Variable Angle X-ray Photoelectron Spectroscopy Research Articles

KPFM and XPS Metrology of Self-Assembled Monolayer Barrier for Copper Metallization

Silane based Self assembled monolayer (SAM) has been demonstrated as a diffusion barrier layer on lowK dielectrics for sub 10 nm Cu interconnects for Integrated Circuit (IC) applications. A key problem in developing barrier layer is its monitoring capability, especially its thickness, uniformity, its coverage and defect density. The aim of this work is to develop surface analysis methods for characterizing those variables providing in line monitoring techniques that can predict barrier quality and reliability. The approach presented in this paper was to examine the defect density and coverage properties of the SAM on LowK dielectric using physical methods for the characterization of monolayer thick films, i.e. Variable Angle X-Ray Photoelectron Spectroscopy (VA -XPS) and Kelvin Probe scanning Force Microscopy (KPFM). The SAMs were deposited on three different substrates: bare-Si wafers, thermal oxide/Si and Low-k dielectrics on silicon wafers. The silanization was performed by chemical deposition from various solvents, both polar and non-polar, containing 1-2% silane in ethanol as a solvent at temperature range between 60oC to 120oC. The deposited films where characterized as follows: Variable Angle XPS measurement of High Resolution Multiplex . Next, the XPS data was analyzed as follows: a plot of ln [\U0001d475\U0001d494\U0001d496\U0001d483 \U0001d740\U0001d494\U0001d496\U0001d483 \U0001d470\U0001d490)/(\U0001d475\U0001d490 \U0001d740\U0001d490 \U0001d470\U0001d494\U0001d496\U0001d483+1] Versus 1/sin(α) was drawn , where Nsub is the atomic number density for the substrate , No is the atomic number density for the overlayer, \U0001d740\U0001d494\U0001d496\U0001d483 is the substrate Inelastic Mean free Path, \U0001d740o is the overlayer Inelastic Mean free Path, Isub is the signal intensity of electrons coming from the substrate, Io is the signal intensity of electrons coming from the overlayer and α is the take of angle from the sample surface. The Thickness of the overlayer was calculated from the slope of the graph. Using that data thickness of the SAM was obtained. The method and results will be shown and compared to other methods such as TEM. The XPS data yielded average values on large areal spots (> 10-4 cm2). To achieve high resolution analysis a Kelvin probe force microscopy (KPFM) were performed on SAM. KPFM gives a good image of SAM on low K material. We can learn a lot about Homogeneity and Coverage properties. A study of the nucleation and growth of the SAM, dependent on temperature and time was conducted. It seems that after 60 minutes, the SAM had the best homogeneity and surface coverage. (Figure 1). After mastering the use of the two methods for SAM, the results are compared in order to find the most suitable method for SAM metrology and monitoring that can be employed by the Semiconductor industry. Figure 1

The water-dependent decay mechanism of biaxially-oriented corona-treated polyethylene terephthalate films

In moist environments biaxially-oriented corona-treated polyethylene terephthalate (BOPET) film undergoes a decay in surface energy with time. This decay is a significant and well-known problem and it considerably restricts the industrial application of BOPET film. In the present study the decay effect and the dynamics of corona-treated BOPET film in an aqueous environment have been studied using water contact angle and variable angle X-ray photoelectron spectroscopy (XPS) measurements. In addition the surface decay mechanism of the corona-treated BOPET film in aqueous environments was analyzed and a molecular moving model for the decay mechanism is proposed.

Surface Modification of Ti45Nb Alloy with an Alkylphosphonic Acid Self-Assembled Monolayer

A new low-modulus β Ti−Nb alloy with low elastic modulus and excellent corrosion resistance is currently under consideration as a surgical implant material. The usefulness of such materials can be dramatically enhanced if their surface structure and surface chemistry can be controlled. This control is achieved in two stages. Electropolishing and anodic oxidation of the Ti45Nb alloy provide a surface with a uniform oxide layer that is a mixture of TiO2 and Nb2O5. The impact of each of these two steps on the morphology of the surface and on the thickness and chemistry of the oxide layer has been assessed. In addition, as a first step toward controlling the surface chemistry of this material, a self-assembled monolayer (SAM) based on hexadecylphosphonic acid (HDPA) is attached to the anodized surface. The SAM is characterized based on its wetting properties and by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. Using variable angle XPS analysis, detailed information is ...

Surface Pretreatments of Aluminum Alloy AA2024-T3 and Formation of Chromate Conversion Coatings : I. Composition and Electrochemical Behavior of the Oxide Film

Aluminum alloy AA2024-T3 has been subjected to various pretreatments including those routinely carried out in the industry prior to conversion coating of the alloy. The surface chemistry of the samples after pretreatment was analyzed using variable angle X-ray photoelectron spectroscopy (VAXPS). Electrochemical techniques were used to evaluate the corrosion behavior of the samples in quiescent 0.05 M NaCl solution. The results were compared with those obtained from an untreated sample used in as-received condition that acted as a control. The surface of the alloy was observed to be enriched in copper and magnesium after certain pretreatments. Composition of the surface oxide film as well as the electrochemical behavior was found to vary significantly depending on the pretreatment. In all cases, the overlayer formed on the alloy was less than the sampling depth of the XPS (∼90 Å). Pretreatment of the alloy using Alconox® was found to result in the formation of a highly protective aluminum oxide surface film. The corrosion current of the samples was observed to be directly proportional to the aluminum oxyhydroxide content of the film, while the polarization resistance of the sample was inversely proportional to the surface copper content. © 2004 The Electrochemical Society. All rights reserved.

Ellipsometric investigation of the Si/SiO 2 interface formation for application to highly reflective dielectric mirrors

We present a study of the Si/SiO 2 interface formation during the growth of Si on SiO 2 using in situ ellipsometry measurements performed at one wavelength (λ=0.4 μm). Variable angle X-ray photoelectron spectroscopy (XPS) is also used to confirm the ellipsometric measurements. In situ ellipsometry and XPS provide evidence for the formation of a SiO x (0< x<2) interlayer between the SiO 2 and Si layers. The variation of x with depth is analysed from (cos Δ, tan ψ) trajectories and the results obtained allow reproduction of the spectroscopic ellipsometry spectra too. The effects of the substrate temperature on the growth are investigated and show that the higher the substrate temperature the larger the interface. The utilisation of a SiO 2/Si multilayer stack for elaborating an omnidirectional reflector, angle-insensitive in the near infrared range, is also presented.

Surface Properties of Hydroxyl Groups in the Air‐Formed Oxide Film on Titanium

The nature of surface hydroxyls present in the native air‐formed oxide film on titanium has been studied by X‐ray photoelectron spectroscopy (XPS), variable angle XPS, and secondary ion mass spectroscopy (SIMS). The surface isoelectric point of the oxide film on titanium is 5.0, as determined from XPS measurements; and the concentration of surface hydroxyl groups on oxide‐covered titanium is , as determined by quantitative XPS. © 1999 The Electrochemical Society. All rights reserved.

Oxidation of gold by ultraviolet light and ozone at 25 °C

Gold surfaces have been found to be hydrophilic only after exhaustive preparation and with the ultimate care in sample preparation and treatment. The use of a combination of ultraviolet (UV) light and ozone has been described as a viable method of producing a clean, hydrophilic, gold surface. We have found that gold surfaces, which have been either stored in the laboratory after vacuum deposition or purchased as high purity standards, are oxidized by a combination of UV light and ozone generated from a mercury lamp. The samples were characterized with x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) prior to and after exposure to UV/ozone in a stainless steel box in laboratory air. After the cleaning process gold surfaces were found by XPS to contain less carbon and to be enriched in oxygen. The O 1s on the cleaned surface, which was not present on the untreated surface, consisted of two peaks that are attributed to gold oxide and hydroxyl. The oxide layer was found to be 17±4 Å thick by variable angle XPS depth profiling with an initial stoichiometry of Au2O3. The oxide was found to be stable to extended exposure to UHV and water and ethanol rinses. ISS compositional depth profiles confirmed the oxide layer thickness and that the hydrated surface layer is removed in the initial sputtering of the oxidized gold. Implications of these results related to the mechanism of self-assembly of thiols on gold are discussed.

Surface and blood‐contacting properties of alkylsiloxane monolayers supported on silicone rubber

Self-assembled monolayers of alkylsiloxanes supported on polydimethyl siloxane (PDMS) rubber were used as model systems to study the relation between blood compatibility and surface chemistry. The inner lumen of PDMS tubes was first treated with an oxygen plasma. The resultant oxidized surfaces were postderivatized by reacting them with alkyltrichlorosilanes to form the monolayer films. The chemical properties of the monolayers were controlled by varying the head-group chemical compositions. Surface derivatization was verified using variable-angle X-ray photoelectron spectroscopy (XPS or ESCA). Blood compatibility was evaluated using a canine ex vivo arteriovenous series shunt model. Surfaces grafted with hydrophobic head-groups as -CH3 and -CF3 had significantly lower platelet and fibrinogen deposition than the surfaces composed of hydrophilic groups such as -CO2CH3, -(CH2CH2O)3COCH3, and -(OCH2CH2)3OH.

Comparison of Mo–N and W–N synergism during passivation of stainless steel through x-ray photoelectron spectroscopy and electrochemical analysis

In high nitrogen stainless steels and nitrogen surface-doped Mo-containing alloys, nitrogen has been shown to enhance passivity. The mechanism of this apparent Mo–N synergism appeared to be twofold. First, the formation of stable surface nitrides affects a reduction in active dissolution, and, second, reactions between the surface nitride and the electrolyte lead to an increase in interfacial pH, a condition favorable to the formation of an enhanced bipolar passive film. In this study, we compare and contrast the effect of surface nitriding of a Fe–19Cr–9Ni–2W on passivity to the effects previously reported for analogous systems alloyed with Mo. Electrochemical potentiodynamic polarization in deaerated 0.1 M HCl is used to examine the general effects on corrosion inhibition. Qualitative and quantitative analysis of the surface of each alloy following doping with nitrogen and passivation was conducted with variable angle x-ray photoelectron spectroscopy to provide depth-dependent information on the types and amounts of chemical species present. The synergism between W and N is found to be similar to that of Mo and N in enhancing the bipolar nature of the passive film by increasing the amount of tungstate incorporated into the outer layer of the passive film. The primary differences between the structures of the passive films in the two cases result from the passive nature in acidic media of the trioxide of tungsten as opposed to that of molybdenum.

Evaluation of the effect of surface roughness on thin film thickness measurements using variable angle XPS

The effects of specimen surface roughness of XPS peak intensities can be experimentally observed by using the variable angle X-ray photoelectron spectroscopy (VAXPS) technique. Surface topography can be qualitatively revealed by calculating the film thickness of ultra-thin overlayer/substrate systems over a wide range of take-off angles. Results are presented for two systems, Al 2O 3/Al and SiO 2/Si. Critical angles corresponding to differing levels of surface roughness are defined to ensure accurate quantitative analysis.

Characterization of supported metal oxide particles by variable angle x-ray photoelectron spectroscopy

The preliminary results of a newly developed method to determine the particle size distribution of a solid supported dispersed phase are presented. It is based on a modification of a theoretical model proposed by Kuipers et al. and employed intensity data obtained using variable angle x-ray photoelectron spectroscopy (VAXPS). The heart of the computer program generated is a nonlinear least-squares algorithm based on the Marquardt-Levenberg procedure. The test calculations show that the average particle size diameter of particles in heterogeneous catalysts can be determined with an accuracy of 16%. Comparison of particle size distributions obtained from transmission electron microscopy and VAXPS shows significant differences, which can partly be explained by fundamental differences of the techniques. The method appears to be a promising approach, which we hope to improve in the near future.

The adsorption of lysozymes: A model system

AbstractHen egg white lysozyme was adsorbed onto clean borosilicate glass and n‐pentyl silane‐treated glass surfaces. Both modified (reductively methylated) and native lysozyme were studied. Variable angle X‐ray photoelectron spectroscopy (VA‐XPS) suggested differences in the nature of the adsorbed layer depending on substrate properties, as well as on degree of methylation of the protein. Adsorbed film thickness (as measured in the dehydrated state by XPS) ranged from 14 Å on hydrophilic glass to 25 Å on the hydrophobic surface. Degree of surface coverage ranged from 45% on the hydrophobic to 69% on the hydrophilic surface. The results suggest that lysozyme unfolds to a greater extent and covers more surface on the hydrophilic glass, possibly due to strong electrostatic interactions at the pH 7.4 conditions used in the study. An analysis of the surface structure of native hen lysozyme by molecular graphics has also been performed, suggesting that adsorption on hydrophobic surfaces should occur via the hydrophobic patch opposite the enzyme active site cleft.A comparison with human lysozyme has also been made using total internal reflection fluorescence (TIRF) spectroscopy to measure protein adsorption on model surfaces. The two proteins have significantly different interfacial properties.

Variable angle x-ray photoelectron spectroscopy and ion scattering spectroscopy study of the Ag/SiO2 interface

Thin Ag films of up to one monolayer on high purity fused silica have been investigated using variable angle x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). Silvered samples were prepared using the wet chemical process without reducers or by vacuum evaporation. After sensitization with a tin complex, it was determined from ISS that Sn is a surface species only and covers up to 30% of Si surface sites. Variable angle XPS verified these findings and suggested that the Sn is located above the Si surface plane. After silvering with the wet chemical process so that less than a monolayer of Ag is present on the surface, XPS showed that up to 60% of the surface Si is bound to Ag, while 20% of the surface Si sites remain covered by a Sn complex. ISS verified that Ag is a surface species and that 80% of the surface is covered by Ag and Sn. Variable angle XPS showed that Ag is raised out of the surface plane, and that it probably also resides over the Si. Analysis of one monolayer Ag films formed by vacuum evaporation on SiO2 show similar results. Using XPS peak positions and Auger parameter shifts, evidence was found for Ag–Si bonding. Variable angle ISS gave strong evidence of Ag residing over the Si.