Threshold stoichiometry for beam induced nitrogen depletion of SiN

Measurements of the stoichiometry of silicon nitride films as a function of the number of incident ions using heavy ion elastic recoil detection (ERD) show that beam-induced nitrogen depletion depends on the projectile species, the beam energy, and the initial stoichiometry. A threshold stoichiometry exists in the range 1.3>N/Si1, below which the films are stable against nitrogen depletion. Above this threshold, depletion is essentially linear with incident fluence. The depletion rate correlates non-linearly with the electronic energy loss of the projectile ion in the film. Sufficiently long exposure of nitrogen-rich films renders the mechanism, which prevents depletion of nitrogen-poor films, ineffective. Compromising depth-resolution, nitrogen depletion from SiN films during ERD analysis can be reduced significantly by using projectile beams with low atomic numbers.     

An ERD/RBS/PIXE apparatus for surface analysis and channeling

A system for surface analysis, lattice localisation of impurities, defect studies in crystalline solids and routine ERD (elastic recoil detection) is described. The apparatus features a high vacuum chamber, a computer controlled precision goniometer and an energy plus time-of-flight mass discrimination system. First results of channeling/ERD experiments using 15–30 MeV ³⁵Cl beams on silicon crystals implanted with B⁺ and BF₂⁺ are presented, as well as data on the effect of beam induced damage on the boron distribution.     

Deuterium depth profiling in polymers using heavy ion elastic recoil detection

We have used ²⁰Ne and ⁴⁰Ar beams with energies between 3 and 8 MeV for elastic recoil detection (ERD) analysis of hydrogen isotopes in polymer samples and have also studied the depth resolution and the radiation damage. For the investigation of polymer mixtures it was possible to improve the depth resolution of ERD down to 8 nm FWHM with-out changing the experimental setup of conventional ERD, due to the higher energy loss factor of heavier ions and a reduced stopper foil thickness. For an improved surface depth resolution heavier ions are suitable, whereas lighter elements have a larger profiling depth. We found a ²⁰Ne beam with an energy between 4 and 6 MeV to have a maximum analysing depth of 380 nm with a near surface depth resolution of 9 nm; however, for high resolution ⁴⁰Ar-ERD measurements this maximum profiling depth is reduced to 90 nm. Due to the larger Rutherford scattering cross-section of heavier ions the measuring time decreases with increasing ion mass. We have investigated the ion beam radiation damage in polymer samples and introduced beam current density limits related to polystyrene samples. These results are supported by model calculations which give approximated values of the radiation damage.     

Depth profiling of hydrogen by detection of recoiled protons

The elastic recoil detection technique (ERD) using a 2.5 MeV ⁴He beam for depth profiling of hydrogen in the near-surface regions of solids is described. The optimization of the experimental conditions such as scattering geometry and analyzing beam energy is discussed. The factors limiting the depth resolution of the method have been evaluated showing that a depth resolution of the order of 20 nm can be obtained. Also presented are typical applications for hydrogen profiling in a silicon matrix.     

Simulation of ERD spectra for a surface with a periodic roughness

For the purpose of identifying hydrogen isotope distribution in a microscopically rough surface, the geometrical effect on elastic recoil detection (ERD) spectra is examined using an optical grating base coated with a thin film of deuterated polyethylene (CD₂). It is shown that the ERD spectra from such surfaces with a periodic roughness agree well with the simulation spectra using the roughness parameters determined by the simultaneous Rutherford backscattering spectroscopy (RBS) quantification of the roughness, the “Pb coating-RBS method”. The microscopic structure of the sample surface is reflected well in the spectral shape. This means that the true distribution of the hydrogen isotopes in a sample could be determined by correcting the ERD spectra for the roughness. Potential applicability of the present method, Pb coating of the sample followed by simultaneous RBS-ERD analysis, to correction of ERD spectra for the surface roughness is thus demonstrated.     

DEPTH PROFILING OF ~1H AND/OR ~4He IN SOLIDS BY ERD WITH ~(19)F IONS

1H or 4He depth profiling in 1H or 4He implanted silicon samples was performed by elastic recoil detection (ERD) with multicharged 19F ions at a small accelerator. Optimization of the experimental parameters such as incident ions energy and scattering geometry were calculated by computer simulation. Depth resolution of about 20-30nm at depth of 400nm for 1H and at depth of 300nm for 4He can be obtained, respectively.     

Characterisation of ferromagnetic magnetic storage media surfaces by complementary particle induced X-ray analysis and time of flight-energy dispersive elastic recoil detection analysis

Thin (10 nm–1 μm) films of ferromagnetic material constitute an important class of materials that are difficult to analyse by conventional ion beam analytical (IBA) techniques because they are based on the ferromagnetic elements (Co, Fe, Mn, Ni, and Cr). The similar or overlapping isotope masses makes it difficult to separate the elemental signals using time of flight and energy dispersive elastic recoil detection (ToF-E ERD). In this exploratory study we have investigated the use of Particle Induced X-ray Emission (PIXE) measurements to refine the mass dispersive depth profile information from ToF-E ERD. The surfaces of two commercial magnetic media were investigated. One sample was a double density diskette with a coating of ferrite particles in an organic binder. The other sample was a complex C/Co/Cr/Ni–P/Al multilayer structure taken from a standard hard disc. The Lund nuclear microprobe with a 2.55 MeV proton beam was used for PIXE analysis. ToF-ERD measurements were carried out using a 55 MeV ¹²⁷I¹⁰⁺ ion beam incident at 67.5° to the surface normal. The time of flight and kinetic energy of recoils ejected at 45° to the ion beam direction was measured in a detector telescope. The findings demonstrate that by detailed analysis of the PIXE spectra it is possible to remove the ambiguities in mass assignment of the ToF-ERD data associated with the ferromagnetic elements.     

^16O弹性前冲测量氦的深度分布

利用１２ＭｅＶ的１６Ｏ离子弹性前冲测量（ＥＲＤ）方法，研究了以２０ｋｅＶ和４０ｋｅＶ注入４Ｈｅ的镀钛样品。通过分析ＥＲＤ能谱，得到了注入４Ｈｅ的深度分布，并与非卢瑟福背散射结果进行了比较。对４０ｋｅＶ注入的样品观察到有双峰分布，２０ｋｅＶ注入的样品没有双峰分布，实验结果与ＴＲＩＭ模拟计算结果进行了比较。     

钛膜中氘氚浓度的弹性反冲法测量

研究采用弹性反冲探测(ERD)方法测量钛膜中氘、氚的浓度。实验所用Ti膜用磁控溅射法制备，膜厚小于100nm，以石英玻璃（SiO₂）为底衬，Ti膜加镀了1层Ni保护膜，以防Ti膜氧化和增强Ti膜吸氢。以6.0MeVO粒子作为入射粒子，在30°方向上探测反冲粒子，在此实验条件下，O粒子对D、T的碰撞截面为卢瑟福截面。对两个样品用ERD方法测量钛膜中的D、T含量，获得了D、T的面密度。测量结果表明，采用如上方法测量Ti膜中D、T浓度的误差小于7％。     

High resolution elastic recoil detection analysis of polystyrene depth profiles using carbon ions

The resolution of conventional elastic recoil detection (ERD) is enhanced by using ions which are efficiently stopped by matter. We describe an ERD experiment using a 2.4 MeV carbon ion beam which has a surface resolution of 80 Å FWHM in polystyrene. The maximum analysable depth for this geometry is 1000 Å. We show that by cumulating spectra with a low enough dose on different points of the same sample it is possible to avoid a substantial beam-induced modification of the true depth profile. The technique is demonstrated with experiments showing the decrease in the surface segregation of deuterated polystyrene (dPS) as a function of its molecular weight (Mw) in films of blends of deuterated and protonated polystyrene.     

Precise nitrogen depth profiling by high-resolution RBS in combination with angle-resolved XPS

Nitrogen depth profiling in a high-k gate stack structure, SiON/HfO₂/SiON/Si(0 0 1) was performed by high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The nitrogen depth profile is determined so that both the HRBS spectrum and the angular dependence of the XPS yield are reproduced. The obtained nitrogen profile is compared with the result of high-resolution elastic recoil detection (ERD) which is the most reliable technique for depth profiling of light elements. The agreement between the result of the present combination analysis and that of high-resolution ERD is fairly good, showing that the present combination analysis is a promising method for the analysis of light elements.     

Unique capabilities of heavy ion elastic recoil detection with gas ionization detectors

Specific aspects of heavy ion elastic recoil detection (ERD) with gas ionization detectors have been studied using representative measurements. A particular strength of the technique is the detection and direct quantification of elements with atomic numbers in the range Z=2–8, which are often not accessible with other ion beam techniques. Within the wider spectrum of analytical techniques in materials science, heavy ion ERD has unique capabilities, when the particular problem requires in addition the analysis of heavy elements or hydrogen detection. Whenever only heavy element analysis or only hydrogen profiling is of interest, alternative techniques tend to be superior.     

贮氢金属中氢同位素的离子束分析方法评估

文章介绍用离子束方法分析贮氢金属中氢同位素含量与分布的实验条件与设计，并分析各自的优、缺点。通过实验测量与分析表明，用离子束分析方法可获得氢同位素含量与分布的丰富信息和精确数值。用6.0MeV的O离子束进行ERD分析的优点是截面为卢瑟福截面，所用的Mylar膜薄，能使H、D、T明显分开，测量精确，缺点则是对样品制备要求高，分析深度小；用7.4MeV的⁴He离子束进行ERD分析能得到H、D、T的分布信息，对Ti的分析深度可达到3.0μm，缺点则是三者的谱图相互重叠，模拟解谱的误差较大；用3.0MeV的质子进行PBS分析，只能获得D、T的分布信息，但分析深度更深。      

用弹性反冲分析法测定吸附剂中氢的含量

本文介绍用弹性反冲分析技术分析了对二甲苯吸附剂中的氢含量。首先测定已知氢含量的Mylar膜的原子比,实验结果与预期值一致。实验中用Kapton膜作为标样,测定了各种工艺条件的吸附剂中的氢含量,为实际使用提供了依据。 本方法在E_0=2MeV下,可探测深度范围为0.5μm左右,深度分辨率约为700A,灵敏度为0.1％原子数。     

Cross-section for D(p,p)D elastic scattering from 1.8 to 3.2 MeV at the laboratory angles of 155° and 165°

The D(p,p)D cross-sections for elastic scattering of proton on deuterium over incident proton energy range from 1.8 to 3.2 MeV at both laboratory angles of 155° and 165° were measured. A thin solid state target Ni/TiD_x/Ta/Al used for cross-section measurement was fabricated by firstly depositing layers of Ta, Ti and Ni film on the Al foil substrate of about 7 μm in turn using magnetron sputtering and then deuterating under the deuterium atmosphere. The areal density of metal element in each layer of film was measured with RBS analysis by using a 4.0 MeV ⁴He ion beam, while the areal density of the deuterium absorbed in the Ti film was measured with ERD analysis by using a 6.0 MeV ¹⁶O ion beam. The results show that the cross-sections of p-D scattering under this experimental circumstance were much enhanced over the Rutherford cross-section value. It was found that the enhancement increases linearly as the energy of the incident beam increases. The total uncertainty in the measurements was less than 7.5%.     

Isothermal Re-Emission of Hydrogen Implanted into Isotropic Graphite

Isothermal re-emission of hydrogen from graphite implanted with 5 keV H₂ ⁺ ion beam up to saturation (3×10¹⁸/cm²) at room temperature has been studied by means of the elastic recoil detection (ERD) technique at temperatures of 450, 500, 550 and 600°C. It is found that the concentration of retained hydrogen decreases rapidly in the beginning and then decreases very gradually as the annealing time increases.

The re-emission profiles have been analyzed taking into account local molecular recombination between activated hydrogen atoms and that between an activated hydrogen atom and a trapped one together with retrapping of the activated hydrogen atom. It is shown that the re-emission of hydrogen by isothermal annealing occurs mainly due to the former type of local molecular recombination and that the activation energy of the thermally activated detrapping rate constant is 0.50±0.04eV. Moreover, it is shown that an analytical expression for the re-emission profile reproduces reasonably well the observed thermal desorption spectra.     

Influence of additional UV-light illumination on preparation of TiN by ion beam assisted deposition

Titanium nitride films were prepared by a newly developed photon and ion beam assisted deposition system at room temperature. Titanium was deposited on Si(111) in a controlled nitrogen environment and simultaneously bombarded with low-energy N ions or illuminated with UV-light. The influence of UV-light illumination during deposition is compared with the influence of ion bombardment on film properties like structure, topography and composition, measured by XRD, AFM and ERD, respectively. The results demonstrate that photon assisted deposition (PHAD) is also a good method to modify film characteristics like ion beam assisted deposition (IBAD).     

Effect of electric charge accumulation on low energy ion implantation in insulators

Charge accumulation at the surface of insulators during low energy ion implantation is related to two processes: ion impinging on the sample and secondary electron emission. Samples composed of a piece of Si (having the size of the ion beam) fixed on the centre of polyethylene (PE) coupons have been implanted with 2.2 keV H₂ ions to a fluence of 2 × 10¹⁶ H/cm². ERD (Elastic Recoil Detection) depth profiles of the implanted ions are shallower with an increase of the PE coupon size. The relative critical Si/PE size to repel all the incident ions is around 1.1 × 1.1 cm²/2.5 × 2.5 cm². The potential of the secondary electron suppressor has been varied from −500 V to +500 V. It changes the secondary electron distribution around the implanted area and, consequently, affects the accumulation of charges at the sample surface. When the potential is 0 V, a uniform ion implantation with little effect of charge accumulation for all sizes of PE coupons is obtained. A two-dimension model has been performed and gives a good explanation for the mechanism of the electric charge neutralisation.     

离子注入对超高分子聚乙烯磨损性能的影响

用８０ｋｅＶ不同剂量的Ｃ３Ｈ＾＋８,Ｎ＾＋２对超高分子聚乙烯样品进行离子注入,通过反冲探测分析表明注入层Ｈ含量的变化,对样品表面在离子注入前后的磨损性能进行了测试。实验结果显示,离子注入以后样品表面氢含量减少,磨损性能增强。     

Energy Dependence of MeV He+ Ion-Induced Re-Emission of Hydrogen Isotopes Implanted into Graphite

The energy dependence of MeV He⁺ ion-induced re-emission of hydrogen isotopes (H and D) implanted into graphite has been measured by means of the elastic recoil detection (ERD) technique in order to clarify the collision process for the ion-induced detrapping. The experimental re-emission profiles have been analyzed by solving the mass balance equations, in which the ion-induced detrapping cross section σ _d and the rate constants of the retrapping Σ ^T and local molecular recombination K between an activated hydrogen atom and a trapped one are taken into account. The values of σ _d and K/Σ _T have been determined from the best-fit analytical solution to the experimental re-emission profiles. It has been found that the average values of σ _d and K/Σ _T for H are twice as large as those for D, which is the so-called isotope effect.

It has been shown that the experimental values of σ _d and their energy dependence agree well with the theoretical ones, which are calculated using the power-law approximations for Thomas-Fermi potential, on the assumption that the ion-induced detrapping of hydrogen isotopes takes place due to elastic displacement collisions with energetic carbon recoils produced by incident MeV He⁺ ions.