Ultratrace Metallic Impurities Research Articles

Direct determination of impurities in high purity chemicals by electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES)

An ELCAD-AES method was reported for direct determination of metallic impurities in different high purity chemicals such as ammonium hydroxide, hydrogen peroxide and sulphuric acid. Direct analysis of these chemicals for their impurities was found to be feasible by ELCAD-AES without going for chemical processing/treatment like dilution or evaporation of matrix. 100% solutions of NH4OH and H2O2 chemicals produced stable ELCAD plasma, whereas 0.5% solution produced stable plasma for H2SO4. As standard addition calibration method to quantify impurities in these chemicals could not be useful, an alternative aqueous calibration method was examined and found to be suitable for their quantification by ELCAD-AES. As the certified reference materials for these chemicals were not available, the ELCAD-AES results were validated with the corresponding graphite furnace atomic absorption spectrometer (GF-AAS) results for NH4OH and H2O2 whereas for sulphuric acid they were validated with inductively coupled plasma optical emission spectrometer (ICP-OES) and supplier's results. ELCAD-AES method was free from matrix related problems and did not demand for the dilution of NH4OH and H2O2. The method was found to be useful for direct determination of trace and ultra trace metallic impurities in NH4OH and H2O2 pure chemicals and also for trace impurities in H2SO4 chemicals. Repeatability and accuracy of this method were found to be <10% and between 10 and 20% respectively. Thus ELCAD-AES could be an alternative analytical, rapid and direct analysis technique to check levels of metallic impurities (i.e. metal salts) and quality of these high purity chemicals for various industries.

Determination of Ultra-trace Metal Impurities in High-purity Cadmium Using Inductively Coupled Plasma Mass Spectrometry after Matrix Separation with Anion Exchange Resin.

The analytical method for ultra-trace metal impurities at μg kg-1 level in high-purity Cd was examined by inductively coupled plasma mass spectrometry (ICP-MS) combined with matrix separation by Bio-Rad AG MP-1M anion exchange resin. After the separation of Cd, the metal impurities such as Li, In, Cr, Mn, Fe, Co, Ni, Cu, Ga, Sr, Ba and Pb were measured by an ICP-quadrupole mass spectrometer (ICP-QMS) and ICP-sector field mass spectrometer (ICP-SFMS). From the comparison of measured results, it was evaluated that the analytical sensitivity by ICP-SFMS was 10 times higher than ICP-QMS. In addition, ICP-SFMS could obtain determined values of Li and Fe that could not be determined by ICP-QMS. These results suggest the ICP-SFMS combined with matrix separation by anion exchange resin could be utilized for the determination of ultra-trace metal impurities in high-purity materials for the assessment of the purity of the materials.

Chemiluminescence system for direct determination and mapping of ultra-trace metal impurities on a silicon wafer

A highly sensitive chemiluminescence (CL) system which consumed low sample and reagent volumes in the microlitre range was developed for direct determination and mapping of ultra-trace metal contaminants on solid surfaces, such as silicon wafers or flat display panels. The analytical result of the system was confirmed with ICP-MS. The system was composed of a scanner, sensor and a wafer moving stage. The scanner, with a scanning tip made of 0.03'' i.d. PTFE tubing, was used to collect metal impurities on the wafer surface with 5 μL of scanning solution. A coaxial sensing head of about 13 mm o.d. and 110 mm height was designed both to inject a luminescent reagent of luminol-H(2)O(2) mixture and to collect the luminescence light resulting from the reaction with metal ions of Co(2+), Fe(2+), Cu(2+), and Ni(2+). Due to the almost zero background, an extremely low limit of detection of 20.8 pg/mL for Co(2+) in 1% hydrofluoric acid (HF) was obtained from the calibration curve. In order to map the spatial distribution of the impurities, 11 cross sections of a Co-contaminated wafer were selected and scanned individually with a diluted HF solution. A contaminant level of 1.45-7.11 × 10(11) atoms cm(-2) was obtained for each section with an average of 4.21 × 10(11) atoms cm(-2), which was similar to the analytical result of 5.48 × 10(11) atoms cm(-2) obtained from vapor phase deposition-inductively coupled plasma-mass spectrometry (VPD-ICP-MS). Although this CL system does not have selectivity for each specific metal ion, its high sensitivity facilitates the monitoring and mapping of metal impurities of Co, Fe, Cu, etc. on the wafer directly and it can be used as an on-line inspection sensor for the first time in the semiconductor industry.

Improvement in Linearity of Calibration Curves Using of Palladium Modifier in Electrothermal Vaporization/ICP-MS and Determination of Ultratrace Metallic Impurities on Silicon Wafers

An electrothermal vaporization (ETV)/inductively coupled plasma mass spectrometry (ICP-MS) technique has been developed to determine the ultratrace metallic impurities of 10 elements (Na, Mg, Al, Cr, Mn, Fe, Ni, Cu, Zn, and Pb) in the natural oxide layer on a Si wafer. SiO2 reacts to form SiF6 2- with hydrofluoric acid in vapor-phase decomposition. The pyrolysis temperature (150°C) for eliminating SiF6 2- was added to the ETV operating conditions, because the existence of 28Si, 28Si2, and 28SiO2 due to SiF6 2- influences the ion intensities of 27Al, 56Fe, and 60Ni, respectively. Furthermore, adding 25 ng of a palladium modifier improved the linearity of each calibration curve. As a result, it was possible to determine the 10 elements in concentration ranges of 20 (40)-10000 pg ml-1. The recovery percentages obtained by adding the mixed standard solution to the sample solution were 95-105%, showing that the ETV/ICP-MS measurements are accurate. The detection limit (3σ) was approximately 106 (Pb)-108 (Na) atoms cm-2 for a Si wafer with a diameter of 130 mm. This method can be applied to the above wafer to determine the 10 metallic elements (109-1011 atoms cm-2).

Estimation of metal impurities in high-purity nitric acids used for metal analysis by inductively coupled plasma-mass spectrometry.

A simple method to estimate the amounts of ultra-trace metal impurities in nitric acid reagents has been developed. The determination of sixty-four metals in nitric acid was accomplished by direct measurements of 0.1 M nitric acids accurately diluted with ultrapure water by ICP-MS. Though accurate metal concentration could not be obtained for all of the elements, we could effectively evaluate the nitric acid quality by comparing the ion counts of the samples, ultrapure water and standard metal solutions for a calibration prepared with Ultrapur nitric acid.

Determination of ultratrace metallic impurities in polysilane and siloxane polymers for microelectronic devices

Ultratrace metallic elements in polysilane, siloxane and other such organic silicon compounds used in the fabrication of semiconductor devices are determined so as to understand their effects on the devices. Separating organic silicon by means of hydrolysis to SiO2 is a high sensitivity analysis. The established procedures involve dissolution of organic silicon compounds and the hydrolyzed products of organic silicon samples in hydrofluoric acid-containing reagents followed by evaporation of the silicon matrix as H2SiF6. The residual metallic elements in the treated sample solution were then determined by electrothermal atomic absorption spectrometry (ETAAS). The results indicated that a small amount of sulfuric acid was helpful in yielding SiO2 from organic silicon compounds, and that proper controls of the evaporation process are effective in preventing chemical interferences of some metallic elements during recovery and reproducible analysis. The methods developed were applied to the determination of metallic elements such as sodium, iron, and copper in various kinds of organic silicon compounds used for microelectronic devices. The limit of detection for seven metallic elements was as low as 0.1 ng g−1 levels.

Determination of Ultratrace Impurities in High Purity Tantalum Materials by On-line Anion Exchange Matrix Separation and Inductively Coupled Plasma Mass Spectrometry

Ultratrace metal impurities (Be, Al, Ti, Cr, Ni, Nb, Mo, Sn, W, Th, and U) in high purity tantalum metal, tantalum(V) oxide, and tantalum pentaethoxide were determined by a combined system of flow injection with an anion exchange column and inductively coupled plasma mass spectrometry (ICP-MS). In the present combined system, the on-line matrix separation and multielement determination of impurity elements could be performed. When 2 M HCl/0.1 M HF mixed solution and 1 M HNO3/0.1 M HF mixed solution were used as the carrier solutions, Be, Al, and Ti for the former, and Cr, Ni, Nb, Mo, Sn, W, Th, and U for the latter were eluted from the column without any tantalum matrix. The detection limits (3σ) of analyte elements were in the range over 0.003 - 0.14 ng/ml as the sample solution basis. The present method was applied to the determination of metal impurities in high purity tantalum materials. The concentrations of Be, Ti, Mo, Sn, Th, and U were at the ng/g level, while those of other elements were in the range over the μg/g - ng/g level.

An accurate and sensitive analysis of trace and ultratrace metallic impurities in plastics by NAA

Neutron activation analysis (NAA) has been studied to improve the accuracy and sensitivity of the analysis of trace and ultratrace metallic impurities in plastic materials. There are two main problems in the analysis of plastics by NAA. First the contamination during sample preparation, especially sample crushing procedure is very serious for ultratrace analysis. Another problem is the destruction of the sample capsule due to the pressure build-up by the gases formed during neutron irradiation. A simple preparation technique of the sample crushing method using liquid nitrogen and reducing the capsule pressure by a pin hole was developed to solve the above problems. Two different irradiation and seven cooling conditions were also investigated to optimize the experimental conditions. A SRM from NIST (1632b coal) has been used to investigate the accuracy of the analysis. More than thirty elements could be analyzed in the range of sub-ppb to percent. Samples analyzed in this work were polyethylene and polypropylene which were made by different manufacturing procedure, and pigments. Two kinds of plastic products used for food and drug containers were also analyzed. It was found that NAA could be a powerful technique for the analysis of metallic impurities in plastics even though their concentrations were at ultratrace levels.

ＩＣＰ質量分析法の進歩と半導体関連材料中超微量不純物元素分析への適用

Over the past decade, inductively coupled plasma mass spectrometry (ICP-MS) has been regarded to be one of the most powerful techniques for ultra-trace elemental analysis. This technique offers excellent analytical characteristics, (1) simplicity of spectra compared with ICP-AES, (2) extremely low detection limits (pg/ml) for most elements, (3) a broad linear dynamic range, (4) rapid multi-element determination, (5) isotope ratio and isotope dilution method capability, and (6) rapid qualitative analysis for ultra-trace metal impurities. However, even the most modern ICP-MS instruments still suffer from a number of spectral and non-spectral interferences. In order to avoid isobaric overlaps, manufacturers adopted two different concepts. One is a combination of shield-torch and chamber-gas flow for a quadrupole type MS and the other is the usage of a double-focusing high resolution (HR) mass spectrometer. Nowadays, there are ten manufacturers of ICP-MS all over the world.In this paper, the history of development of ICP-MS is briefly reviewed at first. Applications of ICP-MS to ultra-trace elemental analysis of semiconductor materials (from water to Si wafer) are then documented, focusing the present conditions and meaning of ICP-MS analysis in this industrial field. The increase of memory capacity in the integrated circuit demands the cleanliness as high as possible for each production process. The analytical techniques of (HR-)ICP-MS including ETV is becoming an essential technology to improve their productivity.

Determination of ultratrace metallic impurities in fluorocarbon polymers by electrothermal atomic absorption spectrometry after decomposition with a combustion system

A combustion system method for determining ultra-trace impurities in fluorocarbon polymers was developed. 200 mg polytetrafluoroethylene (PTFE) material samples were inserted into a quartz combustion system and decomposed for 30 min in air. Sodium-, potassium-, calcium-, copper-, and iron-concentrations in the raw PTFE materials ranged between 2–96, 1–35, 4–18, <1 and 12–97 ng g −1, respectively, with blank levels of 0.3, 0.2, 0.4, 0.2, and 0.5 ng/analysis, respectively. The impurity profiles of the fluorocarbon polymers indicated that the polymers were contaminated as a result of the polymer processing procedures. The technique reported herein gives low blank concentrations and is a rapid and safe analytical method for fluorocarbon polymers.

Preconcentration and Spectrographic Determination of Ultra-trace Metallic Impurities in Potassium Chloride.

Preconcentration and Spectrographic Determination of Ultra-trace Metallic Impurities in Potassium Chloride.