. The physics of the effect is discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

State of Art in the SIMS (Secondary Ion Mass Spectrometry) Application to Archaeometry Studies

One of the main problems of cultural heritages in all the different forms (buildings, monuments, painting) is their deterioration caused by natural and artificial decay processes. To address the conservation issue specific studies are required to determine, for example, origin, date, materials composition, technology processes involved, etc. The use of microanalysis techniques, in particular secondary ion mass spectrometry (SIMS), in the cultural heritage area has been demonstrated extremely useful to approach and provide this kind of information and support the experts involved in studies within this area (art historians, archaeologists, curators etc.). In this work, an up to date overview of possible SIMS applications to archaeological topics is given, pointing out the peculiarity and the main limitations and drawbacks of this analytical approach. One example of SIMS application to archaeological glasses is reported. Moreover the wide technique flexibility and its strength in combination with other complementary techniques are remarked.     

Surface analysis of semiconductors with SIMS

Characterization of semiconductor devices or materials is one of the most demanding tasks for analytical chemistry because the dopant elements which have to be determined are distributed within a thin surface layer. Their distribution has to be characterized with a spatial (depth) resolution of a few nanometers and high analytical accuracy. Since the local concentration of these dopant elements ranges from several percent to less than 1 ng g^?1, only those methods with the highest detection power can be successfully used. Secondary ion mass spectroscopy (SIMS) has emerged in the last few years as the most powerful analytical technique due to new instrumental and methodological developments.     

Cr-AlN界面的二次离子质谱研究

采用电子束蒸发的方法在２００℃抛光的氮化铝（ＡｌＮ）陶瓷衬底上淀积２００ｎｍ的Ｃｒ膜,并在高真空中退火。利用ＭＣｓ＋－ＳＩＭＳ技术（在Ｃｓ＋一次离子轰击下检测ＭＣｓ＋型二次离子）对样品进行了深度剖析,给出了界面组分分布随退火温度与时间的变化关系。结果表明,ＭＣｓ＋－ＳＩＭＳ技术是研究金属－陶瓷界面扩散与反应的有效方法。