Automated nanoliter solution deposition for total reflection X-ray fluorescence analysis of semiconductor samples

In this study, a BioDot BioJet dispensing system was investigated as a nanoliter sample deposition method for total reflection X-ray fluorescence (TXRF) analysis. The BioDot system was programmed to dispense arrays of 20 nL droplets of sample solution on Si wafers. Each 20 nL droplet was approximately 100 μm in diameter. A 10 × 10 array (100 droplets) was deposited and dried in less than 2 min at room temperature and pressure, demonstrating the efficiency of the automated deposition method. Solutions of various concentrations of Ni and Ni in different matrices were made from stock trace element standards to investigate of the effect of the matrix on the TXRF signal. The concentrations were such that the levels of TXRF signal saturation could be examined. Arrays were deposited to demonstrate the capability of drying 100 μL of vapor phase decomposition-like residue in the area of a typical TXRF detector.     

Ionophore‐Based Biphasic Chemical Sensing in Droplet Microfluidics

Droplet microfluidics is an enabling platform for high‐throughput screens, single‐cell studies, low‐volume chemical diagnostics, and microscale material syntheses. Analytical methods for real‐time and in situ detection of chemicals in the droplets will benefit these applications, but they remain limited. Reported herein is a novel heterogeneous chemical sensing strategy based on functionalization of the oil phase with rationally combined sensing reagents. Sub‐nanoliter oil segments containing pH‐sensitive fluorophores, ionophores, and ion‐exchangers enable highly selective and rapid fluorescence detection of physiologically important electrolytes (K⁺, Na⁺, and Cl^?) and polyions (protamine) in sub‐nanoliter aqueous droplets. Electrolyte analysis in whole blood is demonstrated without suffering from optical interference from the sample matrix. Moreover, an oil phase doped with an aza‐BODIPY dye allows indication of H₂O₂ in the aqueous droplets, exemplifying sensing of targets beyond ionic species.     

Electrospray sample deposition for matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure MALDI mass spectrometry with attomole detection limits

Electrospray sample deposition was explored for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). In this method, nanoliter volumes of matrix/analyte mixture were electrosprayed from a high voltage biased (1-2 kV) fused-silica capillary onto a grounded MALDI plate mounted 100-500 microm from the capillary outlet. Electrospray deposition with these conditions produced sample spots 200-300 microm in diameter thus matching the laser spot size. Varying spray voltage and distance resulted in different crystal sizes and volatilization rates for alpha-cyano-4-hydroxycinnamic acid matrix. Best results were obtained when the sample was deposited as wet droplets as opposed to deposition as dried solid. Under 'wet-spray' conditions, 2-4 microm diameter crystals were formed and detection limits for several neuropeptides were 0.7-25 amol. Samples could be pre-concentrated on the plate by spraying continuously and allowing sample to evaporate in a small spot. Sample volumes as large as 580 nL were deposited yielding a detection limit of 35 pM for neurotensin 1-11. Electrospray sample deposition yielded similar results when using atmospheric pressure-MALDI coupled with a quadrupole ion trap mass spectrometer, except that the sensitivity was approximately seven-fold worse.     

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.     

Quantification issues of trace metals analysis on silicon oxide and nitride films by using VPD‐ICP‐MS and VPD‐GF‐AAS

Vapor phase decomposition (VPD) is a pretreatment technique for collecting trace metal contaminants on the surface of a Si wafer. Such trace metals can be identified and quantified by inductively coupled plasma mass spectrometry (ICP‐MS) or graphite furnace atomic absorption spectroscopy (GF‐AAS). However, the analytical results can be influenced by the Si‐matrix in the VPD samples. This article discusses the approaches to eliminate the interference caused by Si‐matrix. When the thickness of oxide film on wafer surface is less than 100 Å, the quantification results of ICP‐MS analysis will not be affected by Si‐matrix in the VPD samples. Except this, the Si‐matrix must be removed before analysis. An improved heating pretreatment approach has been adopted successfully to eliminate the Si‐matrix. For GF‐AAS analysis, the Si‐matrix will influence the sodium and aluminum analyses. Adding HNO₃ to the graphite furnace tubing after sample injection could also eliminate the interference caused by the Si‐matrix. The method detection limits (MDLs) of VPD‐GF‐AAS and VPD‐ICP‐MS range from 0.04 to 0.55 × 10¹⁰ atoms cm^?2 and 0.05 to 1.73 × 10⁹ atoms cm^?2, respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Detection of metallic trace impurities on Si(100) surfaces with total reflection X-ray fluorescence (TXRF)

Summary The physical principles and analytical capabilities of TXRF are discussed and compared to other surface sensitive techniques. Metallic trace impurities on silicon surfaces are readily identified with detection limits down to 10¹¹ atoms/cm² (10^–4 monolayers). Other advantages are simple sample preparation and the possibility of analyzing insulating layers without charging problems. The method has been applied to quantify coverages of Fe, Ni, Cu and Au on Si(100) surfaces, deposited from intentionally doped solutions (NH₃/H₂O₂ and HF/NH₄F). It turns out that certain metal/solution combinations cause large surface coverages on the silicon wafer, even if the metal concentration in the solution is very low (g/kg range).

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Nachweis von metallischen Spurenverunreinigungen an Si(100)-Oberflächen mit der Totalreflexions-Röntgenfluorescenzanalyse (TXRF)

     

Determination of depth profiling of metal trace impurities on Si surface using total reflection X-ray fluorescence

Summary Total reflection X-ray fluorescence (TXRF) is used for non-destructive determination of depth profiling. A numerical processing is presented as impurity quantification in the continuum excitation TXRF without using standards. Dependences of concentration of impurities on depths ranging from a few tens to thousands Angströms are given for Fe and Cu on Si-wafer. The detection limits are in the range of 10¹⁰ atoms/cm². The method was checked with Secondary Ion Mass Spectrometry (SIMS) and the agreement is reasonably good.     

Novel methods of TXRF analysis for silicon wafer surface inspection

TXRF became a standard, on-line inspection tool for controlling the cleanliness of polished Si wafers for semiconductor use. Wafer makers strive for an all-over metallic cleanliness of < 10¹⁰ atoms · cm^–2. The all-over cleanliness can be analyzed using VPD/TXRF. For VPD preparation and scanning we have developed an automatic system coupled with TXRF. With synchrotron radiation TXRF we were able to detect 13 fg of Ni in a residual microdroplet, i.e.10⁵ atoms · cm^–2. Received: 8 January 1998 / Revised: 13 July 1998 / Accepted: 30 July 1998     

Determination of Si,Al, Ti,Fe and Zr in glass sand samples by 14 MeV neutron activation analysis

Fast neutron activation analysis technique was applied for the determination of Si, Al, Ti, Fe and Zr in glass sand rock samples. The samples and standards were irradiated with a mono-energetic neutron flux of 10⁸n · cm^– · s^–1. Pneumatic facility was used. The gamma activities from samples and standards were counted using a 30 cm³ Ge(Li) detector, with FWHM of 2.9 keV at 1.332 MeV, coupled to an on-line computer facility.     

An Arrayed Micro‐glutamate Sensor Probe Integrated with On‐probe Ag/AgCl Reference and Counter Electrodes

Complete all‐in‐one multi‐arrayed glutamate (Glut) sensors have been constructed on a silicon‐based micromachined probe composed of micro‐platinum (Pt) working electrodes, a micro‐silver/silver chloride (Ag/AgCl) reference electrode (RE), and a micro‐Pt counter electrode (CE). The OCP shift of the electrodeposited Ag/AgCl on‐probe micro‐reference electrode compared with a Ag/AgCl wire is <0.1 mV/h. The composition ratio of Ag, Cl, and Pt on the electrodeposited on‐probe micro‐reference electrode is observed to be 1.00 : 0.48 : 0.02 analyzed by EDS. The miniaturized amperometric Glut biosensors were constructed on working electrode sites (electrode area: ∼8.5×10⁻⁵ cm²) of the microprobe modified with glutamate oxidase (GlutOx) enzyme layers for the selective, fast, and continuous detection of L‐glutamate. The sensor selectivity towards common electroactive interferents has been improved significantly by coating the electrode surface with perm‐selective polymer layers, overoxidized polypyrrole (PPY) and Nafion®. The sensitivity, detection range, and response time of the proposed all‐in‐one Glut biosensors are 204.7±5.8 nA μM⁻¹ cm⁻² (N=5), 4.99–109 μM, and 2.7±0.3 sec, respectively and no interferent signals of AA and DA were observed. The sensor can be reused over 19 times of continuous repetitive operation (total measurement time: ∼4 hours) and the sensor sensitivity can retain up to four weeks of storage.     

草甘膦锆:干燥方法对微形貌的影响及甲醛吸附行为

本文运用扫描电子显微镜、X射线粉末衍射仪等手段对在不同干燥方法下得到的层状材料草甘膦锆分子聚集体的形貌及其对甲醛吸附性能进行了深入研究,探讨了干燥条件对材料形态的影响以及化合物形态对甲醛吸附不同的内在因素。研究结果表明:干燥方法不同,所得草甘膦锆的形貌有明显差别,应用超临界干燥技术得到的产物是具有大比表面(445m2·g-1)和大比孔容(5.32cm3·g-1)的三维网状结构,应用冷冻干燥技术得到的产物具有介孔结构,而使用喷雾干燥技术得到的产物为微孔与介孔共存微球。在对4种不同干燥产物对甲醛吸附性能的研究发现,甲醛分子在不同形态载体上的吸附能力差距很大,超临界干燥得到的草甘膦锆对甲醛吸附最大百分率(被吸附甲醛的质量占吸附组装体的百分含量)达到7.8%,且甲醛被吸附后热稳定性较好,具有较好的应用前景。     

Preparation of Fe−Co−LDH/MXene modified electrode for sensitive determination of arsenic (III) in aquatic system

3-dimensional (3D) Fe−Co−LDH/MXene composite was synthesized by in-situ synthesis and assembly of Fe−Co−LDH rod around MXene under hydrothermal condition. Due to the unique 3D configuration and good conductivity, the obtained Fe−Co−LDH/MXene modified glassy carbon electrode (Fe−Co−LDH/MXene/GCE) showed excellent electrochemical activity for As(III) detection. Via square-wave anodic stripping voltammetry, the response current on Fe−Co−LDH/MXene/GCE had good linear relationship with As(III) concentrations (1∼1000 ppt) with superior sensitivity (0.22 μA ppt⁻¹ cm⁻²) and low detection limit (0.9 ppt). The mechanism of As(III) adsorption was demonstrated. The electrode showed excellent anti-interference ability. Real water sample analysis demonstrated the Fe−Co−LDH/MXene/GCE was deployable in aqua-system.     

An investigation of hydrogen depth profiling using ToF‐SIMS

Hydrogen depth distributions in silicon, zinc oxide, and glass are of great interest in material research and industry. Time‐of‐flight SIMS has been used for hydrogen depth profiling for many years. However, some critical information, such as optimal instrumental settings and detection limits, is not easily available from previous publications. In this work, optimal instrumental settings and detection limits of hydrogen in silicon, zinc oxide, and common glass were investigated. The recommended experimental settings for hydrogen depth profiling using time‐of‐flight SIMS are: (i) keeping pressure in the analysis chamber as low as possible, (ii) using a cesium beam for sputtering and monitoring the H^– signal, (iii) employing monatomic ion analysis beams with the highest currents, and (iv) using interlace mode. In addition, monatomic secondary ions from a matrix are recommended as references to normalize the H^– signal. Detection limits of hydrogen are limited by the pressure of residual gases in the analysis chamber. The base pressure of the analysis chamber (with samples) is about 7 × 10^?10 mbar in this study, and the corresponding detection limits of hydrogen in silicon, zinc oxide, and common glass are 1.3 × 10¹⁸ atoms/cm³, 1.8 × 10¹⁸ atoms/cm³, and 5.6 × 10¹⁸ atoms/cm³, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of oxygen and carbon impurities in polycrystalline silicon by IR spectrometry

The possibility of using infrared spectrometry for the determination of the total oxygen and carbon impurity in polycrystalline silicon of the natural isotope composition and that enriched with the ²⁸Si isotope was studied for samples synthesized by different methods. The results of determining these impurities by the optical method are compared to those obtained by independent methods of analysis. The conditions of IR spectrometric analysis of the silicon synthesized by deposition from the gas phase are determined. It is shown that, for IR spectrometry, the upper boundaries of the analytical range of oxygen and carbon in polycrystalline silicon are 1 × 10¹⁸ and 2 × 10¹⁸ cm^?3; and the limits of their detection are 8 × 10¹⁵ and 5 × 10¹⁵ cm^?3 at a sample thickness of 0.5 and 0.2 cm, respectively.     

A low-dose electron diffraction assay for protection of protein structure against damage from drying.

A new assay using low-dose electron diffraction to measure the protection of protein structure against damage from drying is described. When thin single crystals of catalase are dried within water alone, low-dose electron diffraction yields no Bragg spots. Drying within an experimental aqueous solution that permits detection of diffraction spots thereby indicates a positive result, and the extent of these Bragg reflections into the high angle range gives a quantitative measure of the degree of protection. Bragg spots out to 3.73.9 are recorded for drying within 100 mM solutions of the known structure-preserving sugars, sucrose, tannin, and trehalose. The ability of trehalose to maintain native protein structure during drying starts between 10 and 25 mM, and changes only slightly at concentrations above this threshold; with drying in 150-mM trehalose, catalase crystals yield diffraction spots out to 3.7. Drying within the organic nonsugar polymer polyvinylpyrrolidone gives Bragg spots to 4.0. This new assay should be useful to measure the unexamined structure-preserving capabilities of modified sugars, other nonsugars, and mixtures to identify which protective matrix maintains native protein structure to the greatest extent during drying; electron crystallography using that optimal matrix should yield protein structure at improved levels of high resolution.     

Thin polymer films on semiconductors: From their protection to the realization of molecular electronic devices

When homogeneously grafted as thin films on small band-gap inorganic semiconductors (n-GaAs, n-CdS), organic conjugated polymers such as poly-methylthiophene afford interesting new structures. In their doped conducting state, these polymer films bring a long-term protection of these semiconductors against their photocorrosion in aqueous medium, and the subsequent inclusion of metallic aggregates in these films allows increased catalytic activity for achieving photoelectrochemical reactions. In their undoped semiconducting state, they lead to the realization of “organic-on-inorganic” p-n junctions which show very low leakage current and high allowed current density. As photovoltaic cell, an energy conversion efficiency of 17.5% has been obtained under 100 mW.cm⁻² irradiation with a p-PMeT/n-GaAs cell. The larger number of work already devoted to organic conjugated polymers such as polyacetylene, polypyrrole, polythiophene, has shown that these compounds can be switched between a doped oxidized state, with a nearly metallic conductivity, σ ∼ 10²-10³S.cm⁻¹, and an undoped neutral state which presents semiconducting properties, σ ∼ 10⁻⁷ -10⁻⁹ S. cm⁻¹. Either as free standing film or grafted on an electrode, these polymers exhibit interesting organic electrode properties which have been widely characterized. On the other hand much less is known on their behavior when deposited on inorganic semiconductors. In the following, this area will be discussed on two examples, the protection of narrow band-gap semiconductors against their photo-degradation in aqueous solution, and the new junction properties presented by “organic-on-inorganic” electronic devices.     

Femtosecond photoexcitation dynamics in polydiacetylene 4BCMU film

Femtosecond pulses were used to study photoexcitation dynamics in polydiacetylene 4BCMU film. Ultrafast photoinduced dichroism and optical Kerr gate responses were observed. These measurements allowed estimation of the diffusion constant (D ∼ 0.1 cm²/s), the nonlinear index of refraction (n₂ ∼ 10⁻⁸ esu), and third-order susceptibility (δχ⁽³⁾ ∼ 6 × 10⁻¹⁰ esu), in the film. We also found that the sign of the photoinduced transmission signal was dependent on the pump energy at the low energy absorption edge of the film. Possible explanations are proposed.     

A secondary laser cavity system for spectrophotometry of trace elements based on intracavit6y quenching and thermal lens effects

A system based on correlated cavities is described for quantitative measurements of small absorbances by means of intracavity quenching and the thermal lens effect. Theory suggesting the possibility of such measurements was confirmed experimentally. Methods for determining traces of arsenic and phosphorus in semiconductor silicon were developed; the procedures are based on the formation of reduced 12-molybdophosphoric and 12-molybdoarsenic heteropoly acids and measurement of absorbances either for aqueous solutions or for extracts into isobutanol. The total effect of intracavity quenching and thermal lensing was applied. The detection limits were 100 pg cm^?3 for arsenic and 10 pg cm^?3 for phosphorus. Layer-by-layer determination of phosphorus in silicon wafers was possible over a concentration range of 10¹⁵–10²⁰ atoms cm^?3, with a sample area of 1 cm² and layer thicknesses of 0.35–0.6 μm. The minimum detectable absorbance via the thermal lens effect was 5 × 10^?5, and that via the total effect of intracavity quenching and thermal lensing was 6 × 10^?6.     

Method and mechanism of vapor phase treatment–total reflection X-ray fluorescence for trace element analysis on silicon wafer surface

Vapor phase treatment (VPT) is a pretreatment with hydrofluoric acid vapor to raise the sensitivity of total reflection X-ray fluorescence spectroscopy (TXRF) for trace metal analysis on silicon wafers. The International Organization for Standardization/Technical Committee 201/Working Group 2 (ISO/TC201/WG2) has been investigating the method to analyze 10⁹ atoms/cm² level of metallic contamination on the silicon wafer surface. Though VPT can enhance the TXRF signal intensity from the metallic contamination, it has turned out that the magnitude of the enhancement varies with the type of methods and the process conditions. In this study, approaches to increase TXRF intensity by VPT are investigated using a fuming chamber in an automated VPD instrument. Higher signal intensity can be obtained when condensation is formed on the sample surface in a humidifying atmosphere and with a decreasing stage temperature. Surface observations with SEM and AFM show that particles with ~ 4 μm in diameter are formed and unexpectedly they are dented from the top surface level.     

Free-standing boron doped CVD diamond films grown on partially stabilized zirconia substrates

Boron doped diamond films have been grown adhered to silicon substrates by chemical vapor deposition using boron containing gases. In this work it was shown that it is possible to grow free-standing boron doped CVD diamond films on partially stabilized zirconia substrates using boron powder as the source for doping. Results from Raman spectroscopy confirmed the boron incorporation with concentration up to ∼10²⁰ cm⁻³. X-ray diffraction and scanning electron microscopy showed that the effect of boron incorporation in the microstructure of the diamond film is negligible. The measurement of the resistivity as a function of temperature confirmed the semiconductor behavior, as expected for p-type diamond.