Dual purpose laser ablation-inductively coupled plasma mass spectrometry for pulsed laser deposition and diagnostics of thin film fabrication: Preliminary study

PLD (pulsed laser deposition) is an attractive technique to fabricate thin films with a stoichiometry reflecting that of the target material. Conventional PLD instruments are more or less black boxes in which PLD is performed virtually “blind”, i.e. without having great control on the important PLD parameters. In this preliminary study, for the first time, a 213 nm Nd-YAG commercial laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS) intended for microanalysis work was used for PLD under atmospheric pressure and in and ex situ ICPMS analysis for diagnostics of the thin film fabrication process.A PLD demonstration experiment in a He atmosphere was performed with a Sm_13.8Fe_82.2Ta_4.0 target-Ta-coated silicon wafer substrate (contraption with defined geometry in the laser ablation chamber) to transfer the permanent magnetic properties of the target to the film. Although this paper is not dealing with the magnetic properties of the film, elemental analysis was applied as a means of depicting the PLD process. It was shown that in situ ICPMS monitoring of the ablation plume as a function of the laser fluence, beam diameter and repetition rate may be used to ensure the absence of large particles (normally having a stoichiometry somewhat different from the target). Furthermore, ex situ microanalysis of the deposited particles on the substrate, using the LA-ICPMS as an elemental mapping tool, allowed for the investigation of PLD parameters critical in the fabrication of a thin film with appropriate density, homogeneity and stoichiometry.     

XRF and SIMS/SNMS analyses of Ba<Subscript>x</Subscript>Sr<Subscript>1−x</Subscript>TiO<Subscript>3</Subscript> dielectrics

The development of analytical tools and procedures for process control is a prerequisite for the integration of high permittivity and/or ferroelectric materials in CMOS devices. The thickness and composition of perovskite oxide films were determined by wavelength dispersive X-ray fluorescence analysis (XRF) with special emphasis on the ratio of the group-II elements to the Ti content, and a precision of 0.5% was achieved for a typical film thickness of 20-30 nm. Secondary ion mass spectrometry (SIMS) and sputtered neutrals mass spectrometry (SNMS) was used for depth profiling to determine film homogeneity and elemental interdiffusion at hetero-interfaces. Examples are given for Ba(x)Sr(1-x)TiO(3) and SrTiO(x) thin films which were grown in a prototype MOCVD production tool. No interdiffusion was observed for films grown at 600 degrees C on Pt electrodes in contrast to films grown directly on Si.     

SNMS and XRD investigations of laser deposited YSZ buffer layers

Summary Secondary Neutral Mass Spectrometry (SNMS) and X-Ray Diffraction (XRD) were used to find optimum parameters for the in-situ pulsed laser deposition of ZrO₂/Y₂O₃ (YSZ) buffer layers on silicon (100) substrates. Homogeneous and nearly stoichiometric concentration depth profiles were found by SNMS for the laser deposited YSZ films. A peak of the SiO intensity during profiling of the YSZ/Si interface points to a SiO₂ intermediate layer. An increasing Y-deficit of the YSZ films was found by decreasing the laser energy density at the target. Epitaxial growth of the YSZ thin films was observed at an oxygen partial pressure lower than 10^–3 mbar, a substrate temperature of 600–800°C and a laser energy density at the target of about 8 J/cm².     

Investigation of the surface topography for the characterization of microstructures of amorphous SiNx-coatings

SiN_x-coatings have been deposited by reactive magnetron sputtering. Gas pressure and film thickness have been varied. Scanning electron microsopic views of the cross sections show a columnar structure as well as polycrystalline films varying with deposition parameters. For quantitative comparisons of the film morphology an average column diameter has been used as a characteristic value obtained from TEM images. Similar results have been obtained by scanning tunneling microscope avoiding a large expenditure of preparation. Scanning tunneling microscopy is suitable for investigations of the fractal nature of top surface of thin films and to determine the height function of thin SiN_x-coatings on silicon wafers directly. Computer simulations of sputter processes allow to discuss the evolution of microstructures qualitatively.     

Surface topography effects on glow discharge depth profiling analysis

Glow discharge optical emission spectroscopy (GD‐OES) has been shown to be of immense value in elemental depth profiling of thin or thick films on conductive or non‐conductive substrates. For aluminium, GD‐OES has been employed to examine locations of markers and tracers in anodic films, thereby assisting understanding of transport phenomena. In order to investigate the influence of surface topography on depth profiling analysis, anodic aluminium oxide films of various thicknesses, with incorporated electrolyte species, were produced on superpure aluminium substrates of controlled roughnesses. The distributions of incorporated species in the films were subsequently probed. Surface topography modifications and consequent depth resolution degradation were examined during depth profiling analysis performed by GD‐OES. The results reveal that the sputtering process leads to the roughening or smoothing of the surface topography of the specimen for a ratio of the film thickness to the amplitude of the substrate texture less, or greater, than 1 respectively. As a consequence of the surface topography dependence of the ion bombardment, analysis of thin films over rough surfaces suffers from depth resolution limitations due to sputtering‐induced topography changes, thereby limiting quantification of the resultant spectra. Copyright © 2010 John Wiley & Sons, Ltd.     

X-ray diffraction measurements and depth profiling by secondary neutral mass spectrometry on epitaxially grown high-Tc superconducting thin films

YBa₂Cu₃O_7– thin films were deposited by pulsed laser deposition (PLD) on various substrates with different misfit. X-ray diffraction (XRD) measurements were performed in order to characterize the growth quality of the films and to study the orientation between the films and the substrates. On the used substrates all investigated films are relaxed independently, and epitaxially grown who show a long range ordered two domain structure. The elemental concentration depth profiles of these films detected by secondary neutral mass spectrometry (SNMS) show homogeneous stoichiometric element distributions with slight deviation of the Y content.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

OTS自组装单层膜诱导定向生长SrTiO3功能陶瓷薄膜

采用自组装单层膜技术,以三氯十八烷基硅烷(octadecyl-trichioro-silane,OTS)为模版,在玻璃基片上成功制备了钛酸锶晶态薄膜.改性基板的亲水性测定与金相显微镜测试表明,紫外光照射使基板由疏水转变为亲水,OTS单分子膜对薄膜的沉积具有诱导作用:X射线衍射(XRD)与扫描电镜(SEM)表征显示,制备成功的钛酸锶薄膜结晶良好,样品表面均匀,在垂直基板表面方向上呈花状生长:EDS能谱测试为钛酸锶薄膜的化学组成提供了有力的证据;同时探讨了白组装单层膜和钛酸锶薄膜的形成机理.     

Piranha改性玻璃基板液相沉积制备SrTiO3功能陶瓷薄膜

以Piranha溶液处理玻璃基板,采用液相沉积技术,制备了钛酸锶晶态薄膜。改性基板的亲水性测定与偏光显微镜测试表明,Piranha溶液能够有效改善玻璃基板的亲水性,并且基板表面的硅烷醇对钛酸锶薄膜的沉积具有积极指导作用;X射线衍射(XRD)与扫描电镜(SEM)表征显示,制备成功的钛酸锶薄膜纯度高,结晶良好,样品表面均匀,在垂直基板表面方向上呈纤维花簇状生长。文章同时对基板表面硅烷醇形成过程进行了研究。     

The effect of different gas atmospheres on the structure,morphology and photoluminescence properties of pulsed laser deposited Y3(Al,Ga)5O12:Ce3+ nano thin films

Luminescent properties of Y₃(Al,Ga)₅O₁₂:Ce³⁺ phosphor powder and thin films were obtained. The phosphor powder was used as target material for Pulsed Laser Deposition (PLD) of the thin films in the presence of different background gases. Excitation peaks for the powder were obtained at 439, 349, 225 and 189 nm and emission peaks at 512 and 565 nm. X-ray diffraction indicated that better crystallization took place for films deposited in a 20 mTorr O₂ atmosphere. Atomic force microscope revealed an RMS value of 0.7 nm, 2.5 nm and 4.8 nm for the films deposited in vacuum, O₂ and Ar atmospheres, respectively. The highest PL intensity was observed for films deposited in the O₂ atmosphere. A slight shift in the wavelength of the PL spectra was obtained for the thin films due to a change in the crystal field. The thickness of the films varied from 120 nm to 270 nm with films deposited in vacuum having the thin layer and those in Ar having the thick layer. The stoichiometry of the powder was maintained in the film during the deposition as confirmed by Rutherford backscattering spectroscopy.     

Investigation of the surface topography for the characterization of microstructures of amorphous SiNx-coatings

SiN(x)-coatings have been deposited by reactive magnetron sputtering. Gas pressure and film thickness have been varied. Scanning electron microsopic views of the cross sections show a columnar structure as well as polycrystalline films varying with deposition parameters. For quantitative comparisons of the film morphology an average column diameter has been used as a characteristic value obtained from TEM images. Similar results have been obtained by scanning tunneling microscope avoiding a large expenditure of preparation. Scanning tunneling microscopy is suitable for investigations of the fractal nature of top surface of thin films and to determine the height function of thin SiN(x)-coatings on silicon wafers directly. Computer simulations of sputter processes allow to discuss the evolution of microstructures qualitatively.     

Surface analysis of films and film systems produced by pulsed laser deposition

Ceramic films and film systems (ZrO₂ films, ZrO₂/Ti multilayers, and BN films) are deposited by pulsed laser deposition (PLD) and analyzed using X-ray photoelectron (XPS), Auger electron (AES), and micro-Raman spectroscopies. The electron spectroscopies are used to determine the film stoichiometry, the nature of the bonding, and to specify contaminant species. The micro-Raman spectroscopy gives information on crystal structure, grain size, and mechanical stress within the films. In ZrO₂ films a stoichiometry is achieved with typically 5%, with only weak dependencies on processing variables. The only contaminants are a small amount of water from the ambient gas and a carbonaceous surface layer. Multilayers consisting of alternating ZrO₂ and Ti layers exhibit a TiC contamination within the Ti layers. Depending on the processing variables, BN films may be nearly stoichiometric or may have significant, even dominant contaminations throughout the film from elemental B, B₂O₃, and/or a boron-oxynitride species. The first component is due to the non-stoichiometric material removal from the target (N-depletion) at low laser fluences, as confirmed by XPS measurements on irradiated targets. The second and third arise from H₂O in the ambient, and exhibit a complex dependence on processing variables. Micro-Raman spectra show only amorphous or hexagonalphase BN. Depending on the position on the substrate relative to the laser-induced vapour/plasma plume, there may be a particle deposition or mechanical stress within the films, as evidenced from large shifts (up to 15 cm^–1) of the Raman spectral peaks.     

Optical constants,dispersion energy parameters and dielectric properties of ultra-smooth nanocrystalline BiVO4 thin films prepared by rf-magnetron sputtering

BiVO₄ thin films have been prepared through radio frequency (rf) magnetron sputtering of a pre-fabricated BiVO₄ target on ITO coated glass (ITO-glass) substrate and bare glass substrates. BiVO₄ target material was prepared through solid-state reaction method by heating Bi₂O₃ and V₂O₅ mixture at 800 °C for 8 h. The films were characterized by X-ray diffraction, UV–Vis spectroscopy, LCR meter, field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. BiVO₄ thin films deposited on the ITO-glass substrate are much smoother compared to the thin films prepared on bare glass substrate. The rms surface roughness calculated from the AFM images comes out to be 0.74 nm and 4.2 nm for the films deposited on the ITO-glass substrate and bare glass substrate for the deposition time 150 min respectively. Optical constants and energy dispersion parameters of these extra-smooth BiVO₄ thin films have been investigated in detail. Dielectric properties of the BiVO₄ thin films on ITO-glass substrate were also investigated. The frequency dependence of dielectric constant of the BiVO₄ thin films has been measured in the frequency range from 20 Hz to 2 MHz. It was found that the dielectric constant increased from 145 to 343 at 20 Hz as the film thickness increased from 90 nm to 145 nm (deposition time increased from 60 min to 150 min). It shows higher dielectric constant compared to the literature value of BiVO₄.     

Effect of surface modification on the properties of plasma-polymerized hexamethyldisiloxane thin films

Plasma-polymerized hexamethyldisiloxane (pp-HMDSO) thin films have been deposited in a radiofrequency (RF) remote plasma-enhanced chemical vapor deposition (PECVD) system, on different types of substrates: silicon wafers, glass, quartz crystals, and chemiresistor structure. The as-grown thin films have been post treated in two types of reactive plasmas produced in SF₆ and O₂ gases. The effect of this surface modification on different properties of the as-grown pp-HMDSO thin film (chemical structure, elemental composition, surface morphology, film density and thickness, optical bandgap, and electrical resistivity) has been investigated. It is found that SF₆ plasma and O₂ plasma surface modifications of the as-grown pp-HMDSO thin film induce property changes different from each other. SF₆ plasma converted the as-grown pp-HMDSO film to a more porous material and caused a narrowing of its optical band gap of about 33%, while O₂ plasma induced a lowering of film electrical resistivity of about two orders of magnitude.     

Quantitative Analysis of Thin Aluminium-Oxynitride Films by EPMA

 Thin films of aluminium oxynitride with diverse composition were prepared by dc-magnetron sputtering of aluminium, utilising sputtering power as well as argon, oxygen and nitrogen gas flows to vary the composition. Since film properties depend mainly on the content of incorporated oxygen and nitrogen, a method for quantitative analysis of the main constituents based on electron probe micro analysis with energy dispersive detection was developed. The excellent precision of the quantitative results for aluminium as well as oxygen and nitrogen are shown. Furthermore, a film layer analysis program was applied for the quantification of several films deposited under the same deposition parameters on silicon wafers, from 520 nm down to 40 nm thickness, showing that electron probe micro analysis with energy dispersive detection is a reliable method for quantitative compositional analysis of thin aluminium oxynitride films down to approximately 20 nm thickness. Since this method of analysis provides only bulk information, expected inhomogeneities of the depth distribution of the film components were checked by secondary ion mass spectrometry depth profiles of two thin films and correlated to the EPMA results. The thickness of the films was determined by ellipsometry. Received September 1, 1998     

Photo-Induced Hydrophilicity of TiO<Subscript>2</Subscript> Films Deposited on Stainless Steel via Sol-Gel Technique

The photo-induced hydrophilicity of TiO₂ films deposited on stainless steel substrates and silicon wafers using two different sol-gel routes has been investigated. The results indicate that crystalline titanium oxide films with excellent hydrophilic properties can be obtained on silicon wafer with both routes. XPS and XRD data reveal that films deposited on stainless steel exhibit crystallization features similar to those of films deposited on silicon wafers, and only differ by their oxidation degree owing to a TiO₂ reduction process associated to a diffusion of iron ions during deposition of the acidic sol and/or high temperature post-treatment. Consequently, hydrophilic properties of films deposited on stainless steel are inhibited. The deposition of a SiO_x barrier layer at the film/substrate interface allows preventing such a detrimental substrate influence. A low temperature deposition route of the TiO₂ film associated to the presence of a barrier layer yields best results in preventing iron contamination of the films.     

Analysis of thin films and molecular orientation using cluster SIMS

A study of phenylalanine films of different thicknesses from submonolayer to 55 nm on Si wafers has been made using Bi_n⁺ and C₆₀⁺ cluster primary ions in static SIMS. This shows that the effect of film thickness on ion yield is very similar for all primary ions, with an enhanced molecular yield at approximately 1 monolayer attributed to substrate backscattering. The static SIMS ion yields of phenylalanine at different thicknesses are, in principle, the equivalent of a static SIMS depth profile, without the complication of ion beam damage and roughness resulting from sputtering to the relevant thickness. Analyzing thin films of phenylalanine of different thicknesses allows an interpretation of molecular bonding to, and orientation on, the silicon substrate that is confirmed by XPS. The large crater size for cluster ions has interesting effects on the secondary ion intensities of both the overlayer and the substrate for monolayer and submonolayer quantities. This study expands the capability of SIMS for identification of the chemical structure of molecules at surfaces. © Crown copyright 2010.     

Ion-beam analysis of CuInSe<Subscript>2</Subscript> solar cells deposited on polyimide foil

CuInSe₂ (CIS) solar cells deposited on polyimide foil by the Solarion company in a web-coater-based process using sputter and evaporation techniques were investigated in the ion beam laboratory LIPSION of the University of Leipzig by means of Rutherford backscattering spectrometry (RBS) and particle-induced X-ray emission (PIXE) using high-energy broad ion beams and microbeams. From these measurements the composition of the absorber and the lateral homogeneity and film thicknesses of the individual layers could be determined on the basis of some reasonable assumptions. For the first time, quantitative depth profiling of the individual elements was performed by microPIXE measurements on a beveled section prepared by ion-beam etching of a CIS solar cell. Within the CIS absorber layer no significant concentration–depth gradients were found for Cu, In, and Se, in contrast with results from secondary neutral mass spectrometry (SNMS) depth profiling, which was applied to the same samples for comparison. Furthermore, both PIXE and SNMS showed the presence of a remarkable amount of Cd from the CdS buffer layer in the underlying absorber.     

Deposition and characterization of thin boron-carbide coatings

Summary Thin boron-carbide films were deposited using a PACVD process on Si substrates at room temperature. Various mixtures of B₂H₆/He and CH₄, as well as the less hazardous B(CH₃)₃, have been used as process gases. The composition of the deposited films has been correlated with the B₂H₆/He/CH₄ mixture used. When using B(CH₃)₃, the coatings were found to be slightly boron enriched compared to the gas phase stoichiometry. In both cases oxygen contaminants were additionally found (up to 5 at %) in the films. Most of the oxygen was incorporated from the residual gas at the beginning of the deposition. The coatings were hard and showed good adherence to the substrate; no film peel-off was observed after exposure to air. The films have been characterized, in-situ, by electron spectroscopy (XPS, UPS, AES), and by other methods (AES depth profiling, SEM, -step).     

Depth profile analysis of thin film solar cells using SNMS and SIMS

SNMS (sputtered neutrals mass spectrometry) and SIMS (secondary ion mass spectrometry) are used for the depth profile analysis of thin film solar cells based on amorphous silicon. In order to enhance depth resolution, model systems are analyzed only representing parts of the layered system. Results concerning the TCO (transparent conducting oxide)/p interface and the n/i interface are presented. To minimize matrix effects, SNMS is used when the sample consists of layers with different matrices. Examples are the TCO/p interface (where the transition lengths of the depth profiles are found to be sharper when ZnO is used as TCO compared to SnO₂) and SnO₂/ZnO interfaces in coated TCO layers (where a Sn contamination inside the ZnO layer is found depending on the plasma pressure during the ZnO deposition). SIMS is used when the limits of detection reached by SNMS are not sufficient. Examples are H depth profiles in ZnO layers or P depth profiles near the n/i-interface.     

Spectroscopic investigation of the technique of plasma assisted pulsed laser deposition of titanium dioxide

The characterization of plasma assisted pulsed laser deposition (PA-PLD) of titanium dioxide with biased substrate is discussed. Both the stage of plasma expansion and deposition have been studied. Optical emission spectroscopy was employed to estimate laser-induced plasma parameters, while different techniques [optical microscopy, scanning electron microscopy (SEM), spectrophotometry, X-ray photoelectron spectrometry (XPS)] were used to characterize the film properties. It is shown that PA-PLD prevents contamination of the deposited films by particles ejected during the interaction of the KrF excimer laser radiation with the titanium dioxide targets. Investigation made on the film deposited by conventional PLD and PA-PLD, has shown that the PA-PLD technique allows to improve the quality of the deposited films for what concerns their stoichiometry, morphology and deposition rate.