Surface and interface analysis of titanium nitride diffusion barriers

Titanium nitride films were produced on silicon substrate by ion beam assisted deposition in the alternate mode: first, thin titanium layers were deposited by electron beam evaporation and then titanium nitride was formed by nitrogen implantation at room temperature; this cycle was then iterated many times in order to obtain thicker titanium nitride layers. The obtained films were characterized with respect to atomic composition by Rutherford backscattering spectrometry and nuclear reaction analysis techniques, while chemical bonding was investigated by Auger line-shape analysis. We observe that nitrogen implantation, along with the production of titanium nitride, induces silicon migration into the film. Silicon transport is connected to point defects produced by ion implantation as well as by chemical driving forces associated with silicides formation.     

Study of the first nucleation steps of thin films by XPS inelastic peak shape analysis

The initial steps in the formation of thin films have been investigated by analysis of the peak shape (both inelastic background and elastic contributions) of X‐ray photoelectron spectra. Surface coverage and averaged height of the deposited particles have been estimated for several overlayers (nanometre range) after successive deposition cycles. This study has permitted the assessment of the type of nucleation and growth mechanisms of the films. The experiments have been carried out in situ in the preparation chamber of an XPS spectrometer. To check the performance of the method, several materials (i.e. cerium oxide, vanadium oxide and cadmium sulfide) have been deposited on different substrates using a variety of preparation procedures (i.e. thermal evaporation, ion beam assisted deposition and plasma enhanced chemical vapour deposition). It is shown that the first deposited nuclei of the films are usually formed by three‐dimensional particles whose heights and degree of surface coverage depend on the chemical characteristics of the growing thin film and substrate materials, as well as the deposition procedure. It is concluded that XPS peak shape analysis can be satisfactorily used as a general method to characterize morphologically the first nanometric moieties that nucleate a thin film. Copyright © 2006 John Wiley & Sons, Ltd.     

Novel alignment mechanism of liquid crystal on a hydrogenated amorphous silicon oxide

The mechanism of liquid crystal (LC) alignment has been investigated during the last few decades for inorganic materials as well as for organic materials; however, it has not been clearly confirmed for some alignment materials. Inorganic alignment materials such as amorphous silicon oxide (a-SiOx) and hydrogenated amorphous silicon oxide (a-SiOx:H) are deposited on indium tin oxide (ITO) films on glass by reactive sputtering deposition. After deposition, the inorganic alignment materials are irradiated using an Ar+ ion beam (IB) for LC alignment. On the basis of the experimental results, a-SiOx films deposited by the sputtering do not align the LC, but a-SiOx:H films treated with varying IB energies, IB incident angles, IB doses, and IB irradiation times have excellent alignment properties and electrooptical properties, identical to those of polyimide (PI). These results imply that inorganic alignment layers irradiated by IB can be adopted as an LC alignment layer instead of rubbed PI. Additionally, hydrogen plays an important role in LC alignment because of the difference in alignment properties between a-SiOx films and a-SiOx:H films. We investigate the mechanism of IB-treated inorganic alignment layers and suggest that LCs are aligned by chemical effects, such as van der Waals interaction, more than by physical effects, such as morphology effects, in the inorganic alignment layer irradiated by IB.     

Effect of the cadmium ion source on the structural and optical properties of chemical bath deposited CdS thin films

The chemical bath deposition (CBD) technique has been successfully used to deposit cadmium sulphide from cadmium chloride and cadmium acetate as the cadmium ion source and thiourea as the sulphur source on both glass microscope slide and indium tin oxide coated glass substrates. Various properties of the films such as surface morphology, crystallinity, optical properties and resistivitiy have been investigated. XRD patterns reveal that the CdS films deposited from cadmium chloride have an hexagonal structure. Their preferential orientation changes from (002) to (100) with the thermal annealing. Films deposited from cadmium acetate are amorphous but improve their crystallinity with annealing. SEM analysis shows that the grains of the as deposited films are randomly shaped and appear to be bigger in the case of the CdS prepared from cadmium chloride. The optical transmission of the layers are in the 70–80 % range for wavelength above the band gap absorption which makes them more appropriate as window material in heterojunction solar cells.     

Chemical Vapor Deposition of FeOCl Nanosheet Arrays and Their Conversion to Porous α‐Fe2O3 Photoanodes for Photoelectrochemical Water Splitting

FeOCl nanosheet arrays were deposited on fluorine‐doped tin oxide glass substrates through a chemical vapor deposition method and further converted to hematite porous nanosheet arrays. A much enhanced photocurrent was obtained for such hematite films, which was three times higher than that of a planar hematite film at 1.23 V versus a reversible hydrogen reference electrode.     

Elemental distribution in fluorinated amorphous carbon thin films

Focused ion beam-secondary ion mass spectrometry (FIB-SIMS) with 20 nm spatial resolution has been used to analyze amorphous fluorinated carbon thin films, deposited by plasma assisted chemical vapor deposition (PACVD), at micro- to nano-scale. Mass spectra and ion imaging of film surface were acquired and the presence and distribution of contaminants were investigated. Surface images show the secondary ion distribution for F(-), CH(-), CF(-). A change in size and topology of fluorine-rich areas is correlated with film hardness and with microstructure transition from diamond-like to polymer-like, as indicated by infrared and Raman spectroscopies. Based on the surface distributions of CF(-) and CH(-) and on the vibrational spectroscopy results, a mechanism of fluorine substitution for hydrogen and an attempt to explain the film structure and microstructure is proposed.     

Study of Thin Polymeric Film Deposited by the PECVD Process for use at 193 nm

A plasma enhanced chemical vapor deposition (PECVD) reactor was used to deposit thin polymeric films with high absorption at 193 nm. The reactor is suitable to deposit uniform and pinhole free thin polymeric films with conformality over 95%. Conformal films with thickness as low as 200 Å have been deposited on silicon, glass, and quartz substrates, as well as silicon oxide, silicon nitrate, and aluminum films. Deposited films had variations in thickness of 3 to 5% over an area of 8 inches in diameter. Thin films deposited on silicon substrates under varying levels of RF power were scanned using the AFM technique. The measurements show increasing surface roughness of the scanned samples as the RF power increases.     

The influence of electrode metals and its configuration on the response of tin oxide thin film CO sensor

Thin films of tin oxide were deposited by electron beam evaporation. The effects of the electrode materials (Ag, Al, Au and Pt) and different electrode configurations on the CO-sensing of tin oxide thin films were investigated. The Pt and Au electrodes with bottom electrode configuration show much higher response than Ag and Al electrodes. The sensor response and recovery times have also been measured. The films were characterized using X-ray diffraction and X-ray photoelectron spectroscopy. All the films were found to be amorphous. It was found that the CO-sensing properties depend both on the electrode materials and configuration.     

Characterization and electrochemical deposition of natural melanin thin films

Melanin is an important class of biological pigments because of its distinct chemical and physical properties. The electrochemical deposition of natural melanin thin films was studied using two different techniques; constant potential and cyclic voltammetry along with a deposition time of five hours. The thin films deposited electrochemically on a fluorine-doped tin oxide conductive glass substrate using the constant potential method, exhibited faster growth rate and better adhesion to the fluorine-doped tin oxide working electrodes than those deposited using the cyclic voltammetry method. The thin films deposited on the fluorine-doped tin oxide conductor glass using the constant potential method were also more homogeneous than those deposited via the cyclic voltammetry technique. The increase of film thickness is related to the increase of electrochemical deposition time. Interestingly, the electrochemical deposition using the constant potential method had the advantage of consuming less electric charge. The physical and chemical structures of the melanin thin films were characterized using ultraviolet–visible absorption spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. The ultraviolet–visible absorption spectra showed the correlation between the variation of deposition rates of melanin and the type of electrochemical technique employed as well as the thickness of the film. The average thickness of the film is 500 nm which absorb 40% of light in both type of films. The atomic force microscopy images illustrated the homogeneous deposition of the melanin molecules on the fluorine-doped tin oxide conductive glass substrate, indicating that the thickness of the thin films can be controlled. We estimated an average grain size of 14.093 Å. The ease of preparing such thin films of organic materials can open new avenues towards the use of soft conductors, in contrast to the complex preparation of industrial semiconductors.     

Thermal crystallization kinetic and electrical properties of partly crystallized amorphous indium oxide thin films sputtering deposited in the presence or the absence of water vapor

Partly crystallized amorphous indium oxide thin films were deposited under water vapor atmosphere by magnetron sputtering. XRD analysis revealed that appropriate water vapor could suppress the film’s crystallinity. In situ thermal crystallization process was monitored by high-temperature XRD. The crystallization data were analyzed using the Kolmogorov–Johnson–Mehl–Avrami equation. The kinetic exponent n is determined to be approx. 1/2 and 3/2 for film deposited in the absence and the presence of water vapor, respectively. The activation energy of crystallization for film deposited under 1 × 10^?5 Torr water vapor pressure was determined to be 30.7 kJ mol^?1, which is higher than 18.9 kJ mol^?1 for film deposited in the absence of water vapor. The increased activation energy caused by the chemically bonded hydrogen and embedded O–H bonds from the water vapor resulted in the suppression of crystallization. Introduction of appropriate water vapor during the deposition decreased the resistivity because of the increase of Hall mobility. The resistivity of the films after annealing increased due to the evaporation of water vapor resulted in crystal defects.     

Growth mechanism of textured MgO thin films via SSCVD

Magnesium oxide thin films have been deposited with use of single source chemical vapor deposition (SSCVD). The resultant films were examined by using transmission electron microscopy, X-ray texture analysis, and pole figure analysis. Due to the nature of the chemical reactions occurring at the surface during SSCVD growth, which result in a high growth rate/low flux environment, films of (111) orientation have been achieved without an amorphous underlayer, an unusual result for films of this orientation. Moreover the films have a strong degree of biaxial texturing in the x-y plane as found with X-ray texture analysis. These findings have important implications for buffer layers in perovskite thin film devices. The mechanism producing these structures has been revealed by using TEM and is discussed here.     

CO-sensing properties of undoped and doped tin oxide thin films prepared by electron beam evaporation

Undoped thin films of tin oxide and those doped with indium oxide and nickel oxides were deposited by electron beam evaporation. The effects of the film thickness and preparation conditions (films prepared with or without the presence of oxygen environment during deposition) on the optical and carbon monoxide sensing properties of the films were studied. The films were characterized using X-ray diffraction and X-ray photoelectron spectroscopy and optical spectroscopy techniques. All the films were found to be amorphous. It was found that the sensitivity of the films to CO increased with the thickness and the porosity of the films. It was found that their selectivity to CO gas relative to CO₂ and SO₂ gases could be improved upon doping the films with indium (or nickel) oxide.     

Formation of intra-island grain boundaries in pentacene monolayers

To assess the formation of intra-island grain boundaries during the early stages of pentacene film growth, we studied sub-monolayers of pentacene on pristine silicon oxide and silicon oxide with high pinning centre density (induced by UV/O(3) treatment). We investigated the influence of the kinetic energy of the impinging molecules on the sub-monolayer growth by comparing organic molecular beam deposition (OMBD) and supersonic molecular beam deposition (SuMBD). For pentacene films fabricated by OMBD, higher pentacene island-density and higher polycrystalline island density were observed on UV/O(3)-treated silicon oxide as compared to pristine silicon oxide. Pentacene films deposited by SuMBD exhibited about one order of magnitude lower island- and polycrystalline island densities compared to OMBD, on both types of substrates. Our results suggest that polycrystalline growth of single islands on amorphous silicon oxide is facilitated by structural/chemical surface pinning centres, which act as nucleation centres for multiple grain formation in a single island. Furthermore, the overall lower intra-island grain boundary density in pentacene films fabricated by SuMBD reduces the number of charge carrier trapping sites specific to grain boundaries and should thus help achieving higher charge carrier mobilities, which are advantageous for their use in organic thin-film transistors.     

ALD resist formed by vapor-deposited self-assembled monolayers

A new process of applying molecular resists to block HfO2 and Pt atomic layer deposition has been investigated. Monolayer films are formed from octadecyltrichlorosilane (ODTS) or tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and water vapor on native silicon oxide surfaces and from 1-octadecene on hydrogen-passivated silicon surfaces through a low-pressure chemical vapor deposition process. X-ray photoelectron spectroscopy data indicates that surfaces blocked by these monolayer resists can prevent atomic layer deposition of both HfO2 and Pt successfully. Time-dependent studies show that the ODTS monolayers continue to improve in blocking ability for as long as 48 h of formation time, and infrared spectroscopy measurements confirm an evolution of packing order over these time scales.     

单晶硅上化学气相沉积铜薄膜的机理研究

A versatile metal-organic chemical vapor deposition (MOCVD) system was designed and constructed. Copper films were deposited on silicon (100) substrates by chemical vapor deposition (CVD) using Cu(hfac)2 as a precursor. The growth of Cu nucleus on silicon substrates by H2 reduction of Cu(hfac)2 was studied by atomic force microscopy and scanning electron microscopy. The growth mode of Cu nucleus is initially Volmer-Weber mode (island), and then transforms to Stranski-Rastanov mode (layer-by-layer plus island).The mechanism of Cu nucleation on silicon (100) substrates was further investigated by X-ray photoelectron spectroscopy. From Cu2p, O1s, F1s, Si2p patterns, the observed C=O, OH and CF3/CF2 should belong to Cu(hfac) formed by the thermal dissociation of Cu(hfac)2. H2 reacts with hfac on the surface, producing OH. With its accumulation, OH reacts with hfac, forming HO-hfac, and desorbs, meanwhile, the copper oxide is reduced, and thus the redox reaction between Cu(hafc)2 and H2 occurs.     

Highly conducting and transparent sprayed indium tin oxide

Spray pyrolysis process has been used to deposit highly transparent and conducting films of tin doped indium oxide onto glass substrates. The electrical, optical and structural properties have been investigated as a function of various deposition parameters namely dopant concentrations, temperature and nature of substrates. X-ray diffraction patterns have shown that deposited films are polycrystalline without second phases and have preferred orientation [400]. Indium tin oxide layers with small resistivity value around 7.10⁻⁵Ω.cm and transmission coefficient in the visible and near IR range of about 85–90 % have been easily obtained.     

Chemical Solution Deposition of Epitaxial Metal‐Oxide Nanocomposite Thin Films

Epitaixial metal‐oxide nanocomposite films, which possess interesting multifunctionality, have found applications in a wide range of devices. However, such films are typically produced by using high‐vacuum equipment, like pulse‐laser deposition, molecular‐beam epitaxy, and chemical vapor deposition. As an alternative approach, chemical solution methods are not only cost‐effective but also offer several advantages, including large surface coating, good control over stoichiometry, and the possible use of dopants. Therefore, in this Personal Account, we review the chemistry behind several of the main solution‐based approaches, that is, sol‐gel techniques, metal‐organic decomposition, chelation, polymer‐assisted deposition, and hydrothermal methods, including the seminal works that have been reported so far, to demonstrate the advantages and disadvantages of these different routes.     

Rapid growth and flow-mediated nucleation of millimeter-scale aligned carbon nanotube structures from a thin-film catalyst

We discuss the rapid growth of films and lithographically templated microstructures of vertically aligned small-diameter multiwalled carbon nanotubes (VA-MWNTs), by atmospheric-pressure thermal chemical vapor deposition (CVD) of C2H4/H2/Ar on a Fe/Al2O3 catalyst film deposited by electron beam evaporation. The structures grow to 1 mm height in 15 min and reach close to 2 mm in 60 min. The growth rate and final height of CNT microstructures grown from catalyst patterns depend strongly on the local areal density of catalyst, representing a reverse analogue of loading effects which occur in plasma etching processes. Abrupt transitions between areas of micrometer-thick tangled CNT films and millimeter-scale aligned CNT structures are manipulated by changing the duration of pretreatment by H2/Ar prior to introduction of C2H4 and by changing the configuration of the substrate sample in the furnace tube. This demonstrates that the flow profile over the sample mediates the supply of reactants to the catalyst and that pretreatment using H2 significantly affects the initial activity of the catalyst.     

The mechanism of formation and some properties of thin fluorocarbon films deposited onto silicon plates by electron-beam polymerization of hexafluoropropylene from the vapor phase

The results of studying thin fluorocarbon films deposited onto single-crystal silicon plates through electron beam polymerization of hexafluoropropylene from the vapor phase are presented. The films are deposited under the action of an electron beam with an energy of 40 keV at a monomer vapor pressure of 5- 20 hPa. It is shown that plastic solid films consisting of a low-molecular-mass polymer with low thermal stability are formed at a beam current density on the order of 20 μA/cm², while at current densities on the order of 150 μA/cm², rigid brittle films of three-dimensional crossl inked polymer are formed with a thermal stability of about 350°C. It is assumed that the films are formed via chain polymerization, which at high current densities, is accompanied by polyrecombination processes leading to efficient chain crosslinking. It is found that polymer clusters are ordered in the course of film formation.     

Chemical Vapor Deposition of SnO2 Thin Films from Bis(β‐diketonato)tin Complexes

A series of bis(β‐diketonato)tin compounds have been systematically synthesized and examined as precursors for chemical vapor deposition of SnO₂ thin films. These complexes were characterized by elemental analyses and NMR, IR and mass spectroscopic methods. X‐ray single‐crystal determination of Sn(tfac)₂ reveals that the complex possesses a distorted trigonal bipyramidal structure. The SnO₂ films can be deposited on the substrates such as silicon, titanium nitride, and glass by using Sn(hfac)₂, Sn(tfac)₂ and Sn(acac)₂ as CVD precursors at deposition temperatures of 300‐600°C with a carrier gas of O₂. The deposition rates range from 20 to 600 Å/min. Deposited films have been characterized by XRD, SEM, AFM, AES and AAS analyses.