The concept of plasma cleaning in glow discharge spectrometry (original) (raw)
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Glow Discharge as a Tool for Surface and Interface Analysis
Applied Spectroscopy Reviews, 2006
This review article focuses on the analytical capabilities of glow discharge optical emission spectrometry (GD-OES) and mass spectrometry (GD-MS) to perform compositional depth profiling (GD-CDP). The properties of the Grimmtype glow discharge as well as basic processes of sputtering are described and their influence on the GD as a surface and interface analytical tool are discussed. A series of examples from recent literature ranging from computer hard disks to molecular monolayers on copper substrates are presented to illustrate the excellent depth resolution that can be achieved with GD surface analytical techniques. The conditions for obtaining nanometer or even atomic-layer depth resolution are discussed. Following this introduction is the possibilities of the technique a selection of applications principally chosen from our laboratories, demonstrating that GD-OES and GD-MS can be successfully employed as an analytical tool assisting the development of new materials and coatings. The applications cover common industrial tasks such as heat treatments, studies of diffusion processes at interfaces, and electrochemical depositions for biocompatible material. However, limitations and known artifacts are also discussed.
Analytical and Bioanalytical Chemistry, 2002
While the array of analytical methods routinely applied for depth profile analysis was fairly static over the decades of the 1980s and 1990s, there appears to be an emerging technique that has a number of very positive and complementary attributes, and warrants serious consideration by the thin film community. Radio frequency glow discharge optical emission spectroscopy (rf-GD-OES) is a technique that provides depth-resolved elemental composition information on a wide variety of sample types. In a manner very much like most depth profiling methods, the rf-GD plasma utilizes an ion sputtering step to ablate sample material in a layer-by-layer fashion. Different from the more commonly applied methods, the device operates at elevated pressures [2-10 Torr Ar (266-1,330 Pa)] and has the inherent capability of sputtering electrically insulating materials directly, without any auxiliary means of charge compensation. In addition, sputtering rates on the order of 1 µm/min provide rapid analysis, with depth resolving powers that are comparable to high-vacuum sputtering methods. Three examples of the use of the rf-GD-OES method are presented as examples of its analytical potential: (1) boron-implanted silicon wafer, (2) a barrier-type alumina film, and (3) a porous-type alumina film. It is believed that the method holds a great deal of promise as part of the arsenal of weapons in the thin films laboratory.
Glow discharge mass spectroscopy (GDMS) is a direct solid sampling technique with growing importance for high sensitivity trace elemental analysis of advanced materials used in aerospace, semiconductor, energy and medical device industries. In this article, several case studies were given, covering the applications in quality control, production support and failure analysis. GDMS is the technique of choice for full survey analysis, in particular monitoring the critical bulk trace impurity in advanced alloys such as S, Se, Pb, etc., due to its exceptional long-term reproducibility (yearly measurement variation RSD < 10%). The GDMS equipped with a fast flow GD source is also a highly sensitive technique for depth profiling of trace impurities in engineering coatings (up to 100s mm thick) in the direct current mode, and in thin metal oxide film (100s nm thick) in the modulated GD mode. We also demonstrated that this GDMS configuration is also an effective tool for near surface chemical analysis of coarse surfaces.
Oxide-based Materials and Devices IV, 2013
Plasma Profiling Techniques provide direct measurement of the chemical composition of materials as a function of depth, with nanometre resolution and the capability to measure both thin and thick layers. These techniques rely on the fast sputtering of a representative area of the material of interest by a high density (10 14 /cm 3 ) and low energy plasma. The unique characteristics of this plasma allow very fast erosion (2 -10 nm/s) with minimum surface damage (as the incident particles have an average energy of about 50 eV) which has been shown to be advantageous for SEM sample preparation. When coupled to a high resolution optical system, the resulting technique is called RF GD-OES and is well established, when coupled to TOFMS detection, it is named Plasma Profiling Time of Flight Mass Spectrometry, a newly commercialized variation of the same technique. Both instruments feature an advanced pulsed RF source allowing the measurements of conductive and non conductive layers. Various applications will be presented ranging from thin film analysis for composition, contamination detection, surface area measurements and doping level to characterization of diffusion mechanisms. Aspects of analytical performance with regards to sensitivity, quantification, repeatability and sample throughput will be discussed.
H2/Ar direct current glow discharge mass spectrometry at constant voltage and pressure
Spectrochimica Acta Part B: Atomic Spectroscopy, 2005
The addition of hydrogen to a direct current (dc)-argon glow discharge (GD) coupled to a time of flight mass spectrometer has been studied using a fixed voltage between the electrodes and a fixed discharge pressure. Hydrogen contents investigated were 0.5%, 1% and 10% v/v in the argon discharge and the samples under study consisted of a copper-base, a nickel-base and an iron-base homogeneous materials. Also, the in-depth profile analysis of a tin plate was investigated. Results have shown that hydrogen addition gives rise to significant changes in the slope of the linear relationship between the electrical current and the discharge voltage. Clearly, the electrical resistance of the discharge at the typical operation voltages in the interval 600-1000 V increases with hydrogen added to pure argon. A decrease of the sputtering rates was observed the higher the hydrogen concentrations. Besides, the ''reduced sputtering rates'', i.e. the sputtering rates divided by the corresponding electrical current, were also lower for the H 2 /Ar discharges than for pure argon. However, the analytical ion signals observed using discharge voltages higher than 900 V turned out to be higher in a 0.5% H 2 /Ar discharge than in pure argon for the copper and nickel materials. Besides, for the three samples investigated the ion yields were from 1.5 up to 3 times higher in 0.5% H 2 /Ar discharges as compared to the pure argon. Finally, the effect of 0.5% H 2 addition to the Ar discharge on the in-depth profile of a tin plate has also been investigated. As compared to the use of a pure Ar GD, higher sensitivity for major and minor components of the coating were observed without loss of the relative depth resolution achieved.
Isij International, 2002
Glow discharge optical emission spectroscopy (GD-OES) as a depth profiling teohnique is briefly reviewed, The quantification technique based on emission yields, defin8d as the analytical signal per unit weight of the analyte, is described. Current standardisation work on applications to zinc and aluminium based metallic ooatings is reviewed. Recent work on non-conduotive applications using radio frequency (RF) sources is presented. It is shown that practioal possibilities to determine disoharge parameters exist, but is more complex to use than for the DC source. Furthermore, the strong influence of hydrogen on emission yields is demonstrated. A "matnx correction" technique to deal with this probl8m is discussed. It is also shown that in spite of all the corrective measures, there still exist artefacts not completely understood, making it neoessary to do "matrix-matched" calibrations for certain applications. For thin film applications, it is demonstrated that state-of-the-art GD-OES system8 are capable of a depth resolution similar to e.g. SIMS and AES. For quantifioation of very thin layers, the hydrogen corr80tion must be considered, In addition, it is shown that short-lived molecular emission oan influence the analyiioal results. A method to deal with this effect is presented and discussed,
Radiofrequency glow-discharge devices for direct solid analysis
Analytical and Bioanalytical Chemistry, 2004
The enormous potential of radiofrequency glow discharges (rf-GD) as photon, atom, or ion sources, coupled to spectrometric techniques, for rapid direct analysis of almost any conductor, semiconductor, or insulating material with good in-depth resolution has been demonstrated worldwide. This outstanding performance has prompted a great effort to develop and characterise rf-GD for direct materials analysis in recent years. The state of the art of rf-GD coupled to atomic absorption spectrometry, optical emission spectrometry, and mass spectrometry for direct solid analysis is reviewed here. A description of the principles of operation of the rf-GD and attempts to model these discharges are also given. Rf-GD instrumentation, both developed at research laboratories and commercially available, is described. Several practical examples are given demonstrating the capabilities of these techniques for bulk and depth-profile analysis. Finally, the research gaps to be filled for full implementation of rf-GD spectrometric techniques in industry and research centres alike for materials science studies and technical development are discussed.
Analytica Chimica Acta, 2011
In recent years particular effort is being devoted towards the development of pulsed GDs because this powering operation mode could offer important analytical advantages. However, the capabilities of radiofrequency (rf) powered glow discharge (GD) in pulsed mode coupled to optical emission spectrometry (OES) for real depth profile quantification has not been demonstrated yet. Therefore, the first part of this work is focussed on assessing the expected advantages of the pulsed GD mode, in comparison with its continuous mode counterpart, in terms of analytical emission intensities and emission yield parameters. Then, the capability of pulsed rf-GD-OES for determination of thickness and compositional depth profiles is demonstrated by resorting to a simple multi-matrix calibration procedure. A rf forward power of 50 W, a pressure of 600 Pa, 1000 Hz pulse frequency and 50% duty cycle were selected. The quantification procedure used was validated by analysing conductive layers of thicknesses ranging from a few tens of nanometer up to about 20 m and varied compositions (hot-dipped zinc, galvanneal, back contact of thin film photovoltaic solar cells and tinplates).
Quantitative depth profile analysis by glow discharge
Spectrochimica Acta Part B: Atomic Spectroscopy, 1994
Ahstrati-The development of dc glow discharge spectrometry for depth profile analysis is reviewed. Different approaches to quantification of depth protile measurements into elemental concentrations vs depth are discussed. Methods for quantitative glow discharge optical emission spectrometry (GD-OES), based on the concept of emission yield (emission intensity/sputtered weight), are described in detail. The alternative quantification method developed at the Swedish Institute for Metals Research, which also incorporates compensation for variations in excitation parameters, is presented. Current work on GD mass spectrometry (GD-MS) for quantitative depth profile analysis is briefly reviewed. Several applications of quantitative GD spectrometry to metallic and non-metallic surface layers are presented. Some of the remaining problem areas with regard to quantification are discussed; reference materials, accuracy of the depth determination, intIuence of released gaseous species, and correction for background signals.