Auger electron spectroscopy and secondary ion mass spectrometry depth profiling with sample rotation

Recently, there has been a rapid increase in the application of multilayered structured materials, as opposed to bulk materials, in many areas of technological development. Accurate characterization of the structure and composition of advanced multilayers such as superlattices, quantum wells, contacts, and coatings is important for materials and device fabrication technology. Surface analysis techniques including Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy, and secondary ion mass spectrometry (SIMS) in conjunction with ion beam sputtering (sputter depth profiling) are at present the most widely used methods for characterization of modern multilayer thin film materials and devices. Ion-beam-induced surface topography, however, can limit depth resolution, and with SIMS, can also cause changes in the secondary ion yield. These changes are due to the high sensitivity of secondary ion yield to the local angle of incidence on sputter-roughened surfaces. Degradation of depth resolution and changes in secondary ion yields during sputter depth profiling have often limited studies of thin film interdiffusion, segregation, oxidation at interfaces, and impurity effects. Much theoretical and experimental work has been carried out to try to improve depth resolution including the use of low ion beam energy, high angle of incidence, and two ion guns. Recent studies of AES and SIMS with sample rotation have shown that depth resolution can be improved substantially and that constant secondary ion yields in SIMS can be achieved. We will first provide an overview of the studies made by various groups to improve depth resolution of metal multilayers using AES with rotation. Next we will review recent investigations of SIMS using sample rotation including studies of the effects of sample rotation on O₂⁺ ion-beam-induced topography, secondary ion yield, and the depth resolution of electronic, metallurgical and dielectric materials. The results presented demonstrate that SIMS with sample rotation provides constant secondary ion yield, and depth-independent depth resolution because sample rotation prevents ion-beam-induced roughness and reduces the effect of the inhomogeneity of low energy ion beams.     

Molecular depth profiling of multilayer polymer films using time-of-flight secondary ion mass spectrometry

The low penetration depth and high sputter rates obtained using polyatomic primary ions have facilitated their use for the molecular depth profiling of some spin-cast polymer films by secondary ion mass spectrometry (SIMS). In this study, dual-beam time-of-flight (TOF) SIMS (sputter ion, 5 keV SF(5)(+); analysis ion, 10 keV Ar(+)) was used to depth profile spin-cast multilayers of poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate) (PHEMA), and trifluoroacetic anhydride-derivatized poly(2-hydroxyethyl methacrylate) (TFAA-PHEMA) on silicon substrates. Characteristic positive and negative secondary ions were monitored as a function of depth using SF(5)(+) primary ion doses necessary to sputter through the polymer layer and uncover the silicon substrate (>5 x10(14) ions/cm(2)). The sputter rates of the polymers in the multilayers were typically less than for corresponding single-layer films, and the order of the polymers in the multilayer affected the sputter rates of the polymers. Multilayer samples with PHEMA as the outermost layer resulted in lowered sputter rates for the underlying polymer layer due to increased ion-induced damage accumulation rates in PHEMA. Additionally, the presence of a PMMA or PHEMA overlayer significantly decreased the sputter rate of TFAA-PHEMA underlayers due to ion-induced damage accumulation in the overlayer. Typical interface widths between adjacent polymer layers were 10-15 nm for bilayer films and increased with depth to approximately 35 nm for the trilayer films. The increase in interface width and observations using optical microscopy showed the formation of sputter-induced surface roughness during the depth profiles of the trilayer polymer films. This study shows that polyatomic primary ions can be used for the molecular depth profiling of some multilayer polymer films and presents new opportunities for the analysis of thin organic films using TOF-SIMS.     

Impact energy dependence of SF5+-induced damage in poly(methyl methacrylate) studied using time-of-flight secondary ion mass spectrometry

Ion-induced damage of polymers is a critical factor in the depth profiling of polymer surfaces using polyatomic primary ions. In this study, time-of-flight secondary ion mass spectrometry was used to measure the damage of spin-cast poly(methyl methacrylate) (PMMA) films under 5-keV Cs(+) and 2.5-8.75-keV SF(5)(+) bombardment. Under 5-keV Cs(+) bombardment, the characteristic PMMA secondary ion intensities decreased rapidly for primary ion doses above 5 x 10(13) ions/cm(2). The damage profiles of PMMA under SF(5)(+) bombardment contained three distinct regions as a function of SF(5)(+) ion dose: a surface transient, an extended quasi-stabilization of the characteristic PMMA secondary ion intensities, and the decay of these intensities as the silicon substrate was reached. The PMMA film sputtered in a controlled manner for SF(5)(+) ion doses up to 4 x 10(14) ions/cm(2), with the maximum ion dose limited by the thickness of the PMMA film. Furthermore, the chemistry at the bottom of the sputter crater was significantly less modified by SF(5)(+) bombardment when compared with Cs(+) bombardment. The sputter rate was linearly correlated with the SF(5)(+) impact energy while the damage to the PMMA film varied minimally with the SF(5)(+) impact energy. These results were compared with Monte Carlo (SRIM) calculations of the penetration depth and vacancy production for SF(5)(+) at different impact energies. Since the SF(5)(+) impact energy only affected the sputter rate, selection of the appropriate SF(5)(+) impact energy for polymer depth profiling depends solely on the desired sputter rate.     

Energy deposition during molecular depth profiling experiments with cluster ion beams

The role of the location of energy deposition during cluster ion bombardment on the quality of molecular depth profiling was examined by varying the incident angle geometry. Cholesterol films approximately 300 nm in thickness deposited onto silicon substrates were eroded using 40-keV C60(+) at incident angles ranging from 5 degrees to 73 degrees with respect to the surface normal. The erosion process was evaluated by determining at each incident angle the total sputtering yield of cholesterol molecules, the damage cross section of the cholesterol molecules, the altered layer thickness within the solid, the sputter yield decay in the quasi-steady-state sputter regime, and the interface width between the cholesterol film and the silicon substrate. The results show that the total sputtering yield is largest relative to the product of the damage cross section and the altered layer thickness at 73 degrees incidence, suggesting that the amount of chemical damage accumulated is least when glancing incident geometries are used. Moreover, the signal decay in the quasi-steady-state sputter regime is observed to be smallest at off-normal and glancing incident geometries. To elucidate the signal decay at near-normal incidence, an extension to an erosion model is introduced in which a fluence-dependent decay in sputter yield is incorporated for the quasi-steady-state regime. Last, interface width calculations indicate that at glancing incidence the damaged depth within the solid is smallest. Collectively, the measurements suggest that decreased chemical damage is not necessarily dependent upon an increased sputter yield or a decreased damage cross section but instead dependent upon depositing the incident energy nearer the solid surface resulting in a smaller altered layer thickness. Hence, glancing incident angles are best suited for maintaining chemical information during molecular depth profiling using 40-keV C60(+).     

溅射深度剖析的定量分析及其应用

本文对溅射深度剖析定量分析中广泛应用的MRI模型及其应用作了一个综述.MRI模型考虑了在深度剖析实验中,引起真实元素成分深度分布失真的三个主要因素:溅射导致的原子间混合(M),样品表面/界面的粗糙度(R),测量技术的信息深度(Ⅰ).通过考虑在溅射过程中发生的择优溅射效应,这一模型得以进一步完善.利用这一模型,可以定量分析深度剖析实验的深度分辨率,以及定量确定纳米薄膜中的互扩散系数.     

Fluence Dependence of Mean Sputter Depth for Bombarded Pt-Cu and ~(10)B-~(11)B Binary Materials

The mean sputter depth depends on the surface composition gradient during ion implantation.For the high fluence ion implantation into a Pt-Cu alloy, the surface composition gradient of Cu is so large that the difference in mean sputter depth between Pt and Cu, is significant. However, for the high fluence ion implantation into 10B-11B isotope mixture, the surface composition gradient of 10B is so small that the difference in mean sputter depth between 10B and 11B is insignificant.     

Irradiation effects of water cluster ion beam on PMMA surface

We investigated the irradiation effects of a water cluster ion beam on a PMMA surface. The incident angle dependence of the sputter depth of the PMMA surface induced by the irradiation of a water cluster ion beam was measured. The sputter depth had a broad peak around the incident angle of 60°. The surface roughness caused by the irradiation of the water cluster ion beam was small compared with the sputter depth.     

X-ray photoelectron spectrometry depth profiling of organic thin films using C60 sputtering

A buckminsterfullerene (C(60)) ion beam was used for X-ray photoelectron spectrometry depth profiling of various organic thin films. Specimens representing different interfaces in organic light-emitting diode devices, including hole-conducting poly(ethylenedioxythiophene), poly(styrenesulfonic acid) (PEDOT:PSS) thin films on ITO with and without polysilicic acid doping, light-emitting Ir-containing 4,4'-bis(carbazol-9-yl)biphenyl (CBP) molecules on PEDOT:PSS, and electron-conducting 2,2',2' '(1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBi) molecules on CBP, were studied. In all cases, a clear multilayer structure was observed. The chemical composition and elemental state were preserved after C(60+) ion sputtering. The sputter rate was found to decrease with sputtering time. This is due to the deposition of amorphous carbon on the surface, with the rate of implantation highly dependent on the surface interacting with the ion beam.     

Sputter deposition of multilayered structures for use in sputter depth profile calibration

The development of standards and methods for calibration and comparison of depth scales, sputter removal rates and sputter depth profiling by surface analytical techniques (e.g. AES, SIMS, RBS and X-ray absorption) requires well controlled deposition of multilayered structures. The plasma beam-sputter deposition technique was used to produce combinations of multilayered structures, consisting of metal and oxide layers on Si(100) substrates. Ni, Cr, Ag, Ta, Au, Cr₂O₃ and Ta₂O₅ films were combined and produced in three structural designs of standard reference materials (SRM's), to be used for sputter depth profiling calibration namely, single thin film types, periodically modulated multilayered thin film structures and multilayered ‘marker’ structures. Tetrode sputtering equipment (SPUTRON II¹ of Balzers) was found to be an appropriate apparatus for the deposition of the chosen materials on the small production scale. Four in situ interchangeable targets were used to make highly reproducible layers, having the required quality and especially minimal layer and inter-layer contamination. Characterization of some of the multilayered structures developed showed, that periodically modulated system Ni/Cr/Ni … with well defined repetitive profiles and interface depth resolution is primarily suited for use in sputter depth profiling calibration. This multilayered structure is issued by NBS, Washington as Standard Reference Material No 2135.     

Depth resolution during C60+ profiling of multilayer molecular films

Time-of-flight secondary ion mass spectrometry is utilized to characterize the response of Langmuir-Blodgett (LB) multilayers under the bombardment by buckminsterfullerene primary ions. The LB multilayers are formed by barium arachidate and barium dimyristoyl phosphatidate on a Si substrate. The unique sputtering properties of the C60 ion beam result in successful molecular depth profiling of both the single component and multilayers of alternating chemical composition. At cryogenic (liquid nitrogen) temperatures, the high mass signals of both molecules remain stable under sputtering, while at room temperature, they gradually decrease with primary ion dose. The low temperature also leads to a higher average sputter yield of molecules. Depth resolution varies from 20 to 50 nm and can be reduced further by lowering the primary ion energy or by using glancing angles of incidence of the primary ion beam.     

Measurement of the interlayer between aluminum and silicon dioxide using ellipsometric,capacitance-voltage and auger electron spectroscopy techniques

Ellipsometric and capacitance-voltage measurements were combined to detect both the AlSiO₂ interlayer and the SiSiO₂ interlayer for the Si/SiO₂/Al system. The AlSiO₂ interlayer was characterized by Auger electron spectroscopy (AES), combined with argon ion sputter profiling, of the Al/SiO₂/Si structure and also of the remaining SiO₂/Si structure after the aluminum had been chemically removed. An effective interlayer thickness is defined as the product of the interlayer thickness and the fractional change in the dielectric SiO₂ constant. The results of these experiments indicate that the Alz.sbnd;SiO₂ effective interlayer thickness has a range of 0.1–0.5 nm. The AES data can be readily interpreted if it is assumed that collision cascade mixing and recoil implantation occur as a consequence of sputter depth profiling through the aluminum.     

SIMS studies of scale growth processes

Abstract

The penetration of ¹⁸O tracer into single layered and duplex NiO scales formed on Ni has been examined by sputter depth profiling and imaging modes of secondary ion mass spectrometry (SIMS). Preoxidation annealing in hydrogen and superficial contamination during substrate surface preparation were found to promote inward scale growth. The principles for selecting SIMS techniques for studying oxide scales and the influence of substrate condition on mechanisms for gaseous oxygen transport in NiO are discussed.

MST/950     

Secondary ion mass spectrometry of dopant and impurity elements in wide bandgap semiconductors

Based on secondary ion mass spectrometry (SIMS) measurements, we have compiled state-of-the-art data concerning dopant elements and natural impurities in the wide bandgap semiconductor materials diamond, SiC, ZnSe, GaN and AlN. Samples were prepared by ion implantation of different elements into these materials and post-implantation thermal annealing. SIMS depth profiling techniques were used to determine atomic depth profiles of implanted elements and subsequent changes produced by annealing. Range statistics and SIMS relative sensitivity factors were established for major dopant and impurity elements in these wide bandgap materials. Results of these studies are presented in tabular form along with representative depth profile figures.     

Auger electron spectroscopy depth profiling studies on stationary and rotated samples of a new model metal/semiconductor multilayer structure

Multilayer structures for application in microelectronics are becoming increasingly complex. A sputter deposited multilayer structure composed of chromium, nickel and silicon layers with a total thickness of 310 nm on a smooth silicon substrate was characterized by transmission electron microscopy (TEM) and by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) depth profiling. AES depth profiles of the Ni/Cr/Si multilayers were obtained with Ar⁺ ion bombardment at various angles of incidence using stationary and rotated samples. In some cases a strong influence of semiconductor structure on the experimentally obtained metal-metal and metal-semiconductor interface widths was observed. Owing to ion beam induced Si(LVV) Auger electrons in the crater wall of the Ni/Cr/Si sample, a distortional influence on depth resolution during simultaneous AES analysis and ion sputtering was found. Silicide formation during sputtering at the silicon-metal interfaces was confirmed by XPS. The measured compositional depth profiles are explained with respect to the influence of polycrystalline metallic and amorphous semiconductor structures; the effects of ion beam induced topography, atomic mixing and silicide formation are discussed.     

The erosion energy efficiency of sputtering

A new parameter of sputtering, the erosion energy efficiency, is defined as the ratio of the theoretical energy required to eject atoms to the experimental energy. This efficiency η (E) is shown to be proportional to the ratio of the sputtering yield Y(E) to the energy E and, even under optimum conditions never exceeds ～ 10%. The relationship of this efficiency to the broadening process occurring during sputter profiling resulting from recoil atomic motion and mixing is examined. It is shown that the ion energy conditions employed in both technological etching and sputter profiling systems are near optimum for energy utilization and profile broadening minimization.     

On the surface analysis of copper oxides: the difficulty in detecting Cu3O2

The existence of Cu₃O₂, a gross defect structure of Cu₂O, has been documented experimentally since the early 1960s. However, discussions of the oxidation of copper often neglect the importance of this phase; in fact, it is often omitted entirely from such discussions. This results from the difficulty in determining the chemical state during sputter depth profiling and relying on techniques that have difficulty providing chemical state information. The occurrence of sputter reduction during the depth profiling of copper oxide layers has been demonstrated with XPS depth profiles on a series of copper samples oxidized, for varying lengths of time, in air at a temperature of either 423 or 523 K. Under these conditions, a thin layer of CuO/Cu(OH)₂ terminates the oxide layers. Beneath this layer, the presence of Cu₃O₂ is expected on the samples prepared at 423 K. However, immediately upon the beginning of sputtering, only Cu¹⁺ is detected in the oxide layers. A zone of constant Cu:O ratio of (approximately ∼1.5) is found throughout most of the oxide layer even though Cu²⁺ is not detected. On the samples prepared at 523 K, the presence of CuO is anticipated. However, Cu²⁺ is not detected after sputtering is initiated and a region of constant Cu:O ratio of ca. 1.5 is detected. The inherent difficulties involved in investigating oxide layer growth and vertical oxide layer structure using sputter depth profiling are discussed in light of this experimental data.     

爆破振动的BP神经网络预测方法研究

爆破所引起的震动强度在很大程度上具有随机性,它受到众多因素的影响,而且各因素之间存在着极其复杂的非线性关系.运用人工神经网络原理,以孔深、孔数、孔距、最大齐爆药量、总药量和爆源距作为影响爆破振动的主要因素,建立BP神经网络模型1,对爆破振动速度进行预测,并与仅考虑最大齐爆药量和爆源距作为输入量的BP神经网络模型2和萨道...     

Determination of relative sputtering yield of Cr/Si

To understand the various effects induced by the ion bombardment one needs to know the sputtering yields for the sputtering conditions applied. Experimental data are rare however, and the reliability of the calculated values should be checked. Thus the measurement of sputtering yield is important. Recently, we have published a work where we have applied AES depth profiling to determine the relative sputtering yield [Barna A, Menyhard M, Kotis L, Kovacs GyJ, Radnoczi G, Zalar A, et al. J Appl Phys 2005; 98:024901-6]. In this communication, we will describe the method in a more detailed way discussing the reliability as well. It will be applied for Si/Cr multilayer structure (similar to those used in devices of integrated electronics) consisting three Si and three Cr layers sputter deposited onto smooth silicon substrates. The ion energy and projectile were 1 keV and Ar⁺, respectively. The angle of incidence varied in the range 22°-87°. The reliability of the derived relative sputtering yields will be discussed and will be compared with those provided by the available simulation.     

因子分析法在Ta_2O_5/Ta俄歇深度剖析上的应用

将一种基于多元统计方法的因子分析法用于俄歇深度剖面分析,采用Ar~ 离子轰击Ta_2O_5/Ta样品,俄歇峰采用具有高表面灵敏度和化学态灵敏的NOO俄歇跃迁,用因子分析可得到Ta的三种可区别的不同化学态即Ta、Ta_2O_5和Ta_xO_y,并且能提高探测灵敏度。     

应用神经网络模型对大学毕业生就业质量的预测

目的:尝试应用BP人工神经网络模型预测大学毕业生的就业质量。方法:以476名大学毕业生为研究对象,将毕业生的各种心理特质作为预测因子,利用Clementine数据挖掘软件构建大学毕业生就业质量的BP人工神经网络模型。结果:神经网络模型的拟合精度达到99.98%,对就业质量的平均绝对预测误差值为0.083。结论:该神经网络模型可用来预测和诊断大学毕业生找到工作后的就业质量,为就业指导工作提供技术与理论依据。