EPMA‐Analyse dünner PVD‐ und CVD‐Schichten

EPMA analysis of thin PVD and CVD layers Electron Probe Micro Analysis (EPMA) is an X‐ray spectroscopic method for determining the chemical composition of solid substances in the near‐surface region. It has a high detection sensitivity, a high spatial resolution, an adjustable depth of analysis and is easy and accurate to quantify. Less well known is the fact that the EPMA is also able to analyze the chemical composition and layer thicknesses of thin multi‐layer systems non‐destructively and with only one single measurement. In particular, it is possible to determine, for example, the composition and thickness of a layer buried under one or more other layers. Conversely, with a known film thickness, the density of thin layers can be determined, a quantity that is generally difficult to access with thin layers. The following article describes the physical basics of EPMA analysis and compares them with energy dispersive X‐ray spectroscopy (EDX) and X‐ray fluorescence analysis (XRF), which are also widely used. The principle of so‐called thin film analysis for multilayer systems is explained, and the possibilities and limitations of this method are illustrated by a number of industrial application examples.     

BN薄膜的制备及BPXN1-X薄膜的紫外光敏特性

采用热丝和射频等离子体辅助化学气相沉积方法(HF-PECVD),以单晶硅为衬底在低温(< 500℃)条件下沉积氮化硼(BN)薄膜材料.通过傅立叶变换红外光谱(FTIR)、 X射线衍射(XRD)及扫描电镜(SEM)对薄膜样品的组成和结构进行了分析,探讨了温度和等离子体对沉积BN薄膜的影响.此外,用紫外-可见光分光光度计(UV)测试了石英衬底上生长磷掺杂氮化硼(BPXN1-X)薄膜样品的紫外吸收特征,分析了磷掺杂对 BN光学能隙的调节作用以及 BPXN1-X薄膜在紫外空间探测领域的应用前景.结果表明,以单晶硅和光学石英玻璃为衬底在低温条件下用 HF-PECVD方法可以沉积较高质量的 BN薄膜,BN的光学能隙宽度通过磷的掺杂可以得到连续调节,在紫外空间光探测领域具有很大的应用潜力.     

STO/BTO Modulated Superlattice Multilayer Structures with Atomically Sharp Interfaces

A comparative study is carried out investigating the microstructure and the electrical properties of Ba_xSr_1‐xTiO₃ films with x = (0.25, 0.5, 0.75) deposited as modulated superlattice (SL) multilayer structures by laser ablation on both LaAlO₃ and MgO substrates. The SL structures are examined using high‐resolution transmission electron microscopy and scanning transmission electron microscopy . Their interfaces and chemical composition are investigated using energy dispersive X‐ray spectroscopy, complemented with electron energy loss spectra analysis performed to give insight to the local chemistry, structure and bonding. It is found that all modulated SL samples consisted of continuous well defined 1 nm SrTiO₃ and 4 nm BaTiO₃ layers. When modulated SL multilayered structures are compared with their single target deposited equivalents, they exhibit similar electrical properties (e.g. dielectric constant and dielectric loss) but undergo phase transition in a broader temperature region. A very important observation is that the oxygen K‐edges in SrTiO₃ and BaTiO₃ layers are distinctive. Therefore it can be used as finger‐print signature for analysis of ultra‐thin SrTiO₃/BaTiO₃ layers and their interfaces. Finally it is demonstrated that by varying the modulation period it is possible to develop structures with engineered ferroelectric properties and improved thermal stability.     

Mikrostrukturelle und röntgenographische Analysen an einem plasmanitrierten Schnellarbeitsstahl

Microstructural analysis of a plasmanitrided tool steel by means of metallography and X‐ray diffraction Nitriding leads to improved tribological and corrosive properties of iron alloy components. In order to study the effect of plasma nitriding parameters on the structure of compound layer and diffusion zone, a systematic variation of process parameters, temperature and process gas atmosphere has been carried out. Metallographic inspection, X‐ray diffraction and Glow Discharge Optical Spectroscopy analysis (GDOES) were used in this investigation. The results clarified that depending on the amount of nitrogen in the gas atmosphere nitrided layers with and without compound layer can be generated in the surface of M2 tool steel for temperatures from 350°C to 500°C. For plasma nitriding in 5 vol.% Nitrogen and 95 vol.% Hydrogen no compact compound layer was formed. The gas mixture of 76 vol.% Nitrogen resulted in compound layer formation for all temperatures from 350°C to 500°C. X‐ray phase analysis indicated an almost 100% ε‐(carbo)nitride phase but the existence of the γ′‐(carbo)nitride could not be excluded completely from the X‐ray phase diagrams. After corrections to account for the nitrogen gradient, high compressive surface residual stresses have been measured in the diffusion zone. They increased with temperature. After a qualitative correction for chemical composition gradients high tensile residual stresses were found probably existing in the ε‐(carbo)nitride phase for the investigated plasma nitrided tool steel samples.     

Untersuchung von Grenzflächen in Chalkopyrit‐Dünnschichtsolarzellen

Examination of interfaces in chalcopyrite thin film solar cells using synchrotron radiation Two examples from current research at the division of solar energy research of the Helmholtz‐Zentrum Berlin für Materialien und Energie (HZB) are described, showing the use of synchrotron radiation for the analysis of interface reactions in chalcopyrite thin film solar cells. Deeper knowledge of interface reactions leads to better understanding of the functionality of these solar cells and thus to possibilities to further improve them in terms of efficiency and stability. We show how x‐ray emission spectroscopy can elucidate the oxidation of sulfide at the interface between chalcopyrite solar cell absorbers and zinc oxide window layers. In a second example we demonstrate how high energy photo electron spectroscopy can be used to follow in‐situ the diffusion of copper ions from a chalcopyrite absorber into an indium sulfide buffer layer.     

Nanoscale Probing of a Polymer‐Blend Thin Film with Tip‐Enhanced Raman Spectroscopy

Fundamental advances have been made in the spatially resolved chemical analysis of polymer thin films. Tip‐enhanced Raman spectroscopy (TERS) is used to investigate the surface composition of a mixed polyisoprene (PI) and polystyrene (PS) thin film. High‐quality TER spectra are collected from these nonresonant Raman‐active polymers. A wealth of structural information is obtained, some of which cannot be acquired with conventional analytical techniques. PI and PS are identified at the surface and subsurface, respectively. Differences in the band intensities suggest strongly that the polymer layers are not uniformly thick, and that nanopores are present under the film surface. The continuous PS subsurface layer and subsurface nanopores have hitherto not been identified. These data are obtained with nanometer spatial resolution. Confocal far‐field Raman spectroscopy and X‐ray photoelectron spectroscopy are employed to corroborate some of the results. With routine production of highly enhancing TERS tips expected in the near future, it is predicted that TERS will be of great use for the rigorous chemical analysis of polymer and other composite systems with nanometer spatial resolution.     

Untersuchung dünner Schichten mittels Röntgenreflektometrie

Thin film characterization by means of X‐ray reflectometry X‐ray reflectometry and diffractometry are widely used non‐destructive methods to characterize thin films in the total thickness range which is typically between 2nm and approximately 500nm. On special arrangements a resolution up to 1000nm layer thickness has been demonstrated. Layer stack morphology, surface topography, layer structure, material density, single layer or period thickness and surface and interface roughness are the typical structural parameters both of single layers and of multilayers which can be described by the measured data. The performance of the measurement setup is mainly influenced by the parameters of the incident X‐ray beam like beam divergence, monochromatism and photon energy. In the following the influence of the optical components in the beam path to angle and energy resolution of X‐ray reflectometry is discussed.     

Fabrication of x-ray zone plates by surface-plasma chemical vapor deposition

A new cost-efficient sputter-slice technology for hard x-ray (10-30 keV) Fresnel zone plates fabrication, imposing no limitation to aspect ratio, is proposed. By means of a plasma chemical process, SiO(2)/Si(1-x)Ge(x)O(2) glassy film multilayer structures are deposited on a lateral surface of a silica rod, outermost layers being as thin as 100 nm. It has been shown by numerical simulation that for x=0.2 germanium fraction, 100-300 microm zone plate thickness and the number of zones of about 1000, first order diffraction efficiency as high as 20%-30% at the energy of approximately 20 keV can be achieved.     

Elektrospray‐Ionisation (ESI)

EElectrospray‐ionization (ESI) – pinhole‐free electrophoretic deposition of ultra thin polymer layers Electrospray ionization (ESI) of polymer solutions is used in mass spectroscopy to analyze the molar mass of macromolecules. The singularized polymer molecules are transferred into the mass spectrometer after separating through a special mechanism under high voltage and normal pressure conditions. This process can be adapted for plane deposition of single polymer molecules. Structure, composition and molar mass distribution of polymers are retained. Layers of polar or ionic polymers can be deposited in a thickness of monolayers up to hundreds of nanometers. It is interesting to mention that the ESI‐process belongs to the electrophoretic techniques. Therefore, deposition of pinhole‐free layers on electrical conductive substrates is not only possible on the nozzle facing side of the substrate but although on the back side. This behavior was used to enwrap closely packed carbon fiber bundles with adhesive polymer layers.     

Strong Improvement of Long‐Term Chemical and Thermal Stability of Plasmonic Silver Nanoantennas and Films

Silver (Ag) nanostructures and thin films are advantageous plasmonic materials as they have significantly lower losses than gold (Au). Unfortunately, Ag nanostructures suffer from poor chemical and thermal stability, which limit their applications. Here, the mechanisms leading to the deterioration of Ag nanostructures are clarified. It is first shown that oxygen alone cannot oxidize Ag nanostructures. Then, experiments using X‐ray photoelectron spectroscopy reveal that the amount of sulfur in ambient air is too low for efficient tarnishing of the Ag surface. Finally, water is found to be the most critical factor for the degradation of Ag nanostructures and thin films. At high relative humidity, adsorbed water forms a thin film enabling the migration of Ag ions at the Ag/air interface, which deteriorates the Ag nanostructures. A dehydration treatment is developed which alters the morphology of the deposited silver, leading to an improved chemical and thermal stability of the Ag nanostructures and films, which then remain stable for more than 14 weeks under ambient laboratory conditions. In addition, dehydration also improves significantly the root‐mean‐square roughness for Ag thin films deposited on a glass substrate.     

Charakterisierung von Plasmapolymeren mittels Thermolumineszenzmessungen

Characterization of Plasmapolymers by Thermoluminescence Thin plasma polymer films were deposited using the pulsed plasma (pp) mode. These plasma polymers should possess a more chemically regular structure because of the lower monomer fragmentation during the short plasma pulses and the chemical chain propagation during the plasma‐less periods than those produced by the conventional continuous‐wave (cw) mode. In addition to the use of the classic thin film characterization method XPS the method of thermoluminescence was applied to characterize defects and structural specifics in the polymer films produced by pp or cw‐plasma mode. The thermoluminescence method was applied to functional groups‐carrying plasma polymer layers, which are used in medical technology for forming biocompatible and bioactive coatings or in metal‐polymer composites as adhesion‐promoting interlayers.     

Nanoscale characterization of the dielectric charging phenomenon in PECVD silicon nitride thin films with various interfacial structures based on Kelvin probe force microscopy

This work presents a novel characterization methodology for the dielectric charging phenomenon in electrostatically driven MEMS devices using Kelvin probe force microscopy (KPFM). It has been used to study plasma-enhanced chemical vapor deposition (PECVD) silicon nitride thin films in view of application in electrostatic capacitive RF MEMS switches. The proposed technique takes the advantage of the atomic force microscope (AFM) tip to simulate charge injection through asperities, and then the induced surface potential is measured. The impact of bias amplitude, bias polarity, and bias duration employed during charge injection has been explored. The influence of various parameters on the charging/discharging processes has been investigated: dielectric film thickness, SiN(x) material deposition conditions, and under layers. Fourier transform infrared spectroscopy (FT-IR) and x-ray photoelectron spectroscopy (XPS) material characterization techniques have been used to determine the chemical bonds and compositions, respectively, of the SiN(x) films being investigated. The required samples for this technique consist only of thin dielectric films deposited over planar substrates, and no photolithography steps are required. Therefore, the proposed methodology provides a low cost and quite fast solution compared to other available characterization techniques of actual MEMS switches. Finally, the comparison between the KPFM results and the discharge current transients (DCT) measurements shows a quite good agreement.     

Transparente und leitfähige Veredelung von Kunststoffoberflächen

Deposition Techniques for Transparent Conducting Thin‐Films on Glass and Polymer Substrates We report on thin films deposited at atmospheric pressures on glass and polymer substrates with various techniques. The introduced thin‐film materials show intrinsic properties being suitable for different applications while maintaining the principle properties of the substrates themselves (e. g. shape. rigidity/flexibility, transparency). With the main focus on optical and electronic applications the properties of the deposited films can be adjusted by the choice of coating material (e. g. metal oxide, CNT), the film's shape (compact, particulate) and the deposition process itself. We compare deposition and properties of different TCO‐materials with CNT‐based thin film techniques and demonstrate approaches for the integration of these processes in production lines.     

Herstellung von Präzisionsschichten mittels Ionenstrahlsputtern

Precise thin film synthesis by ion beam sputter deposition Ion beam sputter deposition (IBSD) is a promising technique for the fabrication of high performance thin films because of the well defined and adjustable particle energies, which are rather high in comparison to other PVD techniques. Recent developments concerning long‐term stability and lateral uniformity of the ion beam sources strengthen the position of the IBSD technique in the field of precise thin film synthesis. Furthermore, IBSD offers a more independent choice of relevant deposition parameters like particle energy and flux, process gas pressure and deposition rate. In this paper we present our currently installed large area IBSD facility “IonSys 1600”, which was developed by Fraunhofer IWS Dresden and Roth & Rau company (Hohenstein‐Ernstthal). Substrate sizes of up to 200 mm (circular) or up to 500 mm length (rectangular) can be coated and multilayer stacks with up to six different materials are possible. Tailored 1‐ or 2‐dimensional film thickness distributions with deviations of < 0.1 % can be fabricated by a relative linear motion of the substrate holder above an aperture. In order to demonstrate the advantages of the IBSD technique especially for sophisticated materials and films with high requirements concerning purity, chemical composition or growth structure, several examples of deposited multilayers for various applications are presented.     

Field electron emission from hydrogen plasma treated nano-ZnO thin films

A nano-Zno films are deposited on the Mo film/ceramic substrates by using the electron beam vapor deposition technique. Then a hydrogen plasma treated method is used to improve the characteristics of ZnO thin films by microwave plasma chemical vapor deposition system. Effects of process parameters on morphologies and structures of the ZnO thin films are detected and analysed by field emission scanning electron microscopy, X-ray diffraction spectrum and energy dispersive spectrum. The experimental result indicates that the hydrogen plasma treated techniques can essentially reduce the surface resistance and improve the field emission current density of the nano-ZnO thin films. For the hydrogen plasma treated sample, its field emission current density can increased more than three times at 2.2 V/microm electric field condition.     

Optisch dünne Schichten mit kontrollierten Eigenschaften durch plasmaunterstütztes Magnetronsputtern

Optical thin films with controlled properties by plasma enhanced magnetron puttering A new reactive magnetron sputter process was investigated in which an additional plasma source was implemented to support the magnetron sputter process. The plasma source is determined by high ion current density and moderate ion energy. At the beginning of the work, extensive investigations of the interaction of the magnetron with the plasma source during the deposition process were performed. Also, the plasma parameters in the region of the substrate were determined. A stable process which can be controlled very precicely was obtained with the set‐up used here. In the following, different oxide materials such as zirconia (ZrO₂) and titania (TiO₂) were deposited and investigated. It shows that because of the precise process control, different optical and morphological properties can be directly influenced by tuning the ion‐to neutral fraction of the process.     

A Single‐Chamber System of Initiated Chemical Vapor Deposition and Atomic Layer Deposition for Fabrication of Organic/Inorganic Multilayer Films

A single‐chamber system capable of depositing both organic and inorganic layers by initiated chemical vapor deposition (iCVD) and atomic layer deposition (ALD) is demonstrated to facilitate the fabrication of organic/inorganic hybrid thin film encapsulation (TFE). The chamber geometry and the process conditions of iCVD and ALD are similar to each other, which enabled the design of the single‐chamber system. Both organic and inorganic films deposited via the single‐chamber system produces films with their properties equivalent to those deposited in separate iCVD and ALD reactors. Alternating the deposition mode between iCVD and ALD produces organic/inorganic multilayers with outstanding barrier properties as well as optical transparency mechanical flexibility.     

Plasmachemische Gasphasenabscheidung – eine Technologie zur Deposition organischer und anorganischer Schichten. Plasma Enhanced Chemical Vapor Deposition – a Thin Film Technique for Organic and Inorganic Layers

Plasma enhanced chemical vapor deposition (PECVD) has a wide range of interest for thin films up to some μm thickness. It has widespread applications for high quality dielectric and semiconducting silicon alloys at deposition temperatures below 450 °C and pressures at 1 mbar on plane substrates and attracts growing attention for the surface modification of polymers. The PECVD takes advantages of the possibility to alter the film properties in a wide range easily, and the coatings can achieve a variety of useful properties unobtainable by other coating techniques. An environmentally friendly plasma chemical reactor etch cleaning of SiO_x, SiN_x and other film materials can be applied by changing the process gas and without breaking the vacuum. PECVD can be used in a fixed substrate and continuous substrate flow mode. An capacitively coupled parallel‐plate electrode assembly using radio‐frequency (RF) excitation of the discharge is most widely used for substrate areas up to a few square meters. Among the capacitively excitation an inductively and electromagnetically excitation at frequencies in the RF and UHF range has also succeeded in achieving a high rate PECVD. Two applications are presented to show the characteristics and the potential of this technique, the PECVD of semiconducting hydrogenated amorphous silicon, intrinsic or doped, with low power densities using monosilane as a source gas for solar cells, thin films transistors and digital image sensors and the plasma polymerisation of organosilicon protection layers employing the HMDSO monomer and high power densities for mirrors and lenses.     

Decoupled Control of Carbon Nanotube Forest Density and Diameter by Continuous‐Feed Convective Assembly of Catalyst Particles

The widespread potential application of vertically aligned carbon nanotube (CNT) forests have stimulated recent work on large‐area chemical vapor deposition growth methods, but improved control of the catalyst particles is needed to overcome limitations to the monodispersity and packing density of the CNTs. In particular, traditional thin‐film deposition methods are not ideal due to their vacuum requirements, and due to limitations in particle uniformity and density imposed by the thin‐film dewetting process. Here, a continuous‐feed convective self‐assembly process for manufacturing uniform mono‐ and multi‐layers of catalyst particles for CNT growth is presented. Particles are deposited from a solution of commercially available iron oxide nanoparticles, by pinning the meniscus between a blade edge and the substrate. The substrate is translated at constant velocity under the blade so the meniscus and contact angle remain fixed as the particles are deposited on the substrate. Based on design of the particle solution and tuning of the assembly parameters, a priori control of CNT diameter and packing density is demonstrated. Quantitative relationships are established between the catalyst size and density, and the CNT morphology and density. The roll‐to‐roll compatibility of this method, along with initial results achieved on copper foils, suggest promise for scale‐up of CNT forest manufacturing at commercially relevant throughput.     

Single‐ and Double‐Sided Chemical Functionalization of Bilayer Graphene

An experimental study on the interaction between the top and bottom layer of a chemically functionalized graphene bilayer by mild oxygen plasma is reported. Structural, chemical, and electrical properties are monitored using Raman spectroscopy, transport measurements, conductive atomic force microscopy and X‐ray photoelectron spectroscopy. Single‐ and double‐sided chemical functionalization are found to give very different results: single‐sided modified bilayers show relatively high mobility (200–600 cm² V^?1 s^?1 at room temperature) and a stable structure with a limited amount of defects, even after long plasma treatment (>60 s). This is attributed to preferential modification and limited coverage of the top layer during plasma exposure, while the bottom layer remains almost unperturbed. This could eventually lead to decoupling between top and bottom layers. Double‐sided chemical functionalization leads to a structure containing a high concentration of defects, very similar to graphene oxide. This opens the possibility to use plasma treatment not only for etching and patterning of graphene, but also to make heterostructures (through single‐sided modification of bilayers) for sensors and transistors and new graphene‐derivatives materials (through double‐sided modification).