Magnetron sputter deposition of A-15 and bcc crystal structure tungsten thin films

The effect of processing parameters on the crystal structure and electrical resistivity of magnetron sputter deposited tungsten thin films was investigated. Formation of body centered cubic (bcc) W was favored when the concentration of impurity oxygen atoms in the films was <5 at.% while the formation of A-15 W was favored between 6 and 10 at.% oxygen. A transition from A-15 W films to bcc W films occurred as the oxygen was removed from the deposition chamber by presputtering the target for extended periods of time. The binding energies of the W atoms in A-15 and bcc W films are similar, as is the binding energy of the O atoms in the two different crystal structures, indicating that the oxygen is not present as a tungsten oxide compound. The resistivity of A-15 W films is always higher than the resistivity of bcc W films due to the increased oxygen concentration and small grain size of the A-15 films. However, the sputter deposition pressure is found to have a greater effect on resistivity. This is attributed to the formation of cracks in the film.     

Defect microstructure in single crystal silicon thin films grown at 150° C-305° C by remote plasma-enhanced chemical vapor deposition

Defect microstructure in terms of defect density and impurity concentration of epitaxial Si films grown by low temperature Remote Plasma-enchanced Chemical Vapor Deposition (RPCVD) in the temperature range of 150–305° C has been investigated using Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectroscopy (SIMS), Reflection High Energy Electron Diffraction (RHEED) and defect etching/Nomarski microscopy. Defect density in the epitaxial Si films is found to be a strong function of growth temperature in the temperature range under study, indicating that thermal excitation is an important source of energy, in addition to plasma excitation, for driving surface reactions in the RPCVD expitaxial process. Impurity concentrations of H, O and C in the epitaxial films have been determined by SIMS analysis. The trace amounts (∼1 ppm) of oxygen and water vapor in the reactant gas (2%SiH₄/He) was identified to be an important source of oxygen in the epitaxial Si films. An oxygen concentration as low as 3 × 10¹⁸ cm^-3 in the epitaxial Si film grown at 150° C has been achieved through the use of a gas purifier. The higher hydrogen concentration in the films grown at lower temperatures is believed to be due to insufficiently rapid hydrogen desorption from the surface during growth. The results of characterization using TEM and SIMS are discussed to elucidate the atomistic mechanisms of Si epitaxial growth by RPCVD.     

Spray deposition and characterization of zirconium-oxide thin films

Zirconium oxide films were prepared by the pyrosol process using zirconium acetylacetonate as source material onto clear fused quartz and (100) silicon at substrate temperatures ranging from 300°C to 575°C. X-ray diffraction (XRD) measurements show that samples prepared at substrate temperatures lower than 425°C are amorphous. Films deposited at higher temperatures and short deposition times show a cubic crystalline structure. However, for long deposition times, the samples show monoclinic crystalline structure. A similar phase transformation is observed on samples deposited at short time if they are annealed at high temperature. The cubic and monoclinic phases of the corresponding samples were confirmed by infrared (IR) and Raman spectroscopy, respectively. The ZrO₂ films with cubic phase show an almost stoichiometric chemical composition and refractive index values of the order of 2.1 with an energy band gap of 5.47 eV. The current-density electric-field characteristics of metal-oxide semiconductor (MOS) structures show a small ledge from 2 MV/cm to 4.5 MV/cm, indicating current injection and charge trapping. For higher electric fields, the current is associated with oxygen ion diffusion through the zirconium oxide film. The dielectric breakdown is observed at 6 MV/cm, which is a value higher than those observed in the monoclinic and tetragonal phases.     

LaAlO3单晶基片上制备Ba0．5Sr0．5TiO3薄膜的透射电镜研究

铁电钛酸锶钡(Ba1-xSrx)TiO3(BSTO)薄膜材料具有很好的可调性，在微电子工业有广阔的应用前景。本文采用脉冲激光沉积(PLD)技术在(001)LaAlO3单晶基片上外延生长了Ba0.5Sr0.5TiO3薄膜。利用透射电子显微镜对薄膜的截面样品进行了微结构和界面行为的研究。     

Electrospray deposition and characterization of cobalt oxide thin films

Cobalt oxide thin films were fabricated by means of electrospray deposition. The obtained films were characterized by Raman spectroscopy, X-ray diffraction and Scanning electron microscopy. The solution that was used gave the Co₃O₄ phase at different growth temperatures. The best granular surfaces were obtained at 250 °C as verified by all characterization techniques, while flaky surfaces were obtained at higher temperatures. The surface morphology is mostly granular except for high temperatures where the cobalt oxide is formed as flakes instead of grains.     

Electromigration resistance and long term stability of textured silver thin films on LTCC

Silver (Ag) is regarded as advanced material for metallization purposes in microelectronic devices because of its high conductivity and its enhanced electromigration resistance. Besides the typical use of silicon based substrate materials for device fabrication, thin film metallization on ceramic and glass-ceramic LTCC (low temperature co-fired ceramics) substrates gets more and more into focus as only thin film technology can provide the required lateral resolutions of structures in the μm-range needed for e.g. high frequency applications. Therefore, the reliability of Ag thin films is investigated under accelerated aging conditions, utilizing test structure which consists of 5 parallel lines stressed with current densities up to 1.5 × 10⁷ A cm⁻² at temperatures ranging from room-temperature up to 300 °C. To detect the degradation via the temporal characteristics of the current signal a constant voltage is applied taking the overall resistance of the test structure into account. The mean time to failure of the Ag metallization substantially depends on the degree of (1 1 1)-orientation which, in turn, is strongly affected by the plasma power P_P during deposition. Therefore, Ag thin films deposited at P_P = 1000 W feature a 7 times higher reliability than those deposited at P_P = 100 W. Due to the enhanced stability of grains being (1 1 1)-oriented in textured thin films the material transport predominantly occurs along grain boundaries, whereas in Ag films without a (1 1 1)-orientation volume-related diffusion effects dominate due to the lower stability of these grains.     

Chemical bath deposition of nanocrystalline ZnS thin films: Influence of pH on the reaction solution

Zinc sulfide (ZnS) thin films were deposited onto glass substrates using chemical bath deposition technique (CBD). The deposition were carried out in a bath solution with pH ranged from 9 to 11. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to characterize the films structure and morphology respectively. The amorphous structure of as-deposited films is converted to a nanocrystalline one after a thermal annealing at 550 °C. The deposited ZnS films exhibit a high optical transmission in the UV–visible range (≥80%). They have a direct band gap. Using a solution with pH equal to 10 yields to films with larger optical band gap, smoother surface and lower electrical conductivity.     

NiO薄膜的脉冲激光沉积及其结构和光学特性研究

利用脉冲激光沉积法在ITO玻璃衬底上制备了NiO薄膜,利用XRD、AFM对样品的晶体结构和表面形貌进行了表征,并对其透射光谱进行了测试,研究了衬底温度及脉冲激光能量对所制NiO薄膜的结构、形貌和光学特性的影响。结果表明:在脉冲激光能量为180 mJ、衬底温度为600~700℃条件下所制备的样品为沿(111)晶面择优取向生长的多晶NiO薄膜,薄膜结晶质量良好,表面颗粒排列均匀,可见光透射率较高,禁带宽度为3.40~3.47 eV。     

Pulsed laser deposition of ITO thin films and their characteristics

The indium tin oxide (ITO) thin films are grown on quartz glass substrates by the pulsed laser deposition method. The structural, electrical, and optical properties of ITO films are studied as a function of the substrate temperature, the oxygen pressure in the vacuum chamber, and the Sn concentration in the target. The transmittance of grown ITO films in the visible spectral region exceeds 85%. The minimum value of resistivity 1.79 × 10⁻⁴ Ω cm has been achieved in the ITO films with content of Sn 5 at %.     

脉冲激光沉积制备TiN/AlN多层薄膜及其工艺研究

本文采用脉冲激光沉积（PLD）法,在单晶硅试样表面上沉积制备了TiN/AlN多层硬质薄膜;研究了激光能量、靶衬距离和基体温度等工艺参数对薄膜性能的影响。采用X射线衍射（XRD）、扫描电子显微镜（SEM）和显微硬度仪方法研究了薄膜的性能。结果表明：薄膜由TiN和立方AlN细晶和无定型的非晶TiN、AlN组成,薄膜的调制周期尺寸均在λ=（50-200）nm范围内,多层结构界面清晰;当多层薄膜调制周期在100nm以下时,薄膜的显微硬度明显高于TiN和AlN的混合硬度值。     

碳纳米管薄膜的电泳沉积与场发射性能

采用电泳法在Si基片上沉积碳纳米管(CNTs)薄膜。研究了电泳极间距、电泳时间及电泳电压等对沉积的薄膜形貌结构与场发射性能的影响。SEM、高倍光学显微镜和场发射性能测试结果表明,保持阴阳极间距为2cm,在100V的直流电压下电泳2min所获得的CNTs薄膜均匀、连续、致密且具有最好的场发射性能,其开启电场强度仅为1.19V/μm,当外加电场强度为2.83V/μm时,所获得的最大发射电流密度可达14.23×10–3A/cm2。     

Pulsed laser deposition and physical properties of carbon nitride thin films

Carbon nitride thin films were grown using an approach that combines pulsed laser deposition and atomic beam techniques. The composition and phases of the carbon nitride materials obtained from the reaction of laser ablated carbon and atomic nitrogen have been systematically investigated. The nitrogen composition was found to increase to a limiting value of 50% as the fluence was decreased for laser ablation at both 532 and 248 nm. Analysis of these experiments show that the growth rate determines the overall nitrogen composition, and thus suggests that a key step in the growth mechanism involves a surface reaction between carbon and nitrogen. Infrared spectroscopy has also been used to assess the phases present in the carbon nitride thin films. This spectroscopic measurement indicates that a cyanogen-like impurity occurs in films with nitrogen compositions greater than 30%. Investigations of the effects of thermal annealing have been carried out, and show that the impurity phase can be eliminated to yield a single phase material. In addition, systematic measurements of the electrical resistivity and thermal conductivity of the carbon nitride films were made as a function of nitrogen content. The implications of these results are discussed.     

Oriented growth of rubrene thin films on aligned pentacene buffer layer and its anisotropic thin-film transistor characteristics

Oriented growth of polycrystalline rubrene thin film on oriented pentacene buffer layer was investigated. The oriented pentacene buffer layer was created by thermal evaporation of pentacene on a rubbed polyvinylalcohol (PVA) surface. The pentacene layer in turn induced the oriented growth of rubrene crystals upon thermal deposition. The structures of successive layers were characterized by using grazing incidence X-ray diffraction (GIXD) and atomic force microscopy. Highly oriented rubrene crystallites with the a-axis aligning along the surface normal and the (0 0 2) plane preferentially oriented 45° away from the rubbing direction were found. In contrast, the rubrene thin film deposited on PVA or rubbed-PVA substrate without a pentacene buffer layer only gave amorphous phases. With the aligned pentacene/rubrene film as the active layer of organic field-effect transistor, anisotropic mobilities were observed. The highest field-effect mobility (0.105 cm²/V s) was observed along the direction 45° away from the rubbing direction and is ∼4 times higher than that for similar device prepared on unrubbed PVA. The direction was consistent with the GIXD observation that a large number of rubrene crystallites are having their [0 0 2] direction aligning in this direction. A favourable C–H⋯π interaction between an oriented pentacene layer and the rubrene layer on the control of molecular orientation in the conduction channel of the OFET is suggested.     

Modulated reflectance and absorption characterization of single crystal GaN films

The results of the first application of electrolyte electroreflectance and photoreflectance to single crystal films of gallium nitride grown by organometallic vapor phase epitaxy on sapphire are presented. Absorption measurements were also performed and used to complement the results of the other techniques. The crystalline quality of the samples was evaluated, and the effects of impurity reductions and different nucleation processes were studied.     

Determination of crystal orientation in organic thin films using optical microscopy

The electrical behavior of devices based on highly crystalline thin films of organic semiconductors is inherently anisotropic. Thin film optimization requires simple and accessible means to characterize the orientation of the constituent crystals. The standard polarized light microscopy (PLM) provides a contrast between different crystallites but fails to distinguish crystals with relative orientation of 90°. In this paper, we discuss two methods that enable the unambiguous identification of crystal orientation in thin films of optically anisotropic materials: PLM with a full-wave retardation plate and differential interference contrast (DIC). The latter is standard on most microscopes and delivers images with high contrast and good color balance.As an illustration, we use DIC to extract the optical properties of highly crystalline thin films of three high-performance organic semiconductors: rubrene, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C₈-BTBT). Building on the relation between optical properties and crystal orientation, we demonstrate how DIC characterizes the in-plane crystal orientation of these thin films. This leads to the identification of the fast growth direction of the crystal front.     

Electrical characterization of semiconducting diamond thin films and single crystals

Naturally occurring semiconducting single crystal (type IIb) diamonds and boron doped polycrystalline thin films were characterized by differential capacitance-voltage and Hall effect measurements, as well as secondary ion mass spectroscopy (SIMS). Results for natural diamonds indicated that the average compensation for a type IIb diamond was >17%. Mobilities for the natural crystals varied between 130 and 564 cm²/V·s at room temperature. The uncompensated dopant concentration obtained by C-V measurements (2.8 ± 0.1 × 10¹⁶ cm⁻³) was consistent with the atomic B concentration measured by SIMS performed on similar samples (3.0 ± 1.5 x 10¹⁶ cm⁻³). Measurement of barrier heights for three different metals (platinum, gold, and aluminum) found essentially the same value of 2.3 ± 0.1 eV in each case, indicating that the Fermi level was pinned at the diamond surface. Polycrystalline semiconducting diamond thin films demonstrated a complex carrier concentration behavior as a function of dopant density. This behavior may be understood in terms of a grain boundary model previously developed for polycrystalline silicon, or by considering a combination of compensation and impurity band conduction effects. The highest mobility measured for a polycrystalline sample was 10 cm²/V·s, indicating that electrical transport in the polycrystalline material was significantly degraded relative to the single crystal samples.     

PET柔性衬底上生长绒面ZnO-TCO薄膜及其在薄膜太阳电池中的应用

利用低压金属有机化学气相沉积(LP-MOCVD)技术在PET柔性衬底上低温生长绒面结构ZnO-TCO薄膜,DEZn和H2O作为源材料,B2H6作为掺杂剂.详细研究了薄膜掺杂流量对ZnO薄膜微观结构以及光电性能影响.优化获得的PET/ZnO:B薄膜厚约为1 500nm时,绒面结构PET/ZnO薄膜的方块电阻约为10Ω,可...     

反应磁控溅射直接生长绒面结构ZnO:Al-TCO薄膜及其特性研究

利用反应磁控溅射技术,在玻璃衬底上直接生长获得了"弹坑状"绒面结构的ZnO:Al-TCO薄膜。通过梯度O2生长(GOG,gradual oxygen growth)方法改善ZnO薄膜的透过率和绒度特性,并且具有较好的电学性能。通过优化实验,GOG方法生长ZnO:Al薄膜(薄膜结构:11.0sccm/10R+9.5sccm/15R)的"弹坑状"特征尺寸为300～500nm,可见光范围透过率达到90%,方块电阻约为4.0Ω/□,电子迁移率为17.4cm2/V-1.s-1。大面积镀制的ZnO:Al具有良好的绒面结构和电学均匀性,可应用于光伏(PV)产业化推广应用。     

The role of lattice mismatch in the deposition of CdTe thin films

Cadmium telluride (CdTe) is the most well-established II–VI compound largely due to its use as a photonic material. Existing applications, as well as those under consideration, are demanding increasingly stringent control of the material properties. The deposition of high-quality thin films is of utmost importance to such applications. In this regard, we present a report detailing the role of lattice mismatch in determining the film quality. Thin films were deposited on a wide variety of substrate materials using the pulsed laser deposition (PLD) technique. Common to all substrates was the strong tendency toward the preferential alignment of CdTe’s (111) planes parallel to the substrate’s surface. X-ray diffraction analysis, however, revealed that the crystalline quality varied dramatically depending upon the substrate used with the best results yielding a single-crystal film. This tendency also manifested itself in the surface morphology with higher structural perfection yielding smoother surfaces. The film quality showed a strong correlation with lattice mismatch. Texture analysis using the [111] pole figure confirmed that improvements in the lattice mismatch led to a higher degree of in-plane alignment of the (111) grains.     

Electrochemical deposition and characterisation of CdTe thin films from an ethylene-glycol-based bath

CdTe films were deposited on Ni and conducting glass (SnO₂) substrates from an ethylene-glycol-based bath by galvanostatic and potentiostatic methods. The film composition and electrical properties depend on parameters such as working electrode potential current density, deposition temperature, substrate type and post-deposition treatments. It is possible to improve the grain size and stoichiometry of the film by post-deposition heat treatment in air. The conductivity type was determined from the photocurrent-working electrode potential behaviour of the film. Dark capacitance measurements in a 0.5 M H₂SO₄ solution at 10 kHz showed a linear behaviour, from which the flatband potential V_fb= −0.365 V vs. a saturated calomel electrode (SCE) and the doping density N_D = 1.35 × 10¹⁸ cm⁻³ were determined. © 1997 John Wiley & Sons, Ltd.