Electrochemical characterization of surface complexes formed on Cu and Ta in succinic acid based solutions used for chemical mechanical planarization

Open-circuit potential measurements, cyclic voltammetry and Fourier transform impedance spectroscopy have been used to study pH dependent surface reactions of Cu and Ta rotating disc electrodes (RDEs) in aqueous solutions of succinic acid (SA, a complexing agent), hydrogen peroxide (an oxidizer), and ammonium dodecyl sulfate (ADS, a corrosion inhibitor for Cu). The surface chemistries of these systems are relevant for the development of a single-slurry approach to chemical mechanical planarization (CMP) of Cu lines and Ta barriers in the fabrication of semiconductor devices. It is shown that in non-alkaline solutions of H₂O₂, the SA-promoted surface complexes of Cu and Ta can potentially support chemically enhanced material removal in low-pressure CMP of surface topographies overlying fragile low-k dielectrics. ADS can suppress Cu dissolution without significantly affecting the surface chemistry of Ta. The data analysis steps are discussed in detail to demonstrate how the D.C. and A.C. electrochemical probes can be combined in the framework of the RDE technique to design and test CMP slurry solutions.     

Superhydrophobic surfaces via electroless displacement of nanometric Cu layers by Ag

This paper explores the possibility of making hydrophobic and superhydrophobic surfaces from electroless displacement of Cu by Ag⁺, in the case where Cu oxidation is limited owing to Cu layers of nanometric thicknesses. The morphology of the Ag layers is studied by scanning electron microscopy for Cu thicknesses between 10 and 80 nm. The mapping of the elemental content of the layers by electron dispersive X-ray analysis also has been used to clarify the particle growing by diffusion limited aggregation. It is shown that the average size and the shape complexity of the Ag particles increase with the Cu thickness. The addition of dimethyl sulfoxide in the Ag⁺ aqueous solution improves the surface homogeneity, increases the particle density and decreases their sizes. The wetting behaviour of the surfaces, after grafting with octadecanethiol, has been studied from measurements of the contact angles of a drop of water. According to the thickness of the initial Cu layer and the morphology of the Ag layer, contact angles range between 110° and 154°. Superhydrophobic surfaces are obtained from 80 nm thick Cu layers.     

Photoluminescence of very thin oxide/a-Si:H structures passivated in HCN solutions

In this contribution we present new experimental facts concerning evolution of the a-Si:H photoluminescence (PL) spectra, recorded at 6 K, induced by both formation of very thin oxide layer in the surface region of the semiconductor by nitric acid solutions and passivation of a-Si:H defect states using HCN aqueous solutions. a-Si:H layers were deposited on both n-type of crystalline Si and the Corning glass. The analysis of the set of PL spectra - their interpretation - indicates that two explanations of blue shifts of the PL band maxima are possible. The first is connected with formation of several structurally different a-Si:H-based phases inside the amorphous matrix and/or with the Street model of recombination of localized electron-hole pairs coupled with the optical phonon in Si.Additionally, as it was stated, the wet chemical oxidation of 1 μm thick a-Si:H layers deposited on the glass can induce formation of hydrogenated micro-sized a-Si grains. Passivation procedure performed in the HCN solution can transform an equivalent part of the a-Si:H semiconductor to a-Si:CN. If the multiphase model is accepted for interpretation of the PL spectra then the following main PL transitions related with different phases were observed: 1.20, 1.25, 1.38, 1.41, 1.44, and 1.48 eV.     

CaO高温脱除氰化氢试验研究

本文在石英反应器内试验了高温脱除HCN反应机理,研究了CaO对氰化氢的脱除作用,探讨了温度、体积空速和氰化氢浓度对脱除氰化氢的影响.试验结果表明:当T<45℃,CaO促使HCN中的N元素转化到CaCN_2,当T>800℃,CaO促使HCN中的N元素全部转化为N_2;CaO在800℃时,只要体积空速小于12000 h~(-1),CaO对HCN均有接近100%的脱除效果;在体积空速10000 h~(-1)、温度800℃工况下,CaO对初始浓度范围127×10~(-6)-512×10~(-6)的HCN均有接近100%的脱除效果.     

Nitric acid method for fabrication of gate oxides in TFT

We have developed low temperature formation methods of SiO₂ layers which are applicable to gate oxide layers in thin film transistors (TFT) by use of nitric acid (HNO₃). Thick (>10 nm) SiO₂ layers with good thickness uniformity (i.e., ±4%) can be formed on 32 cm × 40 cm substrates by the two-step nitric acid oxidation method in which initial and subsequent oxidation is performed using 40 and 68 wt% (azeotropic mixture) HNO₃ aqueous solutions, respectively. The nitric acid oxidation of polycrystalline Si (poly-Si) thin films greatly decreases the height of ridge structure present on the poly-Si surfaces. When poly-Si thin films on 32 cm × 40 cm glass substrates are oxidized at azeotropic point (i.e., 68 wt% HNO₃ aqueous solutions at 121 °C), ultrathin (i.e., 1.1 nm) SiO₂ layers with a good thickness uniformity (±0.05 nm) are formed on the poly-Si surfaces. When SiO₂/Si structure fabricated using plasma-enhanced chemical vapor deposition is immersed in 68 wt% HNO₃, oxide fixed charge density is greatly decreased, and interface states are eliminated. The fixed charge density is further decreased by heat treatments at 200 °C, and consequently, capacitance-voltage characteristics which are as good as those of thermal SiO₂/Si structure are achieved.     

Passivation of defect states in Si-based and GaAs structures

Formation of defect states on semiconductor surfaces, at its interfaces with thin films and in semiconductor volumes is usually predetermined by such parameters as semiconductor growth process, surface treatment procedures, passivation, thin film growth kinetics, etc. This paper presents relation between processes leading to formation of defect states and their passivation in Si and GaAs related semiconductors and structures. Special focus is on oxidation kinetics of yttrium stabilized zirconium/SiO₂/Si and Sm/GaAs structures. Plasma anodic oxidation of yttrium stabilized zirconium based structures reduced size of polycrystalline silicon blocks localised at thin film/Si interface. Samarium deposited before oxidation on GaAs surface led to elimination of EL2 and/or ELO defects in MOS structures. Consequently, results of successful passivation of deep traps of interface region by CN⁻ atomic group using HCN solutions on oxynitride/Si and double oxide layer/Si structures are presented and discussed. By our knowledge, we are presenting for the first time the utilization of X-ray reflectivity method for determination of both density of SiO₂ based multilayer structure and corresponding roughnesses (interfaces and surfaces), respectively.     

A novel surface cleaning method for chemical removal of fouling lead layer from chromium surfaces

Most products especially metallic surfaces require cleaning treatment to remove surface contaminations that remain after processing or usage. Lead fouling is a general problem which arises from lead fouling on the chromium surfaces of bores and other interior parts of systems which have interaction with metallic lead in high temperatures and pressures. In this study, a novel chemical solution was introduced as a cleaner reagent for removing metallic lead pollution, as a fouling metal, from chromium surfaces. The cleaner aqueous solution contains hydrogen peroxide (H₂O₂) as oxidizing agent of lead layer on the chromium surface and acetic acid (CH₃COOH) as chelating agent of lead ions. The effect of some experimental parameters such as acetic acid concentration, hydrogen peroxide concentration and temperature of the cleaner solution during the operation on the efficiency of lead cleaning procedure was investigated. The results of scanning electron microscopy (SEM) showed that using this procedure, the lead pollution layer could be completely removed from real chromium surfaces without corrosion of the original surface. Finally, the optimum conditions for the complete and fast removing of lead pollution layer from chromium surfaces were proposed. The experimental results showed that at the optimum condition (acetic acid concentration 28% (V/V), hydrogen peroxide 8% (V/V) and temperature 35 °C), only 15-min time is needed for complete removal of 3 g fouling lead from a chromium surface.     

Method of observation of low density interface states by means of X-ray photoelectron spectroscopy under bias and passivation by cyanide ions

X-ray photoelectron spectroscopy (XPS) measurements under bias can observe low density interface states for metal-oxide-semiconductor (MOS) diodes with low densities. This method can give energy distribution of interface states for ultrathin insulating layers for which electrical measurements cannot be performed due to a high density leakage current. During the XPS measurements, a bias voltage is applied to the rear semiconductor surface with respect to the ∼3 nm-thick front platinum layer connected to the ground, and the bias voltage changes the occupation of interface states. Charges accumulated in the interface states shift semiconductor core levels at the interface, and thus the analysis of the bias-induced shifts of the semiconductor core levels measured as a function of the bias voltage gives energy distribution of interface states. In the case of Si-based MOS diodes, the energy distribution and density of interface states strongly depend on the atomic density of silicon dioxide (SiO₂) layers and the interfacial roughness, respectively. All the observed interface state spectra possess peaked-structures, indicating that they are due to defect states. An interface state peak near the Si midgap is attributable to isolated Si dangling bonds at the interface, while those above and below the midgap to Si dangling bonds interacting weakly with Si or oxygen atoms in the SiO₂ layers. A method of the elimination of interface states and defect states in Si using cyanide solutions has been developed. The cyanide method simply involves the immersion of Si in KCN solutions. Due to the high Si-CN bond energy of ∼4.5 eV, the bonds are not ruptured at 800 °C and upon irradiation. The cyanide treatment results in the improvement of the electrical characteristics of MOS diodes and solar cells.     

Wet-chemical nanoscale patterning of GaAs surfaces using atomic force microscope lithography

Sub-100 nm V-grooves in GaAs(001) surfaces have been fabricated by patterning a thin photoresist layer with an atomic force microscope (AFM) and subsequent wet-chemical etching. The nanolithography is based on the dynamic ploughing technique. Anisotropic etchants under investigation are bromine–methanol–isopropanol, sulfuric acid–hydrogen peroxide–water, citric acid–hydrogen peroxide–water, and ammonium hydroxide–hydrogen peroxide–water. Along the [11&#x0304;0] direction the etched grooves are V-shaped, along [11&#x0304;0] the profile is U-shaped. Best results of 50–60-nm wide V-grooves with straight edges and smooth sidewalls are obtained from bromine–methanol–isopropanol, the other etchants form rough grooves. Concerning the reproducibility of the patterning process, the aqueous etch solutions exceed the bromine etchant.     

Studies on Trace Labelling of Bromsulphalein (BSP) with Radioiodine

Two methods have been studied for high specific activity trace iodination of Bromsulphalein (BSP) with radioiodine (¹³¹I). In the first method, BSP in aqueous solution is reacted with iodine and an oxidising agent – hydrogen peroxide or chloramine T. In the second method, iodination is carried out by electrolytically liberated iodine. The electrolytic method gives labelled BSP free from any labelled degradation products. The stability of ¹³¹I-labelled BSP in aqueous solution has been studied. The product has been found to remain more stable in aqueous solutions at a slightly acid pH (4…6.5) than in dilute alkaline solutions (pH 7…9.5).     

稀氢氟酸中硅表面氢终端的原位拉曼光谱研究

本文用共焦显微拉曼系统原位观察了Ｓｉ（１００）表面氢终端原子在稀氢氟酸中的变化过程。研究表明：在硅片浸入氢氟酸溶液的初期,表面主要被硅和三个氢原子的结合体（Ｓｉ Ｈ３）以及硅和两个氢原子的结合体（Ｓｉ Ｈ２）所覆盖。随着腐蚀过程的延长,Ｓｉ Ｈ３越来越少,Ｓｉ Ｈ２的信号不断增强,并且,硅和单个氢原子的结合体（Ｓｉ Ｈ）的信号也开始出现。最终,硅表面主要被Ｓｉ Ｈ２所覆盖,有少量Ｓｉ Ｈ３和Ｓｉ Ｈ键。本文还表明,拉曼光谱用来原位观察半导体材料表面终端原子键在溶液中的变化是很有用的工具     

Effect of self-assembled Ge nanostructures on Si surface electronic properties

Incorporating self-assembled Ge islands on Si surfaces into electronic devices has been suggested as a means of forming small features without fine-scale litho- graphy. For use in electronic devices, the electrical properties of the deposited Ge and their relation to the underlying Si substrate must be known. This report presents the results of a surface photovoltage investigation of the surface energy barrier as increasing amounts of Ge are added to a Si surface by chemical vapor deposition. The results are interpreted in terms of band discontinuities and surface states. The surface barrier increases as a wetting layer is deposited and continues to increase as defect-free islands form. It saturates as the islands grow. As the amount of Ge continues increasing, defects form, and the surface barrier decreases because of the resulting allowed states at the Ge/Si interface. Qualitatively similar behavior is found for Si(001) and Si(111). Covering the Ge with Si reduces the surface-state density and possibly modifies the wetting layer, decreasing the barrier to one more characteristic of Si. Initial hydrogen termination of the surface decreases the active surface-state density. As the H desorbs, the surface barrier increases until it stabilizes as the surface oxidizes. The behavior is briefly correlated with scanning-tunneling spectroscopy data. Received: 13 November 2000 / Accepted: 14 November 2000 / Published online: 23 May 2001     

Heterogeneity of activated carbons in adsorption of aniline from aqueous solutions

The heterogeneity of activated carbons (ACs) prepared from different precursors is investigated on the basis of adsorption isotherms of aniline from dilute aqueous solutions at various pH values. The APET carbon prepared from polyethyleneterephthalate (PET), as well as, commercial ACP carbon prepared from peat were used. Besides, to investigate the influence of carbon surface chemistry, the adsorption was studied on modified carbons based on ACP carbon. Its various oxygen surface groups were changed by both nitric acid and thermal treatments. The Dubinin-Astakhov (DA) equation and Langmuir-Freundlich (LF) one have been used to model the phenomenon of aniline adsorption from aqueous solutions on heterogeneous carbon surfaces. Adsorption-energy distribution (AED) functions have been calculated by using an algorithm based on a regularization method. Analysis of these functions for activated carbons studied provides important comparative information about their surface heterogeneity.     

Growth of Cu Films on Si(111)-7×7 Surfaces at Low Temperature: A Scanning Tunnelling Microscopy Study

Morphologies of Cu(111) films on Si(111)-7×7 surfaces prepared at lowtemperature are investigated by scanning tunnelling microscopy (STM) andreflection high-energy electron diffraction (RHEED). At the initial growth stage, Cu films are flat due to the formation of silicide at the interface that decreases the mismatch between Cu films and the Si substrate. Different from the usual multilayer growth of Cu/Cu(111), on the silicide layer a layer-by-layer growth is observed. The two dimensional (2D) growth is explained by the enhanced high island density at low deposition temperature. Increasing deposition rateproduces films with different morphologies, which is the result of Ostwald ripening.     

Hydrogen on Si: Ubiquitous surface termination after wet-chemical processing

The manufacture of microelectronic devices based on silicon technology is largely dominated by wet chemical processes. By ultraclean sample preparation in air and a fast transfer into UltraHigh Vacuum (UHV) we open up a way for the atomic-scale structural and chemical characterization of silicon surfaces immediately after wet-chemical processing. Using Scanning Tunneling Microscopy (STM), ThermoDesorption (TDS) and InfraRed Spectroscopy (IRS), we find that a surface termination predominantly by hydrogen results from all the different wet-chemical treatments investigated (etching with hydrofluoric acid, rinsing with hot water, chemomechanical polishing)-despite the different chemical ambients and process parameters involved. Microscopically, a crystallographically preferential attack of the silicon is observed in all these processes which results, to a different extent, in anisotropic defect structures on the surfaces. This is explained by an interplay of aqueous reaction kinetics and sterical hindrance on the silicon surface. It is pointed out how a UHV surface analysis of the micromorphology of wet-chemically treated silicon surfaces, so far carried out mostly on Si(111) due to its easier preparation and experimental accessability, may help to provide the in-depth understanding of the atomic-scale mechanisms during wet-chemical processing demanded by the progressing miniaturization of microelectronic devices. The atomically smoother and chemically more homogeneous Si(111) obtained after preferential etching with NH₄F suggests that in future applications Si(111) may gain importance over Si(100), which still dominates in today's semiconductor technology, since future devices increasingly rely on tailor-made and ideal properties on an atomic scale. Due to their structural and chemical simplicity and well-controlable characteristics, H-teminated surfaces after wet-chemical preparation also form ideal substrates for conventional UHV surface studies such as absorption and MBE-growth experiments.     

Nonlinear optical investigations of the dynamics of hydrogen interaction with silicon surfaces

Optical second-harmonic generation (SHG) from silicon surfaces may be resonantly enhanced by dangling-bond-derived surface states. The resulting high sensitivity to hydrogen adsorption combined with unique features of SHG as an optical probe has been exploited to study various kinetical and dynamical aspects of the adsorption system H₂/Si. Studies of surface diffusion of H/Si(111)7×7 and recombinative desorption of hydrogen from Si(111)7 × 7 and Si(100)2 × 1 revealed that the covalent nature of hydrogen bonding on silicon surfaces leads to high diffusion barriers and to desorption kinetics that strongly depend on the surface structure. Recently, dissociative adsorption of molecular hydrogen on Si(100)2×1 and Si(111)7×7 could be observed for the first time by heating the surfaces to temperatures between 550 K and 1050 K and monitoring the SH response during exposure to a high flux of H₂ or D₂. The measured initial sticking coefficients for a gas temperature of 300K range from 10^–9 to 10^–5 and strongly increase as a function of surface temperature. These results demonstrate that the lattice degrees of freedom may play a decisive role in the reaction dynamics on semiconductor surfaces.     

Surface passivation of crystalline silicon by sputter deposited hydrogenated amorphous silicon

This letter shows that intrinsic hydrogenated amorphous silicon (a‐Si:H) films deposited by RF magnetron sputtering can provide outstanding passivation of crystalline silicon surfaces, similar to that achieved by plasma enhanced chemical vapour deposition (PECVD). By using a 2% hydrogen and 98% argon gas mixture as the plasma source, 1.5 Ω cm n‐type FZ silicon wafers coated with sputtered a‐Si:H films achieved an effective lifetime of 3.5 ms, comparable to the 3 ms achieved by PECVD (RF and microwave dual‐mode). This is despite the fact that Fourier transform infrared spectroscopy measurements show that sputtering and PECVD deposited films have very different chemical bonding configurations. We have found that film thickness and deposition temperature have a significant impact on the passivation results. Self‐annealing and hydrogen plasma treatment during deposition are likely driving forces for the observed changes in surface passivation. These experimental results open the way for the application of sputtered a‐Si:H to silicon heterojunction solar cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Surface pore tension and adsorption characteristics of polluted sediment

Most natural sediment particles have numerous pores and a complex surface texture which facilitates their adsorption of contaminants. Particle surface structure, therefore, is an important instrumental factor in the transport of contaminants, especially in water environments. This paper reports on the results of adsorption-desorption experiments to analyze polluted sediment surface pore tension characteristics performed on samples from the bottom of Guanting Reservoir. In our analysis, the Frenkel-Halsey-Hill (FHH) equation is applied to calculate the fractal dimensions of particles to quantify the surface roughness and pore tension characteristics. The results show that the surface fractal dimensions of sediment particle surfaces normally measure from 2.6 to 2.85. The volume of pores smaller than 10 nm changes significantly after being contaminated with pollutants and the fractal dimension decreases because the pores adsorb the contaminants. Supported by the National Science Fund for Distinguished Young Scholars (Grant No. 50325929) and the National Key Technology R&D Program during the 11th Five-Year Plan Period (Grant No. 2006BAB05B05)     

EXAFS研究硫酸硫脲反萃季铵氰化金的机理

季铵盐可以直接从氰化浸出液中萃取金 ,但反萃困难。酸性硫脲通空气反萃体系是目前从季铵盐中反萃氰化金最有效的体系 ,但对其机理的研究很少。文章采用扩展X射线吸收精细结构 (EXAFS)等方法研究了硫酸硫脲从负载氰化金季铵盐中反萃金的机理。研究结果表明 ,在反萃过程中 ,硫酸、硫脲和硫脲金都能以中性分子进入有机相 ,中性缔合在季铵盐反萃过程中不可忽视。反萃机理如下 :(1)硫酸和硫脲首先进入有机相被萃取 ;(2 )在有机相中 ,硫脲争夺金的氰根配位 ,使氰化金变成硫脲金 ,同时游离出来的氰根与硫酸中的氢离子作用变成氢氰酸 ,在鼓空气搅拌条件下氢氰酸被空气迅速带走排除 ;(3)硫脲金配合物在有机相和水相中分配 ,大部分硫脲金进入水相 ,从而达到反萃的目的。     

Thermal and kinetic surface roughening studied by scanning tunneling microscopy and atomic force microscopy

Recent studies of thermal roughening on Si surfaces and kinetic roughening of some growing films, copper and tungsten, by using scanning tunneling microscopy and atomic force microscopy are reviewed. A logarithmic divergence of the surface height fluctuations of Si(111) vicinal surfaces is confirmed, in agreement with the theoretical prediction of rough surface in thermal equilibrium. For the kinetically formed rough surfaces, power law dependences of the interface width on the system size are clearly observed. Furthermore, the tungsten films show a short-range scaling regime and a long-range “smooth” regime. The roughness exponents α are compared with theoretical predictions: for the typical Cu electrode position condition (α=1/2), the exponent appears to be close to that found for local growth models, and for tungsten films (0.7～0.8), it is consistent with recent predictions for growth where surface diffusion is predominant.