Electrical properties of multilayered Al/Ni and Al/Mo films

The structural and electrical properties of multilayered metallic systems prepared by r.f. sputtering are reported. The multilayers consist of alternating layers of aluminium and molybdenum or nickel, with superlattice periodicities in the range of 1.5–9.0 nm. The resistivity and its temperature dependence were measured at temperatures between 170 and 320 K. The most striking feature is the change in sign of the temperature coefficient of resistivity as the thickness of the aluminium layer is varied. The experimental results are interpreted in terms of a grain boundary reflection model.     

Al/Al2O3多层膜的研究

用真空蒸镀及自然氧化方法在玻璃基底上制备纳米量级的4、5、6、7对层的Al／Al2O3多层膜。采用称重法测定薄膜的厚度；在常温和低温下使用三点法测定多层膜的电特性；用扫描电镜（sEM）观察薄膜的表面和截面的形貌及成分。结果表明：制备的是纳米量级非晶态的Al／Al2O3多层膜，在常温和低温（77K）下均具有类似负阻的特性。     

Diffusion during annealing of Al/Cu/Fe thin films

The Al-Cu-Fe system is interesting due to the existence of the quasicrystalline phase Al_62.5Cu₂₅Fe_12.5 as well as its approximant phases. A two-step procedure of thin film preparation is considered: deposition of a multilayer structure of individual elements and consequential annealing. To analyze the diffusion processes trilayers of individual elements were deposited by sputtering with a total thickness of about 400 nm. Afterwards, the samples were annealed in tube furnace in inert atmosphere. Rutherford backscattering spectrometry, Auger electron spectrometry and X-ray diffraction were used to quantify the depth profiles. The results point out to a three-stage process as a function of rising temperature: first Al and Cu form the γ-Al₄Cu₉ compound layer; second the aluminium spreads throughout the film with copper and iron mainly divided. The β-Al(Cu,Fe) phase is observed. Complete homogenization is followed afterwards.     

Mo/Si and Mo/Be multilayer thin films on Zerodur substrates for extreme-ultraviolet lithography

Multilayer-coated Zerodur optics are expected to play a pivotal role in an extreme-ultraviolet (EUV) lithography tool. Zerodur is a multiphase, multicomponent material that is a much more complicated substrate than commonly used single-crystal Si or fused-silica substrates. We investigate the effect of Zerodur substrates on the performance of high-EUV reflectance Mo/Si and Mo/Be multilayer thin films. For Mo/Si the EUV reflectance had a nearly linear dependence on substrate roughness for roughness values of 0.06-0.36 nm rms, and the FWHM of the reflectance curves (spectral bandwidth) was essentially constant over this range. For Mo/Be the EUV reflectance was observed to decrease more steeply than Mo/Si for roughness values greater than approximately 0.2-0.3 nm. Little difference was observed in the EUV reflectivity of multilayer thin films deposited on different substrates as long as the substrate roughness values were similar.     

Bi2MoO6 dielectric thin films fabricated by thermal oxidation of Bi/Mo thin films at ultra-low temperature

Bi/Mo multilayer thin films are deposited on Si/SiO₂/Pt substrates by direct current magnetron sputtering. The effect of annealing temperature on the microstructure, dielectric and electrical properties of the as-sputtered films is characterized systematically. X-ray diffraction data indicate that the films annealed at 450–600 °C are a mixture of diphase with the main phase Bi₂MoO₆ and secondary phase Bi₂Mo₂O₉. Results of scanning electron microscope observation show that the films annealed at 500–550 °C are dense and uniform, in particular the films annealed at 500 °C exhibit optimal dielectric and electrical properties with dielectric constant as high as 37.5, dielectric loss 1.06 %, temperature coefficient of dielectric constant ?10.86 ppm °C^?1 at 1 kHz, and leakage current density of 1.46 × 10^?7 A mm^?2 at an electric field of 18.2 kV mm^?1. With the advantages of ultralow densification temperature (500 °C) and very high sputtering deposition rate (76 nm min^?1), it is anticipated that thermal oxidation method of the sputtered Bi/Mo thin films could be a promising technique for fabrication of Bi₂MoO₆ ceramic thin film embedded-capacitors.     

Diffusion barrier performances of thin Mo, Mo-N and Mo/Mo-N films between Cu and Si

In this work, we have studied the diffusion barrier performances of Mo, Mo-N and Mo/Mo-N metallization layers deposited by sputtering Mo in Ar/N₂ atmospheres, respectively. Samples were subsequently annealed at different temperatures ranging from 400 to 800 °C in vacuum condition. The film properties and their suitability as diffusion barriers and protective coatings in silicon devices were characterized using four-point probe measurement, X-ray diffractometry, scanning electron microscopy, Auger electron spectroscopy and transmission electron microscopy analyses. Experimental results revealed that the Mo (20 nm)/Mo-N (30 nm) layer was able to prevent the diffusion reaction between Cu and Si substrate after being annealed at 600 °C for 30 min. The adhesion between layers and the content of N atoms are the key parameters to improve the properties of Mo-based barrier materials. The Mo layer interposed between Cu and Mo-N diluted the high nitrogen concentration of the barrier and so enhanced the barrier performances.     

Oxidation characteristics of artificially layered Fe/Al and Fe/Mg thin films

Investigations were carried out on the oxidation characteristics of artificially layered Fe/Al and Fe/Mg thin films using X-ray diffraction and Raman spectroscopy at 303, 473, 673 and 773 K in the laboratory atmosphere. X-ray diffractograms and Raman spectra reveal diffusion phenomena occurring in Fe/Al thin films. Individual oxides and a spinel-phase MgFe₂O₄, were the oxidation products in Fe/Mg multilayers while intermetallics were found to be present in the Fe/Al system at 773 K, in addition to FeAl₂O₄.     

Tin sulfide thin films and Mo/p-SnS/n-CdS/ZnO heterojunctions for photovoltaic applications

Tin sulfide (SnS) is one of the most promising materials for photovoltaics. Here we report on the preparation as well as chemical, structural and physical characterization of the Mo/p-SnS/n-CdS/ZnO heterojunctions. The SnS thin films were grown by hot wall deposition method on the Mo-coated glass substrates at 270-350 °C. The crystal structure and elemental composition were examined by X-ray diffraction and Auger electron spectroscopy methods. The CdS buffer layers were deposited onto the SnS films by chemical bath deposition. The ZnO window layers were deposited by a two step radio frequency magnetron sputtering, resulting in a ZnO bilayer structure: the first layer consists of undoped i-ZnO and the second of Al-doped n-ZnO. The best junctions have an open circuit voltage of 132 mV, a short circuit current density of 3.6 mA/cm², a fill-factor of 0.29 and efficiency up to 0.5%.     

Texture and sheet resistance of Al alloy thin films on Ti and TiN thin films

Ti films prepared by ionized physical vapor deposition (I-PVD) and TiN films prepared by metalorganic chemical vapor deposition (MOCVD) were examined as the underlayers of the Al interconnect films. The crystallographic texture of the Al films and the sheet resistance of the thin-film stacks were investigated at various thicknesses of the Ti or TiN thin film. The sheet resistance of the thin-film stacks was also measured after annealing at 400 °C in an N₂ ambient. For the I-PVD Ti underlayer, the excellent texture of the Al (1 1 1) was obtained even on a 5-nm thick Ti film. However, the sheet resistance of the multilayer structure increased after the annealing due to the reaction between Al and Ti. MOCVD TiN layers between the Ti film and the Al film could suppress the Al–Ti reaction without severe degradation of the Al (1 1 1) texture. Excellent texture of the Al film was obtained with thin MOCVD TiN films below 5 nm.     

Structural and residual stress changes in Mo/a-Si multilayer thin films with annealing

The thermal and mechanical stability of molybdenum and amorphous silicon (Mo/a-Si) optical multilayers (3 and 4 nm nominal thickness of Mo and Si) at 316 °C were studied by annealing experiments. Growth of amorphous Mo-Si interlayers with a stoichiometry of 12 was observed at the Mo/a-Si interfaces. In addition, residual stresses significantly changed in the crystalline Mo and amorphous Si layers with annealing. High resolution electron microscopy, selected area electron diffraction, and X-ray diffraction of the crystalline Mo revealed that tensile stresses increased from 2 to about 10 GPa in the lateral direction (parallel to the interface plane). The compressive strains that developed in the vertical direction (perpendicular to the interface plane) are consistent with Poisson's ratio. Laser deflectometer measurements of thicker (0.1 m) amorphous silicon layers may indicate compressive-stress relaxation in the amorphous silicon with annealing, consistent with other investigations. Overall, the residual stress in a 40-bilayer film changes from about –0.5 to about +1.5 GPa. Structural transformation after relatively short annealing times at the interfaces in the thin amorphous Mo-Si interlayers may rationalize increased tensile strains in the Mo layers.     

Reaction between permalloy and several thin metal films

To develop the electrode materials for thin permalloy film devices, the reactions between the permalloy Ni-19%Fe and several metal films were investigated. From the results of the annealing behaviour for thin bilayer films including the permalloy, it was clarified that aluminium, copper, chromium and gold films react with the permalloy below 250–350°C. However, molybdenum and tantalum do not react up to 400°C. Therefore it is considered that molybdenum and tantalum are good electrode materials for thin permalloy film devices.     

Plasma oxidation of Al thin films on Si substrates

In this study, Al thin films deposited on silicon wafers by direct current magnetron sputtering were oxidized under radio frequency 13.56 MHz O₂ plasma at temperatures up to 550 °C. During oxidation, plasma powers as well as oxidation temperature and time were varied to investigate the oxidation behavior of the Al films. X-ray photoelectron spectroscopy and Auger electron spectroscopy results show that the apparent alumina could be observed after O₂ plasma treatment with powers above 200 W as well as at temperatures above 250 °C. However, no alumina increment could be discerned after individual either heat treatment at 550 °C or plasma treatment at room temperature. The thickness of alumina layers increased remarkably with plasma power and could reach about 60 nm when undergone 400 W O₂ plasma treatment at 550 °C for 2 h. Moreover, the thickness of alumina increased parabolically with time during plasma oxidation aided by thermal treatment. The deduced activation energy of such plasma oxidation was 19.1 ± 0.5 kJ/mol.     

Interfacial diffusion effect on phase transitions in Al/Mn multilayered thin films

Thin films of Al and Mn multilayers were synthesized using thermal evaporation under high vacuum conditions. The whole film thickness containing three bilayers of Al and Mn is about 120 nm. The global concentration of the samples was varied between 10 and 46.5 at.% Mn, by changing the thickness of the bilayer. The as-evaporated samples were heat treated at different temperatures (473, 623, 823 and 873 K) for 2 and 8 h to investigate the interfacial diffusion induced phase transformations in the multilayered thin films. Transmission electron microscopy (TEM) has been mainly used to characterize the crystalline structure of a variety of phases revealed on annealing, such as μ, λ and φ phases up to 823 K, δ phase at 823 K and T6 phase at 873 K. The occurrence of a variety of structures on annealing has been attributed to the interfacial reactions at the Al–Mn bilayers, and, therefore, the global composition of the composite films is not significant during the process of phase transformations. The crystallographic relationships of Al–Mn approximant structures of the decagonal quasicrystal are discussed to understand the evolution and stability of the T6 phase at high temperature.     

Synthesis of C-axis-oriented AlN thin films on high-conducting layers: Al, Mo, Ti, TiN, and Ni

Thin piezoelectric polycrystalline films such as AlN, ZnO, etc., are of great interest for the fabrication of thin film bulk/surface acoustic resonators (TFBARs or TFSARs). It is well-known that the degree of c-axis orientation of the thin films correlates directly with the electromechanical coupling. However, the degree of c-axis orientation of the piezoelectric film is, in turn, influenced by other parameters such as the structure of the substrate material, the matter of whether the c-axis is up or down (polarity), and the growth parameters used. The correlation of these three aspects with the electromechanical coupling of the AlN-thin films, is studied here. Thin AlN films, prepared in a magnetron sputtering system, have been deposited onto thin Al, Mo, Ni, Ti, and TiN films. Such thin high-conducting layers are used to form the bottom electrode of TFBAR devices as well as to define a short-circuiting plane in TFSAR devices. In both cases, they serve as a substrate for the growth of the piezoelectric film. It has been found that the degree of orientation and the surface roughness of the bottom metal layer significantly affects the texture of the AlN films, and hence its electroacoustic properties. For this reason, the surface morphology and texture of the metal layers and their influence on the growth of AlN on them has been systematically studied. Finally, FBARs with both Al and Ti electrodes have been fabricated and evaluated electroacoustically.     

掺Er-Al2O3薄膜发光特性的研究

通过离子束辅助沉积(IBAD)在热氧化SiO2上沉积Al2O3薄膜,在120keV下注入5×10115cm-2Er离子,Ar气氛下773～1273K退火1h.低温下测试PL谱线,随退火温度升高,发光强度上升.973K退火下发光强度特别低,并观察到Si衬底的1140nm峰.光透射谱表明几乎在所有的测试范围内尤其在1530nm处973K退火样品的透射谱强度最强,波导损耗最低.1530nm发光强度随退火温度的变化跟发光强度的变化相反.说明Er离子在514.5nm泵谱吸收界面σ跟Al2O3的光吸收损耗有一定关系.     

Determination of hydrogen absorption in Pd coated Al thin films

Al films, 80–85 nm in thickness and 10–30 μΩ cm in resistivity, are coated with Pd (8–40 nm). The bilayer is exposed to a hydrogen atmosphere of up to 4.0 kPa. The hydrogen concentration is calculated from the frequency change in a quartz crystal microbalance and the electrical resistance of the Pd film, the Al film and the bilayer is measured as function of hydrogen pressure. Concentration and resistance measurements indicate that the Pd coating enables the Al films to absorb hydrogen from the gas phase.     

Calorimetric and other studies of intermetallic phase formation in Ag/Al bilayer thin films

Silver and aluminium bimetallic thin film couples have been studied using constant heating rate differential scanning calorimetry both on cleaned glass substrates and freshly cleaved NaCl crystals. The most striking feature was the occurrence of two maxima in the reaction rate during the formation of a single product phase, Ag₂Al, suggesting a two-step growth process. The activation energy for this reaction was 0.98 eV in the first step and 0.93 eV in the second step. These values are in good agreement with values obtained by a different technique, i.e. Rutherford back-scattering. Transmission electron microscopy, thin film X-ray diffraction, the change in resistance of bilayer films with temperature and thermodynamic and kinetic analyses have been used to investigate the intermetallic phase formation. It was observed that substrate plays an important role in the kinetics of thin-film reaction.     

Preparation of Mo/Cu(In, Ga)Se2 thin films by one-step sputtering

An attempt was made for preparing CIGS absorber layers by one-step sputtering of a quaternary target for eventual use such as large area CIGS solar cells. For fabricating the layers, a single quaternary target with pre-determined compositions of the constituents, Cu, In, Ga and Se was employed and the in-situ and post-annealing by RTP were performed. Then the layers were characterized by SEM, AFM, XPS, XRD and EDX. Indeed, the CIGS absorber layers with chalcopyrite structure could be successfully obtained. In addition, it was found that the very smooth surfaces could be obtained since the deposition was conducted by single-step sputtering. The present work shows that the one-step sputtering method can be a potential route for the economic preparation of CIGS absorber layers.