Anisotropic angular distribution of sputtered atoms

The sputtering yield angular distributions have been calculated on the basis of the ion energy dependence of total sputtering yields for Ni and Mo targets bombarded by low-energy Hg⁺ ions. The calculated curves show excellent agreement with the corresponding Wehner's experimental results of sputtering yield angular distributions. This fact clearly demonstrates the intrinsic relation between the ion energy dependence of total sputtering yields and the sputtering yield angular distribution. This intrinsic relation had been ignored in Yamamura's papers [Yamamura, Y. (1982). Theory of sputtering and comparison to experimental data, Nucl. Instr. and Meth., 194, 515–522; Yamamura, Y. (1981). Contribution of anisotropic velocity distribution of recoil atoms to sputtering yields and angular distributions of sputtered atoms, Rad. Eff., 55, 49–55.] due to some obvious mistakes.     

Study of the interaction of argon and nitrogen ions with the silicon dioxide surface

Angular dependences of the sputtering yield, surface layer composition, and changes in the mass spectra of residual atmosphere upon irradiation of silicon dioxide with argon and nitrogen ions are measured. It is found that the sputtering yield of SiO₂ bombarded by N ₂ ⁺ ions is almost two times higher than for Si. The sputtering yields of SiO₂ and Si irradiated with Ar ions are identical, although the binding energy of atoms in SiO₂ is almost two times higher than in Si. An analysis of the surface composition and residual atmosphere near the sample during its irradiation suggests that a chemical reaction is involved in SiO₂ sputtering. Molecules of SiO and NO gases form in the surface layer, whose subsequent desorption increases the SiO₂ sputtering rate.     

Field-induced ionization and Coulomb explosion of nitrogen

Femtosecond-laser field-induced ionization and Coulomb explosion of diatomic nitrogen were systematically investigated using time-of-flight mass and photoelectron spectrometry. Both linearly and circularly polarized femtosecond laser pulses were used at intensities varying from 5×10¹³ to 2×10¹⁵ W/cm². Strong N₂ ⁺, N₂ ²⁺, N⁺, N²⁺ and N³⁺ ion signals were observed for horizontally polarized pulses. Moreover, signals from the atomic ions exhibited a double-peak structure. Suppression of ionization was observed for circularly polarized pulses, while for vertically polarized pulses, only N₂ ⁺ and N₂ ²⁺ ions were observed. The angular distributions of the ions were measured under zero-field conditions in the ionization zone. The atomic ions N⁺, N²⁺ and N³⁺ exhibited highly anisotropic distributions, with maxima along the laser polarization vector and zeroes normal to the laser polarization vector. In contrast to the atomic ions, N₂ ⁺ exhibited a strong isotropic angular distribution. These observations indicate that dynamic alignment is responsible for the observed anisotropic angular distribution of the atomic ions. The kinetic energy spectrum of the photoelectrons is featureless and broad, extending above the ponderomotive potential of the laser pulse. The angular distribution is markedly anisotropic, with a maximum along the laser polarization vector. These observations further support the notion that the field-ionization mechanism is dominant under our experimental conditions. Received: 29 January 2002 / Revised version: 15 March 2002 / Published online: 12 July 2002     

Angular distribution of atoms sputtered from germanium by 1–20 keV Ar ions

The angular distribution of atoms sputtered from germanium under 1–20 keV Ar⁺ ion bombardment (normal incidence) has been studied experimentally and using computer simulations. A collector technique combined with Rutherford backscattering to analyze the distribution of collected material was used. In addition, the surface topography was under control. It was found that the experimental angular distribution of sputtered atoms (E ₀=3–10 keV) could be approximated by the function cos ⁿ θ with n≈ 1.65. Such a high value of n is connected with the surface scattering of ejected atoms and a noticeable contribution of backscattered ions to the formation of the sputter flux (the mass effect). The target surface was found to be practically flat even at ion fluencies ～10¹⁸ ions/cm². The results obtained are compared with data from the literature, including our recent data on Si sputtering.     

Analysis of temperature and enhanced diffusion effects in sputtering of CrSi2

Previously reported experimental results on sputtering and enhanced diffusion processes in CrSi₂ during 100 keVXe⁺ bombardment at different temperatures have been quantitatively analyzed.The framework for the analysis is a simple theoretical model in which the Si atoms are considered mobile in a matrix of Cr atoms whose density is assumed constant and diffusivity is considered zero everywhere. Erosion velocity of the matrix (due to the sputtering of Cr atoms), sputtering and enhanced diffusion processes of Si atoms are taken into account in the mathematical model.In our analysis we show that the time evolution of the total number of sputtered atoms in binary solids cannot yield an unambigous conclusion as to the existence of preferential sputtering.Further, it is found that in the case of CrSi₂ the preferential sputtering of Si atoms depends on the suicide temperature.     

N2微空心阴极放电特性及其阴极溅射的PIC/MC模拟

采用两维PIC/MCC模型模拟了氮气微空心阴极放电以及轰击离子 (N₂⁺,N⁺) 的钛阴极溅射. 主要计算了氮气微空心阴极放电离子 (N₂⁺,N⁺) 及溅射原子Ti的行为分布, 并研究了溅射Ti 原子的热化过程. 结果表明: 在模拟条件下, 空心阴极效应是负辉区叠加的电子震荡; 在对应条件下, 微空心较传统空心放电两种离子 (N₂⁺,N⁺) 密度均大两个量级, 两种离子的平均能量的分布及大小几乎相同; 在放电空间N⁺的密度约为N₂⁺的1/6, 最大能量约大2倍; 在不同参数 (P, T, V)下, 轰击阴极内表面的氮离子(N₂⁺,N⁺)的密度近似均匀, 其平均能量几乎相等; 从阴极溅射出的Ti原子的初始平均能量约6.8 eV, 离开阴极约0.15 mm处几乎完全被热化. 模拟结果为N₂微空心阴极放电等离子体特性的认识提供了参考依据. 关键词： 微空心阴极放电 PIC/MC模拟 2等离子体')" href="#">N₂等离子体     

Surface topography effect on sputtering angular distributions from a Fe–W alloy

Abstract

An observation of the surface structures of Fe-W alloy target irradiated by 27 keV Ar⁺ ions with a fluence of 1 × 10¹⁷/cm² is carried out to investigate the surface topography effect on the sputtering angular distributions of individual elements. The angular distribution of sputtered Fe atoms is more outward-peaked than the cosine distribution. The found pit structures with an enriched Fe concentration may be one of the major causes of the deviation of the angular distribution of sputtered Fe atoms from Sigmund's theory.     

Angular characteristics of processes of electron detachment from negative ions and hydrogen atoms in gases

The results of experimental measurement of spatial-angular distributions of hydrogen particles (H⁻, H⁰, H⁺) obtained in scattering of a collimated ribbon beam of H⁻ ions and H⁰(1s) atoms in He, Ar, Kr, Xe, H₂, O₂, and CO₂ gas targets for certain values of energy in the range from 0.6 to 15 MeV are reported. The experimental setup and the measurement procedure with an angular resolution of 5×10⁻⁶ rad are described. The angular characteristics of measured distributions, i.e., full width at half maximum and standard deviation, were determined. It is shown that the shape of distribution for a beam of hydrogen atoms produced by neutralization of H⁻ ions in a gas target varies with the type and thickness of the target, and the angular spread is smallest for the H₂ target. The variations in the shape of distribution are due to the contribution of scattering processes without changing the charge of particles.     

Comparison of profile tailing in SIMS analyses of various impurities in silicon using nitrogen,oxygen, and neon ion beams at near-normal incidence

We have performed a systematic SIMS study into the effect of (i) the chemical nature and (ii) the energy of the primary ions on the decay length which characterizes the exponential fall-off of impurity sputter profiles. The samples consisted of low resistivity, p-type Si covered with thin metallic overlayers. Bombardment was carried out at 2° off normal. Aspect (i) was investigated for tracers of Cu and Ga using N ₂ ⁺ , O ₂ ⁺ , and Ne⁺ primary ions at an energy of 5 keV/atom. The effect of the beam energy, aspect (ii), was studied for eight different tracer species and N ₂ ⁺ primary ions at energies between 2 and 5 keV/atom. In the case of Ga, was found to be shorter with N ₂ ⁺ or O ₂ ⁺ primary ions (=7.0 and 7.5 nm, respectively) than with Ne⁺ (=12 nm). This effect is attributed to beam induced formation of Si₃N₄ or SiO₂ layers, whereby the effective width of the internal distribution of intermixed Ga impurities in the Si subsystem is reduced significantly. In contrast to Ga, the decay length for Cu is smallest under bombardment with Ne⁺ (=16 nm), quite large with N ₂ ⁺ (26 nm) and extremely large with O ₂ ⁺ (2.2 m). Segregation of Cu atoms at the Si₃N₄/Si and the SiO₂/Si interface, respectively, is responsible for this depressed impurity removal rate. Within experimental accuracy the observed variation of the decay length with N ₂ ⁺ energy E [keV/atom] can be written in the form =kE ^p, where k and p are element specific parameters which range from k=1.2 nm for Pb to 10 nm for Cu and from p=0.6 for Cu and Ag to 1.0 for Pb. The results are discussed with reference to conceivable shapes of the distribution of intermixed impurity atoms.On leave from NTT Applied Electronics Laboratories, 3-9-11, Midori-cho, Musashino-shi, Tokyo 180, Japan     

Ion-enhanced gas-surface chemistry: The influence of the mass of the incident ion

There are many examples of situations in which a gas-surface reaction rate is increased when the surface is simultaneously subjected to energetic particle bombardment. There are several possible mechanisms which could be involved in this radiation-enhanced gas-surface chemistry. In this study, the reaction rate of silicon, as determined from the etch yield, is measured during irradiation of the Si surface with 1 keV He⁺, Ne⁺, and Ar⁺ ions while the surface is simultaneously subjected to fluxes of XeF₂ or Cl₂ molecules. Etch yields as high as 25 Si atoms/ion are observed for XeF₂ and Ar⁺ on Si. A discussion is presented of the extent to which these results clarify the mechanisms responsible for ion-enhanced gas-surface chemistry.     

Theoretical energy distributions of atoms sputtered from elastic collision spikes by monomer and dimer ion bombardment

The energy spectra of atoms sputtered from metal targets by bombardment with heavy monomer and dimer ions have been investigated on the basis of a standard model for elastic collision spikes. In particular we calculated the energy distributions for a Au sample bombarded by 4 keV I⁺ and 8 keV I ₂ ⁺ ions. The results were compared with the recent time of flight measurements performed by de Vries and coworkers. It was shown that the model described accurately most of the experimental observations: the count rates and the relative cascade to spike ratios for both I⁺ and I ₂ ⁺ projectiles, and the energy spectrum for dimer sputtering. The spectrum for monomer bombardment, however, was shifted towards lower energies in comparison to the experimental one. The possible source of this discrepancy is discussed.This work was supported by the Central Research Program CPBP 01.09     

Al-50wt% Sn合金的离子溅射研究

用捕获膜技术和卢瑟福背散射(RBS)分析,测定Al-Sn多相合金在30keV Ar⁺离子轰击时Al和Sn的溅射原子角分布。溅射后的样品用扫描电子显微镜(SEM)进行观察,并用电子微探针分析仪(EPMA)对轰击样品(靶点)和未轰击样品作成分分析。结果表明,Al的溅射原子角分布近于cosine形状,而Sn却是over-cosine型角分布。本文给出一个按不同表面形貌特征划分的各元素富集区i进行叠加的产额表达式,Y(θ)=∑Y_i(θ),解释了实验结果。 关键词：     

BaF2晶体的取向和入射束的剂量对溅射的影响

２７ｋｅＶ Ａｒ^＋离子束沿法向分别入射在ＢａＦ₂单晶（１１１），（１００）和（１１０）的晶面上，用捕获器方法和Ｒｕｔｈｅｒｆｏｒｄ背散射分析法测定了Ｂａ原子的溅射角分布和溅射产额。结果发现不同取向的晶体表面，它们的溅射产额有明显差异。当用剂量为５×１０¹⁷ｉｏｎ／ｃｍ²的Ａｒ^＋离子分别轰击这三种晶面时，其溅射产额的顺序Ｙ_１００＞ｙ_１１１＞ｙ_１１０．对已被上述剂量辐照过的晶面再作相同剂量轰击时，测得的溅射产额明显增大。这些结果被认为是由于在离子辐照过程中表面晶格受损逐步增大所致。 关键词：     

Three-dimensional damage distributions of molecular ions implanted into silicon,as recorded by RBS/channeling combined with tomography

The depth distributions of damage of 1.4 MeV nitrogen molecular ions (N ₂ ⁺ ) implanted into Si crystals at doses slightly below the value for amorphization have been measured by means of standard RBS/channeling for different directions of impact. These damage distributions were fed into our modified tomographic program MO-TOR [1, 2], by which we could reconstruct the spatial distributions of nuclear energy transfer. These distributions are compared with the three-dimensional theoretical prediction of a modified TRIM code [3].It turns out that there exists a pronounced deviation from the purely ballistic damage distribution insofar as the reconstructed damage distribution is twice as broad in the lateral direction than predicted. This is essentially explained by deviations in flight geometry of molecular ions in comparison with single-atomic ones.     

Angular dependent photon-stimulated desorption of ions from a V2O5(010) surface

Using a display-type analyzer, we have measured the angular and energy distribution of O⁺ ions desorbed from a V₂O₅(010) surface by incident photons. The desorbed ions were mass-analyzed using time-of-flight gating techniques. The angular distribution of desorbed ions was found to be strongly peaked in the direction of the surface normal. This strongly directional desorption pattern reflects the local bonding geometry of the topmost oxygen atoms in the surface. The observed photoexcitation spectrum of the ion yiel can be explained with the core level Auger decay model formulated by Knotek and Feibelman.     

Study of the plasmas produced during the deposition of TiC/SiC thin films in a hybrid magnetron-laser system

Time- and spatially-resolved optical emission spectroscopy was performed to characterize the plasma produced in a hybrid magnetron-sputtering-laser deposition system, which is used for TiC or SiC thin films preparation. A graphite target was ablated by a KrF excimer laser (λ=248 nm,τ=20 ns) and either Ti or Si targets were used for DC magnetron sputtering in argon ambient. Spectra were measured in the range 250–850 nm. The evolution of the spectra with varying magnetron powers (0–100 W) and argon pressures (0.3–10 Pa) was studied. Spectra of the plasmas produced by a) the magnetron alone, b) the ablation laser alone, and c) the magnetron and the ablation laser together, were recorded. Spectra (a) were dominated by Ar atoms and Ar⁺ ions. Emission lines of Ti and Si were detected, when Ti target and Si target was used, respectively. Spectra (b) revealed emission of C, C⁺, C₂, Ar, Ar⁺. Spectra (c) showed presence of all previously mentioned species and further of Ti⁺ ions emission was detected. The research was supported by Grant Agency of the Czech Republic No. 202/06/02161, GA ASCR project number A1010110/01 and Institutional Research Plan AV CR No. AV0Z 10100522.     

Modification of GaAs by medium-energy N<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> ions

The modification of GaAs with a 2500-eV beam containing N ₂ ⁺ and Ar⁺ ions is examined with Auger electron spectroscopy. Most implanted nitrogen atoms are found to react with the matrix, substituting arsenic atoms to produce a several-nanometer-thick layer of the single-phase GaAs_1−x N_x (x=6%) solid solution. The GaN phase is absent. Displaced arsenic atoms and nitrogen atoms unreacted with the matrix are present in the layer and on its surface. The former segregate, whereas the latter form molecules.     

Observation of a new atomic-like peak in the ion-induced Auger spectrum of Si

We have observed Si L-shell Auger electrons from a silicon surface bombarded with 20 keV Ar⁺ ions at different angles of incidence. The measurements of angle-resolved electron energy distributions allowed us to separate the contributions to the Auger electron spectra coming from de-excitations inside and outside the solid. At grazing angles of incidence and observation, the Auger electron distributions resemble those from gas-phase atomic collisions. In these conditions we observed an atomic-like Auger peak with an energy close to that of the high energy edge of the Si L_2,3VV transition.     

Surface analysis by ion-electron spectroscopy; Silicon target

The energy spectra of secondary elections emitted from a Si(111) surface due to bombardment by 6 keV He⁺ and O⁺₂ ions have been examined. The fine structure in the spectra is explained on the basis of a novel mechanism of creation of Auger electrons at the surface. There are two stages of interaction between incoming ions and the substrate via adsorbed atoms. In the first stage, due to a level promotion mechanism, vacancies in the adsorbed atoms are created. In the second stage, Auger neutralization processes accompanied by the emission of electrons from a solid with characteristic energies take place. These electrons provide a good indication of the degree of coverage of the silicon surface with contaminant atoms. The energy losses of escaping electrons are also discussed.