bluuebunny/crossref_metadata_2025 huggingface dataset:
High Performance Conductive Adhesives for Lead-Free Interconnects
Authors: Li Yi , Wong ChingPing
Published: April 2011

Tin-lead solder alloys are widely used in the electronic industry. With the recognition of toxicity of lead, however, electrically conductive adhesives (ECAs) have been considered as one of the most promising alternatives of tin-lead solder. While silver is the most widely used conductive fillers for ECA, silver migration has been the major concern for the high power and fine pitch applications. In this paper, a novel approach of using self-assembled monolayers (SAMs) passivation has been introduced to control the silver migration in nano-Ag ECAs. The protection of silver nano particles with SAMs reduced the silver migration dramatically and no migration was observed upon application of high voltages (up to 500 V) due to the formation of surface chelating compounds between the SAM and nano silver fillers. Unlike other migration control approaches which sacrifice electrical performance, the SAM passivated nano Ag fillers also enhanced the electrical conductivity and current carrying capability of adhesive joints significantly due to the improved interfacial properties and high current density of those molecular monolayers. The joint resistance of the SAM incorporated nano-Ag conductive adhesive could be achieved as low as 10−5 Ohm (the contact area is 100 ×100 μm2) and the maximum allowable current was higher than 3500 mA. As such, a fine pitch, high performance, non-migration and high reliability adhesives are developed for potential solder replacement in high voltage, high power device applications.
Surface Flatness and Interface Stability of Ni-P Film using New Electroless Plating Method with the Emulsion of Supercritical CO2
Authors: Uchiyama Hiroki , Sone Masato , Ishiyama Chiemi , Higo Yakichi
Published: April 2011

This paper proposes a novel coating method combining supercritical fluid technology and electroless plating in a hybrid technique. The electroless plating reactions are carried out in an emulsion of supercritical carbon dioxide (sc-CO2) and an electroless plating solution with surfactants. The Ni-P film obtained by this proposed technique was a uniform and conformal film without the pinholes and nodules. The Ni-P film fabricated by our technique was smoother and more uniform than the substrate after pretreatment and the conventional electroless plating.
Influence of Full-filled Polymer Molding on High-frequency Circuits
Authors: Nakanishi Kiyoshi , Fujimoto Masayuki
Published: April 2011

The influence of full-filled polymer molding on high-frequency circuits in cellular phones is evaluated using computer simulations and high-frequency measurements. Polymer-molded high-frequency circuits of cellular phones increase radiation harmonics and line and antenna phase errors. High-frequency properties are degraded due to a decrease in line impedance and an increase in stray capacitance of land electrodes that are used in the assembly of components. Degradation problems caused by full-filled polymer molding can be alleviated by appropriate circuit design, such as by adjusting the distance of components and creating more effective electromagnetic shielding. Better circuit design must satisfy the specifications of several different types of cellular phones, including global systems mobile telecommunications and digital cellular systems.
An Approach for Characterizing Residual Mechanical Stress Caused by Packaging Processes
Authors: Hirsch Soeren , Schmidt Bertram
Published: April 2011

this paper reports on a method for estimation and minimization of mechanical stress on MEMS sensor and actuator structures due to packaging processes based on flip chip technology. For studying mechanical stress a test chip with silicon membranes was fabricated. Finite element method simulation was calculate the stress profile and to determine the optimum positions for placing the resistor network.
Recent Advances in 3D Integration at IMEC
Authors: De Moor Piet , Ruythooren Wouter , Soussan Philippe , Swinnen Bart , Baert Kris , Van Hoof Chris , Beyne Eric
Published: April 2011

IMEC is focusing its 3D-integration technology developments in 3 distinct directions: 3D-System-in-a-Package (3D-SiP), 3D-Wafer-Level-Packaging (3D-WLP) and 3D-Stacked-IC (3D-SiC). First, the background of these separate approaches will be given. Next the materials and technologies involved, the typical characteristics and the ongoing developments will be discussed. Finally, the roadmap for the 3D-integration in IMEC will be presented.
Through Wafer Interconnects for 3-D Packaging
Authors: Moll Amy J. , Knowlton William B. , Oxford Rex
Published: April 2011

Semiconductor technology has reached a point in its evolution where the package now plays an important role in the overall performance of the device. In MEMs devices, the package is often more than 75% of the cost and has a significant impact in the overall size. Through wafer interconnects allow for advanced 3-D packaging schemes. Additional miniaturization, increased interconnection density, and higher performance is possible by stacking die with through wafer interconnects. Key technologies for creating TWIs are the ability to create a via through the silicon wafer, dielectric isolation of the via metal from the substrate, and filling or coating the via with a conducting material. Through wafer interconnects have been demonstrated in silicon wafers. The process to create TWIs has been optimized. The TWI has been tested electrically and proven reliable. TWIs were incorporated into an active device wafer and a two die stack connected through solder bump technology. In current work, specific applications which take advantage of the benefits of TWI's are being explored including 3-D inductors, unique sensor packages and MEMs applications.
Design and Fabrication of 3D Microprocessors
Authors: Morrow Patrick , Black Bryan , Kobrinsky Mauro J , Muthukumar Sriram , Nelson Don , Park Chang-Min , Webb Clair
Published: April 2011

Stacking multiple device strata can improve system performance of a microprocessor (μP) by reducing interconnect length. This enables latency improvement, power reduction, and improved memory bandwidth. In this paper we review some of our recent design analysis and process results which quantitatively show the benefits of stacking applied to μPs.

We report on two applications for stacking which take advantage of reduced wire length- “logic+logic” stacking and “logic+memory” stacking. In addition to optimizing minimum wire length, we considered carefully the thermal ramifications of the new designs. For the logic+memory application, we considered the case of reducing off-die wiring by stacking a DRAM cache (32 to 64MB) onto a high performance μP. Simulations showed 3x reduced off-die bandwidth, Cycles Per Memory Access (CPMA) reduction of 13%, and a 66% average bus power reduction. For logic+logic applications, we considered a high performance μP where the unit blocks were repartitioned into two strata. For this case, simulations showed that stacking can simultaneously reduce power by 15% while increasing performance by 15% with a minor 14° C increase in peak temperature compared to the planar design. Using voltage scaling, this translates to 34% power reduction and 8% performance improvement with no temperature increase. We found that these results can be further improved by a secondary splitting of the individual blocks. As an example, we split a 32KB first level data cache resulting in 25% power reduction, 10% latency reduction, and 20% area reduction.

We also discuss the fabrication of stacked structures with two complimentary process flows. In one case, we developed a 300mm wafer stacking process using Cu-Cu bonding, wafer thinning, and through-silicon vias (TSVs). This technology provides reliable bonding with non-detectable bonding-interface resistance and inter-strata via pitch below 8μm. We investigated the impact of this wafer stacking process to the transistor and interconnect layers built using a 65nm strained-Si/Cu-Low-K process technology and found no impact to either discrete N- and P-MOS devices or to thin 4Mb SRAMs. We verified fully functional SRAMs on thinned wafers with thicknesses down to 5μm. Although wafer stacking leads itself well to tight-pitch same-die-size stacking, die stacking enables integration of different size dies and includes opportunity to improve yield by stacking known good dies. We demonstrated a die stack process flow with 75μm thinned die, TSV, and inter-strata via pitch below 100μm. We also found negligible impact to transistors using this process flow. Multiple stacks of up to seven 75μm thin dies with TSVs were fabricated and tested. Prospects for high volume integration of 3D into μPs are discussed.
Silicon Layer Stacking Enabled by Wafer Bonding
Authors: Tan Chuan Seng , Chen Kuan-Neng , Fan Andy , Chandrakasan Anantha , Reif Rafael
Published: April 2011

Three-dimensional integrated circuits (3-D ICs), in the form of a vertical stack of several interconnected device layers, have many performance, form factor, and integration advantages. The main objective of this work is to develop reliable process technology to enable the fabrication of a vertically interconnected silicon multi-layer stack.

Low temperature wafer bonding processes, both copper thermo-compression bonding and silicon dioxide fusion bonding, are studied extensively as key enabling technology. Cu thermo-compression bonding is studied for its feasibility as a permanent bond between active layers in a multi-layer stack. Silicon dioxide wafer bonding, on the other hand, is used as a temporary bond to attach a donor wafer to a handle wafer during donor wafer thinning and subsequent layer transfer. Sufficiently high bond strength is obtained with careful surface preparation and activation prior to bonding.

Silicon layer can be stacked either in a “face down” or “face up” orientation. Using a combination of wafer bonding and thinning, double-layer stacks in both orientations are fabricated. By repeating these steps on two “face down” double-layer stacks, a four-layer stack is successful demonstrated.
Current Status of LSI Micro-fabrication and Future Prospect for 3D System Integration
Authors: Okamoto Kazuya
Published: April 2011

Micro-fabrication technology for LSI devices has been progressing technically over time. However, the scenario of continuing to produce ever-finer feature geometries has a low probability. Resolution capabilities will reach a critical limit due to conventional CMOS performance threshold and chip economy. Therefore, to assure continued performance improvements for future devices, front-end fabricators should consider a new 3 dimensional structure (3D-LSI) using a “Through-Si-Via” process. At the same time, the definition of the semiconductor device should be updated to “System & Design Integration (S&DI).” S&DI will provide the needed feedback to launch a new field of clear applications, based on a total system solution with innovative design, fabrication, inspection and evaluation equipment. 3D-LSI and S&DI will have a tremendous impact on the future electronics industries.
The Effects of Sn Element on Hydrogen Storage Characteristics of Mg2-xSnxNi(x=0, 0.05, 0.1, 0.15, 0.2) Alloys
Authors: Guo Jin , Huang Cunke , Yang Kun , Li Guangxu , Jiang Weiqing
Published: April 2011

Mg2-xSnxNi (x=0, 0.05, 0.1, 0.15, 0.2) hydrogen storage alloys were prepared and the effects of substitution of Sn for Mg on hydrogen storage performances of the alloys were investigated. In the alloys, Mg2Ni is main phase and the amorphous degree increases gradually with amount of Sn content increasing. Partial substitution of Sn for Mg can change the temperature of hydrogen absorption reaction effectively. The Mg1.85Sn0.15Ni alloy absorbs hydrogen at about 330K which is about 80K lower than that of Mg2Ni alloy. Discharge capacity increases quickly with amount of substitution Sn for Mg increasing. Suitable amount of substitution of Sn for Mg and amorphous can improve the thermodynamic and electrochemical characteristics of hydrogen absorption reaction for Mg2Ni-based alloy.
Crystal Structure Analysis in the Dehydrogenation Process of Mg(NH2)2-LiH System
Authors: Noritake Tatsuo , Aoki Masakazu , Towata Shin-ichi , Nakamori Yuko , Orimo Shin-ichi
Published: April 2011

Mg(NH2)2-LiH system which have the properties of reversible hydrogenation and dehydrogenation is one of the promising candidates for new hydrogen storage materials. For understanding of the reversible reaction mechanism, we investigated the crystal structure changes in 3Mg(NH2)2-12LiH system using the pressure-composition (p-c) isotherm measurement and synchrotron X-ray diffraction. The sample was prepared by the hydrogenation of Mg3N2 + 4Li3N. At the several dehydrogenation stages of the p-c isotherm measurement at temperature 523 K, the sample was taken out and X-ray diffraction measurement was performed. By the amount of desorbed hydrogen, the reaction was expressed as the following formula, Mg(NH2)2 + 4LiH → LixMg(NH2)2-x(NH)x + (4-x)LiH + xH2 (x = 0∼2). The crystal structures of LixMg(NH2)2-x(NH)x, similar to CaF2-type one, formed during the dehydrogenation reaction were determined by Rietveld analysis. As a result, it is considered that the dehydrogenation process might relate to the diffusion of Li+ ion in cation sites of Mg(NH2)2.
Solid Oxide Fuel Cells based on Proton Conducting Electrolytes
Authors: Balachandran U. , Lee Tae H , Ma Beihai , Dorris Stephen E
Published: April 2011

We have fabricated a solid oxide fuel cell (SOFC) using BaCe0.8Y0.2Ox (BCY) proton conductor as the electrolyte. An ≈ 15-μm-thick dense BCY film was prepared on a porous Ni/BCY cermet (i.e., ceramic/metal composite) substrate by a colloidal spray deposition technique. The gas permeable Ni/BCY cermet substrate backed with nickel mesh was used as the anode, and platinum paste backed with platinum mesh served as cathode. The current-voltage characteristics of the BCY-based SOFC were measured in the temperature range 600-800°C using wet air on the cathode side and wet hydrogen on the anode side. The open circuit voltage was close to the theoretical value at all operating temperatures. The power density of the fuel cell was ≈240 and ≈875 mW/cm2 at 600 and 800°C, respectively.
Analysis of Composition and Valence States in Positive Electrode Materials (Fe-Substituted Li2MnO3) for Lithium Ion Batteries by Analytical Transmission Electron Microscopy
Authors: Kikkawa Jun , Akita Tomoki , Tabuchi Mitsuharu , Shikano Masahiro , Tatsumi Kuniaki , Kohyama Masanori
Published: April 2011

Analytical transmission electron microscopy (ATEM) was applied to investigate local variation of composition of transition metals in each particle of Fe-substituted Li2MnO3, which reveals high specific capacity and high voltage as a positive electrode. Crystal lattice images of primary particles were observed by means of high-resolution TEM (HRTEM), where local composition of Fe and Mn was determined by electron energy-loss spectroscopy (EELS). It was found that there exist both manganese (Mn)-rich and iron (Fe)-rich regions in a primary particle, where concentration of Fe and Mn fluctuates irregularly in nanometer scale. The relationship between composition and crystal structure in each local region is discussed.
Li Batteries with Porous Sol-Gel Cathodes
Authors: Dima Antonela , Casalino Maurizio , Della Corte Francesco , Rendina Ivo
Published: April 2011

Lithium batteries have found a wide range of applications due to their very compact energy packing and effective cost. Theoretically Li-cells can hold up to 5V, however to date no mass-produced rechargeable battery surpasses 4 V. The structure here analyzed consists of: lithium porous cathode, solid electrolyte and silver anode. A spinel LiNi0.4X0.1Mn1.5O4 sol-gel layer was deposited on a porous substrate in order to obtain higher specific surface for single chips. The anode was thermally evaporated Ag. The electrolyte used was a sol-gel hybrid layer containing Li ions. The devices, fabricated on ceramic wafers, displayed high capacities.
Magnetic Studies of Layered Cathode Materials for Lithium Ion Batteries
Authors: Chernova Natasha A. , Ma Miaomiao , Xiao Jie , Whittingham M. Stanley , Cabana Jiménez Jordi , Grey Clare P.
Published: April 2011

The magnetic properties of layered LiNi0.5Mn0.5O2 and NaNi0.5Mn0.5O2 cathode materials are studied using AC susceptibility and DC magnetization techniques in order to elucidate magnetic interactions within transition metal (TM) layers and between them in samples with various TM distributions. In NaNi0.5Mn0.5O2 antiferromagnetic (AF) ordering transition is found at 60 K and a spin-flop transition at high magnetic field. In LiNi0.5Mn0.5O2 obtained by ion exchange from NaNi0.5Mn0.5O2 ferrimagnetic ordering is found at around 100 K. The saturation magnetization and the hysteresis loop size of ion-exchanged compounds vary from sample to sample, which implies that the Ni2+ ions migrate upon ion exchange process. Magnetic properties of high-temperature and ion-exchanged LiNi0.5Mn0.5O2 are compared; magnetic ordering models for all compounds are proposed based on experimental results and Goodenough-Kanamori rules.
A New Lithium Iron Phosphate LiFe2P3O10 Synthesized at 600 °C from Precursor Obtained by Wet Chemistry
Authors: Ait-Salah Atmane , Ramana Chintalapalle V , Gendron François , Morhange Jean-François , Mauger Alain , Selmane Mohamed , Julien Christian M
Published: April 2011

We present the synthesis and characterization of a novel lithium iron polyphosphate LiFe2P3O10 prepared by wet-chemical technique from nitrate precursors. The crystal system is shown to be monoclinic (P21/m space group) and the refined cell parameters are a=4.596 Å, b=8.566 Å, c=9.051 Å and β=97.46°. LiFe2P3O10 has a weak antiferromagnetic ordering below the Néel temperature TN=19 K. Electrochemical measurements carried out at 25 °C in lithium cell with LiPF6-EC-DEC electrolyte show a capacity 70 mAh/g in the voltage range 2.7-3.9 V.
Local Structure and Magnetic Properties of LixFePO4 Glasses
Authors: Jozwiak Pawel , Garbarczyk Jerzy , Gendron François , Mauger Alain , Julien Christian M
Published: April 2011

A series of LixFePO4 samples (0≤x≤1) have been synthesized in the vitreous state by fast quenching technique. Characterization methods include XRD, TG, FTIR, magnetic susceptibility and electrical measurements. FTIR studies reveal that in the entire composition range the local structure is identical to the olivine lattice including PO43− oxo-anions linked to FeO6 octahedra. Magnetic susceptibility data show that the antiferromagnetic ordering does not exist so far and the paramagnetic behaviour follows the Curie-Weiss law above 30 K. Both the Curie parameter and the Weiss temperature suggest a strong weakness of the superexchange interactions that are consistent with the analysis of infrared spectra. Electrical conductivity shows an activated conduction mechanism with Ea=0.67 eV.
Preparation and Characterization of ALD TiN Thin Films on Lithium Titanate Spinel (Li4Ti5O12) for Lithium Ion Battery Applications
Authors: Snyder Mark Q. , Trebukhova Svetlana , Ravdel Boris , Wheeler M. Clayton , DiCarlo Joseph , Tripp Carl P. , DeSisto William J.
Published: April 2011

Lithium titanate spinel (Li4Ti5O12, or LTS) has received an increasing level of attention as a nanopowder lithium-ion battery anode. Nanopowder electrodes may provide a higher energy density than currently available. Furthermore, the surface of the spinel nanopowder has been studied in air, under vacuum, and at varying temperatures with diffuse reflectance infrared Fourier transform spectroscopy revealing surface hydroxyls, carbonates and water. Applying a TiN thin film, a film that is both conducting and chemically inert to harmful reactions with the solvent/electrolyte, by atomic layer deposition (ALD) may enhance battery cycle life. A 200-layer film was deposited at 500 °C. We have characterized the influence of a TiN thin film on Li-ion battery performance. Total nitrogen content and transmission electron microscopy were used to verify the presence of nitrogen and formation of a thin film, respectively, on LTS. Modifying the powder with an ALD thin film coating produced an anode material with a voltage profile that demonstrated longer charge maintenance with shorter transient periods. It also held a more consistent charge capacity over varying discharge rates in coin cell testing than unmodified LTS.
A Survey of Diverse Approximations for Microstructural Characterization using Powder Diffraction Data: β-Ni(OH)2, a Case Study
Authors: Casas-Cabanas Monste , Rodriguez-Carvajal Juan , Oro-Sole Judith , Palacin M. Rosa
Published: April 2011

The microstructural features of diverse samples are studied by powder X-ray diffraction using different methods for the analysis of the diffraction peak broadening. The results obtained are thoroughly analyzed taking into account the assumptions and simplifications done in each of the chosen methods (Scherrer, Stokes and Wilson, Williamson-Hall and Rietveld refinement) and direct observation of the studied specimens by transmission electron microscopy is used in order to contrast the results obtained. Classic simple methods that consider only size effects (Scherrer, Stokes and Wilson) or the combined effects of size and strains (Williamson-Hall) provide a rapid overview of the origins of line-broadening but the most reliable results are obtained when the whole diffraction pattern is taken into account (Rietveld refinement).
Intermediate Phases in LixFePO4
Authors: Yamada Atsuo , Nishimura Shinichi , Koizumi Hiroshi , Kanno Ryoji , Seki Shiro , Kobayashi Yo , Miyashiro Hajime , Dodd Joanna , Yazami Rachid , Fultz Brent
Published: April 2011

Rietveld analysis for the time of flight powder neutron diffraction profile for LiFePO4 at room temperature was performed. Refined tensor elements of the unisotropic thermal factor under the elliptic approximation showed the principal axis of the lithium vibration is toward the face shared vacant tetrahedral space and is consistent with the theoretical prediction; lithium ions diffuse along curved one-dementional chain along b-axis. Impact of temperature on the phase diagram of LixFePO4 with > 200nm particle size was slight under the unmixing line around 200 C. While the reduction in particle size down to <100 nm seems to have significant effect to the room temperature miscibility gap. The thermodynamic concepts for the extended solution in smaller particles are discussed, followed by a demonstration of very high rate capability observed for the small spherical particles < 80 nm.
Demonstration of a Novel Alkaline Battery Cathode Material: Periodate Salts
Authors: Licht Stuart , Yu Xingwen
Published: April 2011

An unusual solubility domain for KIO4 in KOH solution is observed, which is consistent with a potential use of periodate as a cathode for alkaline batteries. With increasing alkalinity, the solubility of KIO4 first increases, then drops from 2.9 M to < 10−4 M with increase from 6 to 10 M KOH. The unusual rapid transition from high to low solubility with increasing KOH is attributed to the formation of insoluble periodate complex. Accompanying the favorable low solubility in concentrated KOH is a high degree of cathodic electroactivity in accord with two electron storage: IO4− ⊒ IO3−. Low cathode salt solubility minimizes interference with the anode. Zn anode alkaline batteries are studied with KIO4 and NaIO4 cathodes, have a potential of 1.4-1.5 V and discharge to over 95% of the intrinsic 2e− charge capacity. The cathode also exhibits good quasi reversibility (rechargeability) with an alkaline metal hydride anode.
Comparison of Techniques for Measuring Recombination Lifetime in Photovoltaic Materials: Trapping Effects
Authors: Ahrenkiel Richard K , Johnston Steven W. , Metzger Wyatt K
Published: April 2011

Here we will compare four techniques that are commonly used for diagnosis of the lifetime of photovoltaic materials. The strengths and weaknesses of these techniques will be shown and discussed.
Optimization of Textured Photonic Crystal Backside Reflector for Si Thin Film Solar Cells
Authors: Zeng Lirong , Bermel Peter , Yi Yasha , Feng Ning-ning , Alamariu Bernard A. , Hong Ching-yin , Duan Xiaoman , Joannopoulos John , Kimerling Lionel C.
Published: April 2011

A new backside reflector, textured photonic crystal, is introduced into Si thin film solar cells. Scattering matrix method is used to systematically optimize all the parameters of the two components of the backside reflector, grating and distributed Bragg reflector, to achieve the highest power conversion efficiency for a given solar cell thickness. Experimentally, Si-on-insulator solar cells are being fabricated to verify the tremendous efficiency enhancement and optimal design. It is found that while the optimal period and etch depth of the grating, the Bragg wavelength of the distributed Bragg reflector, as well as the antireflection coating thickness all decrease as the cell becomes thinner, the optimum duty cycle of the grating remains almost constant at 0.5. For a 2 μm thick cell, the relative efficiency enhancement can be as high as 52% using the optimized design.
Solar Cells Using Solution-derived Oxide Films as Photoelectrodes
Authors: Gao Yanfeng , Nagai Masayuki
Published: April 2011

This paper reports the development of morphology-tuned TiO2/ZnO films and their application to the electrode in dye-sensitized solar cells. Amorphous TiO2 precursor films with different morphologies can be synthesized under different processing conditions by our previously developed peroxotitanate-complex deposition process, which employs a supersaturated peroxotitanate aqueous solution. The ZnO nanowire aligns were grown by a two-step method, in which well oriented arrays of ZnO nanowires were prepared on a pre-prepared ZnO seed layer. The cell performance using the prepared TiO2/ZnO films shows the possibility to integrate these films into solar cells. However, the crystallization and morphology should be further optimized to improve the conversion efficiency to be a competitive level.
Photocatalytic Hydrogen Evolution over Tantalate Photocatalysts
Authors: Jitputti Jaturong , Pavasupree Sorapong , Suzuki Yoshikazu , Yoshikawa Susumu
Published: April 2011

Tantalate and titanate photocatalysts were prepared by solid-state reaction at 1273 K using various ratios of SrCO3, Ta2O5, and TiO2 as starting materials. The prepared solid photocatalysts were characterized using XRD and SEM analysis. These prepared tantalate and titanate photocatalysts showed high photocatalytic H2 evolution activity by water splitting without co-catalyst loading. The highest H2 evolution rate of prepared photocatalysts was found to be 138 μmolh−1 with the starting materials ratio of 2/0.5/1.5 (Sr/Ta/Ti; mol). Furthermore, this photocatalyst showed photocatalytic activity for H2 evolution from distilled water.
Crystalline Titania Nanoplatelet Templated by Block Copolymer of PMMA-b-PEO and its Photophysical Properties
Authors: Cheng Yajun , Memesa Mine , Nett Sebastian , Gutmann Jochen Stefan
Published: April 2011

A Titanium dioxide ultrathin film composed of nanoplatelet structures was prepared and characterized with AFM, SEM, and GISAXS measurement, whose photophysical properties are also studied.
Spin Density in Thin Film Silicon Before and After Electron Bombardment
Authors: Astakhov Oleksandr , Carius Reinhard , Petrusenko Yuri , Borysenko Valeriy , Barankov Dmitry , Finger Friedhelm
Published: April 2011

The defect density in thin film silicon was increased using low temperature 2MeV electron irradiation up to a factor of 1000. More than 30 samples of different structure from highly crystalline to amorphous were prepared with PECVD and irradiated to study the dynamics of defect accumulation and role of the material structure in this process.
Light Soaking and Thermal Annealing Effects on the Micro-Electrical Properties of Amorphous and Nanocrystalline Mixed-phase Silicon Solar Cells
Authors: Jiang Chunsheng , Yan B. , Moutinho H. R. , Al-Jassim M. M. , Yang J. , Guha S.
Published: April 2011

We report on the measurement of local current flow in hydrogenated amorphous and nanocrystalline mixed-phase n-i-p silicon solar cells in the initial, light-soaked, and annealed states using conductive atomic force microscopy (C-AFM). The C-AFM measurement shows that the nanometer-size grains aggregate, and the local current densities in the nanocrystalline aggregation areas decreased significantly after light soaking and recovered to values similar to the initial state after annealing at a high temperature in a vacuum. This result supports the model of two parallel-connected diodes for explaining the light-induced open-circuit voltage increase in the mixed-phase solar cells.
High Open-Circuit Voltage in Silicon Heterojunction Solar Cells
Authors: Wang Qi , Page Matt R. , Iwancizko Eugene , Xu Yueqin , Roybal Lorenzo , Bauer Russell , Levi Dean , Yan Yanfa , Wang Tihu , Branz Howard M.
Published: April 2011

High open-circuit voltage (Voc) silicon heterojunction (SHJ) solar cells are fabricated in double-heterojunction a-Si:H/c-Si/a-Si:H structures using low temperature (<225°C) hydrogenated amorphous silicon (a-Si:H) contacts deposited by hot-wire chemical vapor deposition (HWCVD). On p-type c-Si float-zone wafers, we used an amorphous n/i contact to the top surface and an i/p contact to the back surface to obtain a Voc of 667 mV in a 1 cm2 cell with an efficiency of 18.2%. This is the best reported p-type SHJ voltage. In our labs, it improves over the 652 mV cell obtained with a front amorphous n/i heterojunction emitter and a high-temperature alloyed Al back-surface-field contact. On n-type c-Si float-zone wafers, we used an a Si:H (p/i) front emitter and an a-Si:H (i/n) back contact to achieve a Voc of 691 mV on 1 cm2 cell. Though not as high as the 730 mV reported by Sanyo on n-wafers, this is the highest reported Voc for SHJ c-Si cells processed by the HWCVD technique. We found that effective c-Si surface cleaning and a double-heterojunction are keys to obtaining high Voc. Transmission electron microscopy reveals that high Voc cells require an abrupt interface from c-Si to a-Si:H. If the transition from the base wafer to the a-Si:H incorporates either microcrystalline or epitaxial Si at c Si interface, a low Voc will result. Lifetime measurement shows that the back-surface-recombination velocity (BSRV) can be reduced to ~15 cm/s through a-Si:H passivation. Amorphous silicon heterojunction layers on crystalline wafers thus combine low-surface recombination velocity with excellent carrier extraction.
Low Temperature Epitaxy of n-Doped Silicon Thin Films Using Plasma Enhanced Chemical Vapor Deposition
Authors: Farrokh Baroughi Mahdi , El-Gohary Hassan G. , Cheng Cherry Y. , Sivoththaman Siva
Published: April 2011

Highly conductive epiraxial silicon thin films, with conductivities more than 680 ¥Ø-1cm-1, were obtained using plasma enhanced chemical vapor deposition (PECVD) technique at 300¢ªC. The effect of hydrogen in growth of low temperature extrinsic Si thin films was studied using conductivity, Hall, and Raman measurements, and it was shown that epitaxial growth was possible at hydrogen dilution (HD) ratios more than 85%. The epitaxial growth of the extrinsic Si thin films at high hydrogen dilution regime was confirmed by high resolution transmission electron microscopy (HRTEM).
Boron Doping Effects in Microcrystalline Silicon
Authors: Beyer Wolfhard , Niessen Lars , Pennartz Frank
Published: April 2011

Conditions leading to high conductivities (up to 300 S/cm) in chlorosilane-based boron-doped microcrystalline Si:Cl:H films are investigated. It is found that the high conductivity originates primarily from the growth of highly crystalline material with a high concentration of boron. Furthermore, these films grow with relatively low chlorine and hydrogen concentrations of a few percent and, according to effusion measurements of hydrogen and implanted helium, in a relatively compact structure. At a boron doping level of 1%, admixture of 10% silane to the tetrachlorosilane results in the growth of amorphous material of low conductivity while for admixture of up to 90% of silicontetrafluoride, microcrystalline Si films with high conductivities can be grown.
Optical Readout in Pinpi'n and Pini'p Imagers: A Comparison
Authors: Louro P. , Vieira M. , Vygranenko Y. , Fernandes M. , Garção A.
Published: April 2011

Optimized a-SiC:H multilayer devices based on two different tandem configurations (TCO/pinpi'n/TCO and TCO/pini'p/TCO) are compared and tested for proper image recognition and color separation process using an optical readout technique. In both configurations the doped layers are based on a-SiC:H to increase image resolution and to prevent image blurring. To profit from the light filtering properties of the active absorbers, the intrinsic layer of the front diode (i layer) is based on a-SiC:H and the back one (i'layer) on a-Si:H.

The effect of the applied voltage on the color selectivity is discussed. Results show that the relative spectral response curves demonstrate rather good separation between the red, green and blue basic colors. Combining the information obtained under positive and negative applied bias a colour image is acquired, using the same optical technique either in pinpi'n or in the pini'p configuration, without colour filters or pixel architecture.
High Rate Deposition of Amorphous Silicon Based Solar Cells using Modified Very High Frequency Glow Discharge
Authors: Yue Guozhen , Yan Baojie , Yang Jeffrey , Guha Subhendu
Published: April 2011

We report our recent progress on high rate deposition of hydrogenated amorphous silicon (a-Si:H) and silicon germanium (a-SiGe:H) based n-i-p solar cells. The intrinsic a-Si:H and a-SiGe:H layers were deposited using modified very high frequency (MVHF) glow discharge. We found that both the initial cell performance and stability of the MVHF a-Si:H single-junction cells are independent of the deposition rate up to 15 Å/s. The average initial and stable active-area cell efficiencies of 10.0% and 8.5%, respectively, were obtained for the cells on textured Ag/ZnO coated stainless steel substrates. a-SiGe:H single-junction cells were also optimized at a rate of ~10 Å/s. The cell performance is similar to those made using conventional radio frequency technique at 3 Å/s. By combining the optimized component cells made at 10 Å/s, an a-Si:H/a-SiGe:H double-junction solar cell with an initial active-area efficiency of 11.7% was achieved.
Modeling the Laser Scanned Photodiode S-shaped J-V Characteristic.
Authors: Fernandes Miguel , Vieira Manuela , Martins Rodrigo
Published: April 2011

The devices analyzed in this work present an S-shape J-V characteristic when illuminated. By changing the light flux a non linear dependence of the photocurrent with illumination is observed. Thus a low intensity light beam can be used to probe the local illumination conditions, since a relationship exists between the probe beam photocurrent and the steady state illumination. Numerical simulation studies showed that the origin of this S-shape lies in a reduced electric field across the intrinsic region, which causes an increase in the recombination losses. Based on this, we present a model for the device consisting of a modulated barrier recombination junction in addition to the p-i-n junction. The simulated results are in good agreement with the experimental data.

Using the presented model a good estimative of the LSP signal under different illumination conditions can be obtained, thus simplifying the development of applications using the LSP as an image sensor, with advantages over the existing imaging systems in the large area sensor fields with the low cost associated to the amorphous silicon technology.
Growth and Electronic Properties in Hot Wire Deposited Nanocrystalline Si Solar Cells
Authors: Muthukrishnan Kamal , Dalal Vikram , Noack Max
Published: April 2011

We report on the growth and properties of nanocrystalline Si:H grown using a remote hot wire deposition system. Unlike previous results, the temperature of the substrate is not significantly affected by the hot filament in our system. The crystallinity of the growing film and the type of grain structure was systematically varied by changing the filament temperature and the degree of hydrogen dilution. It was found that high hydrogen dilution gave rise to random nucleation and <111> grain growth, whereas lower hydrogen dilution led to preferable growth of <220> grains. Similarly, a high filament temperature gave rise to preferential <111> growth compared to lower filament temperature. The electronic properties such as defect density and minority carrier diffusion length were studied as a function of the degree of crystallinity. It was found that the lowest defect density was obtained for a material which had an intermediate range of crystallnity, as determined from the Raman spectrum. Both highly amorphous and highly crystalline materials gave higher defect densities. The diffusion lengths were measured using a quantum efficiency technique, and were found to be the highest for the mid-range crystalline material. The results suggest that having an amorphous tissue surrounding the crystalline grain helps in passivating the grain boundaries.
CMP Active Diamond Characterization and Conditioner Wear
Authors: Borucki Leonard , Zhuang Rumin , Zhuang Yun , Philipossian Ara , Rikita Naoki
Published: April 2011

Using a pad substitute material, we measure the number of active or working diamonds on a conditioner and find that it is generally a small fraction of the total number on the disc. The number of active diamonds also increases with the applied load and varies somewhat with sliding direction. However, even among the active diamonds, most do relatively little cutting. A few diamonds on a disc do most of the deep bulk cutting, a larger fraction skim the higher areas of the pad surface and most of the diamonds on the disc apparently merely help to support the load. While all of the diamonds that make contact, cutting or otherwise, may show evidence some of mechanical wear, wear of the small number of deep bulk cutting diamonds may be responsible for declining cut rates and for surprisingly low observed conditioner lifetimes.
Determining Pad-Wafer Contact using Dual Emission Laser Induced Fluorescence
Authors: Gray Caprice , Rogers Chris , Manno Vincent P. , White Robert , Moinpour Mansour , Anjur Sriram
Published: April 2011

It is becoming increasingly clear that understanding the small scale polishing mechanisms operating during CMP requires knowledge of the nature of the pad-wafer contact. Dual Emission Laser Induced Fluorescence (DELIF) can be used to study the fluid layer profile between the polishing pad and the wafer during CMP. Interactions between the polishing pad surface and the wafer can then be deduced from the fluid layer profile. Previous investigations of pad-wafer interactions using DELIF include in-situ measurements of average fluid layer thickness and asperity layer compressibility, surface roughness measurements and polishing pad rebound into etched wells. In this paper, DELIF is used to determine pad-wafer contact, the point at the fluid film thickness goes to zero. We present a technique and some preliminary data for instantaneous measurement of in-situ pad-wafer contact using DELIF. The imaging area is 1.30×1.74 mm with a resolution of 2.5 μm/pixel. At this magnification, some regions imaged contain contact, whereas others do not. For the contact regions discussed in this paper, contact percentage varies from 0.07% to 0.27% on a Cabot Microelectronics D100 polishing pad. The asperity contact area increases with applied load, which was varied from 0.28 to 3.1 psi.
Fundamentals of Post-CMP Cleaning
Authors: Park Jin-Goo , Kim Tae-Gon
Published: April 2011

Post CMP cleaning is necessary for contaminant removal after CMP process. The zeta potential of slurry particle and substrate has been considered to be a critical factor in terms of particle adhesion and removal. The fundamental research such as the calculation and measurement of adhesion forces between slurry particle and wafer surfaces can enhance the understanding of cleaning mechanism and development of cleaning process. The presence of more than two different materials during CMP introduces new defects at the materials interface, corrosion and severe scratches. Device specific chemistry and cleaning process should be introduced and developed for future and current CMP. The highest particle removal efficiency is observed when using cleaning solutions that yields the lowest adhesion force. The effect of frictional and adhesion forces attributed to slurry particles on the quality of Cu surfaces was experimentally investigated during metal CMP process. The magnitude of the adsorption of the organic acid on the slurry particle surfaces can have a significant effect on the frictional behavior as well as the adhesion force. Higher particle adhesion forces resulted in higher friction and might induce defects such as particle contamination and scratches on the polished surface after polishing. The magnitude of particle adhesion force on wafer surfaces in slurries can be directly related to the frictional forces and polished surface quality during CMP process. As low k and poly or bare silicon polishing introduced in fabrication process, the hydrophobicity of these surfaces could affect the defects after polishing. The control of wettability during and after polishing becomes more important in reducing the defects. The organic particles are major defects during metal and poly silicon CMP which may be caused by the surface reaction of organic sources with surfaces.
Measurement of Interactions between Abrasive Silica Particles and Copper, Titanium, Tungsten and Tantalum
Authors: Burtovyy Ruslan , Tregub Alex , Moinpour Mansour , Buehler Mark , Luzinov Igor
Published: April 2011

Colloidal probe technique has been widely employed to measure the adhesion between micro- and nanosize objects using atomic force microscopy (AFM). However, majority of studies concerns model systems, which do not incorporate real abrasive particles. The approach applied allows measuring adhesion between real CMP nanoparticles and different surfaces. Thin polymer film with high affinity to the particles was used to anchor the particles to a surface. Hollow glass bead (20-30 μm) representing flat surface was attached to soft AFM cantilever. Application of large hollow bead and the cantilever with small spring constant allows measuring the interactions with high sensitivity. Titanium, tungsten and tantalum metals were sputtered on the bead surface. The effect of different factors such as pH value, concentration and type of a surfactant on adhesion between surfaces of metals and silica slurry has been studied. Character and intensity of interactions at the moment of contact have been evaluated from experimental force-distance curves.
Screening Study on Frictional Force Analysis in Relation to Silica Abrasive and Slurry Properties
Authors: Zhuang Yun , Sampurno Yasa Adi , Sudargho Fransisca , Steward Geoff , Barthel Herbert , Mayer Erwin-Peter , Gottschalk-Gaudig Torsten , Stintz Michael , Kaetzel Uwe , Nogowski Andre , Goldstein Michael , Philipossian Ara
Published: April 2011

In this study, different amounts of standard fumed silica and fumed silica contaminated by coarse particles was added as powder to a standard copper CMP slurry to investigate their effects on large particle count, mean particle size, slurry viscosity, frictional force during wafer polishing, and copper removal rate. Standard silica powder consisted of the same particles used in the standard slurry while contaminated silica powder consisted of the same particles used in the standard slurry and additional large size particles. Large particle count analysis indicated that slurry dispersion itself generated large size particles in the slurries. The addition of 0.3% and 1% contaminated silica to the standard slurry caused significant increases in large particle count, and the mean particle size increased with the amount of contaminated silica added to the standard slurry. The slurry viscosity generally increased with the amount of standard and contaminated silica added to the standard slurry under the shear rate of 100 s−1. The standard slurry and slurries added with 0.3% and 1% contaminated silica were used to polish 200-mm blanket copper wafers on the APD-500 polisher that has the unique ability to measure frictional force in real time during polishing. The coefficient of friction increased with the amount of contaminated silica added to the standard slurry. In general, the removal rates for the slurry added with 1% contaminated silica were higher than the standard slurry and slurry added with 0.3% contaminated silica.
Effect of Wettability of Poly Silicon on CMP Behavior
Authors: Kang Young-Jae , Kang Bong-Kyun , Kim In-Kwon , Park Jin-Goo , Hong Yi-Koan , Han Sang-Yeob , Yun Seong-Kyu , Yoon Bo-Un , Hong Chang-Ki
Published: April 2011

The hydrophobicity of poly Si is reported to introduce different polishing behavior with careful control of post CMP cleaning process. The purpose of this study was to investigate the effect of poly Si wettability on its CMP behavior. The adhesion force of polymeric particle on the poly Si wafer surfaces was measured in the KOH solution (pH 11) as a function of solution A concentration. Adhesion force decreased and saturated as a function of concentration of solution A. The change of surface wettability affects not only the polishing rates but also the level of contamination on wafer because the interactions between particles and substrates are dependent on the wettability of the surface. Also, hydrophobic poly Si surfaces attracted much more pad particles with water marks than hydrophilic
On a Particle-Augmented Mixed Lubrication Approach to Predicting CMP
Authors: Higgs C. Fred , Terrell Elon J , Kuo Michael , Bonivel Joseph , Biltz Sarah
Published: April 2011

Chemical mechanical polishing (CMP) is a process commonly used to planarize or polish thin film surfaces to enable stacking of additional levels to enhance lithographic patterning of wafers. It is used to make surfaces atomically smooth and is also an interim step in integrated circuit (IC) manufacturing. CMP is an example of a tribological regime called Particle-Augmented Mixed Lubrication (PAML) as named by the authors. PAML occurs when two surfaces in relative motion under load are partially separated by an intervening fluid-particle mixture. The load is supported by both asperities and fluid, and the interface is further complicated by the addition of nanoparticles. PAML involves four core components that must be modeled integrally—fluid mechanics, particle dynamics, contact mechanics, and material removal (wear). This work introduces the fundamental tenets of PAML, and describes how it is an effective first principle multi-physics approach to modeling CMP. By inputting the artificial random topographies for the pad and wafer with their actual mechanical properties, the PAML modeling simulation results predict the instantaneous material removal as the wear volume caused by particle-induced wear. These discrete instantaneous material removal events lead to the cumulative wear seen during CMP over a short time. Although only a small fraction of the time of the actual CMP process, tests of 120μs show that the cumulative material removal occurring over the entire simulation is approximately 0.012μm3. This work suggests that a generalized multi-physics modeling simulation of the CMP process is plausible.