The effect of O<Subscript>2</Subscript> ambient annealing on the microstructure of Cu(Mg) in the form of a Cu(Mg)/SiO<Subscript>2</Subscript>/Si multilayer

The effect of annealing in an O₂ ambient on Cu(Mg)/SiO₂/Si multilayer films was investigated. As-deposited Cu(Mg)/SiO₂/Si multilayer samples with film thicknesses in the 1,000–3,000 ? range were annealed for 30 min in oxygen ambients at pressures ranging from vacuum to 100 mtorr. The results showed that annealing in an 8-mtorr O₂ ambient significantly decreased the electrical resistivity of a 1,000 ? sample from 10.5 μΩ-cm to 3.7 μΩ-cm. Annealing in the O₂ ambient enhanced Mg diffusion to the surface in comparison to vacuum annealing. Furthermore, O₂ ambient annealing leads to excessive grain growth. However, the effect of O₂ ambient annealing on resistivity is less when the thickness of the film increases.     

High electric-field-induced strain beahvior of single-crystal Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-xPbTiO<Subscript>3</Subscript> multilayer piezoelectric actuators

Two 10-mm-long multilayer prototype actuators were fabricated by a stack method using 55 pieces of 5 mm×5 mm×0.15 mm Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) single crystals and PZT-5A ceramics, respectively. The strain values for PMNT multilayer piezoelectric actuators are twice those of PZT-5A multilayer actuators, and 20.8-μm displacements can be achieved at the same E-field of 15 kV/cm. Although thermal and electrical history markedly impact dielectric and piezoelectric performance of PMNT crystals, the PMNT multilayer actuator can still achieve large displacements with approximately linear behavior below 60°C. Broad stable dynamic displacement characteristic and fast displacement response make the new-type actuators promising candidates for the application in new-generation high-performance solid-state actuators.     

Superior suppression of gate current leakage in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> bilayer-based AlGaN/GaN insulated gate heterostructure field-effect transistors

AlGaN/GaN-based metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with Al₂O₃/Si₃N₄ bilayer as insulator have been investigated in detail, and compared with the conventional HFET and Si₃N₄-based MIS-HFET devices. Al₂O₃/Si₃N₄ bilayer-based MIS-HFETs exhibited much lower gate current leakage than conventional HFET and Si₃N₄-based MIS devices under reverse gate bias, and leakage as low as 1×10⁻¹¹ A/mm at −15 V has been achieved in Al₂O₃/Si₃N₄-based MIS devices. By using ultrathin Al₂O₃/Si₃N₄ bilayer, very high maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been obtained in the MIS-HFET device with gate length of 1.5 μm, a reduction less than 5% in maximum transconductance compared with the conventional HFET device. This value was much smaller than the more than 30% reduction in the Si₃N₄-based MIS device, due to the employment of ultra-thin bilayer with large dielectric constant and the large conduction band offset between Al₂O₃ and nitrides. This work demonstrates that Al₂O₃/Si₃N₄ bilayer insulator is a superior candidate for nitrides-based MIS-HFET devices.     

Optimization of pretreatment for liquid-phase deposition of SiO<Subscript>2</Subscript> on ARTON plastic substrate

This study extends our previous work on liquid-phase deposition (LPD) of dense, high-quality, silicon-dioxide (SiO₂) films deposited on Si and GaAs substrates from supersaturated, hexafluorosilicic-acid aqueous at near room temperature. Pretreatment to coat the substrate surface with hydroxyl groups was found to be necessary for rapid and high-quality growth. More recent work has extended the range of LPD SiO₂ to plastic. The current paper studies optimal LPD pretreatment of a plastic (ARTON) substrate. It is shown that treating ARTON plastic, first, by exposure to oxygen plasma, second, by potassium manganese (KMnO₄) etching, and finally, by H₂O₂ etching, provides the plastic surface with rich OH-radical formation. The resulting SiO₂/ARTON film is of good quality and reliability. Deposition rate is up to 659 Å/h, and the refractive index is about 1.44 with growth at 40°C. A growth mechanism for LPD-SiO₂ deposition on plastic is proposed.     

The properties of photo chemical-vapor deposition SiO<Subscript>2</Subscript> and its application in GaN metal-insulator semiconductor ultraviolet photodetectors

High-quality SiO₂ insulating layers were successfully deposited onto GaN by a photo chemical-vapor deposition (photo-CVD) technique using a deuterium (D₂) lamp as the excitation source. The interface-trap density, D_it, was estimated to be 8.4×10¹¹ cm⁻²eV⁻¹ for the photo-CVD SiO₂ layers prepared at 300°C. It was found that the leakage current was only 6.6×10⁻⁷ A/cm² with an applied field of 4 MV/cm for the 300°C photo-CVD-grown Al/SiO₂/GaN metal-insulator semiconductor (MIS) capacitor. It was also found that the photo-CVD SiO₂ layer could be used to suppress the dark current of nitride-based photodetectors. A large photocurrent to dark-current contrast ratio higher than three orders of magnitude and a maximum 0.12 A/W responsivity were observed from the fabricated indium tin oxide (ITO)/photo-SiO₂/GaN MIS ultraviolet (UV) photodetectors. Furthermore, it was found that corresponding noise-equivalent power (NEP) and normalized detectivity, D*, of our ITO/photo-SiO₂/GaN MIS UV photodetectors was 2.19×10⁻⁹ W and 2.03 × 10⁸ cmHz_0.5W⁻¹, respectively, for a given bandwidth of 500 Hz.     

Effect of Ionization Characteristics on Electrochemical Migration Lifetimes of Sn-3.0Ag-0.5Cu Solder in NaCl and Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> Solutions

Anodic dissolution characteristics and electrochemical migration (ECM) behavior of Sn-3.0Ag-0.5Cu solder in NaCl and Na₂SO₄ solutions were investigated using anodic polarization tests and water drop tests (WDT). The ECM lifetime of Sn-3.0Ag-0.5Cu solder in NaCl solution (42.4 s) was longer than that in Na₂SO₄ solution (34.8 s). The pitting potential of Sn-3.0Ag-0.5Cu solder in NaCl solution (135 mV, SCE) was higher than that in Na₂SO₄ solution (−367 mV, SCE). The passivity film (SnO₂) formed on Sn-3.0Ag-0.5Cu solder during WDTs in NaCl solution was thicker than that formed in Na₂SO₄ solution. Therefore, the longer ECM lifetime of Sn-3.0Ag-0.5Cu solder in NaCl solution than in Na₂SO₄ solution can be attributed to the higher pitting potential in the NaCl solution, which is ascribed to the formation of a thicker passivity film (SnO₂) in the former. It was confirmed that microelements such as Ag and Cu do not take part in ECM because they form chemically stable intermetallic compounds with Sn. We believe that Sn is the only element that contributes to ECM, and dissolution of Sn at the anode is possibly the rate-determining step of ECM of Sn-3.0Ag-0.5Cu solder.     

AlGaN/GaN metal-oxide semiconductor heterostructure field-effect transistor with photo-chemical-vapor deposition SiO<Subscript>2</Subscript> gate oxide

High-quality SiO₂ was successfully deposited onto GaN by photo-chemicalvapor deposition (photo-CVD) using a D₂ lamp as the excitation source. The AlGaN/GaN metal-oxide semiconductor, heterostructure field-effect transistors (MOSHFETs) were also fabricated with photo-CVD oxide as the insulating layer. Compared with AlGaN/GaN metal-semiconductor HFETs (MESHFETs) with similar structure, we found that we could reduce the gate-leakage current by more than four orders of magnitude by inserting the photo-CVD oxide layer in between the AlGaN/GaN and the gate metal. With a 2-μm gate, it was found that the saturated I_ds, maximum g_m, and gate-voltage swing (GVS) of the fabricated nitride-based MOSHFET were 512 mA/mm, 90.7 mS/mm, and 6 V, respectively.     

Novel pulsed-laser-deposition—VO<Subscript>2</Subscript> thin films for ultrafast applications

VO₂ thin films deposited on fused quartz substrates were successfully fabricated by the pulsed-laser-deposition (PLD) technique. The obtained samples were examined by microscopy and x-ray diffraction (XRD). The films show a fast, passive thermochromic effect of semiconductor-to-metal phase transition (PT) with a characteristic hysterisis at ∼68°C. The thermochromic effect was measured as resistivity, optical transmission, and reflection versus temperature. Under pulsed laser excitation, an optically induced ultrafast PT of VO₂ thin film was observed. Using the degenerate-four-wave-mixing (DFWM) technique, it was found that excited state dynamics is responsible for the induced lattice reorientation polarization, which results in the ultrafast PT.     

Self-limiting growth of ZrO<Subscript>2</Subscript> films on a Si(100) substrate using ZrCl<Subscript>4</Subscript> and O<Subscript>2</Subscript> under atmospheric pressure

The ZrO₂ films were deposited onto a Si(100) substrate using an alternate reaction of ZrCl₄ and O₂ under atmospheric pressure. It is found that the growth rate of ZrO₂ film depends on the growth conditions, such as growth temperature, partial pressure of the sources being supplied, and exposure time of the substrate to the gaseous sources. Self-limiting growth of the ZrO₂ was achieved in the range of the growth temperature of 673–923 K. The x-ray diffractogram of the ZrO₂ films showed a typical diffraction pattern assigned to the tetragonal polycrystalline phase. The obtained ZrO₂ films were of smooth and uniform surface. It was found that the [O]/[Zr] ratio of the ZrO₂ films are similar to that of the ZrO₂ bulk.     

The H<Subscript>2</Subscript> plasma treatment of silver contacts: Impact on wire-bonding performance

The ultrasonic wire-bonding performance on Ag bond pads is limited by the presence of oxides and organic contaminants. These contaminations act as lubricants during wire bonding. They reduce the interfacial friction and decrease the heat dissipation between the two contacting materials, leading to bad bond quality. Plasma processes have proven to be a valuable tool for eliminating such contaminations and boosting wire-bonding performance. We present investigations of the effects of H₂ plasma on oxidized silver films by photoelectron spectroscopy and quartz-crystal microbalance (QCM) measurements. The H₂ plasma treatment of Ag bond pads is not a classical surface-cleaning process. It is a bulk process, and it induces a reduction of silver oxide and recrystallization. The high mass transport caused by large changes in density during reduction leads to the formation of (111)-terminated regions at the surface. This densely packed termination can account for the apparent passivating effect of H₂ plasmas on Ag bond pads, which allows for long-term storage in ambient atmosphere without deteriorating bonding performance.     

Interdiffusion and Growth of the Superconductor Nb<Subscript>3</Subscript>Sn in Nb/Cu(Sn) Diffusion Couples

The confusion over the growth rate of the Nb₃Sn superconductor compound following the bronze technique is addressed. Furthermore, a possible explanation for the corrugated structure of the product phase in the multifilamentary structure is discussed. Kirkendall marker experiments are conducted to study the relative mobilities of the species, which also explains the reason for finding pores in the product phase layer. The movement of the markers after interdiffusion reflects that Sn is the faster diffusing species. Furthermore, different concentrations of Sn in the bronze alloy are considered to study the effect of Sn content on the growth rate. Based on the parabolic growth constant at different temperatures, the activation energy for the growth is determined.     

Electronic properties of Cu(In,Ga)Se2 solar cells on stainless steel foils without diffusion barrier

Compared with rigid glass, manufacturing of Cu(In,Ga)Se₂ (CIGS) solar cells on flexible stainless steel (SS) substrates has potential to reduce production cost because of the application of roll‐to‐roll processing. Up to now, high‐efficiency cells on SS could only be achieved when the substrate is coated with a barrier layer (e.g. SiO_x or Si₃N₄) for hindering the diffusion of impurities, especially Fe, into the CIGS layer. In this paper, the effect of these impurities on the electronic transport properties of the device is investigated. Using admittance spectroscopy, the presence of a deep defect level at around 320 meV is observed, which deteriorates the efficiency of the solar cells. Furthermore, it is shown that reducing substrate temperature during CIGS deposition is an effective alternative to a barrier layer for reducing diffusion of detrimental Fe impurities into the absorber layer. By applying a CIGS growth process for deposition at low substrate temperatures, an efficiency of 17.7%, certified by Fraunhofer Institute ISE, Freiburg, was achieved on Mo/Ti‐coated SS substrate without an additional metal‐oxide or metal‐nitride impurity diffusion barrier layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Rutherford Backscattering Spectrometry Analysis of Self-Formed Ti-Rich Interface Layer Growth in Cu(Ti)/Low-<Emphasis Type="Italic">k</Emphasis> Samples

A new fabrication technique to prepare ultrathin barrier layers for nanoscale Cu wires was proposed in our previous studies. Ti-rich layers formed at Cu(Ti)/dielectric layer interfaces consisted of crystalline TiC or TiSi and amorphous Ti oxides. The primary control factor for the Ti-rich interface layer composition was C concentration in the dielectric layers rather than the formation enthalpy of the Ti compounds. To investigate Ti-rich interface layer growth in Cu(Ti)/dielectric layer samples annealed in ultrahigh vacuum, Rutherford backscattering spectrometry (RBS) was employed in the present study. Ti peaks were obtained only at the interfaces for all samples. Molar amounts of Ti atoms segregated to the interfaces (n) were estimated from Ti peak areas. Log n values were proportional to log t values. Slopes were similar for all samples, suggesting similar growth mechanisms. The activation energy (E) for Ti atoms reacting with the dielectric layers containing carbon (except SiO₂) tended to decrease with decreasing C concentration (decreasing k), while those for the SiO₂ layers were much higher. Reaction rate coefficients [Z · exp(−E/RT)] were insensitive to C concentration in the dielectric layers. These factors lead to the conclusion that growth of the Ti-rich interface layers is controlled by chemical reactions, represented by the Z and E values, of the Ti atoms with the dielectric layers, although there are a few diffusion processes possible.     

Growth of CdTe Films on Amorphous Substrates Using CaF<Subscript>2</Subscript> Nanorods as a Buffer Layer

Continuous biaxially textured CdTe films were grown on biaxial CaF₂ buffer layers. The CaF₂ nanorods were grown by oblique angle vapor deposition and possessed a {111} 〈121〉 biaxial texture. The CdTe film was deposited by metal organic chemical vapor deposition (MOCVD). Film morphology and the CdTe/CaF₂ interface were studied by scanning electron microscopy and transmission electron microscopy. Characterization showed that small CdTe grains formed initially from the CaF₂ surfaces. These small grains then merged into large columnar grains during growth. Analysis revealed that the crystalline orientation of the CdTe film followed the biaxial texture of the CaF₂ nanorods.     

Analysis of the redeposition of AuSn<Subscript>4</Subscript> on Ni/Au contact pads when using SnPbAg,SnAg, and SnAgCu solders

Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printed wiring board and especially the redeposition of AuSn₄ intermetallic compound have been investigated. The following major results were obtained. The first phase to form during soldering in the (SnPbAg)/Ni/Au and the (SnAg)/Ni/Au systems was Ni₃Sn₄. During the subsequent solid-state annealing, the redeposition of AuSn₄ as (Au,Ni)Sn₄ occurred in both systems. This was explained with the help of the concept of local equilibrium and the corresponding ternary phase diagrams. It was concluded that the stabilizing effect of Ni on the (Au,Ni)Sn₄ provided the driving force for the redeposition. Contrarily, when the solder alloy contained some Cu, the first intermetallic to form was (Cu,Ni,Au)₆Sn₅ and no redeposition of AuSn₄ was observed. Thus, a very small addition of Cu to the Sn-rich solder alloys changed the behavior of the interconnection system completely. This behavior was explained thermodynamically by using Cu-Ni-Sn and Au-Cu-Sn ternary phase diagrams. The growth kinetics of the interfacial reaction products in the three systems was observed to be somewhat different. The reasons for the observed differences are also discussed.     

Ga2O3缓冲层厚度对柔性衬底沉积Cu/ITO薄膜性能的影响

Cu and Cu/ITO films were prepared on polyethylene terephthalate （PET） substrates with a Ga2O3 buffer layer using radio frequency （RF） and direct current （DC） magnetron sputtering. The effect of Cu layer thickness on the optical and electrical properties of the Cu film deposited on a PET substrate with a Ga2O3 buffer layer was studied, and an appropriate Cu layer thickness of 4.2 nm was obtained. Changes in the optoelectrical properties of Cu（4.2 nm）/ITO（30 nm） films were investigated with respect to the Ga2O3 buffer layer thickness. The optical and electrical properties of the Cu/ITO films were significantly influenced by the thickness of the Ga2O3 buffer layer. A maximum transmission of 86%, sheet resistance of 45 Ω/□ and figure of merit of 3.96 × 10^-3 Ω^ -1 were achieved for Cu（4.2 nm）/ITO（30 nm） films with a Ga2O3 layer thickness of 15 nm.     

基于SiO2溶胶的稳定性的Cu/SiO2催化体系在化学机械抛光中的应用研究

There is a lot ofhydroxyl on the surface ofnano SiO2 sol used as an abrasive in the chemical mechanical planarization （CMP） process, and the chemical reaction activity of the hydroxyl is very strong due to the nano effect. In addition to providing a mechanical polishing effect, SiO2 sol is also directly involved in the chemical reaction. The stability of SiO2 sol was characterized through particle size distribution, zeta potential, viscosity, surface charge and other parameters in order to ensure that the chemical reaction rate in the CMP process, and the surface state of the copper film after CMP was not affected by the SiO2 sol. Polarization curves and corrosion potential of different concentrations of SiO2 sol showed that trace SiO2 sol can effectively weaken the passivation film thickness. In other words, SiO2 sol accelerated the decomposition rate of passive film. It was confirmed that the SiO2 sol as reactant had been involved in the CMP process of copper film as reactant by the effect of trace SiO2 sol on the removal rate of copper film in the CMP process under different conditions. In the CMP process, a small amount of SiO2 sol can drastically alter the chemical reaction rate of the copper film, therefore, the possibility that Cu/SiO2 as a catalytic system catalytically accelerated the chemical reaction in the CMP process was proposed. According to the van＇t Hoff isotherm formula and the characteristics of a catalyst which only changes the chemical reaction rate without changing the total reaction standard Gibbs free energy, factors affecting the Cu/SiO2 catalytic reaction were derived from the decomposition rate of Cu （OH）2 and the pH value of the system, and then it was concluded that the CuSiO3 as intermediates of Cu/SiO2 catalytic reaction accelerated the chemical reaction rate in the CMP process. It was confirmed that the Cu/SiO2 catalytic system generated the intermediate of the catalytic reaction （CuSiO3） in the CMP process through the removal rate of copper film, infrared spectrum and AFM diagrams in different pH conditions. FinalLy it is concluded that the SiO2 sol used in the experiment possesses stable performance; in the CMP process it is directly involved in the chemical reaction by creating the intermediate of the catalytic reaction （CuSiO3） whose yield is proportional to the pH value, which accelerates the removal of copper film.     

硒化温度对Cu(In, Al)Se2薄膜结构和光学性质的影响

采用了磁控溅射制备Cu-In-Al金属前驱体薄膜,后硒化快速退火得到铜铟铝硒(Cu(In,Al)Se2,CIAS)薄膜.研究了硒化温度对CIAS薄膜晶体结构和光学性质的影响.研究发现CIAS薄膜的晶体结构依赖于硒化温度,其禁带宽度随硒化温度升高发生红移.研究结果表明,CIAS薄膜的最佳硒化温度为540℃,其晶体结构为纯黄铜矿结构,禁带宽度为.34 eV,对应太阳电池理论最大效率的吸收层材料禁带宽度     

新型CIGS阻挡层多横向界面Mo的特性及对器件性能的影响

采用磁控溅射方法,在不锈钢箔上制备多横向界 面Mo(M-Mo,multi-transverse interface Mo)和单横向界面Mo(S-Mo)薄 膜,并利用共蒸发三步法分别在M-Mo和S-Mo薄膜上制备Cu(In,Ga)Se₂(CIGS)薄膜及 器件。通过二次离子质谱仪(SIMS)、X射线衍射仪(XRD)和扫描电子显微镜(SEM)研究了不同 结构的Mo薄膜对CIGS影响。通过I-V测试,表征M-Mo和S -Mo作为背电极的CIGS电池电学性能。XRD结果显示,M-Mo和S-Mo 薄膜均以(110)为择优取向。SEM结果显示,M-Mo薄膜相对 于S-Mo,薄膜晶粒 较小,粗糙度较大。J-V测试结果显示,M-Mo薄膜作为背 电极的电池的开路电压Voc、短路电流J sc和填充因子(FF)均有所提高。     

The effect of Zn1‐xMgxO buffer layer deposition temperature on Cu(In,Ga)Se2 solar cells: A study of the buffer/absorber interface

The effect of atomic layer deposition temperature of Zn_1‐xMg_xO buffer layers for Cu(In,Ga)Se₂ (CIGS) based solar cell devices is evaluated. The Zn_1‐xMg_xO films are grown using diethyl zinc, bis‐cyclopentadienyl magnesium and water as precursors in a temperature range of 105 to 180°C. High efficiency devices are produced in the region from 105 up to 135°C. At a Zn_1‐xMg_xO deposition temperature of 120°C, a maximum cell efficiency of 15·5% is reached by using a Zn_1‐xMg_xO layer with an x‐value of 0·2 and a thickness of 140 nm. A significant drop in cell efficiency due to large losses in open circuit voltage and fill factor is observed for devices grown at temperatures above 150°C. No differences in chemical composition, structure and morphology of the samples are observed, except for the samples prepared at 105 and 120°C that show elemental selenium present at the buffer/absorber interface. The selenium at the interface does not lead to major degradation of the solar cell device efficiency. Instead, a decrease in Zn_1‐xMg_xO resistivity by more than one order of magnitude at growth temperatures above 150°C may explain the degradation in solar cell performance. From energy filtered transmission electron microscopy, the width of the CIGS/Zn_1‐xMg_xO chemical interface is found to be thinner than 10 nm without any areas of depletion for Cu, Se, Zn and O. Copyright © 2008 John Wiley & Sons, Ltd.