bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of 239/238Pu-Zirconolite Ceramic Pellets by Natural Sintering
Authors: Advocat T. , Jorion F. , Marcillat T. , Leturcq G. , Deschanels X. , Boubals J. M. , Bojat L. , Nivet P. , Peuget S.
Published: April 2011

Zirconolite is a potential inorganic matrix that is currently investigated in France, in the framework of the 1991 radioactive waste management law, with a view to provide durable containment of the trivalent and tetravalent minor actinides like neptunium, curium, americium and small quantities of unrecyclable plutonium separated from other nuclear waste. To confirm the actinide loading capacity of the zirconolite calcium site and to study the physical and chemical stability of this type of ceramic when subjected to alpha self-irradiation, zirconolite ceramic pellets were fabricated with 10 wt% plutonium oxide (isotope 239 or 238). The 55 pellets are dense (> 93.3% of the theoretical density on average) and free of cracks. They are characterized by a grain size of between 10 and 20 micrometers. X-ray diffraction analyses confirmed the presence of the zirconolite 2M crystalline structure.
Key Scientific Issues Related to the Evolution of Spent Nuclear Fuel in Long Term Dry Storage and Geological Disposal
Authors: POINSSOT Christophe , FERRY Cécile , GRAS Jean-Marie
Published: April 2011

The anticipated long term evolution of spent nuclear fuel as well as the remaining scientific key issues are presented for the various boundary conditions that can be encountered in long term dry storage and geological disposal. Spent fuel is expected to evolve significantly in closed system conditions which are representative of long term dry storage and the first stages of geological disposal. The mechanical evolution of the grain boundaries, the fate of helium and the evolution of the RN location within the pellet are the three major questions to be addressed which could significantly modify the physical and chemical state of the fuel. In addition, mechanisms and kinetics of fuel alteration by water in deep geological repository are still to be more deeply understood, in particular the inventory of the instant release and the radiolytic dissolution processes, to get a robust and reliable source term.
Effect of Alpha Radiolysis on UO2Dissolution under Reducing Conditions
Authors: Mennecart T. , Grambow B. , Fattahi M. , Blondiaux G. , Andriambololona Z.
Published: April 2011

Effects of water radiolysis on the dissolution rate of UO2were studied by irradiating UO2colloids with an alpha particle beam of a cyclotron. The solution was kept under reducing conditions by applying a current of -10 or -50 nA and an ultrahigh purity argon bubbling. The solution pH was fixed at 6 during experiment. The particle flux was 1.1×1011α.cm−2.s−1entering in solution with an energy of 5 – 6 MeV. Despite initial reducing conditions water radiolysis increased the dissolution rate of uranium dioxide due to reaction with oxidizing radiolytic species such as H2O2, O2, OH•, HO2•, ClO3−. The monitoring of the redox potential showed that the solutions became rapidly oxidizing. The dissolution rate values were between 0.01 and 26 mg·m−2·d−1depending on the ratio of the irradiated UO2mass to the solution volume. This dependency is caused by hydrogen peroxide consumption at the UO2surface. The rate of hydrogen peroxide consumption by reaction with colloids corresponds to an equivalent rate of UO2oxidation/dissolution between 2 and 60 mg.m−2.d−1indicating that only a small fraction of produced H2O2is consumed by the dissolution reaction.
KBS-TR-90 Twenty-five Years On - Progress in the Understanding of the Long-term Corrosion Behaviour of Copper Canisters
Authors: Werme Lars , King Fraser , Ahonen Lasse , Taxén Claes , Vuorinen Ulla
Published: April 2011

In 1978, the Swedish Corrosion Institute published a report describing an assessment of the long-term corrosion behaviour of copper canisters for nuclear waste disposal. They concluded that the canisters would remain intact for a period exceeding 100,000 years in a deep underground repository in the Fennoscandian bedrock. In the intervening 25 years a great deal has been learnt about the corrosion of copper in the expected repository environment. In 2001, SKB and Posiva reviewed this new information and re-assessed the predicted canister lifetime [1]. It was concluded that the original prediction made in 1978 of canister lifetimes exceeding 100,000 years remains valid.
A Weld that Lasts for 100,000 Years: Friction Stir Welding of Copper Canisters
Authors: Cederqvist Lars
Published: April 2011

Friction Stir Welding (FSW) is a novel solid-state joining process where the work pieces are joined together using a rotating non-consumable tool. The process has mainly been used for joining aluminium alloys, and has not yet been used in production for any other metal. However, the results from the development program confirm that FSW can consistently seal 50mm thick copper canisters without creating defects. A new machine is now installed at SKB's Canister Laboratory to further automate the process to production level.
Earthquake Induced Rock Shear Through a Deposition Hole. Effect on the Canister and Buffer
Authors: Börgesson L. , Johannesson L.-E. , Hernelind J.
Published: April 2011

Existing fractures crossing a deposition hole may be activated and sheared by an earthquake. The effect of such a rock shear has been investigated in a project that includes both laboratory tests and finite element calculations.

A number of laboratory tests have been performed with shearing of water-saturated bentonite samples at different densities and shear rates. From those tests a material model of the buffer that takes into account the shear rate has been formulated. Shear rates up to 6 m/s have been tested.

The rock shear has been modelled with finite element calculations with the code ABAQUS. A 3D finite element mesh of the buffer and the canister has been created and a number of calculations with simulation of a rock shear have been performed. The rock shear has been assumed to take place perpendicular to the canister axis in either the centre of the deposition hole or at the ¼ point. The shear calculations have been driven to a total shear of 20 cm. Buffer densities at water saturation between 1950 and 2100 kg/m3 and shear rates between 0.0001 and 1000 mm/s have been modelled. The influence of buffer density, shear plane location, the shear rate and the magnitude of the shear displacement are analysed and discussed.

The results show that the influence of especially the density of the buffer and the location of the shear plane are very strong but also that the shear rate and the magnitude of the shear displacement have a significant effect.
Adsorption and Retention of U-238 and Th-232 from Groundwater Using BIOS
Authors: Anderson Craig R. , Pedersen Karsten
Published: April 2011

Biofilms were grown in situ 296 metres below sea level in the Äspö Hard Rock Laboratory. The prominent organism in these biofilms wasGallionella ferruginea, which is an iron oxidising chemolithotrophic microorganism that grows in low oxygen conditions. This organism grows an organic stalk structure capable of binding and concentrating trace metals. This stalk structure also allows amorphous ferric iron oxyhydroxides, or BIOS, (bacteriogenic iron oxides) to precipitate. The pH of the groundwater within the system was between 7.4 and 7.6, with Eh potential between 150 and 190 mV and oxygen saturation between 3 and 15%. Biofilms developed within two weeks and were sampled every two weeks for three months. Cell number and stalk length was recorded for each sample. The concentration of Cr, Ni, Cu, Zn, Mo, REE (rare earth elements), U-238 and Th-232 was measured by ICP-MS. Early results suggested thatGallionellabiofilms and associated BIOS could potentially concentrate trace metals up to 1000 fold higher than levels within the host rock and over 1 000 000 times the levels in the groundwater over a period of years. These new experiments indicate thatGallionellabiofilms and BIOS can rapidly attenuate metals to levels over 1000 fold higher than the levels in the groundwater. This process can occur anywhere where reduced groundwater enters the waste repository tunnel, open cavities or where groundwater extrudes at the surface. Because of this, there is huge potential to use biofilms and BIOS for retention of radionuclides and pollution control.
Site Investigations of Potential Repository Sites in Sweden
Authors: Wikberg Peter , Ahlbom Kaj , Olsson Olle
Published: April 2011

The Swedish nuclear waste management programme has entered the site investigation phase. Early 2002 SKB received permission from the municipalities of Östhammar and Oskarshamn to perform site investigations for a potential deep geologic repository for spent nuclear fuel. The goal of the site investigation phase is to obtain a permit to build the deep repository for spent nuclear fuel. In parallel with the investigations, consultations will be held with county administrative boards, regulatory authorities and municipalities, as well as with members of the public.
A Preliminary Chemical Toxicity Assessment for the Nirex Disposal Concept
Authors: Askarieh M. M. , Atkinson R. , Baker A. J. , Chambers A. V. , Heath T. G. , Williams S. J.
Published: April 2011

The role of Nirex is to provide the United Kingdom with safe, environmentally sound and publicly acceptable options for the long-term management of all intermediate level and some low level radioactive waste. Nirex has developed its Phased Disposal Concept as one option for the long-term management of radioactive materials. The Phased Disposal Concept represents a stepwise and reversible approach to the disposal of radioactive waste within a deep geological repository that involves the immobilisation of wastes in containers (mainly fabricated from stainless steel) that are surrounded by a cementitious backfill.

The wastes for potential disposal contain materials that may require consideration on the basis of their potential non-radiological hazards. This paper describes a preliminary two-stage methodology for assessing the post-closure impact of the disposal of chemically toxic materials to a conceptual Nirex repository. The study suggests some materials either exceeded current estimates of safe levels, or their impact could not be quantified at this stage but was considered to be of concern. These materials included beryllium, phenol, benzene, and nitrite.
Analogues for the Corrosion-induced Expansion of Iron in HLW containers
Authors: Smart Nicholas R. , Adams Rachel , Werme Lars
Published: April 2011

In Sweden, spent nuclear fuel will be encapsulated in sealed cylindrical canisters, consisting of a cast iron insert and a copper outer container. The canisters will be placed in a deep geologic repository and surrounded by bentonite. If a breach of the outer copper container were to occur the cast iron insert would undergo anaerobic corrosion, forming a magnetite film whose volume would be greater than that of the base metal. In principle there is a possibility that accumulation of iron corrosion product could cause expansion of the copper canister. Anaerobic corrosion rates are very slow, so in the work described in this paper reference was made to analogous archaeological materials that had been corroding for long periods in natural anoxic aqueous environments. This paper describes a number of archaeological artefacts containing iron and copper corroding in constrained geometries in anoxic natural waters. No evidence has been obtained which would suggest that severe damage is likely to occur to waste canisters as a result of expansive corrosion of cast iron under repository conditions.
Amorphous Silicon Backplane with Polymer MEMS Structures for Electrophoretic Displays
Authors: Daniel J.H. , Krusor B.S. , Chopra N. , Street R.A. , Kazmaier P.M. , Ready S.E. , Ho J.H.
Published: April 2011

The development of electronic paper has been a long-term goal and electrophoretic displays are a promising candidate for this application. Apart from developing the electrophoretic display medium there are important issues to solve regarding the overall system. The importance of the electronic addressing method increases with the demand for arbitrary images or text. We have developed and tested active-matrix backplanes based on amorphous silicon technology, as well as the driver electronics. The electrophoretic ink is combined with the backplane employing polymer MEMS cell structures. This system allows us to display high-resolution images and it is a good test bed for investigating various parameters of the electrophoretic display medium and of the electronics.
Tritium Induced Defects in Amorphous Silicon
Authors: Whitaker J. , Viner J. , Zukotynski S. , Johnson E. , Taylor P.C. , Stradins P.
Published: April 2011

We report the growth of tritium induced defects in tritium doped hydrogenated amorphous silicon (a-Si:H,T) as measured by electron spin resonance (ESR) and photothermal deflection spectroscopy (PDS). The measurements allow one to examine the accumulation of defects in a-Si:H,T where the defect production mechanism is known. Defects produced by tritium decay are found to be much less numerous than the number of decayed tritium atoms and they are metastable like Staebler-Wronski defects. These results provide new insight into the metastable defect creation and the role of hydrogen motion.
H Evolution from Nano-Crystalline Silicon- Comparison of Simulation and Experiment
Authors: Biswas R. , Pan B. C.
Published: April 2011

The temperature dependent H evolution from a-Si:H provides unique information on the H-bonding and microstructure. Traditional undiluted a-Si:H films show a high temperature H-evolution peak near 600°C. However device-quality compact nanocrystalline silicon films grown near the phase boundary of amorphous and microcrystalline growth show a new low temperature H- evolution peak near 400°C in addition to a second high temperature peak near 600°C. The origin of this peak cannot be attributed to microvoids or a substantial density of dihydride species typical of porous low-temperature films. We have simulated the H evolution using a molecular dynamics generated model of nanocrystalline silicon, where nano-crystallites reside in a background amorphous matrix. An excess density of H occurs at the crystallite surface. We find a low temperature evolution peak at 250-400°C, where the H-evolution starts from the surface of the nano-crystallite. In addition there is a higher temperature peak at 700-800°C providing good agreement with H-evolution measurements. The mobile H is found to exist in both the bond-centered type of species and H2 molecules – which has implications for H-diffusion models.
The p-channel a-Si:H Thin Film Transistor with Plasma Etched Copper Electrodes
Authors: Nominanda Helinda , Liu Guojun , Lee Hyun Ho , Kuo Yue
Published: April 2011

P-channel thin film transistors (TFTs) with a copper (Cu) gate, source, and drain electrodes, prepared by a novel plasma etching process, have been fabricated and studied. The p-channel TFT characteristics are similar to those of the p-channel TFT with Mo electrodes. The influence of the channel length on the TFT characteristics, such as mobility, threshold voltage, and on-off current ratio, was examined. In spite of its low mobility, good device characteristics, such as ohmic contacts, were obtained. Most of the TFT characteristics, except the threshold voltage, were not affected by an extended high-temperature annealing step. The increase of the threshold voltage was probably due to the lack of a diffusion barrier between the gate Cu and the gate SiNx layer.
Intrinsic and Doped m c-Si:H TFT Layers using 13.56 MHz PECVD at 250°C
Authors: Lee Czang-Ho , Striakhilev Denis , Nathan Arokia
Published: April 2011

Undoped and n+ hydrogenated microcrystalline silicon (μc-Si:H) films for thin film transistors (TFTs) were deposited at a temperature of 250°C with 99 ∼ 99.6 % hydrogen dilution of silane by standard 13.56 MHz plasma enhanced chemical vapor deposition (PECVD). High crystallinity m c-Si:H films were achieved at 99.6 % hydrogen dilution and at low rf power. An undoped 80 nm thick m c-Si:H film showed a dark conductivity of the order of 10−7 S/cm, the photosensitivity of an order of 102, and a crystalline volume fraction of 80 %. However, a 60 nm thick n+ μc-Si:H film deposited using a seed layer showed a high dark conductivity of 35 S/cm and a crystalline volume fraction of 60 %. Using n+ μc-Si:H films as drain and source contact layers in a-Si:H TFTs provides substantial performance improvement over n+ a-Si:H contacts. Finally, fully μ c-Si:H TFTs incorporating intrinsic m c-Si:H films as channel layers and n+ μc-Si:H films as contact layers have been fabricated and characterized. These TFTs exhibit a low threshold voltage and a field effect mobility of 0.85 cm2/Vs, and are far more stable under gate bias stress than a-Si:H TFTs.
Aluminum-Induced Crystallization of PECVD Amorphous Silicon
Authors: Jenq Kenneth , Chang Shawn S. , Lian Yaguang , Pan Grant Z. , Rahmat-Samii Yahya
Published: April 2011

Aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) in a conventional furnace with N2 protection has been studied at reaction temperatures ranging from 200 to 500°C by using optical microscopy, and transmission and scanning electron microscopy. The a-Si and Al layers were deposited with plasma-enhanced chemical vapor deposition (PECVD) and electron beam evaporation, respectively. The structures in the study are Al/a-Si and a-Si/Al on Si or glass wafers coated with 3000 Å PECVD SiO2. It was found that Al induces crystallization of a-Si for both Al/a-Si and a-Si/Al structures by exchanging positions of Al and Si layer through diffusion of Si into Al and the grain size of crystallized Si (c-Si) increases with the decrease of AIC temperature. AIC for Al/a-Si structures starts at a temperature as low as 200°C, which is 100°C lower than that for a-Si/Al structures. Kinetics analysis found that the activation energies are 1.76 eV and 1.65 eV for both Al/a-Si and a-Si/Al structures, respectively. The quality of AIC c-Si depends on the order, thickness and thickness ratio of a-Si to Al. Microstructural observations indicated that the c-Si for Al/a-Si structures is better and more suitable for use in fabrication of thin film transistors (TFTs) than that for a-Si/Al structures.
Initial Interaction of Crystalline Al/Amorphous Si Bilayer during Annealing
Authors: Zhao Yonghao , Wang Jiangyong , Mittemeijer Eric J.
Published: April 2011

Initial interaction of a magnetron sputter deposited Al(100 nm, {111} fibre textured)/Si(150 nm, amorphous) bilayer, induced by isothermally annealing at 523 K for 60 min in a vacuum of 2.0×10−4 Pa, was studied by X-ray diffraction, Auger electron microscopy and focused-ion beam imaging techniques. Upon annealing, the crystalline Si had grown into the grain boundaries of the Al layer with a {111} texture, a crystallite size of approximate 12 nm and a tensile stress of +138 MPa. Simultaneously, the Al grains had grown into the Si layer from the original interface of the a-Si and Al sublayers with the lateral grain growth. The stress parallel to the surface of the Al layer had changed from +27 MPa to +232 MPa after annealing.
In-Situ Aluminum-Induced Crystallization of Si Thin-Films on Glass Substrates above the Eutectic Temperature using HW-CVD
Authors: Ebil Ozgenc , Aparicio Roger , Birkmire Robert
Published: April 2011

The growth of poly-Si films on glass substrates using an in-situ aluminum-induced crystallization (AIC) process above the Si-Al eutectic temperature of 577°C is discussed. Silicon films were deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) onto Al coated Corning 7059 glass substrates. The back surface coverage and the average grain size of the films were compared as a function of growth rate and the Si/Al thickness ratio. SEM and EDS analysis of samples with a Si/Al ratio of 1 revealed two domains in the films which varied in morphology and composition; rougher areas containing a mixture of Si and Al with Al content up to 35%, and relatively smoother areas composed of almost entirely Si. This non-uniform morphology seems to be the result of the absence of a native oxide layer when a liquid phase is formed during the deposition. Si grains as large as 50 m m in diameter and back surface coverage up to 90% were obtained for both the Si/Al ratios of 1 and 5. However, no continuous Si films were obtained. The sample with a Si/Al ratio of 1 had columnar grains reaching to the film surface, whereas on the Si/Al ratio of 5 large Si grains did not extend to the film surface.
A real-time optical signal and image processing p-i-n/p-i-n device
Authors: Vieira M. , Louro P. , Fernandes M. , Fantoni A. , Mendes C. , Martins J.
Published: April 2011

Large area (4x4 cm2) optical signal and image processing (OSIP) devices were produced at low temperatures (110°C) by PE-CVD. The OSIP device consists of two stacked sensing/switching diodes (p(SiC:H)/i(Si:H)/n(SiC:H)) with or without an internal blocking layer between them and two semitransparent contacts. An optical scanner is used for charge readout. In this work the main emphasis will be put on the analysis of the optical characteristics. The use of a metal grid (290x290 μm2 Cr pixels with 40 m m spacing) between the two diodes, working as light screening layer or as floating anode via an a-SiN insulator layer, is analyzed. Its influence on the transfer functions, resolution, responsivity and response time of the sensor is presented. The various design parameters trade-offs are discussed. The optical-to-electrical transfer characteristics show high quantum efficiency, broad spectral response, and reciprocity between the optical and the electrical images. When the light screening floating anode is present an effective optical decoupling from both photodiodes is achieved while maintaining a good electrical conductivity and an increased light-to-dark sensitivity. A trade-off is established between sensor design and light pattern and scanner wavelengths in order to minimize the cross talk between the write and the read beams and to improve the light to dark sensitivity.
Detection Limits of a nip a-Si:H Linear Array Position Sensitive Detector
Authors: Martins R. , Costa D. , Águas H. , Soares F. , Marques A. , Ferreira I. , Borges P. , Fortunato E.
Published: April 2011

This paper presents results of the spatial and frequency detection limits of an integrated array of 32 one-dimensional amorphous silicon thin film position sensitive detectors with a nip structure, under continuous and pulsed laser operation conditions. The data obtained show that 0.45×0.06 cm arrays, occupying a total active area of about 1 cm2 have a spatial resolution better than 10 m m (modulation transfer function of about 0.2), with a cut-off frequency of about 6.8 KHz. Besides that, under pulsed laser conditions the device non-linearity has its minimum (about 1.6%), for a frequency of about 200Hz. Up to the limits of the cut-off frequency, the device nonlinearity increases to values above 4%.
Comparison of Phase Diagrams for vhf and rf Plasma-Enhanced Chemical Vapor Deposition of Si:H Films
Authors: Ferreira G.M. , Ferlauto A.S. , Pearce J.M. , Wronski C.R. , Ross C. , Collins R.W.
Published: April 2011

Deposition phase diagrams are convenient for categorizing the evolution of the surface microstructure and phase with accumulated thickness for hydrogenated silicon (Si:H) films during plasma-enhanced chemical vapor deposition (PECVD). They can also be used to assess the electronic quality and device suitability of Si:H, based on previous correlations. In this study, phase diagrams have been applied in a comparison of Si:H PECVD using two different plasma excitation frequencies (rf: 13.56 MHz; and vhf: 60 MHz). Smooth crystalline Si (c-Si) wafer substrates have been used to obtain the surface roughness evolution with maximum sensitivity in the amorphous silicon (a-Si:H) growth regime. This study has shown that under all explored conditions of plasma power, frequency, and gas pressure, yielding deposition rates of 0.5-20 Å/s, a-Si:H exhibits improved microstructural characteristics with increasing H2-to-SiH4 flow ratio R right up to the amorphous-to-(mixed-phase microcrystalline) [a→(a+μc)] boundary of the phase diagram. For depositions at R values much lower than the a→(a+μc) transition for a thick film, vhf PECVD can provide a significant improvement in microstructural evolution over rf PECVD, for a given deposition rate. For optimum R just below the a→(a+μc) transition, however, vhf and rf a-Si:H films exhibit remarkably similar structural evolution for a given rate.
Identification of Possible Bonding Sites for Post Deposition Oxygen Absorption in Microcrystalline Silicon
Authors: Gedvilas L. M. , Mahan A. H.
Published: April 2011

Using infrared (IR) spectroscopy and x-ray diffraction, the nature of the grain boundaries in twom c-Si films deposited by hot wire CVD, displaying similar crystalline volume fractionsbut very different behavior upon exposure to atmospheric contaminants, is analyzed. For the film exhibiting significant post deposition oxidation, the IR spectrum in the 2100 cm−1 Si-H stretch mode region contains two sharp and very narrow peaks, suggesting that the crystallites have been incorporated into them c-Si films with their hydrogenated surfaces relatively intact.By comparing these peak frequencies to those in the literature for Si-H bonding on c-Si surfaces, we identify certain crystallite orientations which, when comprising the c-Si grain boundaries, are particularly susceptible to oxidation. We further suggest that the distribution of H in this grain boundary/crystallite surface region is crucial for depositing c-Si films with good electronic properties and minimal post deposition oxidation.
High-quality hydrogen-diluted a-SiNx:H films deposited by hot-wire chemical vapor deposition
Authors: Liu Fengzhen , Gedvilas Lynn , Keyes Brian , Sanchez Errol , Wang Shulin , Wang Qi
Published: April 2011

We have studied the effect of H dilution on silicon nitride films deposited by the hot-wire chemical vapor deposition (HWCVD) technique using SiH4, NH3, and H2 gases. We found that H dilution significantly enhances the properties at silicon nitride films. The N content in the film increases by more than 2 times compared to the film without dilution, based on FTIR measurements. As a result, we can achieve high-quality a-SiNx:H films at low substrate temperature using a much lower gas ratio of NH3/SiH4(∼1) compared to a ratio of about 100 for conventional deposition by HWCVD. We also found that dilution decreases the H content in the films. More importantly, diluted SiNx films are conformal. Scanning electron microscopy measurements show a nearly 100% surface coverage over a sharp object. Electric breakdown measurement shows a well-insulated film with more then a few MV/cm for the breakdown field.
Optical and Electronic Characterization of a-SiGe:H Thin Films Prepared by a Novel Hollow Cathode Deposition Technique
Authors: Soukup R. J. , Ianno N. J. , Darveau Scott A. , Exstrom Christopher L.
Published: April 2011

Using a novel hollow cathode plasma-jet reactive sputtering system in which an intense plasma, ignited in an Ar/H2 flow, is directed through silicon and germanium nozzles, a series of a-SiGe:H thin films have been prepared on silicon and glass substrates. These films have been optically characterized by infrared (IR) spectroscopy and spectroscopic ellipsometry (335-1000nm). Total hydrogen concentrations, as determined by FTIR, varied with deposition conditions and ranged from 2.5 × 1021 to 1.6 × 1022 atom cm−3 and correlated with secondary ion mass spectrometry (SIMS) elemental analyses to within 10%. Conductivity measurements in the dark and under simulated AM1 solar illumination have indicated that the films properties are very good. The light to dark conductivity ratio has consistently been greater than 1000 for films with band gaps down to 1.3 eV.
Large-Area Hydrogenated Amorphous and Microcrystalline Silicon Double-Junction Solar Cells
Authors: Yan Baojie , Yue Guozhen , Banerjee Arindam , Yang Jeffrey , Guha Subhendu
Published: April 2011

Hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon ( c-Si:H) double-junction solar cells were deposited on a large-area substrate using a RF glow discharge technique at various rates. The thickness uniformity for both a-Si:H and c-Si:H is well within ± 10% and the reproducibility is very good. Preliminary results from the large-area a-Si:H/m c-Si:H double-junction structures show an initial aperture-area efficiency of 11.8% and 11.3%, respectively, for 45 cm2 and 461 cm2 size un-encapsulated solar cells. The 11.3% cell became 10.6% after encapsulation and stabilized at 9.5% after prolonged light soaking under 100 mW/cm2 of white light at 50°C. High rate deposition of the c-Si:H layer in the bottom cell was made using the high-pressure approach. An initial active-area (0.25 cm2) efficiency of 11.3% was achieved using an a-Si:H/m c-Si:H double-junction structure with 50 minutes of c-Si:H deposition time.
Dominant Effect of p/i Interface on Dark J-V Characteristics in p-i-n Nano-crystalline Si Solar Cells
Authors: Das U. , Bozsa A. , Madan A.
Published: April 2011

Nanocrystalline silicon (nc-Si) based p-i-n solar cells were fabricated onto various substrates using modified pulsed PECVD technique. Dark J-V characteristics of nc-Si p-i-n solar cells were found to depend strongly on the substrates and are studied at different i-layer thickness and varying the p/i interface structures. In this work, we report an almost constant diode quality factor (n = 1.2 – 1.3) up to the thickness of 3.8 μm for the devices grown on “suitably textured” ZnO substrates. The rather insensitive variation of n with i-layer thickness suggests that the dark J-V characteristics are not dominated by bulk recombination for the devices grown on textured ZnO, which prevents grain collision in the i-layer. In contrast to that, a significant change of n (1.8 – 1.3) was found while changing the p/i interface using various duration of H2 plasma treatment of nc-p surface (ST). The p/i interface structure in nc-Si p-i-n device plays the crucial role either by changing the p/i interface defects or the film structure at p/i interface determines the quality of subsequently grown nc-i layer and hence the whole device performance.
Dopant diffusion in amorphous silicon
Authors: Duffy R. , Venezia V.C. , Heringa A. , Hopstaken M.J.P. , Maas G.C.J. , Dao T. , Tamminga Y. , Roozeboom F.
Published: April 2011

In this work we investigate the diffusion of high-concentration ultrashallow boron, fluorine, phosphorus, and arsenic profiles in amorphous silicon. We demonstrate that boron diffuses at high concentrations in amorphous silicon during low-temperature thermal annealing. Isothermal and isochronal anneal sequences indicate that there is an initial transient enhancement of diffusion. We have observed this transient diffusion characteristic both in amorphous silicon preamorphized by germanium ion implantation and also in amorphous silicon preamorphized by silicon ion implantation. We also show that the boron diffusivity in the amorphous region is similar with and without fluorine, and that the lack of diffusion for low-concentration boron profiles indicates that boron diffusion in amorphous silicon is driven by high concentrations. Ultrashallow high-concentration fluorine profiles diffuse quite rapidly in amorphous silicon, and like boron, undergo a definite transient enhancement. In contrast, ultrashallow high- concentration phosphorus and arsenic profiles did not significantly diffuse in our experiments.
Xafs as a Direct Local Structural Probe in Revealing the Effects of C Presence in B Diffusion in Sige Layers
Authors: Sahiner M. Alper , Ansari Parviz , Carroll Malcolm S. , Magee Charles W. , Novak Steven W. , Woicik Joseph C.
Published: April 2011

The local structural information around the germanium atom in boron doped SiGe alloys is important in understanding the dopant diffusion mechanisms. Epitaxial SiGe test structures with B and C markers were grown on Si substrates by using rapid thermal chemical vapor deposition (RTCVD). The local structure around the Ge atom was probed using Ge K-edge x-ray absorption fine structure spectroscopy (XAFS) to determine the effects of the B and C on the Ge sites. The concentration profiles obtained from secondary ion mass spectroscopy are correlated with the Ge XAFS results. The modifications on the local structure around the Ge atoms are revealed from the multiple scattering analyses on the Ge near-neighbors. First and second shell XAFS fits to the B doped SiGe samples indicate a direct evidence of the Ge trapping of the B atoms whereas the C is randomly distributed to the Si lattice sites.
Investigation of Fluorine Effect on the Boron Diffusion by Mean of Boron Redistribution in Shallow Delta-doped Layers
Authors: Halimaoui A. , Hartmann J. M. , Laviron C. , El-Farhane R. , Laugier F.
Published: April 2011

Previously published articles have shown that co-implanted fluorine reduces transient enhanced diffusion of boron. However, it is not yet elucidated whether this effect is due to interaction of fluorine with point-defects or boron atoms. In this work, we have used boron redistribution in a shallow Delta-doped Si structures in order to get some insights into the role of fluorine in the boron diffusion. The structures consisted of 3 boron-doped layers separated by 40nm-thick undoped silicon. The samples were given to Ge preamorphization and F co-implant. SIMS depth profiling was used to analyse boron redistribution after annealing. The results we obtained strongly suggest that fluorine is not interacting with point-defects. The reduction in boron TED is most probably due to boron-fluorine interaction.
Fabrication of p+/n Ultra Shallow Junctions (USJ) in silicon by excimer laser doping from spin-on glass sources
Authors: Coutanson S. , Fogarassy E. , Venturini J.
Published: April 2011

In this work was investigated a simple laser doping method employing doped oxide glass films as dopant source (up to 2.1021cm−3) which are deposited onto silicon by the spin coating technique. Both short (20 ns) and long (200 ns) pulse duration excimer laser beams were used to deposit a large amount of energy in a short time onto the near-surface region. Under suitable conditions, the irradiation leads to surface melting and dopant incorporation by liquid phase diffusion from the surface. Boron distribution profiles in the two pulses duration regimes were studied as well as their electrical properties, and the junction formation of less than 20 nm in depth was demonstrated.
Study of Ge Out-diffusion During Nickel (Platinum ∼ 0, 5, 10 at.%) Germanosilicide Formation
Authors: Jin L. J. , Pey K. L. , Choi W. K. , Fitzgerald E. A. , Antoniadis D. A. , Pitera A. J. , Lee M. L. , Chi D. Z.
Published: April 2011

The interfacial reaction between 10 nm Ni(Pt ∼0, 5, 10 at.%) and (100) Si0.75Ge0.25 substrate after rapid thermal annealing between 400 and 800°C has been studied in detail using Micro- Raman spectroscopy. Only monogermanosilicide phase was detected in the temperature range investigated. The evolution of a broad Ni(Pt)SiGe Raman peak into two distinct peaks with increasing annealing temperature is attributed to a Ge out-diffusion from the germanosilicide grains. In addition, Raman spectroscopy further proves that depletion of Ge concentration in the Ni(Pt)SiGe grains reduces at higher temperature by the addition of Pt. The above phenomena were further supported by X-ray diffraction method.
Accurate Monte Carlo Simulation of Ion Implantation into Arbitrary 1D/2D/3D Structures for Silicon Technology
Authors: Tian Shiyang , Moroz Victor , Strecker Norbert
Published: April 2011

We present an integrated Monte Carlo implant simulator which is capable of accurately simulating ion implantation into any amorphous materials and crystalline Si for 1D/2D/3D structures with arbitrary geometry and topography. With this simulator, we investigate some practical examples which reveal interesting 2D/3D effects, and demonstrate the importance of <110> channeling for sub-100nm silicon technology.
Diffusion of Fluorine at High Concentration in Silicon: Experiments and Models
Authors: Robison Robert R. , Saavedra Antonio F. , Law Mark E.
Published: April 2011

We have developed a model for high concentration fluorine diffusion and fluorine diffusion in amorphous silicon. In this context, we define high concentration fluorine to mean fluorine doses above the threshold of amorphization for implantation into silicon, which is approximately 1×1015/cm2 dose. We pre-amorphized with silicon to create a continuous amorphous region, and samples were subsequently implanted with the fluorine conditions of 16keV at 2×1015cm−2 dose, 30keV at 2×1014 cm−2 dose, or 16keV at 8×1015cm−2 dose. Samples were annealed by either conventional furnace or RTA with an N2 ambient for various times at temperatures of 550-750 °C. SIMS was used for depth profiling, and TEM images were also taken of the samples to check for defects and amorphous depth. We then created the model for the data by extending the fluorine model presented in our previous work, and it models the profile motion and the time dependence well. The model is also still capable of describing our previous work and fits it very well.
Interactions of Indium, Arsenic and Carbon in Silicon Using the Pseudopotential Technique
Authors: Shishkin M. , Yan A. , De Souza M. M.
Published: April 2011

Factors limiting the activation of indium in silicon are examined via the ab initio pseudopotential technique. The role of carbon in the enhancement/retardation of activation/diffusion respectively is clarified. It is found that (1) adjacent substitutional indium atoms are deactivated. Only second neighbour sites of indium are activated unlike the case of boron, where all substitutional sites remain activated. (2) Silicon self-interstitials deactivate indium by trapping them on substitutional sites. Carbon, on the other hand, traps such self- interstitials with higher binding energy and prevents them from deactivating indium. (3) Since both indium and carbon diffusion is interstitial mediated, carbon reduces indium diffusion on account of its higher binding energy with the self-interstitial. Moreover, the release of the carbon interstitial is more favourable than the release of the indium interstitial from a carbon-indium pair. Therefore, carbon minimises indium interstitial diffusion. (4) Arsenic enhances de- activation of indium by neutralisation and by strong binding on adjacent substitutional sites. Furthermore since the release of the indium interstitial is more favourable in comparison to the release of the arsenic interstitial from the indium-arsenic pair, indium diffusion is enhanced in the presence of arsenic.
Evaluation of PECVD deposited Boron Nitride as Copper Diffusion Barrier on Porous Low-k Materials
Authors: Liu J. , Wang W. D. , Wang L. , Chi D. Z. , Loh K. P.
Published: April 2011

Ultra low dielectric constant (κ) material is needed as the inter-metal dielectrics to reduce RC delay when device dimension is scaled to sub-100nm. Porous dielectric films have been considered as good candidates for the application as inter-metal dielectrics due to their ultra low-k properties. Identifying proper dielectric copper diffusion barrier on the porous low-k films is critical for the low-k/Cu damascene fabrication process. In this study, we have evaluated the compatibility of plasma-deposited amorphous Boron Nitride film as a dielectrics copper diffusion barrier on a MSQ-based porous low-k LKD5109 film (from JSR). Both microwave plasma enhanced CVD (2.45 GHz) and radio-frequency plasma enhanced CVD (13.56 MHz) were applied for the BN deposition in order to evaluate the compatibility of the two plasma processes with the porous film. Growth parameters were optimized to minimize the boron diffusion and carbon depletion in the porous low-k films, which were found to have deleterious effects on the dielectric properties of the low-k films. FTIR and micro-Raman were employed for analyzing the changes in chemical structure of the low-k films after BN growth. Capacitance-voltage measurement was used to characterize the dielectric constants of BN film on Si and the BN-deposited porous low-k film. SIMS characterization was carried out to evaluate the performance of the BN film against copper diffusion.
Ellipsometric Porosimetry of Porous Low-k Films with Quazi-Closed Cavities
Authors: Baklanov Mikhail R. , Mogilnikov Konstantin P. , Yim Jin-Heong
Published: April 2011

Evaluation of quasi-closed cavities connected with air through narrow necks is discussed. These cavities behave as closed pores when they are studied by Positron Annihilation Lifetime Spectroscopy (PALS). The reason is a short lifetime of o-positronium (Ps) and energy barrier that exist for Ps diffusion from large pores (d>3 nm) to small ones (d<3 nm). It is shown that more comprehensive information can be obtained using adsorption porosimetry. Standard adsorptives used in adsorption porosimetry have infinite lifetime allowing complete penetration and filling all the cavities during the measurement. Calculation of the neck and cavity sizes is based on the theory of metastable adsorption phases developed by Derjagin, Broekhoff and de Boer (DBdB). Results of evaluation are in good agreement with data obtained by SEM and TEM.
A Novel Organosiloxane Vapor Annealing Process for Improving Elastic Modulus of Porous Low-k Films
Authors: Kohmura Kazuo , Oike Shunsuke , Murakami Masami , Tanaka Hirofumi , Takada Syozo , Seino Yutaka , Kikkawa Takamaro
Published: April 2011

A novel organosiloxane-vapor-annealing method has been developed for improving the mechanical strength of porous silica films with a low dielectric constant. Treatment of a porous silica film with 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) under atmospheric nitrogen above 350 °C significantly enhanced the mechanical strength (i.e., elastic modulus and hardness) of the film. Results of Fourier transform infrared spectroscopy (FT-IR) and thermal desorption spectroscopy (TDS) suggested the formation of cross-linked poly(TMCTS) network on the porous silica internal wall surfaces by the TMCTS treatment. Such TMCTS cross-linked network is thought to enhance the mechanical strength of the low-k film.
Three Dimensional Interconnect Stress Modeling for Back End Process
Authors: Xu Xiaopeng , Moroz Victor
Published: April 2011

A process oriented approach is demonstrated for modeling the stress evolution during the entire back end process flow. Noad hocassumptions regarding stress states are made for layer deposition and etching. Intrinsic stresses from material formation, thermal mismatch stresses from temperature ramps, stress relaxation due to viscous deformation, and stress profile redistribution upon deposition and etching are all considered at each process. Parametric studies are carried out to examine the effects of viscous flow, material selection and layout variations. It is found that the viscous flow of the passivation and dielectric materials have large impact on stress evolution. A TCAD assisted design approach is suggested for lowering stress levels of critical stress components. The implications of the stress modeling results on reliability issues like stress-triggered void formation are discussed.
Stressmigration studies on dual damascene Cu/oxide and Cu/low k interconnects
Authors: Baek Won-Chong , Ho Paul. S. , Lee Jeong Gun , Hwang Sung Bo , Choi Kyeong-Keun , Maeng Jong Sun
Published: April 2011

Stress-induced void formation (SIV) was studied in dual damascene Cu/oxide and Cu/low k interconnects over a temperature range of 140 ∼ 350 °C. Two modes of stressmigration were observed depending on the baking temperature and sample geometry. At lower temperatures (T < 290 °C), voids were formed under the periphery of via connecting to narrow lines. This mode of stressmigration showed a typical behavior of stressmigration with peak damage at 240 °C, and an activation energy (Q) of 0.75 eV for Cu/oxide interconnects. At a higher temperature range (T > 290 °C), voids were found in via bottoms which were connected to wide lines. The rate of high temperature stressmigration increased exponentially with temperature up to 350 °C and did not show a peak at a certain temperature. The activation energy was 1.0 eV for Cu/oxide, 0.86 eV for Cu/OSG, and ∼1.0 eV for Cu/FSG interconnects. The dependence of stressmigration on linewidth, sample geometry, and ILD material is presented in this paper.
“Chlorine-based Reactive Ion Etching Process to Pattern Platinum for MEMS Applications”
Authors: Choi Sung H. , Osborn Jon V. , Morgan Brent A.
Published: April 2011

We have developed platinum (Pt) deposition and chlorine-based Reactive Ion Etch (RIE) processes that are needed to deposit, pattern and embed electrodes deep within a MEMS process flow. Various combinations of chlorinebased gases were tested to find the optimum gas mixture for RIE. A 1: 0.4 mixture ratio of pure chlorine to argon and 100-150 Watts of RF microwave power were found to be optimum conditions for the RIE of platinum metal. The addition of argon gas to chlorine was found to contribute to the anisotropic etching of platinum, obtaining vertical shaped sidewall patterns. A simple model of the platinum etching mechanism is proposed. Following the plasma enhanced formation of platinum and chlorine ions, volatile products of platinum chlorides were formed and driven away at elevated temperature. As a demonstration of our RIE process, micron-sized platinum patterns with vertical sidewalls were fabricated. Etch chemistry was investigated using ToF SIMS analysis. This etch technique will be useful to device developers intending to use the unique properties of platinum metal as an electrode that is deeply embedded within a MEMS process flow.
Low Temperature Poly-Si TFT Technology
Authors: Noguchi T. , Kim D.Y. , Kwon J.Y. , Park K.B. , Jung J.S. , Xianyu W.X. , Yin H.X. , Cho H.S.
Published: April 2011

Low temperature poly-Si TFT technology is reviewed and is discussed from a view point of device, fabrication process, and its possibility as FPD (Flat Panel Display) application. After the appearance of crystallization technique of SPC (Solid Phase Crystallization) using FA (Furnace Annealing) or ELA (Excimer Laser Annealing) using UV (Ultra-Violet) beam, the electronic property of poly-Si thin-film, which relates to the crystalinity of the grains, was improved drastically, and the process temperature for the TFT fabrication had been reduced below 600° down to 400°. As a result, improvement of device characteristic of poly-Si TFT such as an enhancement of carrier mobility or a reduction of leakage current has been studied intensively for the application to FPD (Flat Panel Display) on glass. Currently, extensive study is being done in order to realize a more functional SOG (System on Glass). By reducing the TFT process temperature down to 200° or below and by modifying a design for the device structure or the circuit in the pixel, O-LED (Organic LED) FPD addressed by uniform poly-Si TFTs is expected to mount on flexible plastic substrate such as on PES (PolyEtherSulphone). The poly-Si TFT has a possibility to develop as a smart system on plastic panel for unique applications as well as the conventional Si LSI in the ubiquitous IT (Information Technology) era.