Improved Film Quality Research Articles

Preparation of multilayer films for integrated high- Tc SQUIDs with ramp-edge Josephson junctions

We proposed a novel multilayer structure having a new combination of oxides for integrated high- T c SQUID with ramp-edge Josephson junctions. La 0.1Er 0.95Ba 1.95Cu 3O y (L1ErBCO) and SmBa 2Cu 3O y (SmBCO) were used as counter- and base-electrodes, respectively. An SrSnO 3 (SSO) layer was deposited as an insulating layer. Prior to deposition of SmBCO, Pr 1.4Ba 1.6Cu 2.6Ga 0.4O y (P4G4) and SSO were deposited on MgO (100) substrate in order to improve film quality of L1ErBCO/SSO/SmBCO layers. The black-colored P4G4 layer was expected to work as a temperature homogenizer over a whole substrate area during deposition of the upper layers. All the layers except L1ErBCO were deposited by an off-axis magnetron sputtering. An L1ErBCO layer was deposited by a pulsed laser deposition method. A thin Cu-poor L1ErBCO layer was initially deposited to form an adequate barrier on the ramp-edge of SmBCO. Gradiometer arrays having multilayered feedback coils and pickup loops were made in a chip and their proper operation at 77 K was confirmed. The present multilayer structure is promising for application to SQUIDs with more complicated designs.

A Novel Corrosion-Resistant Internal-Coating Method Provides Improved Hardness

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 114020, "A Novel Corrosion-Resistant Internal-Coating Method Using Hollow-Cathode PECVD Technology With Improved Hardness," by Bill Boardman, Karthik Bonapolly, Deepak Upadhayaya, and Tom Casserly, Sub-One Technology, prepared for the 2008 Western Regional and Pacific Section of AAPG Joint Meeting, Bakersfield, California, 31 March-2 April. The paper has not been peer reviewed. A novel technology has been developed for coating the internal surfaces of parts ranging from small components to production pipe. The coating is appropriate for use in many environments for corrosion, erosion, and wear reduction. The process technology that enables the coating of interior surfaces with a hard, wear- and corrosion-resistant silicon-containing diamond-like carbon (DLC-Si) layer is described. Hardness greater than 25 GPa has been achieved while maintaining a high deposition rate. Introduction A new process technology uses a plasma-enhanced chemical-vapor deposition process that has been modified to use a high-density, hollow-cathode plasma that enables a high deposition rate that is generated based on pipe diameter and pressure. In conjunction with DC plasma pulsing, this enables very high deposition rates greater than 0.3 μm/min. Coating properties along the length of a steel pipe are controlled by adjusting process parameters. Ion bombardment improves film quality by biasing the part negative. The process does not require a traditional vacuum chamber, but uses the pipe or part as the vacuum chamber. In addition to improving corrosion resistance, the films are hard, pure, amorphous, dense, and wear resistant. Environmentally friendly precursors such as acetylene or other hydrocarbons are used to deposit inert corrosion-resistant DLC-based films with the potential to replace environmentally damaging precursors such as hexavalent chromium. Adhesion is improved by adding silicon to the DLC layer at the steel interface, and wear resistance and corrosion are improved with a pure-DLC cap layer. The full-length paper reports the results of a study evaluating use of a range of hydrocarbon precursors with respect to hardness, adhesion, and deposition rate. With the optimization of process parameters, the hardness was improved from an average of 15 GPa using acetylene to 25 GPa using butene, while maintaining a high deposition rate. Several authors have reported the effect of ion energy per carbon atom on the hardness of DLC coatings. Optimum ion energy per car-bon atom of approximately 70 eV is reported for high hardness and high sp3 content, with softer films reported at lower or higher energy per carbon atom. The size of the hydrocarbon precursor molecule affects this energy because the molecule will break apart on impact with the substrate. For example, as an acetylene ion is accelerated across the plasma sheath with an energy of 1,000 eV compared to a butene molecule with the same bias, and assuming a collisionless sheath, the acetylene will have an energy of 500 eV per carbon atom and the butene will have an energy of 250 eV per atom.

Nitride film growth morphology using remote plasma enhanced chemical vapor deposition

Gallium nitride and indium nitride films have been grown by remote plasma enhanced chemical vapor deposition (RPECVD) at temperatures between 570 and 650 °C for GaN and between 350 and 570 °C for InN on different substrates. For GaN vast improvements in film morphology and quality have resulted from reductions in background impurities when compared to previous reports. Epitaxial material can now be grown at 650 °C under optimized growth conditions. Columnar growth still occurs for growth on some substrates, however film coalescence is observed when using appropriate buffer layers and epitaxial growth can also be observed. High resolution SEM images show examples of this. The root-mean-square surface roughness of epitaxial samples, as measured using atomic force microscopy, shows values of as little as 10 Angstroms. While X-ray diffraction shows that these surfaces are not amorphous but have a strong (0001) preferred axis with FWHM limited by instrumental effects to (2θ) 0.085 degrees. The improvement in film quality has allowed heavily doped n-type films to be grown with an electron mobility of 160 cm2/V·s for a carrier concentration of ∼ 1x1019 cm–3 at 650 °C. Moss-Burstein shifted absorption data confirms the high doping level. For InN film growth by RPECVD, columnar growth is commonly observed in the temperature region of interest for films grown directly on sapphire, however film coalescence and epitaxial films are also observed for this material. X-ray diffraction indicates very sharp (0002) peaks with FWHM of (2θ) 0.07 degrees. High resolution SEM images show examples of film morphology at different growth temperatures. Electron backscattered diffraction images indicate a wurtzite structure even for InN films with strong deviations from the accepted lattice parameters. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Low-temperature Deposition of Hydrogenated Microcrystalline Silicon Thin Films by Photochemical Vapor Deposition Technique and Their Application to Thin Film Solar Cells

Hydrogenated microcrystalline silicon (µc-Si:H) thin films were prepared by mercury-sensitized photochemical vapor deposition (photo-CVD) technique at various deposition temperatures. Crystalline volume fraction showed a monotonic decrease with increasing temperature from 125 to 200 °C caused by the enhanced desorption of surface hydrogen atoms. Since a similar decrease has been reported at higher temperatures than 400 °C in plasma-enhanced vapor deposition technique, we conclude that photon energy from ultraviolet radiation serves to activate surface species in photo-CVD process. In spite of the low deposition temperature, the obtained films had excellent material properties. Then, thin film solar cells were fabricated on a Type-U substrate with various haze ratios provided by Asahi Glass using such films as the i-layer. A substrate with a high haze ratio of about 50% was effective in realizing a better light-trapping structure. By decreasing the deposition temperature of the i-layer to 140 °C, conversion efficiency was improved markedly due to the improved film quality brought about by the contributions of photons from ultraviolet radiation to the enhancement of the surface migration of the radicals for reducing defects in the resulting film. Consequently, a maximum solar cell efficiency of 7.4% was obtained.

Overview of Nonlinearity in HTS: What Learned and Prospects for Improvement

The linear surface resistance of the HTS materials is low enough to support a variety of applications that can surpass conventional technology. However, nonlinearity in the form of intermodulation distortion (IMD) is a serious limiting effect for some applications. The nonlinear effects are only weakly correlated with the low-power surface impedance, and considerable material variation has been the hallmark of IMD. With improvement in film quality, the intrinsic nonlinearity now seems to be the most important source of IMD. Presented here is a brief review of the experimental situation and a comparison with the theories of intrinsic nonlinearity. Suggestions for further work are given.

Ｐｄ‐ＰＰＦプロセスに用いられるＰｄめっき液への新規添加剤の効果

Conventionally, IC packaging uses spot-silver plating, die-bonding, wire-bonding and resin molding on copper lead frame materials, along with solder plating of the lead parts to be soldered onto a printed board. This conventional method, however, has some serious problems that need to be addressed, such as Pb in the solder plating. Consequently, Pd-PPF has received attention for both environmental and technical reasons and has been practically applied in lead frame packages. Environmentally, it is Pb-free and the cyan consumption is reduced by the elimination of silver plating, which consumes large amounts of cyan. A number of technical benefits also can be achieved, in addition to the environmental improvement. Currently, it is important to make the Pd-PPF plating thinner, both to improve its properties and to reduce costs in the face of soaring precious metal prices. Thus, a crystalline adjuster was added to a palladium plating solution with a view to improving film quality and solder wettability was examined in order to improve the high-temperature resistance of palladium plated film. With the new additive, solder wettability was dramatically improved, and good solder wettability was obtained even from a thinner Pd-film. Moreover, other properties proved to be equivalent to or better than those achieved with the conventional process.

Effective surface treatments for selective epitaxial SiGe growth in locally strained pMOSFETs

Several dry and wet surface treatment methods are explored for a selective SiGe epitaxial film used to fabricate embedded SiGe pMOSFETs. Pre-clean conditions for the device wafers used in this study were limited by a realistic CMOS process window with tight thermal and chemical budgets due to dopant diffusion and hardmask erosion concerns. The effectiveness of these pre-clean methods is evaluated by SiGe epitaxial film quality and SIMS profiles of key residual contaminants such as C and O at the SiGe–Si substrate interface. As an effective low-temperature dry surface treatment, chemical bake in HCl/H2 at temperature below 800 °C is found to reduce interface C and O peak concentrations by an order of magnitude. Wet clean in multiple cycles of DIW-O3 (ozonated water), SC1 and diluted HF (DHF) is also presented to prepare epitaxial growth surfaces with accumulated damage and chemical residues from previous process steps. SiGe epitaxial film morphology is also observed to improve by increasing DHF clean time. For further improvement of film quality on the most difficult surfaces, Si seed layer was employed to initiate SiGe film nucleation and yield smooth film growth.

Effect of annealing on optical properties and band alignments of ZrO2/Si(1 0 0) by nitrogen-assisted reactive sputtering

ZrO2 films were prepared by nitrogen-assisted radio frequency (RF) reactive sputtering on n-type silicon (100). Optical properties and band alignments of ZrO2 films on Si have been investigated by using x-ray photoelectron spectroscopy (XPS) and spectroscopy ellipsometry (SE). The improved film quality was obtained after annealing in N2/O2 ambient with stable interfacial properties. Optical properties were analysed based on the SE fitting results. According to the valence-band spectrum results, the zero-field energy-band alignments for ZrO2/SiO2/Si stacks were also extracted. Our results indicate that the nitrogen-assisted process shows its outstanding ability in the control of interfaces and has potential application in microelectronics.

Radiology quality assurance in a developing country setting: The 11-valent pneumococcal conjugate vaccine trial, Bohol, Philippines

The endpoint used for a phase 3 pneumococcal conjugate vaccine (PCV) trial in Bohol, Philippines was radiographic consolidation. Only one (Bohol Regional Hospital, BRH) of the four surveillance hospitals had a quality control/quality assurance program (QC/QA) prior to the trial. QC/QA was initiated in the three private hospitals. Radiologists from BRH evaluated radiographs from all hospitals based on recommended standards. Four thousand nine hundred and eighty nine films were analyzed. In 2000, the proportion of good quality films was 65% and 29% in BRH and private hospitals, respectively. By 2004, these increased to 92% and 79%, respectively. Poor film quality was commonly due to absence of collimation and poor contrast. The regular QC/QA implementation was necessary to improve film quality and was particularly important in our PCV trial that used X-ray proven consolidation as an endpoint.

Film quality improvement of CIGS thin film grown by mechanochemical process

We have demonstrated a selenium treatment to enhance the film quality of CIGS films prepared by a mechanochemical process (MCP). It was confirmed that the selenium treatment was useful process in order to improve the film quality by enhancing the sintering and the grain growth. Although the film quality was improved, a selenium layer was deposited on CIGS surface during the selenium treatment. Consequently we developed a selenium removal technique using a Hot Filament Melting (HFM) process, and we succeeded in removing the remained selenium layer on the surface. These results suggested that the selenium treatment followed by the HFM process was useful to improve the film quality grown by the MCP. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoemission, NEXAFS and STM studies of pentacene thin films on Au(1 0 0)

We have investigated the initial stages of the growth of pentacene thin films on the Au(1 0 0) substrate using synchrotron radiation photoelectron spectroscopy (PES), near edge X-ray absorption fine structure (NEXAFS) and scanning tunnelling microscopy (STM). Results indicate a well-ordered structure with the pentacene molecules adopting a predominantly flat orientation with respect to the substrate for coverages of less than three monolayers. NEXAFS and photoemission data indicates the presence of a second molecular orientation for thicker films, with the introduction of a slight tilting away from planar bonding geometry at higher pentacene coverages. STM images of coverages less than three monolayers indicate a well-ordered pentacene structure allowing for the calculation of pentacene unit cell parameters. The pentacene molecular rows adopt a side-by-side bonding arrangement on the surface. For pentacene deposited at room temperature, step edges were observed to act as nucleation centres for film growth. Annealing of the substrate to 373 K was found to remove excess molecules and improve film quality, but did not otherwise change the bonding geometry of the pentacene with respect to the surface.

High frequency broadband PZT thick film ultrasonic transducers for medical imaging applications

A modified sol–gel method is used to prepare PZT thick film on Pt-coated silicon substrate. A new method of vacuum filling sol–gel precursor solution is introduced to improve film quality. The effects of the filling on PZT thick film structure and ferroelectric properties are discussed. The fabrication of a high frequency transducer with the PZT film as the actuating layer is described. The performance of the transducer is measured and results show that the transducer backed by E-Solder without a matching layer has a center frequency of 103 MHz and a bandwidth of 70%. Beam profile measurements show that the transducer has an axial resolution of 9.2 μm and a lateral resolution of 33 μm.

Thirty years trajectory of amorphous and nanocrystalline silicon materials and their optoelectronic devices

A review is given on research trajectory of hydrogenated amorphous and nanocrystalline silicon (a-Si:H and nc-Si) materials with their device applications ongoing since the period of 1970. A brief explanation on the motivation to start amorphous semiconductors research is given to produce a new kind of synthetic semiconductor having continuous energy gap controllability with valency electron controllability. Due to the result of some basic research on the film quality improvement of a-Si:H and nc-Si, some innovative devices had been developed since middle of 1980s in R&D phase such as a-SiC/a-Si heterojunction solar cells, a-Si/a-SiGe and also a-Si/nc-Si tandem type solar cells. Finally, the state of the art on the industrialization of the new devices is introduced and discussed.

Optical and photoelectrical properties of ZnO thin films and the effects of annealing

Single-crystalline ZnO thin films were grown using plasma-assisted molecular beam epitaxy. The effect of post growth annealing was studied using photoluminescence and photoconductivity for characterisation. Photoluminescence of annealed samples shows a strong improvement in response between non-annealed and annealed samples. Sharp excitonic features as well as LO phonon replicas were observed for annealed samples, suggesting improved film quality, although the annealing temperature has to be carefully adjusted. Photoconductivity reveals strong multi-peak features at the bandedge and, therefore helps identifying the features in the photoluminescence spectra. Temperature and chopping speed dependencies show an interesting behaviour of the photoconductivity peaks observed for samples annealed at close to optimum temperatures.

Pulsed laser deposition of Co and growth of CoSi2 on Si(111)

Monolayers of Co were prepared by pulsed laser deposition (PLD) and thermal deposition (TD) on Si(111) substrates. The surface structure and morphology were studied as a function of annealing temperature with scanning tunneling microscopy and low-energy electron diffraction (LEED). Comparing PLD to TD in the monolayer regime, we find surface phases with lower Co content in the top layer for annealing temperatures below 500 °C, indicating an implantation of Co into the Si substrate. The implanted Co leads to an increased intermixing of Co and Si and a higher density of nucleation centers for Co multilayers produced by PLD compared to TD. Multilayer PLD films therefore show an improved film quality, which is detected by an increased intensity of the LEED reflectivity.

Low temperature sintering of 8YSZ electrolyte film for intermediate temperature solid oxide fuel cells

At 200 °C, 8 mol% yttria doped zirconia (8YSZ) nanocrystals were synthesized through a hydrothermal process for 24 h. Characterizations revealed that the as-synthesized 8YSZ powder was weakly agglomerated and had a surface area of 121 m 2/g and an average grain size of ∼9 nm. Sintering behaviors of the 8YSZ powder were studied via isothermal and non-isothermal experiments. It demonstrated that the powder has high sintering activity, where 8YSZ green films prepared via dip coating using the slurry directly formed by the hydrothermal process can be fully densified at 1000 °C. The thickness of the sintered film can be controlled through adjusting the 8YSZ concentration in the slurry and repeating the dipping–coating–sintering cycle. The superior sinterability achieved in the present study was mainly attributed to the high green density and homogeneity of the green bodies with narrow-distributed interparticle pore structure. The low sintering temperature is of great practical importance for improving film quality and facilitating co-sintering of 8YSZ films together with other SOFC components.

Design and Synthesis of Hydroxyapatite Composites Containing an mPEG−Dendritic Poly(l-lysine) Star Polycaprolactone

The design and synthesis of star polycaprolactone−hydroxyapatite films for use as a biodegradable matrix for bone tissue engineering will be presented. mPEG-dendritic-poly(l-lysine) terminated with glycolic acid residues serve as the star polymer cores for attachment of polycaprolactone by ring-opening polymerization of e-caprolactone. Initial studies involved testing physical blends of the tert-butoxycarbonyl (Boc) and glycolamide terminated dendrons, generations zero through six, with varying concentrations of hydroxyapatite (HA). The star polymer had not only drastically different solubility but also greatly improved film quality. Further improvements were made in film quality and homogeneity by utilizing the star polymers in the presence of a chemical synthesis of hydroxyapatite. The improved films were then tested for their mechanical strength properties. The star polymer from generation 6.5 and 20 wt % of hydroxyapatite exhibited good mechanical properties with an average Young's modulus of 1.77 MPa...

Identification of a self-limiting reaction layer in Ni–3 at.% W rolling-assisted biaxiallytextured substrates

Analytical transmission electron microscopy was used to identify the presenceof a self-limiting reaction layer developed within rolling-assisted biaxiallytextured Ni–3 at.% W substrates during the pulsed laser deposition of thickYBa2Cu3O7−δ (YBCO) films. Improvements in YBCO film quality and physicalproperties were attributed in part to the development of aNiWO4 layer at the buffer–substrate interface. The formation ofNiWO4 between NiO and the Ni–3 at.% W substrate was observed to restrict the growth of NiO withinthe coated conductor during YBCO deposition at elevated temperatures. A 5–8 nm thickNiWO4 layer, identified through both electron diffraction and energy dispersive spectroscopy,was found to limit NiO growth to between 20 and 25 nm in thickness. TheNiWO4 layer was found to have a [100] orientation relationship to the substrate normal, withmultiple variants observed.

2-Step Growth Method and Microcrystalline Silicon Thin Film Solar Cells Prepared by Hot Wire Cell Method

Hot Wire Cell (HW-Cell) method has been developed in order to grow microcrystalline silicon (µc-Si:H) thin films. The influence of various deposition parameters on the structural and electrical properties of the films was investigated to improve film quality. It was found that the concentrations of O and C atoms in µc-Si:H films could be reduced from the order of 1021 cm-3 to the order of 1020 cm-3 by decreasing the partial pressure of SiH4 from 100 mTorr to 3 mTorr. Then, a novel 2-step growth method was proposed in order to reduce the incubation layer in the initial growth of µc-Si:H i-layer. By using this method, Jsc largely increased (10.11 → 18.32 mA/cm2), and as a result, the conversion efficiency of 3.9% could be achieved. The influence of the incubation layer on solar cell performances was also investigated by a numerical analysis. To date, a conversion efficiency of 5.3% (Voc: 0.48 V, Jsc: 20.56 mA/cm2, F.F.: 0.54, active area: 0.086 cm2, AM1.5) was obtained for µc-Si:H solar cells with an i-layer thickness of 1.0 µm. Furthermore, high-rate depositions were investigated and a maximum deposition rate of 11.5 nm/s could be achieved. µc-Si:H solar cells fabricated at a high deposition rate of 1.5 nm/s showed a conversion efficiency of 2.8% (Voc: 0.42 V, Jsc: 12.31 mA/cm2, F.F.: 0.54, active area: 0.086 cm2, AM1.5).

Study the effect of O 2 addition on hydrogen incorporation in CVD diamond

The effect of a small amount of O 2 addition on film quality and hydrogen incorporation in chemical vapour deposition (CVD) diamond films was investigated and the films were grown using a 5-kW microwave plasma CVD reactor. Film quality and bonded hydrogen were characterized using micro-Raman and Fourier transform infrared (FTIR) spectroscopy, respectively. It was found that in general for films grown using CH 4/H 2 plasma both without and with O 2 addition, the hydrogen incorporation increases with increasing substrate temperature, while a small amount of O 2 addition (O 2/CH 4=0.1) into CH 4/H 2 (4%) plasma strongly suppresses the incorporation of hydrogen into the film. Raman spectra show that the added oxygen improved film quality by etching and suppressing the amorphous carbon component formed in the film. The above effect of oxygen addition on hydrogen incorporation and film quality is discussed according to the growth mechanism of CVD diamond. The CVD diamond specific hydrogen related IR vibration at 2828 cm −1 appears as a sharp and strong peak only in the FTIR spectra of poor quality films grown at high temperature both without and with O 2 addition, but it appears much stronger in the film grown without O 2 addition. This result experimentally excludes the assignment of the 2828 cm −1 peak arises from hydrogen bonded to oxygen related defect in the literature.