bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallization of Germanium-Carbon Alloys - Structure and Electronic Transport
Authors: John T.-M. , Bläsing J. , Veit P. , Drüsedau T.
Published: April 2011

Amorphous Ge1-xCx alloys were deposited by rf-magnetron sputtering from a germanium target in methane-argon atmosphere. Structural investigations were performed by means of wide and small angle X-ray scattering, X-ray reflectometry and cross-sectional transmission electron microscopy. The electronic transport properties were characterized using Hall-measurements and temperature depended conductivity. The results of X-ray techniques together with the electron microscopy clearly proof the existence of a segregation of the components and cluster formation already during deposition. The temperature dependence of the electronic conductivity in the as-prepared films follows the Mott' T−1/4 law, indicating transport by a hopping process. After annealing at 870 K, samples with x≤0.4 show crystallization of the Ge-clusters with a crystallite size being a function of x. After Ge-crystallization, the conductivity increases by 4 to 5 orders of magnitude. Above room temperature, electronic transport is determined by a thermally activated process. For lower temperatures, the σ(T) curves show a behaviour which is determined by the crystallite size and the free carrier concentration, both depending on the carbon content.
Improved Stability Against Light-Exposure in Deuterated Amorphous Silicon Alloy Solar Cells
Authors: Sugiyama S. , Yang J. , Guha S.
Published: April 2011

We have studied light-induced degradation in hydrogenated and deuterated amorphous silicon alloy solar cells in which intrinsic layers were deposited by using SiH4+H2 and SiD4+D2 gas mixtures respectively. Replacing hydrogen with deuterium in the intrinsic layer of the cell improves stability against light exposure. On the other hand, cells in which intrinsic layers were deposited from SiD4+H2 and SiH4+D2 do not show any improvement in stability. This result shows that improved stability in deuterated cell does not originate from simple replacement of hydrogen with deuterium. From deuterium/hydrogen effusion measurements, we found similar effusion at low temperature (400 °C) in both deuterated film and hydrogenated film prepared with heavy dilution. The latter film was shown to have oriented microstructure which was correlated with higher stability. This correlation strongly indicates that microstructure of the material plays a key role in improving the stability.
Intentional Reconstruction of Silicon Network on the Surface and within Sub-Surface by H and Ar
Authors: Futako W. , Fukutani K. , Shimizu I.
Published: April 2011

Silicon thin films were prepared by “Chemical Annealing” where the deposition of thin layer (<3 nm thick) by RF glow discharge of SiH4 and the treatment with hydrogen atoms (H) or triplet state of argon (3Ar) were repeated alternatating. Consequently, wide gap a-Si:H with the gap of 2.1 eV was made by H-treatmentat rather low substrate temperature (Ts<150 °C), while a-Si:H with the gap narrower than 1.6 eV was obtained by the treatment with 3Ar at high Ts (>300 °C), resulting from the release of excessive hydrogen. Both the wider or the narrower gap films exhibited low defect density lower than 1016 cm−3 and obvious improvements in the stability for light soaking.
Real-Time Kinetic Analysis of Hydrogen Abstraction and Etching Reactions Using Pulsed-Gas PECVD of Amorphous and Microcrystalline Silicon
Authors: Srinivasan Easwar , Parsons Gregory N.
Published: April 2011

Hydrogen elimination reactions, abstraction and etching, are monitored in real-time using a differentially pumped mass spectrometer, while intermittently exposing a hydrogenated silicon surface to atomic deuterium. The mass spectrometer signals are used to predict the kinetics of the abstraction reaction, and to qualitatively treat the etch reaction.
Polarized Electroabsorption in Pulse and Continuous Light-Soaked a-Si:H - Structural Change other than Defect Creation
Authors: Hata H. , Kamei T. , Okamoto H. , Matsuda A.
Published: April 2011

Experimental results on structural change other than defect creation upon light-soaking of hydrogenated amorphous silicon (a-Si:H) are reported. A-Si:H films were light-soaked with laser pulses or with continuous (cw) light to steady-states, and then annealed at 170 °C in vacuum. The changes in electro-absorption (EA) signal, and defect density (Nd) from subgap absorption were measured as functions of light-soaking/annealing time. The results are: (1) EA ratio, which is defined as the ratio of anisotropie to isotropie components in EA signal, increases upon light-soaking with a time constant shorter by almost two orders of magnitude than that for Nd increase, and (2) shows saturation when extensively light-soaked. (3) The saturated values of EA ratio are comparable for both pulsed and cw light-soaking. (4) Both the EA ratio and Nd show recovery to the values in the annealed states. It is suggested that light-soaking causes a structural change in a short time, as manifested by EA ratio, and this changed structure works as the pathway leading to the defect creation. Thermal annealing is also discussed.
ESR Studies on Hot-Wire Amorphous Silicon
Authors: Unold T. , Mahan A. H.
Published: April 2011

We measure a series of hot-wire (HW) amorphous silicon films grown with hydrogen contents cH varying between 0.5–17at.%. From constant photocurrent method (CPM) measurements and the steady-state photocarrier grating method (SSPG) we find good agreement with previous measurements on similar hot-wire films. Electron spin resonance measurements on the same samples, however, yield significantly higher spin densities than expected. A thickness series indicates a highly defective layer close to the substrate interface. We propose that this defective layer may be due to excessive out diffusion of hydrogen during growth at high temperatures, as seen by secondary ion mass spectroscopy. ESR measurements on light-degraded samples indicate an improved stabilityof samples with cH < 9at.%.
Modeling of a-Si:H Alloy Solar Cells on Textured Substrates
Authors: Zeman M. , van den Berg J. H. , Vosteen L. L. A. , Willemen J. A. , Metselaar J. W. , Schropp R. E. I.
Published: April 2011

Computer modeling is used as a tool for determining current matching in hydrogenated amorphous silicon (a-Si:H) alloy tandem cells on textured substrates. The increasing complexity of a-Si:H based solar cells requires continuous extending and testing of the computer models which are used for their simulation. To take light scattering at the textured interfaces of the cell into account we developed a multi-rough-interface optical model GENPR02 which was used for calculating the absorption profiles in the solar cells. The results of a sensitivity study of the parameters of this optical model such as the scattering coefficients of the reflected and transmitted light and the dependence of scattered light on the in-going and out-going angle are presented. In order to simulate multi-junction solar cell as a complete device we implemented a novel model for tunnel/recombination junction (TRJ), which combines the trap assisted tunneling and enhanced carrier transport in the high field region of the TRJ.

The current matching conditions were determined both for a-Si:H and a-SiGe:H bottom cells, while the top cell was an a-Si:H cell. We investigated the influence of light scattering at the textured interfaces and of the thickness of the intrinsic layer of the bottom cell on the optimal ratio (i2/i1) between the thicknesses of the bottom (i2) and top (il) intrinsic layers in the current-matched cell. The results show that increasing amount of scattering at the textured interfaces leads to higher efficiencies and lower ratio (i2/i1) in the current-matched cell. The use of a-SiGe:H material in the bottom cell leads to higher efficiency and 3 to 4 times lower i2/i1 ratio than in case of a-Si:H/a-Si:H cells.
Computer Analysis of a-Si:H Based Double Junction Solar Cells
Authors: Palit N. , Chatterjee P.
Published: April 2011

An integrated electrical-optical model has been used to simulate and examine ways of optimising the performance of double junction solar cells, where both the component cells have a-Si:H absorber layers of identical material quality. In the optical modelling part we take into account both specular interference effects; and diffused reflectances and transmittances due to interface roughness. The model simulates carrier transport in the junction between the two p-i-n subcells with the help of a thin heavily defective recombination layer (RL) having a reduced band gap.

Our results reveal that in order to simulate the current-voltage and the quantum efficiency (QE) characteristics of these cells, window losses and light-trapping effects need to be properly accounted for. Results indicate that the highest open-circuit voltage is attained when the majority carrier quasi-Fermi levels on either side of the RL coincide. Also for the highest multijunction cell efficiency the thicknesses of the component subcells are such that the electric field in both are fairly close to one another. Finally, the QE under AM 1.5 bias light at the maximum power point has been shown to be extremely sensitive to thickness variations of the component subcells and hence an useful tool for multijunction cell optimisation.
Characterization and Modeling of Frequency Dispersion in Amorphous Silicon Thin Film Transistors
Authors: Slade H. C , Shur M. S. , Ytterdal T.
Published: April 2011

The large number of localized energy states in amorphous and polysilicon thin film transistors causes non-crystalline effects in both the DC and AC transistor characteristics. The observed frequency dispersion of the device capacitances is linked to the characteristic times of electron trapping and emission from localized thin film transistors and is modeled analytically by introducing effective RC time constants, which are proportional to the electron transit times, determined by the field effect mobility. The small-signal gate-to-source and gate-to-drain capacitances have been derived using Meyer's approach, which takes into account the non-zero drain-source voltage to achieve a partitioning of the channel capacitance. We have verified the model for amorphous silicon thin film transistors for varying gate lengths and frequencies.
Near-Intrinsic Microcrystalline Silicon for Use in Thin Film Transistors
Authors: Froggatt M. W. D. , Milne W. I. , Powell M. J.
Published: April 2011

Inverted-staggered thin film transistors (TFTs) incorporating hydrogenated microcrystalline silicon for both contact and channel regions have been fabricated by plasma enhanced chemical vapour deposition (PECVD) using the high hydrogen-dilution method. The deposition parameters for the channel region were chosen to yield near-intrinsic material with a dark conductivity activation energy of 0.7 eV and a Tauc gap of 1.98 eV, while the doped contact layer was optimised to produce a high dark conductivity of 10 S/cm.

These devices exhibit a low off-current but the field effect mobility is found to be lower than that of similar devices incorporating an optimised amorphous silicon channel region. The mobility activation energy in these devices is similar to those incorporating an amorphous channel, but the mobility pre-factor is reduced. We propose that this is due to inhomogeneous conduction through a microcrystalline region with a smaller grain size at the dielectric/channel interface.
Amorphous Silicon Thin-Film Transistors with a Hot-Wire Active-Layer Deposited at High Growth Rate
Authors: Chu V. , Jarego J. , Silva H. , Silva T. , Boucinha M. , Brogueira P. , Conde J. P.
Published: April 2011

High-quality thin film transistors (TFT) with hydrogenated amorphous silicon (a-Si:H) deposited by hot-wire (HW) chemical vapor deposition as the active layer at growth rates above 20 Å/s are compared to TFTs with a-Si:H deposited by RF glow discharge at 1 Å/s. The subgap absorption measured by the constant photocurrent method and steady-state photoconductivity measured between source and drain are used to characterize the a-Si:H in the TFT. The activation energy of the dark conductivity is measured as a function of the gate voltage to obtain the position of the Fermi level. The effect of a bias stress on the TFT transfer curve is obtained.
Time Dependence of the Reverse Current in Amorphous Silicon Schottky Diodes
Authors: Aflatooni K. , Hornsey R. , Nathan A.
Published: April 2011

We present measurement results of the time-dependent reverse current in amorphous silicon Schottky diodes for a broad range of bias voltage stress conditions. The resultant behavior can be divided into three regimes, depending on the bias. At low biases, the reverse current exhibits a power-law dependence attributable to dispersive electron transport. In the medium bias regime, the current shows a dramatic increase which may be due to enhanced thermionic emission and tunneling of electrons across the barrier, enabled by hole transport to the metal-semiconductor interface. At high biases, the effects of prolonged stress were found to be irreversible. Here, an eventual decrease in reverse current was observed, with an associated loss of rectifying characteristics.
Structure, Electronic Properties, Defects and Doping of AlN Using a Self-Consistent Molecular Dynamics Method
Authors: Stumm Petra , Drabold D. A.
Published: April 2011

Molecular dynamics simulations are employed to study native defects and dopants in AlN. We use local basis density functional theory within the local density approximation where charge transfer between the ions is included in a self-consistent fashion. Employing this code we find reasonable agreement for the band structure compared to other recent calculations, suggesting the suitability of our method to adequately describe AlN.

Wurtzite and zincblende 96 atom AlN cells are used to study the relaxations and electronic properties of common defects in the crystal structure, including vacancies and antisites. We investigate the electronic signatures of these defects. The local topology of column-IV impurities in anion and cation sites is studied. We analyze the lattice relaxations and electronic consequences of these impurities and identify midgap defect, donor and acceptor levels.
Movpe Growth and Characterization of AlxGa1-xN Layers on Sapphire
Authors: Clur S. , Briot O. , Rouviere J. L. , Andenet A. , Le Vaillant Y-M. , Gil B. , Aulombard R. L. , Demangeot J. F. , Frandon J. , Renucci M.
Published: April 2011

AlGaN is an important material for the realization of nitride heterostructures, involved in most device designs. We have studied the growth of this alloy using low pressure MOVPE (76 Torr), and using triethyl-gallium (TEGa), trimethyl-aluminum (TMA1) and ammonia (NH3) as precursors. First the solid -gas aluminum segregation was studied in order to calibrate the incorporation of Al in the solid phase. We found that aluminum is more readily incorporated than gallium in the solid, leading to an apparent Al segregation coefficient greater than unity. A simple kinetic model is used to fit the experimental data. Scanning electron microscopy has been used to investigate the morphology of the samples through the whole range of Al content (x = 0 to 1), and we observe a clear evolution of the surface features versus aluminum concentration: at low Al contents, small (below 1 pm) hexagonal holes are observed while at high Al, acicular features are observed, with a sudden transition between those morphologies around x = 0.5. Transmission electron microscopy was used to analyze the crystalline structure of these samples. Finally, the samples were studied by low temperature (2K) reflectivity and Raman spectroscopy. We report the evolution of the optical quality of samples (x < 0.4) versus Al content, as evaluated from the broadening of the observed excitonic transitions in the 2K reflectivity.
Photoluminescence of Strain-Engineered MBE-Grown GaN and InGaN Quantum Well Structures
Authors: Krüger Joachim , Kisielowski Christian , Klockenbrink Ralf , Sudhir G. S. , Kim Yihwan , Rubin Michael , Weber Eicke R.
Published: April 2011

The paper describes the influence of strain on the optical quality of GaN films grown by MBE on c-plane sapphire. The photoluminescence (PL) line width of the donor-bound exciton can be designed to be as narrow as 1.2 meV by actively utilizing hydrostatic and biaxial stress components. Unstrained p-type Mg-doped GaN films exhibit comparably narrow near band edge transitions. A sharp PL line at 3.261 eV in some of our films is identified as the donor bound exciton of the cubic phase. The formation of these cubic inclusions can be stimulated by a high III/V flux ratio at the growth temperature of T = 725°C. The PL spectrum of an InGaN multi quantum well structure is significantly broadened compared with the spectra of single quantum well structures. Combination of PL and TEM indicates that this effect relates to a progressive increase of the quantum well widths and their spacing along the growth direction. It is argued that strain affects the growth rate and the incorporation of Indium into the quantum well structures.
Influence of Free Charge on the Lattice Parameters of GaN and Other Semiconductors
Authors: Leszczyński M. , Bąk-Misiuk J. , Domagała J. , Suski T.
Published: April 2011

Lattice parameters of semiconductors depend on the concentration of free electrons via the deformation potentials of the occupied minima of the conduction bands. In the presented work we examined the lattice parameters of variously doped GaN samples (epitaxial layers on sapphire and on SiC, bulk crystals grown at high hydrostatic pressure and homoepitaxial layers). The following dopants were used: Si, Mg and O. The measurements were performed using high resolution X-ray diffractometry. The results indicate that free electrons expand the lattice what confirms a negative value of the deformation potential of the Γ minimum of the conduction band. However, for Mg-doping (acceptor) we observed the lattice expansion as well. This violates the Vegard's law, as Mg ions are smaller than Ga ions.
Processing Challenges for GaN-Based Photonic and Electronic Devices
Authors: Pearton S. J. , Ren F. , Shul R. J. , Zolper J. C. , Katz A.
Published: April 2011

The wide gap materials SiC, GaN and to a lesser extent diamond are attracting great interest for high power/high temperature electronics. There are a host of device processing challenges presented by these materials because of their physical and chemical stability, including difficulty in achieving stable, low contact resistances, especially for one conductivity type, absence of convenient wet etch recipes, generally slow dry etch rates, the high temperatures needed for implant activation, control of suitable gate dielectrics and the lack of cheap, large diameter conducting and semi-insulating substrates. The relatively deep ionization levels of some of the common dopants (Mg in GaN; B, Al in SiC; P in diamond) means that carrier densities may be low at room temperature even if the impurity is electrically active - this problem will be reduced at elevated temperature, and thus contact resistances will be greatly improved provided the metallization is stable and reliable. Some recent work with CoSix on SiC and W-alloys on GaN show promise for improved ohmic contacts. The issue of unintentional hydrogen passivation of dopants will also be covered - this leads to strong increases in resistivity of p-SiC and GaN, but to large decreases in resistivity of diamond. Recent work on development of wet etches has found recipes for AlN (KOH), while photochemical etching of SiC and GaN has been reported. In the latter cases p-type materials is not etched, which can be a major liability in some devices. The dry etch results obtained with various novel reactors, including ICP, ECR and LE4 will be compared - the high ion densities in the former techniques produce the highest etch rates for strongly-bonded materials, but can lead to preferential loss of N from the nitrides and therefore to a highly conducting surface. This is potentially a major problem for fabrication of dry etched, recessed gate FET structures.
Toward Growing III-V Clusters with Metalorganic Precursors
Authors: Demchuk A. , Porter J. , Koplitz B.
Published: April 2011

The present work reports on the formation of GaN-containing clusters from metalorganic precursors by combining pulsed laser photolysis and pulsed nozzle methods. Ammonia (NH3) and triethylgallium (C2H5)3Ga (TEG) or trimethylgallium (CH3)3Ga (TMG) with He, Ar, or N2 as the carrier gas are introduced into a high vacuum chamber via a specialized dual pulsed nozzle source. The light from an ArF excimer laser (193 nm, 23 ns FWHM) is focused into the mixing and reaction region of the nozzle source, and the products are then mass analyzed with a quadrupole mass spectrometer. Efficient laser-assisted growth of (GaN)x-containing clusters is shown with this technique.
InxGa(1-x)N Alloys as Electronic Materials
Authors: Semchinova O. K. , Alexandrov S. E. , Neff H. , Uffmann D.
Published: April 2011

In this work, we present growth of InxGa(1-x)N films by CVD technique and their optical characterization. Experimental results indicate that these films are promising materials for semiconductor device applications. We focus on solar cells and present preliminary experimental data on prototype devices.
Electrical Properties of Schottky Contacts of TiW on RTCVD Si1-x-yGexCy Films
Authors: Mi Jian , Zhang Yilu , Warren Patricia , Yang Cary Y.
Published: April 2011

High-quality epitaxial Si1-x-yGexCy layers were grown on Si by rapid thermal chemical vapor deposition. Schottky diodes of TiW/SiGeC were fabricated using conventional Si processes. I-V and C-V measurements were performed to assess effects of crystal defects in the alloy on the electrical properties. For defective SiGeC films due to non-substitutional carbon, high series resistance and additional tunneling current were measured under forward bias, as well as leakage current under reverse bias. A transport mechanism of deep generation/recombination centers formed by carbon complexes is proposed to explain the I-V characteristics.
Selective Rapid Thermal Chemical Vapor Deposition of Titanium Disilicide on Silicon and Polysilicon
Authors: Nie Lixin , Weintraub Chad E. , Öztürk Mehmet C.
Published: April 2011

Selective rapid thermal chemical vapor deposition (RTCVD) of TiSi2 is a promising alternative to the conventional self-aligned suicide (SALICIDE) process to form low-resistivity contacts to ultra-shallow source/drain junctions of deep submicron MOS transistors. The process makes use of TiCl4 and SiH4 as the Ti and Si source gases in a temperature range of 750 – 825 °C. The primary advantage of the process over the conventional SALICIDE process is that by providing sufficient levels of Si from the gas phase, junction consumption can be eliminated. Furthermore, the process eliminates wet etch and reduces the number of process steps from four to one. For the process to be compatible with CMOS manufacturing, low-resistivity TiSi2 deposition must be achieved on both source/drain junctions as well as the poly cry stalline silicon gate electrode. It is the objective of this paper to compare basic characteristics of the process on these two surfaces. The results indicate that the crystallinity of the surface on which TiSi2 is deposited can impact the nature of the deposited film. Our experimental results indicate enhanced Si consumption on polysilicon, smaller TiSi2 grains and consequently higher sheet resistance. However, the process conditions and TiSi2 thickness can be optimized to achieve consumption free TiSi2 deposition on the junctions with acceptable performance on polysilicon.
Benefits and Limitations of Radiatively Heated Suszeptors
Authors: Kersch A.
Published: April 2011

In radiatively heated single wafer reactors, suszeptors are used to control the wafer temperature. This temperature, however, might be significantly different than the suszeptor temperature. The reason is that the conductive coupling of the suszeptor to the wafer is often small, even when the wafer is placed directly on the suszeptor, and the temperature difference is then determined by the optical properties and the spectral distribution of the illumination.

In this paper these temperature differences are calculated with reactor scale simulation for typical geometries. Furthermore the pattern effect is investigated whose magnitude depends on the pattern and the configuration of wafer and suszeptor.

The radiation is modeled with Monte Carlo and the optical properties of the surfaces are calculated from the electromagnetic theory of thin films.

A commercial system with a thick suszeptor for Si-CVD at reduced pressure serves as an example for the size of the discussed effect. The comparison of the simulation with measurements provides a model validation. Then, a typical RTP system equipped with a thin suszeptor is investigated. The configuration is identified under which the thin suszeptor leads to a reduced temperature variation in case of a changing wafer coating and in case of a pattern.
A New Temperature Compensation Method For Si Wafers In Rapid Thermal Processor Using Separated Si Rings As Susceptors
Authors: Lee Kuo-Chung , Chang Hong-Yuan , Hwu Jenn-Gwo
Published: April 2011

A new temperature compensation concept suitable for rapid thermal processor (RTP) with non-uniform temperature distribution was proposed in this work. Concentric Si rings with different diameters are placed between wafer and planar susceptor and are regarded as a patterned susceptor. By properly arranging the Si rings on the planar quartz or Si susceptor, one can make the semiconductor wafers have more uniform temperature distribution in a non-uniform temperature RTP system. This is a very simple and cheap method for solving the temperature non-uniformity problem in the RTP system.
Understanding the Impact of Batch vs. Single Wafer in Thermal Processing Using Cost of Ownership Analysis
Authors: Hossain-Pas S. , Pas M. F.
Published: April 2011

Introduction

Batch thermal processing satisfies device requirements for 0.5μm and larger technology nodes for silicon semiconductor manufacturing and continues to satisfy these requirements as feature sizes decrease beyond 0.5μm to 0.35μm. At the transition from 0.35μm to 0.25μm, source/drain (S/D) anneal, TiSi form, and TiSi anneal require rapid thermal processing (RTP) because of improvements in thermal budget, lateral dopant diffusion, and in silicidation, with RTP. RTP and rapid thermal chemical vapor deposition (RTCVD) become enabling technology for devices at 0.25μm and smaller technology nodes.

A cost of ownership (CoO) analysis provides a comparison between the financial impact of alternatives and helps in determining the lowest cost answer for that process, assuming all other process parameters can be met equally by all alternatives. This report analyzes primary cost drivers, their importance within each analysis, and potential for improvements which may cause a significant change in CoO values at 200mm.
Gate Stack Formation using a Fully Integrated Single Wafer Cluster Tool
Authors: Frystak David C. , Kuehne John , Wise Rick , Fowler Burt , Grothe Phil , Barnett Joel , Miner Gary
Published: April 2011

A single wafer gate cluster tool has been evaluated in an effort to quantify the effects of gate clustering on defect density, process capability and device performance. The single wafer gate cluster tool consists of a hydrofluoric vapor (HF-vapor) pre-gate cleanup module, a rapid thermal oxidation (RTO) module and a polysilicon rapid thermal chemical vapor deposition (RTCVD) module. The gate dielectric charge to breakdown (Qbd) of capacitor structures formed using the integrated single wafer gate cluster tool process sequence typically averaged 9.1 to 12.3 coulombs per square centimeter (C/cm2). Excellent gate oxide integrity yield values in the range of 99.8% to 100% were also routinely obtained. The films were free of low field and mid field gate dielectric breakdown events and the devices exhibited dielectric breakdown field strength in excess of fourteen megavolts per centimeter (MV/cm). The cluster tool process was successfully integrated into a transistor device flow. The characteristics of devices formed using the cluster tool process were equivalent to those of devices formed using conventional batch processing at the gate level.
Creation and Annealing out Mechanism of Defects in Ion-Implanted Si Crystals Investigated by Positron Annihilation
Authors: Tanigawa S.
Published: April 2011

ABATRACT

Vacancy-type defects in Si crystals introduced by ion implantation have been investigated by an energy-variable positron beam The present paper describes the general feature of point defects induced by ion implantation from the point of view of their dependence on implanted ion species, ion dose, ion energy, implanted targets, thermal after implantation, the presence of oxide overlayers and so on.
Extending the Use of NO Dielectrics for DRAM by Ultrathin Silicon Nitride RTCVD with In Situ Ammonia and Hydrogen Pre-Deposition Surface Conditioning
Authors: Tiner Paul A. , Khamankar Rajesh B. , Johnston Clark D. , Park Song C. , Pas Michael F. , Violette Katherine E. , Wise Rick L.
Published: April 2011

The use of thin nitride/oxide (NO) stacked dielectrics is common in DRAM storage node structures today. The cell capacitance can be increased without increasing the cell plate area by decreasing the thickness of the dielectric. Combinations of novel storage node structures, textured electrode surfaces, and very thin NO films (equivalent oxide thickness equal <30 Angstroms) are being characterized for use in 256 Mb and 1 Gb DRAM devices as an alternative to premature use of high k dielectric materials. However, the native oxide formed on the surface of the polysilicon bottom electrode prior to dielectric nitride deposition in a standard LPCVD furnace reactor causes the leakage current and reliability properties of the dielectric to degrade for very thin films. Using a vacuum load-locked RTCVD single-wafer reactor with appropriate in situ ammonia and hydrogen pre-deposition surface conditioning, the native oxide can be eliminated and very thin nitride films of much higher quality can be deposited. A comparison between standard batch LPCVD processing and single-wafer RTCVD for silicon nitride deposition has been done and electrical characteristics (including leakage current and time dependent dielectric breakdown) of the films have been measured. These results indicate that use of NO dielectric films may be extended 1–2 more generations of DRAM devices. This will allow more time for improving the quality of high k dielectric films.
Rapid Thermal Processing of III-Nitrides
Authors: Hong J. , Lee J. W. , Vartuli C. B. , MacKenzie J. D. , Donovan S. M. , Abernathy C. R. , Crockett R. V. , Pearton S. J. , Zolper J. C. , Ren F.
Published: April 2011

Transient thermal processing is employed for implant activation, contact alloying, implant isolation and dehydrogenation during III-nitride device fabrication. We have compared use of InN, AlN and GaN powder as methods for providing a N2 overpressure within a graphite susceptor for high temperature annealing of GaN, InN, A1N and InAlN. The AlN powder provides adequate surface protection to temperatures of ∼1100°C for AlN, > 1050°C for GaN, ∼600°C for InN and ∼800°C for the ternary alloy. While the InN powder provides a higher N2 partial pressure than AlN powder, at temperatures above ∼750°C the evaporation of In is sufficiently high to produce condensation of In droplets on the surfaces of the annealed samples. GaN powder achieved better surface protection than the other two cases.
Rapid Thermal Annealing and Oxidation of Silicon Wafers with Back-Side Films
Authors: Fiory A. T.
Published: April 2011

Temperatures for lamp-heated rapid thermal processing of wafers with various back-side films were controlled by a Lucent Technologies pyrometer which uses a/c lamp ripple to compensate for emissivity. Process temperatures for anneals of arsenic and boron implants were inferred from post-anneal sheet resistance, and for rapid thermal oxidation, from oxide thickness. Results imply temperature control accuracy of 12°C to 17°C at 3 standard deviations.
Improved Methods for Evaluation of Rapid Thermal Processors
Authors: Speranza Tony , Nakos Jim , Medina Val , Banerjee Sanjay , Williamson Gary , Lysaght Pat , Lindholm Don
Published: April 2011

SEMATECH has worked with numerous commercial suppliers of RTP systems on both evaluation and development projects. It has adopted standardized methods which minimize monitor wafer impact and improve system characterization. RTP temperature control requirements are projected to tighten with each successive technology node (1). This paper discusses issues concerning performance evaluation of Rapid Thermal Processors (RTP).
Emissivtty Studies on Polycrystalline Silicon and a-Si / SiO2 / Si
Authors: Chen W. , Oh M. , Abedrabbo S. , Tong F. M. , Schmidt W. , Narayanan S. , Sopori B. , Ravindra N. M.
Published: April 2011

Experimental studies of the room temperature emissivity of polysilicon are reported here. These measurements have been performed using a spectral emissometer operating in the wavelength range of 0.8 – 20 μm. The measured optical properties are deconvolved to yield the wavelength dependent refractive indices and extinction coefficient of polysilicon. An in house developed computer program, OPCalc, is deployed to perform these calculations. Experimental results of the temperature dependent emissivity of a-Si / SiO2 / Si / SiO2 / a-Si, fabricated on single side polished silicon substrates, in the temperature range of 300 to 1100 K have been reported here. These measurements are performed for a-Si thickness of 2100A. Comparisons of the temperature dependent radiative properties of these structures between the front and the back show that the contribution of surface roughness to emissivity is negligible- The exposure of these a-Si coated structures to high temperatures in open environment has caused these surfaces to oxidize. Interpretations, have been sought by comparisons of the experimental data with those on SiO2 / Si structures.
The Driving Pulse width Dependence of The Hysteresis Effect in ZnS:Mn Electroluminescent Devices: A Possible Addressing Method for Memory Tfel Displays
Authors: Fuh Andy Ying-Guey
Published: April 2011

A pronounced hysteresis effect was observed in the brightness versus pulse width response of memory electroluminescent (EL) devices driven near the threshold voltage. The use of this effect to address memory EL displays is suggested. A benefit of this technique is that the display is always operated near threshold with a relatively low dielectric stress. Longer device life might be therefore expected.
Deposition of Precursor Poly - Silicon Films for Flat Panel Display Applications
Authors: Pethe R. , Deshpandey C. , Dixit S. , Demaray E. , Meakin D. , Orgill D. , Turner N.
Published: April 2011

Large grain poly-Silicon (p-Si) films have been evaluated for high speed TFT for flat panel displays [1,2]. It is expected that with good quality p-Si, “System on Glass” products, in which entire electronic circuitry is incorporated directly onto glass are achievable [3]. This approach therefore has the potential to fabricate Integrated AMLCD's (IAMLCD) and bypass conventional Si wafer based products and integrate CMOS circuits with direct view TFT LCD manufacturing. To realize this potential; it is necessary to develop a production process for depositing repeatable, good quality p-Si films on to large area glass substrates.
Development of High-Efficiency Zn2SiO4:Mn Thin Films for Flat Panel Cathodoluminescent Displays
Authors: Liu J. , Morton D. C. , Miller M. R. , Li Y. , Forsythe E. W. , Tompa G. S.
Published: April 2011

Zn2SiO4:Mn thin films were deposited and studied as thin film phosphors for flat panel cathodoluminescent displays. Crystallized films with improved electrical conductivity were obtained after conventional and rapid thermal annealings in a N2 environment at 850Xy11100 °C for 0.25 to 60 minutes. A maximum cathodoluminescent efficiency of 1.3 Lm/W was achieved under dc excitation at 1500 volts. The luminescent emission from these thin films was peaked around 525 nm. The decay time of these films was controlled in the range of 2 to 10 ms by varying the deposition and annealing parameters. The fast response time of these thin films overcomes the long decay limitation of the Zn2SiO4:Mn powder phosphor in practical display applications.
Nanometer-Scale Investigation of Al-Based Alloy Films for Thin-Film Transistor Liquid Crystal Display Arrays
Authors: Takatsuji H. , Iiyori Hideo , Tsuji S. , Tsujimoto K. , Kuroda K. , Saka H.
Published: April 2011

Annealing effects on Al-Nd (0.19 – 1.82 at. %) thin films deposited on a glass substrate have been investigated. It is found that the resistivity of an Al-Nd-alloy thin film decreases significantly after annealing at 300 °C or higher temperatures. Using cross-sectional transmission electron microscopy (X-TEM), we have observed segregation of Al-Nd inter-metallic precipitates and pure-Al grains during the annealing. The decrease of the resistivity can be attributed to the segregation. Segregation has been also detected from the increase of diffracted X-ray intensities corresponding to Al-Nd inter-metallic compounds in X-ray diffraction (XRD) analysis. Atomic force microscopy (AFM) observation has revealed that the optimum content ratio of Nd in Al-Nd alloys used as interconnect materials for thin-film-transistor liquid crystal display (TFT/LCD) applications is around 0.97 atomic %.
New Insights into The Transport and Field-Enhancement Effects in Sol-Gel Derived Colossal Magnetoresistive Thin Films
Authors: Krishnan Kannan M. , Ju H. L. , Sohn H.-C. , Nelson C. , Modak A. R.
Published: April 2011

The transport mechanism underlying the colossal magnetoresistance (CMR) of doped manganites is not yet understood and their technological applications are limited by the high fields (∼IT) required to obtain any significant MR. Following the development of a polymeric chemical synthesis route, we have investigated the O2p unoccupied density of states in sol-gel derived Lal-xSrxMnO3 (0 < x < 0.7) thin films grown epitaxially on LaA1O3, by electron energy-loss spectroscopy at sub-eV resolution. The spectra show a distinct prepeak in the OK edge at the Fermi level, the intensity of which correlates directly with the conductivity of the film. Similar correlation was also obtained for La0.7Sr0.3MnO3-z annealed in vacuum to obtain well defined oxygen content (z) in the film. This confirms that the charge carriers in these manganese perovskites have significant oxygen 2p hole character and suggests that the “double exchange” mechanism has to be modified. In another set of experiments we have studied room-temperature field amplification effects to enhance the low-field sensitivity of La0.7Sr0.3MnO3-z films sandwiched between two thin rectangular slices of either α-Fe or Mn-Zn ferrite. This field amplification leads to an enhanced low-field MR value as high as 6% at an external field of 500 Oe which is 6 times the value observed without the amplification.
Epitaxial Ferroelectric Aurivillius-Type Phases on Metallic Oxides by Pulsed Laser Deposition
Authors: Curran C. , Senz St. , Pignolet A. , Alexe M. , Welke S. , Hesse D.
Published: April 2011

Bi-based layered perovskites, also called Aurivillius-type phases, are superior to simple perovskite materials with regard to their ferroelectric long-term stability. Another way to alleviate fatigue and aging problems in metal-ferroelectric-metal (MFM) heterostructures is to replace the bottom metallic electrode with a conductive oxide electrode. An attempt to combine the two approaches has been made to investigate whether a further improvement in stability can be achieved. To promote an oriented growth of the ferroelectric films, epitaxial buffer layers (YSZ, Ce02) and epitaxial electrodes of (La0.5Sr0.5 )Co03 (LSC) have been consecutively deposited onto Si (100). Finally a ferroelectric thin film of the layered perovskite Bi4Ti3012 (BiT) has been grown. Rocking curve measurements demonstrate good epitaxial growth of both the buffer and the electrode layers. The ferroelectric thin films show a preferred c-axis orientation. Cross-section TEM images reveal a twinned superstructure in the LSC layer with a tripling of the lattice parameter. EDX line-scans show that a Co-enriched and Bi-depleted layer had formed at the BiT/LSC interface. After deposition of Au electrodes on both the BiT and the LSC layer, a hysteretic behavior could be detected and the ferroelectric properties of the c-oriented BiT film be confirmed.
Interplay Between Electronic Transport and Magnetic Order in Ferromagnetic Manganite Thin Films
Authors: Hundley M. R. , Neumeier J. J. , Heffher R. H. , Jia Q. X. , Wu X. D. , Thompson J. D.
Published: April 2011

The transition metal oxides La1-xAxMnO3 (A = Ba, Ca, or Sr) order ferromagnetically with Curie temperatures ranging from as low as 50 K to well above room temperature. Magnetic order in these compounds results in a concomitant metal-insulator transition. The feature displayed by the manganites that is most important technologically is the extremely large negative magnetoresistance that achieves its largest values near the magnetic ordering temperature. Qualitatively, this colossal magnetoresistance (CMR) phenomenon involves the suppression of the relatively sharp maximum in the resistivity that is centered at Tc. When considered collectively, the anomalous temperature-dependent transport properties, the CMR effect, and the magnetically ordered ground state indicate that a novel interplay between magnetism and electronic transport occurs in the manganites. General features of the magnetic-field and temperature-dependent electrical resistivity and magnetization as displayed by PLD-grown thin films are examined. Particular emphasis is placed on what these measurements tell us about the conduction process both above and below the magnetic ordering temperature.
Electronic Doping in Epitaxial Pb(Zr0>52Ti0.48)03/SrRuO3 Heterostructures using a Ferroelectric Field Effect
Authors: Ahn C. H. , Tybell T. , Antognazza L. , Char K. , Beasley M. R. , Fischer O. , Triscone J.-M.
Published: April 2011

We report on ferroelectric field effect experiments in ultrathin layers of the metallic perovskite SrRuC<3 using Pb(Zr0.52Ti0.48)O3/SrRuO3 epitaxial heterostructures. Switching the ferroelectric polarization of the Pb(Zr0.52Ti0.48)O3 layer induces a ∼ 10% change in the sheet resistance of the SrRuO3 layer that is nonvolatile and also reversible. Hall effect measurements that take into account the anomalous Hall effect reveal a carrier concentration of n ∼ 2 × 1022 electrons/cm3 and allow us to understand quantitatively the sign and magnitude of the observed resistance change. Of key importance for these experiments is the crystalline and surface quality of the SrRuO3 and Pb(Zr0.52Ti0.48)O3 layers. We also discuss how this general approach of nonvolatile doping using ferroelectrics opens new possibilities of directly creating small electronic structures without using traditional lithographic techniques.
AFM Observations on the Growth Mechanisms of Epitaxial Perovskite Oxide SrRuO3 Thin Films
Authors: Rao R. A. , Gan Q. , Eom C. B.
Published: April 2011

The growth mechanism and surface morphology of epitaxial SrRuO3 thin films deposited on exact and vicinal (001) SrTiO3 and exact (001) LaAlO3 substrates has been studied. Vicinal substrates with miscut angle, a, up to 4° toward [010] direction were used. Atomic force microscope images show that the films grown on exact (001) SrTiO3 substrate had a growth mechanism involving two dimensional nucleation. In contrast, characteristic step patterns were observed on the films deposited on vicinal substrates, suggesting that these films had a step flow growth mode. The films deposited on exact (001) LaAlO3 substrates had a three dimensional island growth, due to the incoherence between the film and substrate lattice. These results were found to be consistent with the results of x-ray diffraction analysis of the in-plane domain structure.
Atomic Scale Engineering of SrTiO3 Single Crystal Surfaces and Bicrystal Boundaries for Epitaxial Growth of Oxide Thin Films
Authors: Jiang Q. D. , Zegenhagen J.
Published: April 2011

We introduce a new annealing procedure to prepare well defined surfaces of SrTiO3 single crystal and bicrystal substrates. Annealing SrTiO3 (001) substrates in oxygen and then in ultra high vacuum produces a uniformly TiO2-terminated, atomically flat and ordered SrTiO3 (001) surfaces, as revealed by Auger electron spectroscopy, low energy electron diffraction, and high resolution scanning tunneling microscopy. Applying this annealing procedure to slightly off-cut (∼1.2°) SrTiO3 (001) surfaces has a strong influence on the resulting step structure. Particular annealing procedures can be used to tailor the structure and morphology of the surface and of bicrystal boundaries down to the atomic level. For example, steps of SrTiO3 (001) surfaces can be adjusted to a height of one, two, or multiple times the unit-cell size of STO (aSTO=0.3905 nm). Atomically flat SrTiO3 (001) substrates were used for deposition of SmBa2Cu3O7-δ (SBCO) thin films. The thickness (in a range from 10 nm to 200 nm) dependency of the surface morphology of SmBa2Cu3O7-δ films was investigated with UHV-STM. No spiral growth was observed. Surfaces of all films exhibit stacks of flat terraces which are frequently separated by steps, smaller than the c-axis length cSBCO of SBCO (cSBCO=1.17 nm).
Structural Characterization Of SrBi2Ta209 Thin Films
Authors: Ching-Prado E. , Pérez W. , Reynés-figueroa A. , Katiyar R. S. , Ravichandran D. , Bhalla A. S.
Published: April 2011

Thin films of SrBiTa2O9, (SBT) were deposited on Si using Sol-Gel technique. The thicknesses of the films are 200 nm (A) and 400 nm (B), respectively. SEM studies show isolated grains in both SBT films with a grain size distribution between 0.1 and 0.5 μ. However, most of the grain size in the film is smaller than 0.1 μ. EDX analysis indicates that the films are inhomogeneous. FTIR external reflectivity measurements of the samples show bands around 1260, 936(for SBT2), 955(for SBT4), 770, 600 cm−1. Micro Raman spectra shows inhomogeneities in the SBT films. Bands corresponding to the SBT materials were found, but frequency shifts and broadening were observed in almost every band. Particularly, the band around 818 cm−1 was found to change from 785 to 827 cm−1. Also, due to the stretching of the Ta06 octahedron, the Alg mode was found to be approximately 163 cm−1. This change seems to be related to the Ta-0 bond length.
Chemical Solution Deposited BaTi03 AND SrTi03 Thin Films With Columnar Microstructure
Authors: Hoffmann S. , Hasenkox U. , Waser R. , Jia C. L. , Urban K.
Published: April 2011

We show that CSD processing can be optimized in order to achieve columnar structured BaTiO3 and SrTiO3 thin films at elevated temperatures. In addition to these, columnar grain growth was also obtained for films of the solid solution (Ba0.7Sr0.3)TiO3 By controlling the film formation process, polycrystalline and columnar grained thin films were grown on Pt coated Si substrates at temperatures between 750° and 800°. The films were analyzed by glancing incidence X-ray diffraction and scanning electron microscopy. Detailed analysis on the thin films’ microstructure was performed by means of transmission electron microscopy. Based on these data, the film formation process is discussed with respect to process control and precursor chemistry. Differences in the crystallization process of BaTiO3 thin films compared to SrTiO3 films are pointed out.