Charged Particle Activation Analysis Research Articles

Density and nitrogen content of ultrathin silicon oxide gate films grown using in situ pyrolytic-gas passivation

The density and nitrogen content of 3.5–6.5-nm-thick silicon oxide films grown by ultradry oxidation using the recently proposed in situ passivation method that uses a little pyrolytic N2O gas were determined by a charged-particle activation analysis. It was confirmed that the density increases with decreasing humidity during oxidation as well as before and exhibits a remarkable increase only at a humidity of less than 1 ppb. The humidity dependence is almost the same as that found in our previous reports, where we obtained the electrical characteristics related to the condition of the oxide–silicon substrate interface, such as the potential barrier height energy and the time-dependent dielectric breakdown lifetime. Although the binding states of the N-related bonds are still unclear, it appears that a small microscopic structural change may be brought about near the oxide–silicon substrate interface.

Changes in the density of ultrathin silicon oxide films related to excess Si atoms near the oxide–Si(100) interface

To clarify the considerable changes in the (volumetric) density ρox of 3.5–8.0-nm-thick silicon oxide films on Si(100) oxidized at 800–950 °C, which were confirmed by our previous work, ρoxs and (areal) number densities of the 700–750 °C oxidation films were investigated. The ρoxs and number densities of Si and O atoms were determined by charged-particle activation analysis and Rutherford backscattering spectrometry, respectively. It was confirmed again that excess Si atoms relative to the stoichiometric SiO2 composition exist near the oxide–Si substrate interface and the number densities of them NSi(excess)s were changed with oxidation temperature. The ρoxs were also changed with oxidation temperature but the changes in ρox were diametrically contrasted with those in NSi(excess). For the 2.0–8.0-nm-thick films oxidized at 700–950 °C, the ρox characteristics exhibited a maximum at 850 °C but the NSi(excess) ones exhibited a minimum at 850 °C. It is, therefore, believed that this ρox change is governed mainly by microscopic changes in the atomic arrangement structure due to the NSi(excess) difference.

Determination of rare earth elements by charged particle activation analysis in geological materials

The rare earth elements (REE), Pr, Sm, Eu, Gd, Ho, Er and Tm have been determined by charged particle activation analysis using 40 MeV a-particles through radiochemical approach. The radiochemical separation of REE as a group has been carried out from the bulk matrix. It has been shown from the theoretical computation that the products obtained from (a,xn) reactions (x = 1, 2, 3) are more suitable compared to those from (a,pyn) reactions (y = 0, 1, 2) due to the former having higher cross section (of the order of thousand millibarns).

Development of a Pre-Treatment Procedure for the Determination of Trace Amount of Bulk Oxygen in Iron and Steel

For the determination of trace amounts of oxygen in iron and steel, a pre-treatment procedure was developed using glow discharge. This permits to remove surface oxygen contaminations, which cannot be eliminated by conventional pre-treatment methods such as electropolishing. The analytical values of oxygen obtained after the glow discharge pre-treatment were approximately 1–2 μg/g lower than those without pre-treatment. This difference is consistent with the oxygen surface contamination determined by surface analysis and charged particle activation analysis.

Charged particle activation analysis of oxygen in fluoride and chalcogenide glasses used for fiber amplifiers

The proton activation analysis of oxygen was studied in fluoride and chalcogenide glasses used for fiber amplifiers. First, we studied the interfering nuclear reactions from glass matrices to determine the oxygen concentration in these glasses. By using substoichiometric separation for 18F after irradiation, we found that the oxygen concentration was 12 to 204 ppm in InF3-based fluoride glass and 0.04% to 0.7% in chalcogenide glass containing sodium. We also discuss the relation between oxygen concentration and optical properties such as the infrared absorption spectrum and fluorescence lifetime.

Microscopic composition difference related to oxidizing humidity near the ultrathin silicon oxide–Si(100) interface

The numerical densities of Si and O atoms for 3.5–6.5-nm-thick silicon oxide films grown on Si(100) at oxidizing humidities of 0.5 ppb–500 ppm were determined by Rutherford backscattering spectrometry. Especially, the numerical density near the oxide–Si interface was rigorously investigated by comparing the results with the previous volumetric density evaluations using charged-particle activation analysis (CPAA). It was confirmed that excess Si atoms relative to the stoichiometric SiO2 composition exist near the interface and their number decreases with decreasing humidity. In addition, this humidity dependence was similar to that for the “slight discrepancy of the oxide thickness” (ΔTox) found by CPAA, which was strongly correlated with the humidity dependence of the volumetric density, device reliability, etc. Therefore, it is possible that all the humidity dependence has a common origin: Dehydration results in a reduction of the excess Si atoms near the interface, and thus produces a decrease in Si dangling bonds.

Determination of the electronic energy loss of light ions in a silicon lattice by using the transmission ion channeling method

Charged particle activation analysis (CPAA) is able to analyze light elements such as carbon and oxygen at trace levels in semiconductor materials. This technique requires the knowledge of the stopping powers of these materials for channeled ions. The electronic energy loss for ions entering the crystal lattice in a random direction is well established. The electronic energy losses for protons, deuterons, 3He + and 4He + ions entering a 3.6 μm thick silicon single crystal along the 〈1 0 0〉 direction were measured by using the transmission of particles technique. Data obtained were compared with those obtained by other authors using theoretical and experimental methods.

Feasibility study on the characterization of thin layers by charged-particle activation analysis

The purpose of this feasibility study was to investigate the possibilities and limitations of Charged-Particle Activation Analysis (CPAA) as a thin layer characterization method, i.e., the determination of the mass thickness or the composition of a thin layer. Therefore industrially important layers of sputtered Al, AlOx, TiQx (all three from the packaging industry), YBa2Cu3O6+delta, and Y2O3-stabilized ZrO2 (both superconducting industry) on different substrates were analyzed, and thereby the accuracy, the detection limits, and the precision of the method were studied. To test the accuracy, the same materials were also analyzed with neutron activation analysis (NAA) and inductively coupled plasma mass spectrometry (ICPMS). The results of CPAA compared with the results of NAA and ICPMS showed no significant difference at the 95% confidence level. The detection limits expressed as mass thickness were about 10-2 microg cm-2 or expressed as thickness 0.04 nm for a monatomic layer of Al. The experiments showed that the precision of the method depends only on the counting statistics. Generally we can conclude that CPAA is an absolute method for the characterization of "thin" layers, with respect to composition and mass thickness determinations.

Determination of Trace Amount of Gaseous Elements in Iron and Steel

Accuracy of analytical values of trace amounts of carbon and oxygen (mass ppm level) in iron and steel were investigated. Analytical values obtained by charged particle activation analysis method (CPAA) were compared with those obtained by a combustion-infrared absorption method or fusion-infrared absorption method. Analytical values obtained by the conventional method were 1-2 mass ppm higher than those obtained by CPAA. In the case of carbon, this difference may be due to the incorrect blank value of the combustion method. In the case of oxygen analysis by the fusion method, this is because the oxide layer on the sample surface was not eliminated completely by the pretreatment such as electrochemical polishing.

Analysis of Electrically Active Carbon in Semi-insulating Gallium Arsenide by Infrared Absorption Spectroscopy

Carbon in semi-insulating gallium arsenide (GaAs) crystals has been investigated by Fourier-transform IR absorption spectroscopy, spark source mass spectrometry, and charged particle activation analysis. Procedures for the quantitative evaluation of the 582-cm-1 local mode absorption due to carbon on the arsenic sublattice (CAs) are described. The strength of the mode shows a linear correlation with total carbon content measured by spark source mass spectrometry over the concentration range from 3× 1014 to 2×1016 cm-3. The new calibration factor for the integrated absorption at 77 K is (7.2±0.4)× 1015 cm-1, based on a relative sensitivity coefficient of 3.2±0.1 of the spark source mass spectrometry. Calibration factors for the IR absorption method at room temperature are also given.

Density difference related to humidity during dry oxidation for ultrathin silicon oxide films

The densities of 3.5–6.5-nm-thick silicon oxide films grown on p-type Si(100) at humidities during dry oxidation of 0.5–1.0, 10–100 ppb and 200–500 ppm were determined by charged-particle activation analysis. It was confirmed that the density increases with decreasing humidity and its level is separated into two groups: an ultradry oxidation group that includes the films oxidized at a humidity of less than 100 ppb and a conventional dry oxidation group at a humidity of more than 200 ppm. Since similar humidity dependence was confirmed for several fundamental structural and electrical evaluations, the oxide becomes a homogeneous stoichiometric SiO2 compound and its quality approaches an intrinsic level by dehydrating. These strong similarities also suggest that all the humidity dependence possibly originates from a common cause—the slight microscopic structural change in the oxide near the interfaces. By dehydrating, therefore, its atomic arrangement may be efficiently transferred to a more stable state, and then consequently, the earlier humidity dependence would be confirmed.

Analysis of the oxygen impurity atoms beneath the surface of Cz-silicon by CPAA

Charged particle activation analysis (CPAA) is able to analyze light elements such as carbon, nitrogen and oxygen at trace levels in materials. By comparison with other techniques such as Fourier transform infrared spectroscopy (FTIR), the major advantage of the CPAA is its ability to determine the total concentration of impurities (interstitial, substitutional or incorporated in a complex). Errors due to matrix effects and surface contamination are eliminated. However, this technique does not allow analysis in the first micrometers beneath the surface because the chemical etching, required to rid the surface of superficial contaminants, removes this important part of the compounds’ active zone. The aim of this study is to solve this problem and as a result to be able to determine impurities in the vicinity of the surface. An application on oxygen diffusion profiles in Cz-silicon submitted to a rapid thermal annealing (RTA) will be discussed.

Charged Particle Activation Analysis of Carbon on Silicon Plates and Its Use for the Monitoring of Organic Contamination of the Air

Total carbon on the surface of silicon plates was determined by charged-particle activation with the 12C(d,n)13N reaction. A procedure was established for routine determination, including the methods for the transportation and bombardment of the sample without disturbing the surface carbon and for the separation of the 13N. Silicon plates, after undergoing different surface treatments, were exposed to the air in clean rooms and ordinary living areas, and the surface carbon was analyzed to evaluate the usefulness of this method and to get information required in the semiconductor industry. Surface carbon of (0.2−3) × 1015 atoms/cm2 was found on silicon plates left in usual nonsmoking rooms after any treatment; it was reduced to 5 × 1012 atoms/cm2 by heating to 900 °C for 30 min in purified air and was then kept under 1 × 1013 atoms/cm2 for a few days in high-grade clean rooms. Etching with NH4OH/H2O2 or a fluoride-containing reagent often gave higher and varying surface-carbon quantities. This method of analysis is sensitive to 1 × 1012 atoms/cm2 of total carbon and is hoped to offer meaningful information concerning clean rooms and to be utilized generally for monitoring carbonaceous air pollution.

Feasibility study of cyclic charged particle activation analysis

Abstract The purpose of this research was to enlarge the applicability of CPAA with reactions leading to short-lived radionuclides ( 0.1 s 1/2 s ). Therefore a set-up for cyclic charged particle activation analysis was designed and built for the isochronous cyclotron of the University Gent (Belgium). In order to increase the sensitivity for the determination of short-lived radionuclides, an on-line set-up (comparable to a PIXE or a PIGE set-up) was used. Also a systematic study of the experimental determination of the sensitivity and interferences of the method for some 28 elements was made. Due to some problems (neutron damage of the detector, high γ radiation background due to neutron-induced reactions in the detector and surrounding material, and unfavourable physical constants such as low cross sections), the number of analyzed elements was rather limited and/or the sensitivity obtained was low.

Use of charged particle activation as an analytical technique in the biological field

Some applications of Charged Particle Activation Analysis (CPAA) in the biological field are presented. This technique has been used frequently for the analysis of the light elements which are inaccessible to neutron activation analysis (NAA), but it is especially effective in the detection of medium-heavy trace elements and there is increasing interest in its employment in biological and medical fields. CPAA enables the identification and simultaneous quantification of different isotopes of the same element. Recent applications show that it can be used as a reference method in stable isotope determination for biokinetic studies of selected elements in complex organic matrices such as blood plasma.

The Effect of Heating Conditions on the Removal of Oxide Film on Steel Surface by the Inert Gas Fusion Method.

This study was carried out to establish an analytical technique for accurate evaluation of bulk oxygen in ultra-clean steel using the inert gas fusion method without pre-cleaning such as electrolytic or chemical polishing. This method had a two-step heating pattern, one was a continuous heating stage to remove contamination, and another was a fixed high-temperature stage to analysis oxide inclusions. In this paper, reduction sites of oxide film and the effect of bulk carbon content are also discussed. The results obtained are as follows: (1) The separation of bulk oxygen and contaminant oxygen on the steel surface depended on the heating rate of the steel at heating stage I. The lower the rate was, the better the separation was. (2) The optimum heating rate of the steel was 1 K/s. (3) In the case of high-carbon chromium bearing steel which contained 3.4 ppm of oxygen (a calibration standard sample JSS GS-6a), approximately a half of its total oxygen content was estimated to consist of contaminant oxygen on the steel surface. This value was well compared to the measurement by the charged particle activation analysis method and was found to be reasonable. (4) It was found that both the carbon content in the steel and the feed of carbon from the crucible/steel contact surface affected the removal of oxide film.

Density of ultradry ultrathin silicon oxide films and its correlation with reliability

To clarify the structure of ultrathin silicon oxide gate films less than about 5 nm thick, densities of the films grown on Si(100) at 800–950 °C by the recently proposed rigorous ultradry oxidation process were determined by charged-particle activation analysis. The density curve plotted as a function of oxidation temperature shows a peak, i.e., the density of the 850 °C grown films is largest of all, about 2.38 Mg/m3. Interestingly, a similar relationship is confirmed in the time-dependent dielectric breakdown lifetime characteristic curve, which is the most fundamental index of reliability for the oxide. This suggests that the reliability is closely related to the density. That is, since the density reflects the atomic arrangement of the films, the lifetime enhancement near the same oxidation temperature is possibly caused by changes in the films’ microscopic structure.

Alpha-activation analysis of boron on Si surface and in Si and SiO2 films

The effectiveness of charged particle (alpha) activation analysis in determining the content of ion-implanted boron on the surface of Si wafers and the doped boron in epitaxially grown Si film and SiO2 film was evaluated. The method was found to be accurate and precise if interference from surface contamination and the matrix were accounted for and an appropriate standardization method was used.

Charged particle activation analysis of boron and carbon on the surface of silicon wafer

Boron and carbon on the surface of silicon wafers in ordinary atmospheres were measured by activation with the10B(d,n)11C and12Cd(d,n)13N reaction, respectively. Two sample plates in intimate contact were bombarded by deuterons, and the11C or13N formed at the inside surfaces were measured after chemical separation. From 1.2·1013 to 8.4·1013 atoms/cm2 of boron and from 2.4·1014 to 6.1·1015 atoms/cm2 of carbon were found ,and the sensitivity was extended down to 5·1012 and 3·1012 atoms/cm2 for boron and carbon, respectively.

Residual Oxygen Determination In Silicon Epilayer, Comparison With Ftir Measurements

AbstractFor power devices the use of silicon epilayer on CZ substrate is a solution to make devices with a low oxygen concentration in the active zone. Oxygen is probably one of the most important residual impurities in silicon samples. Usualy the determination of the interstitial oxygen is done by Fourier Transform Infra Red spectroscopy (FTIR). In this work we have determined oxygen by Charged Particle Activation Analysis (CPAA). The main difference between these two techniques is that CPAA gives the total oxygen concentration whereas FTIR gives interstitial oxygen.We have determined the oxygen in 200μm thick silicon epilayer and studied its behavior during thermal treatments. Oxygen concentration is found in the range of 1015/cm3 just after the epitaxial process. After thermal treatment the concentration in the epilayer rose to several 1016/cm3 to 1017/cm3, depending on the treatment. A comparison with FTIR experiment is done and the amount of oxygen precipitate is determined.