bluuebunny/crossref_metadata_2025 huggingface dataset:
High Deposition Rate a-Si:H for the Flat Panel Display Industry
Authors: Hautala J. , Saleh Z. , Westendorp J. F. M. , Meiling H. , Sherman S. , Wagner S.
Published: April 2011

High deposition rates and good quality electrical properties and thickness uniformities over large areas are required for all three films (SiNx, a-Si:H and n+ a-Si:H) composing the thin film transistors (TFTs) for the AMLCD industry, while maintaining high tool up-time and low particle formation. Generally these conditions have been achieved for most single-panel multichamber PECVD systems; however, it has become increasingly apparent that a compromise is drawn between the TFT mobility and the deposition rate of the a-Si:H layer. Thus it becomes essential to clearly assess the industry requirements for both deposition rates as well as TFT performance for the different device structures used for AMLCDs, and to discover and control these underlying material properties.

The TEL VHF (40/60 MHz) PECVD system produces high quality, low defect density a- Si:H at deposition rates exceeding 1500 Å/min when analyzed by FTIR, CPM, photo and dark conductivity. Even though the low deposition rate a-Si:H exhibits very similar bulk properties, higher mobility TFTs are produced with a-Si:H deposited at lower RF power. Having both a high ion flux and low ion energy in the SiH4 discharge are likely the most critical conditions for controlling the a-Si:H quality and thus the TFT mobility. Increasing the RF frequency enhances both of these effects, as well as provides a higher deposition rate for a given power density and a higher power threshold for particle/powder formation. For these reasons it is likely a 40/60 MHz plasma will produce better performing TFTs for a given deposition rate when compared with a conventional 13.56 MHz system. Other process conditions such as diluting the SiH4 in H2 or Ar also seem to play an important role in the optoelectronic properties of the a-Si:H film and ultimately the TFT performance.
Energy Levels of Defects in a-Si:H From Optical and Electrical Characteristics
Authors: Globus T.
Published: April 2011

Two novel characterization techniques for hydrogenated silicon thin films have been recently proposed which show promise in providing critical feedback for evaluating materials and monitoring the device fabrication process. The first technique is the optical interference spectroscopy for a quick non-destructive measurement of absorption coefficient and refractive index spectra of amorphous- and poly-Si thin films in a wide range of the incident photon energies (0.5–3.5 eV) [1]. By using this technique, the absorption related to defects in the subgap energy region has been determined for device quality thin films. The second technique is the novel version of the field effect conductivity (FEC) method for the direct density-of-states (DOS) determination from analysis of thin film transistor (TFT) quasi-static transfer characteristics [2]. This sensitive, fast, and easy to use, method makes it possible to resolve fine-scale features in the midgap DOS of a-Si:H. In this work, data from two methods of spectroscopy are analyzed together. Very close correlation of results is demonstrated which provides a unique opportunity to identify midgap defect states and to understand the fundamental physics of hydrogenated silicon films. The energy map of defect states in the upper half of a-Si:H bandgap is presented. These results permits to use TFT transfer characteristics and optical interference technique measurements as effective tools to control the quality of TFF manufacturing process.
Synthesis of Ferroelectric Liquid Crystalline Polymers by Ring Opening Polymerization
Authors: Hsu C. S. , Lee C. J.
Published: April 2011

The synthesis of two series of side-chain liquid crystalline polyoxetanes and polyoxiranes containing 4-alkanyloxybiphenyl-4′ -yl (2S,3S)-2-chloro-3-methylvalerate side groups is presented. Differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry reveal smectic mesomorphism for all obtained polymers. Most of the prepared polyoxetanes present smectic A and chiral smectic C phases. The polyoxetane containing tweleve methylene units in the spacer is the only one showing two enantiotropic smectic A and B phases. All of the obtained polyoxiranes display two enantiotropic smectic A and B phases. Although the polyoxetane and polyoxirane backbones are more flexible than the polymethacrylate backbone, side-chain crystallization do not occur in any of the synthesized polymers.
Novel Vitrified Liquid Crystals and Potential Applications
Authors: Chen S. H. , Shi H. , Conger B. M. , Katsis D. , Mastrangelo J. C.
Published: April 2011

An overview is presented for a generic approach to low molar mass liquid crystalline materials capable of vitrification into morphologically stable, optically anisotropic thin films. Potential applications as polarization control devices, optical notch filters, and luminescent elements will be explored. Preliminary data for defect formation and annihilation will also be presented to illustrate an advantage of low molar mass materials over polymer analogs.
A Microstructural Model for Liquid Crystalline Polymers
Authors: Hobdell John R. , Windle Alan H.
Published: April 2011

We have developed a numerical technique to investigate the effect of different Frank elastic constants on the microstructure of liquid crystalline materials. In particular the technique is applied to predict microstructure in polymeric materials where the splay elastic constant is high and the twist elastic constant is low. It is found that such a combination of elastic constants leads naturally to the twist escaped features seen experimentally.
High Modulus Liquid Crystalline Thermosetting Resins through Novel Processing Techniques
Authors: Smith M. E. , Douglas E. P. , Benicewicz B. C. , Earls J. D. , Priester R. D.
Published: April 2011

We have demonstrated the effects of magnetic field alignment for the epoxy resin system, the diglycidyl ether of dihydroxy-α-methylstilbene cured with sulfanilamide. With increasing magnetic field, the tensile modulus of the thermoset can be enhanced by a factor of three, without compromise to the transverse value. Measurements of the coefficients of thermal expansion and the order parameter as determined by x-ray diffraction elucidate the high degree of alignment obtained at field strengths of 15–18 Tesla.

The interrelationship between the reaction kinetics of curing with the molecular alignment process is central to successful processing of this class of thermosets. Preliminary relationships between the field strength, time in the magnetic field, reaction rate, and extent of reaction have been developed. Process control and sequencing allow a wide adjustment in the properties of the produced samples. Our studies demonstrate the increased value of multi-mode processing in the development of tailored property, lightweight materials.
Liquid Crystal Photonics: Optical Switching and Image Storage by Means of Azobenzene Liquid-Crystal Films
Authors: Shishido A. , Tsutsumi O. , Ikeda T.
Published: April 2011

Optical switching and image storage were explored by means of azobenzene liquid crystals (LCs). Azobenzene derivatives with monomeric and polymeric forms were prepared, which show nematic LC phase in the trans form while no LC phase in the cis form. On pulse irradiation at 355 nm, which causes trans-cis isomerization of the azobenzene moiety, these azobenzene LC films underwent nematic (N) to isotropic (1) phase transition in 100 ˜ 200 μs as probed by change in transmittance of a He-Ne laser through crossed polarizers (transmission-mode analysis) or change in reflectivity at the interface between the sample and glass substrate (reflection-mode analysis). In the reflection-mode analysis, the decay was faster than that observed in the transmission-mode analysis. The N phase recovered through the cis-trans thermal backisomerization process in the transmission-mode analysis, while it was restored through diffusion of the cis form, followed by reorientation of the trans form which replaced the cis form in the interface region, in the reflection-mode analysis. The photochemical N-I phase transition was also induced in 200 μs below Tg of the polymer azobenzene LC. Image could be stored into the polymer azobenzene LC film on photoirradiation to bring about the N-I phase transition and the stored image remained unchanged even after one year when it was kept below Tg of the polymer.
Theory of Circularly Polarized Light Emission from Chiral Nematic Liquid Crystalline Films
Authors: Shi H. , Chen S. H.
Published: April 2011

Chiral nematic liquid crystalline films with fluorescent chromophores are capable of circularly polarized emission. A theory is presented in which the effects of anisotropic absorption and film thickness are accounted for. The predicted dissymmetry factor is compared with experimental data reported by Stegemeyer et al. and with the theory for the two limiting cases treated by Pollmann et al.
Electro-Optics of Polymer-Dispersed Liquid Crystal Materials
Authors: Drzaic Paul S.
Published: April 2011

The electro-optical properties of polymer dispersed liquid crystal (PDLC) materials depend on both the chemical nature of the liquid crystal and polymer, as well as the morphology of the liquid crystal/polymer composite. The relationship between several aspects of film structure and PDLC film properties are described, emphasizing scattering effects and reorientation fields. In particular, the idea of relative orientation of neighboring droplets as controlling light scattering, and the role of anchoring in determining film voltages, are highlighted.
Surface Anchoring and Electro-Optics in Polymer-Dispersed Liquid-Crystal Films
Authors: Amundson Karl , Srinivasarao Mohan
Published: April 2011

Polymer-dispersed liquid crystal (PDLC) films are composed of micrometer-scale droplets of liquid crystal (typically nematic) in a polymeric matrix. They can be switched with an electric field from a scattering to a transparent state, and are of interest for use in flat-panel displays. The electro-optics of PDLC films, and the director field pattern within the nematic droplets, are strongly influenced by the surface anchoring condition at the liquid crystal - polymer matrix interface. To understand the role of surface anchoring, we studied the electro-optics of photopolymerized PDLC films composed of a liquid crystal and acrylates as a function of temperature. Properties depend strongly upon the choice of the acrylate. With several acrylate matrix materials, the nernatic director field undergoes a reversible, temperature-driven configurational transition, accompanied by dramatic changes in electro-optical properties. We find that the surface anchoring behavior is very sensitive to the polymer structure as well as several parameters of PDLC film formation. Several surface anchoring transitions are used in a study that shows strong evidence for surface memory in PDLC films.
Correlation of Molecular Structures and Properties on Diphenyl-Diacetylene Liquid Crystals
Authors: Wu S. T. , Hsu C. S.
Published: April 2011

Effects of molecular structures on the phase transition temperatures, dielectric anisotropy, elastic constant, and refractive indices of diphenyl-diacetylene liquid crystals are analyzed.
Synthesis of New Chiral Disubstituted Binaphthol Derivatives and their use as the Chiral Dopants
Authors: Deussen H.-J. , Shibaev P. V. , Vinokur R. A. , Schaumburg K. , Bjornholm T. , Bechgaard K. , Shibaev V. P.
Published: April 2011

A number of new chiral binaphthol (BN) derivatives with different substituents in the 6,6'-positions in open and bridged forms have been synthesized. Their possible liquid crystalline properties and their helical twisting power (B) of three different nematic liquid crystals (LCs) were investigated. Derivatives with spatially extended substituents in the 6,6'-positions (e.g. styryl or vinil) show unusual high helical twisting power (up to 120 μm–1). A direct correlation between the magnitude of β and the length of the substituents was found.

From the different temperature dependence of β of the open and bridged BNs, a molecular model was developed relating the molecular conformation and twisting power
Silicon Films Deposited by LPE on Low Cost Multicrystalline Silicon Substrates
Authors: Stemmer M. , Wagner G. , Martinuzzi S.
Published: April 2011

P type silicon layers for photovoltaic applications have been deposited on low cost multicrystalline silicon substrates prepared by directional solidification or by electromagnetic casting with solar grade charges. The thickness is between 4 to 20 μm. The layers were characterized by Light Beam Induced Current (LBIC) mappings at different wavelengthes. Collecting structures are p-n junctions or Al-Si semitransparent diodes. The layer and the substrate can be investigated separately by changing the wavelength of the LBIC maps, or/and by realizing a collecting structure on the free surface of the substrate.

It is found that the same extended crystallographic defects are detected by LBIC in the layer and in the substrate. However their recombination strength in the layer is less marked probably due to a higher purity of the layer. The computed values of minority carrier diffusion length are close or larger than the film thickness and the investigated layers could be used to make solar cells.
ZnO/c-Si Heterojunction Interface Tuning by Interlayers
Authors: Fenske F. , Kliefoth K. , Elstner L. , Selle B.
Published: April 2011

The junction properties of isotype and anisotype n+-ZnO/c-Si heterostructures have been studied by electrical and photoelectrical methods. We present evidence that the junction properties are strongly affected by a 10–30 nm thick ZnO layer closest to the heterointerface with distinctively different properties than those of the ZnO film bulk. This layer supports a dominant current flow via multistep tunnelling-recombination. When a 10 nm thin ZnS or ZnSe interlayer is inserted charge transport is controlled by thermionic emission. The interlayer acts as spacer and increases the band bending in the silicon absorber. However, there is still a too high trap density at the interlayer/c-Si interface, so that Voc does not exceed 0.25–0.32 V.
XPS Analysis of Chemically Treated I-III-VI Semiconductor Surfaces and the Relation to II-VI/I-III-VI Heterojunction Formation
Authors: Nelson A. J. , Schwerdtfeger C. R. , Herdt G. C. , King D. , Contreras M. , Ramanathan K. , O'Brien W. L.
Published: April 2011

Device-grade thin-film CuInSe2 was subjected to various chemical treatments commonly used in photovoltaic device fabrication to determine the resulting microscopic surface composition/morphology and the effect on II-VI/CuInSe2 heterojunction formation. HCI (38%), Br-MeOH (<1% Br), (NH4)2S, and NH4OH/thiourea solutions were used separately to modify the surface chemistry of the CuInSe2 polycrystalline films. Scanning electron microscopy was used to evaluate the resultant surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and Cu 2p, In 3d, Ga 2p and Se 3d core lines were used to evaluate the chemistry of the chemically treated surfaces. CdS overlayers were then deposited in steps on these chemically treated surfaces. Photoemission measurements were acquired after each growth to determine the resultant heterojunction valence-band discontinuity between the CdS and the chemically modified CuInSe2 surface.
Effects of Oxygen During Close-Spaced Sublimation of CdTe Solar Cells
Authors: Rose D. H. , Albin D. S. , Matson R. J. , Swartzlander A. B. , Li X. S. , Dhere R. G. , Asher S. , Hasoon F. S. , Sheldon P.
Published: April 2011

The presence of oxygen during close-spaced sublimation (CSS) deposition of CdTe has been regarded as necessary for high-efficiency CdS/CdTe solar cells. To date, research has focused on the effect of oxygen on the acceptor density in the CdTe absorber. We find that although oxygen may influence the doping density, a perhaps more significant effect is its influence on nucleation and growth of the film. Oxygen partial pressures of 0 to 24 torr and total pressures of 5 to 45 torr (balance He) have been explored for CSS depositions. We find that increasing the O2 partial pressure increases the density of CdTe nucleation sites, thereby suppressing pinhole formation and likely reducing defects at the junction. However, increasing O2 also tends to decrease grain size and faceting in the films. In addition to influencing the film properties, O2 adversely affects the source material, producing non-uniformly oxidized surfaces that reduce deposition rates and impair device uniformity and run-to-run reproducibility.

We have also determined that the graphite susceptors typically used with CSS deposition convert a portion of the oxygen ambient to CO and CO2 during deposition. The amount converted is highly dependent on the type and age of the graphite susceptor used. The COx byproducts are not efficiently incorporated in the CdTe film and do not influence the deposition as oxygen does. We describe the effect of the changing oxygen partial pressure during the course of deposition. Finally, we report high-efficiency solar cells (12.8% AM 1.5) made without oxygen.
Float Line Deposited Transparent Conductors -Implications for the Pv Industry
Authors: Gerhardinger Peter F. , Mccurdy Richard J.
Published: April 2011

The flat glass industry successfully commercialized pyrolytically deposited low emissivity glass based on color-suppressed fluorine-doped tin oxide in 1990. The current production capability of this product approaches 500,000 m2 of coated glass per year. Spin-off products for the photovoltaic (PV) industry were introduced by LOF in 1991 and enjoy considerable success in this emerging technology. Many PV researchers, however, still prefer to produce optimized tin oxide off-line in CVD furnaces as they can be produced on higher performing but higher cost substrates.
In this paper, we discuss the characteristics of on-line production of PV transparent conductors (TCO), including the tradeoffs required when a coating process is incorporated onto a float glass line. We conclude by suggesting that eventual large scale commercialization of thin film photovoltaics dictates the use of on-line TCO based on economics, the excellent uniformity and repeatability, and ready availability. We believe that the PV researchers are best served by understanding the capabilities of on-line tin oxide production, and tailoring their programs towards the characteristics of these new cost effective TCOs.
Electrical Characteristics Of The Transparent Conductive Oxide / p-a-Si:H Interface
Authors: Guse Stephan , Peros Dimitrios , Wagner Michael , Böhm Markus
Published: April 2011

The current-voltage (I-V) characteristics of the interfaces between boron-doped hydrogenated amorphous silicon (p-a-Si:H) and transparent conductive oxides (TCOs) such as tin oxide (SnO2) and indium tin oxide (ITO) are experimentally determined. The measurements are performed on especially developed Kelvin cross bridge structures which allow the direct sensing of the contact region. All contacts exhibit for high dopant concentrations an almost linear I-V characteristic. The values of the contact resistance depend on the TCO type and range between 0.5 and 4 Ω· cm2 at 25°C. Gradual reduction of the boron doping level leads to a remarkable increase of the contact resistance and finally to a rectifying behavior. The results indicate that tunnelling across the interface contributes significantly to the current transport. This conclusion is also supported by the behavior of the I-V characteristics at low temperatures. Regarding degradation of the contacts a systematic reduction of the contact resistance is observed after ageing them for 1000 hours at 80°C.
Degradation of the Acousto-Electric Current Saturation Behavior in C-Axis Fiber-Textured Polycrystalline Zinc Oxide Films
Authors: Pompe T. , Srikant V. , Clarke D. R.
Published: April 2011

Acousto-electric current saturation has been observed in thin, polycrystalline Al-doped zinc oxide films grown on fused quartz. The films, grown by laser ablation, are c-axis textured with high angle grain boundaries between the grains. After annealing at 600°C in 0.1 mtorr oxygen, the films exhibit a current saturation at a current density of 2 105 A/cm2 and electric fields of 5 103 V/cm. However, under constant field the current density falls and the current saturation behavior is not maintained. Current saturation at the same current density can, however, be restored by increasing the electric field. Similarly, the appearance and disappearance of the current saturation behavior can be reversibly controlled by annealing in different oxygen partial pressures at 200°C. The degradation phenomena is attributed to the high acoustic flux enhancing the diffusion of oxygen along the grain boundaries where oxygen can alter the grain boundary potential barrier and hence the electric field in the grains.
Semiconductor Septum ELectrochemical Photovoltaic Cell
Authors: Tien H.Ti , Ren Pengcheng , Luo Wenxiu , Tan Zhongke , Ottova Angelica L.
Published: April 2011

We report the use of semiconductor septum electrochemical photovoltaic (SC-SEP) cell, modeled after green plant photosynthesis, in an application of solar energy conversion. A SC-SEP cell consists of a thin film of CdSe deposited on a metallic substrate (Ti, Ni, or stainless steel) as a bipolar septum electrode separating two aqueous solutions. It has been established that, upon irradiation of the septum electrode with visible light of the solar spectrum, photogenerated electron-hole pairs are separated under the influence of electric field. On the side of the septum electrode facing the light, the most powerful oxidant (holes) will oxidize species in the bathing solution, while the most powerful reducing agent (electrons) present on the dark side will carry out reduction of heavy metal ions or evolve hydrogen from aqueous solutions including seawater. Specifically, we report the use of photon energy generated electrons and ‘holes’ for the cleavage water to hydrogen and/or valuable chemicals in SC-SEP cells.
Correlation Between the Quantized Energies and the Photovoltaic Spectra for a GaAs/A1GaAs Quantum Well Structure
Authors: Russo O. L. , Rehn V. , Nee T. W. , Dumas K. A.
Published: April 2011

We have measured the photovoltaic spectra at 300K for a PIN GaAs/AlGaAs structure containing five coupled wells (50A/28A) grown by molecular beam epitaxy (MBE). The spectra were obtained in the energy range from 1.40 eV to 1.60 eV. This is the region in which optical transitions between the sub-band valence and conduction states are possible. Five direct optical transitions are allowed for this structure. These transitions are normally difficult to measure at room temperature because of broadening, nevertheless, some of the allowed transitions were observed from the photovoltaic spectra and agreed with calculations. We have previously shown that measurements made using electroreflectance (ER) agree with these results. However, with ER, three possible transitions were observed but only one with certainty, possibly because of interference caused by adjacent line spectra interaction. This interference appears to be less pronounced in the photovoltaic spectra, which aids in the identification of transitions.
Structure and Numerical Simulation of Field Effect Solar Cell
Authors: Koinuma H. , Fujioka H. , Hu C. , Koida T. , Kawasaki M.
Published: April 2011

A p-i-n a-Si:H solar cell structure which can eliminate detrimental effect of TCO and a heavily doped window layer has been investigated in detail using a two-dimensional device simulator. The cell is designed to use an inversion layer induced by field effect instead of the heavily doped window layer while maintaining p-i-n junction locally to keep the built-in potential high and stable. Device simulation has revealed that the conversion efficiency of p-in a-Si:H solar cells can be improved by 30% with the use of this cell structure. This improvement is mainly due to the increase in the photo-currents, which can be explained by the increased quantum efficiency for light with short wavelength.
In Situ Observations of Pre-Patterned Void Interactions Under Electromigration-Induced Stress
Authors: Frankovic Richard , Bernstein Gary H.
Published: April 2011

Electromigration (EM) void nucleation and growth is a failure mechanism of integrated circuit (IC) metallization. The time-to-failure of interconnect lines depends on the void nucleation time and the void growth time. The current understanding of the void growth stage is minimal, and characterization of the void growth stage is essential to further explain EM performance of IC metal interconnections. This work used high-resolution electron-beam lithography to define small dimension edge-voids into gold lines at various separation distances from each other, on the same side or opposite sides of the lines. The EM-induced interaction behavior of pre-defined voids was measured in a FESEM in-situ. Results showed that for small separation distances, void-void interaction enabled shape changes in the pre-patterned voids. For larger separation distance, void-void interactions could be characterized by secondary, induced void and hillock area measurements. As the separation distance increased, the void-void interaction diminished, and the voids acted independently of each other.
Experimental Measurements of Grain Boundary Rotation Toward Bamboo in Post-Pattern Annealing
Authors: Barr D. L. , Brown W. L. , Ohring M.
Published: April 2011

The microstructure of 0.8.µm, A1(0.5% Cu) lines has been measured both before and after post-pattern annealing in nitrogen at various times and temperatures. Grain boundary inclinations in single grain segments of lines were determined from Focused Ion Beam (FIB) images of two surfaces of the lines. The statistical distributions of inclination angles before and after annealing reveal the tendency for boundaries to rotate to reduce their area. In these experiments the rotation stagnates with the normals to the grain boundaries having a distribution of inclinations with a FWHM of about 33 degrees around the line direction.
Direct Correlation Between Grain Configuration and Electromigration Damage Development
Authors: Shih W. C. , Ghiti A. , Low K. S. , Greer A. L. , O'Neill A. G. , Walker J. F.
Published: April 2011

The development of electromigration-induced voids and hillocks in Al - 4 wt. % Cu interconnects is monitored by scanning electron microscopy during interrupted testing and is correlated directly with the actual grain configuration including precipitates. The short segments under study and their grain structures are defined and observed using focused ion beam microscopy. The Cu content in precipitate grains is swept away before electromigration damage, and at most such grains there is subsequent grain thinning. The observations are compared with the results from a computer simulation based on a finite-element calculation of self-consistent current density and temperature distributions. For the first time the simulation uses the actual grain configuration and incorporates Cu atom migration, and back-fluxes driven by stress and concentration gradients. In the simulation the grain-boundary diffusivity is taken to be independent of boundary misorientation or is varied according to randomly assigned orientations. The comparison of the voiding in these two simulated cases and the observations shows that some grain configurations are very susceptible to electromigration damage whatever the diffusivities. For most configurations, however, the misorientation dependence of grainboundary diffusivity is significant and must be included if simulations are to be realistic.
Application of Electron Spin Resonance as a Tool for Building In Reliability (BIR)
Authors: Conley John F.
Published: April 2011

Electron spin resonance and its use as a tool for building reliability into MOS oxides is reviewed.
Effect of Growth Conditions on the Reliability of Ultrathin MOS Gate Oxides
Authors: Yang Tien-Chun , Saraswat Krishna C.
Published: April 2011

In this work we demonstrate that in MOS devices the reliability of ultrathin (< 100Å) gate oxide is a strong function of growth conditions, such as, temperature and the growth rate. In addition, for constant current gate injection the degradation of SiO2 is enhanced as the thickness is reduced. We attribute this to physical stress in SiO2 resulting from the growth process. The degradation is always more for those growth conditions which result in higher physical stress in SiO2. Higher temperatures and slower oxidation rates allow stress relaxation through viscous flow and hence result in SiO2 of better reliability. We also found that for constant current stressing, the interface damage is more at the collecting electrode than at the injecting electrode. ΔDit (stress induced interface state generation) can be reduced after a high temperature Ar post anneal after the gate oxide growth.
The Effect of the Passivation Material on the Stress and Stress Relaxation Behavior of Narrow Al-Si-Cu Lines
Authors: Witvrouw A. , Flinn P. , Maex K.
Published: April 2011

800 nm thick and 1 jim wide Al-lwt.%Si-0.5wt.% Cu parallel lines with I μm spacing were passivated with PECVD oxide, oxynitride or nitride. Substrate curvature measurements as a function of temperature and XRD-measurements at room temperature were used to characterize macroscopic samples of these parallel Al-Si-Cu-lines. By using both techniques the average inplane stresses for the Al-Si-Cu lines as well as for the covering passivation material can be determined as a function of temperature. The highest and lowest stresses in the Al-Si-Cu are observed for lines with nitride and oxide passivations, respectively. Also the number of voids in the lines after a storage test at 250 °C is clearly highest for a nitride passivation and lowest for an oxide passivation.

The stress in the passivation itself and its temperature dependence is found to be very different from the stress in a blanket passivation film.
Analysis Of Stresses And Strains In Passivated Metal Lines
Authors: Eppler I. , Schroeder H. , Burges U. , Schilling W.
Published: April 2011

Passivated metal lines, commonly used in integrated circuits, show thermally induced stresses due to the difference of the thermal expansion coefficients of the lines and their surroundings. These stresses cause voidage and plastic flow of the lines. Aim of the analysis was to derive equations connecting experimentally measured strains or stresses by the X-ray diffraction and wafer curvature techniques with the magnitude of voidage and plastic shear deformation of the lines.

Using the concepts of linear elasticity the volume averaged stresses of an array of parallel interconnects embedded in a passivation layer on a flat substrate are analysed. Equations are derived connecting the volume averaged stresses in the metal and in the passivation with the “eigen-strains” of the metal which characterize the true (stress free) thermal strains and plastic deformation strains of the metal. The coefficients entering these equations are determined from (elastic) finite element method (FEM) calculations performed for various geometries and aspect ratios of the metal lines. Choosing the proper values of the coefficients allows the eigen- strains to be determined from the experimental data.

By comparison of the evaluated eigen-strains with the purely elastic eigen-strains ΔaΔT the extent of voidage and/or plastic shear deformation of passivated metal lines caused by thermally induced stresses can be determined model independently.
Local and Global Stress Distributions in BEOL Metallization
Authors: Noyan I. C. , Liniger E. G. , Hu C-K. , Wang P-C. , Cargill G. S.
Published: April 2011

Design of reliable thin film metallization is a complex problem that requires information about local parameters such as composition, microstructure, residual and loading stresses, etc. On the other hand, such information has been traditionally obtained using techniques that have sampling volumes that are appreciably larger than the BEOL dimensions currently in use. In this article, the x-ray residual stress analysis technique and its extensions to micro-domain measurements are reviewed. These concepts are then applied to strain data from in-situ x-ray measurements, obtained in real-time from Al metallization lines subjected to thermal stressing and electromigration.
Self-Interstitial Supersaturation During Ostwald Ripening of End-of-Range Defects in Ion-Implanted Silicon
Authors: Seibt M.
Published: April 2011

Modified Ostwald ripening theory is used to calculate the time evolution of the size distribution function of extended end-of-range defects in ion implanted silicon. This allows to compare the time dependent self-interstitial supersaturation during postimplantation annealing in the presence of Frank-type stacking faults with that in the presence of {311} - defects. It is shown that the latter affect self-interstitial concentrations up to the point where they dissolve whereas the former are irrelevant from the point of view of transient enhanced diffusion.
Measurement of Lateral Dopant Diffusion in Rapid Thermal Annealed W-Polycide Gate Structures
Authors: Schiml T. , Bevk J. , Furtsch M. , Georgiou G. E. , Cirelli R. , Mansfield W. M. , Silverman P. J. , Lufrman H. S.
Published: April 2011

Lateral dopant diffusion is a well known problem in dual-gate W-polycide CMOS devices. We have recently demonstrated that RTA processing helps to alleviate this problem and at the same time ensures sufficient dopant activation. However, due to the complex micro-structural changes in both poly-Si and WSix (x˜2.5) layers during the RTA process, the time dependence of the diffusion processes and dopant distribution are difficult to predict. Consequently, the process optimization and device simulations are rather unreliable. We describe a new experimental technique to measure lateral dopant diffusion and 2-dimensional dopant distribution in RTA processed W-polycide structures using conventional SIMS analysis of lithographically defined test structures. Our experiments show that the technique is capable of measuring lateral dopant diffusion over distances between one and tens of microns without losing the vertical resolution of conventional SIMS profiling. The technique can be used to study diffusion processes in a variety of materials and multi-layer structures.
Rapid Thermal Dopants Diffusion and Surface Passivation for Silicon Solar Cells Applications
Authors: Slaoui Abdelilah , Lachiq Aziz , Ventura Laurent , Muller Jean Claude
Published: April 2011

Limiting thermal exposure time using Rapid Thermal Processing (RTP) is now emerging as a promising simplified process for manufacturing of terrestrial solar cells in a continuous way. In this work, we present results on simultaneous formation of emitter, back-surface field and surface passivation in a single rapid thermal cycle. Spin-on dopants (SOD) solutions are used as dopant sources. Optimal emitter profiles, low sheet resistances and high gettering effect are reached. The residual SOD film is used as a surface passivation layer. Solar cells with efficiencies in the range 10 – 14 % are obtained depending on temperature and time processing.
Bonded-H in Gate Dielectrics Deposited by Plasma Assisted Chemical Vapor Deposition and Subjected to Rapid Thermal Annealing
Authors: Lucovsky G. , Niimi H. , Koh K.
Published: April 2011

The incorporation of bonded nitrogen into ultra thin SiO2 gate dielectrics has become an important technology issue. Nitrogen atoms bonded in the immediate vicinity of the Si-SiO2 interface improve device reliability in n-channel field effect transistors. N- atom incorporation at the monolayer concentration range has been achieved by remote plasma assisted oxidation in N2O at 300°C. The incorporation mechanism and the stability of bonded-N are discussed.
Temperature Measurement at RTP Facilities-An Overview
Authors: Wagner J. , Boebel F. G.
Published: April 2011

Temperature is one of the most important quantities in semiconductor manufacturing. It plays a fundamental role in many standard production techniques and especially at RTP facilities. We will give an overview on standard temperature measurement techniques associated with RTP. Their basic principles, advantages and disadvantages will be discussed with respect to explicit applications.The potential physical and technical possibilities of optical temperature measurement are outlined as well as the problems like scattering, emissivity change and irradiation by halogen lamps. An overview on practical solutions of these problems is given together with explicit examples for applications including costs and benefits of their application.
Pattern Related Non-Uniformities During Rapid Thermal Processing
Authors: Bremensdorfer R. , Marcus S. , Nenyei Z.
Published: April 2011

State of the art rapid thermal processing is able to produce a lateral thermal homogeneity which is within the inherent resolution limits of current meterology. For the most commonly used direct or indirect control methods such as multiple thermocouple measurements, rapid thermal oxidation (RTO), or rapid thermal annealing (RTA) of plain semiconductor wafers this limit is ± 2°C. As homogeneity requirements approach those limits, pattern induced non-uniformities are getting more important.

In order to achieve rapid heating and high substrate temperatures in RTP, heater and substrate are not in equilibrium and their emission spectra differ considerably. Under such circumstances laterally varying optical characteristics on the substrate itself imply thermal non-uniformities. The influence of patterns on a silicon wafer surface on the temperature uniformity is studied. Passive patterns showing interference effects were formed out of thermal oxide and Si3N4. RTO and RTA, as well as embedded thermocouples were used for temperature measurement. The data presented show that major non-uniformities due to interference effects can be reduced by restricting the energy transfer through the patterned side of the wafer. It is shown that independent top and bottom heater bank control and controlled thermal kinetics are suitable methods to reduce the pattern related process non-uniformities.
Low Temperature Selective Si Epitaxy Using Si2H6 and Cl2: Investigations into Selectivity Robustness and Epitaxial Film Quality
Authors: O'Neil Patricia A. , Violette Katherine E. , Öztürk Mehmet C. , Batchelor Dale , Maher Dennis M.
Published: April 2011

In this paper, we explore selective Si epitaxy by UltraHigh Vacuum Rapid Thermal Chemical Vapor Deposition (UHV-RTCVD) using Si2H6, H2, and C12 with particular emphasis on selectivity robustness. Two key parameters considered in this study were partial pressures of Si2H6 and H2. It was found that excessive increases in either partial pressure could lead to selectivity degradation. The two mechanisms by which the observed selectivity degradation can be explained are as follows: A higher Si2H6 partial pressure provides a larger flux of Si atoms which directly influences the probability of reaching the critical nuclei size for stable nuclei formation while an increase in H2 partial pressure reduces the desorption rate of Si adatoms from the insulator surface by reducing the available Cl in the gas phase for SiC12 formation. The impact of process parameters on epitaxial defect density was also evaluated using darkfield imaging. The results clearly indicate increasing defect density upon increases in both the chlorine flow rate and the level of contamination introduced through the silicon source gas.
Strategies for the Reduction of Pattern Effects
Authors: Kerscih A. , Schafbauer T. , Deutschmann L.
Published: April 2011

The pattern effects in hot processes arise from a spatial variation of the radiative heat flux imbalance between emission and absorption. There are two scenarios to reduce the pattern effect: a very reflective chamber facing the patterned side with an illumination from the backside or a controlled double sided illumination on the other hand. The paper demonstrates the mechanism of both scenarios with a simple mathematical model and discusses the limitations of the approaches. The results will be exemplified with the help of reactor scale simulations involving a detailed Monte Carlo radiation model featuring continuous spectral dependence.
How Rapid Isothermal Processing Can be a Dominant Semiconductor Processing Technology in the 21st Century
Authors: Singh R. , Sharangpani R. , Cherukuri K. C. , Chen Y. , Dawson D. M. , Poole K. F. , Rohatgi A. , Narayanan S. , Thakur R. P. S.
Published: April 2011

The growth and advancement of the electronic and photonic industry in the 21 st century hinges on revolutionary new processing techniques that will overcome some of the most fundamental limitations of conventional methods. Rapid isothermal processing (RIP) based on incoherent radiation as the source of optical and thermal energy can play a major role in designing processing systems that offer the tight process control, low thermal budgets, low microscopic defects, high throughput and high yields required for almost every semiconductor device. Conventional RIP can be further optimized by fully exploiting the contribution of quantum photoeffects. The improved performance and reliability offered by RIP will make it the mainstream technology for the green manufacture of microelectronics, optoelectronics, solar cells, flat panel displays and microelectromechanical systems. Key issues related to the cost of ownership, design of RIP system based on the full utilization of photo–thermal effects and model based control systems are described. New experimental results for a number of processing steps are provided. These results demonstrate the importance of advanced RIP systems in providing better performance and lower defects for future devices.
Microwave processing CaO-Al203-SiO2 Glass Using Sol-Gel Technique
Authors: Zhou Y. , Biest O. Van der , Groffils C. , Luypaert P. J.
Published: April 2011

Gels in the CaO-A12O3-SiO2 (CAS) system were successfully converted into glass in a single mode, tuneable, cylindrical microwave applicator, operating at 2.45 GHz in the TM012 mode. Transparent glasses were formed as a result of the direct microwave heating of homogeneous CAS gels to well above their melting temperature (1170°C). The effect of processing parameters, such as incident power level, sample mass and location, and thermal insulation has been investigated. The excellent coupling of the CAS gel with microwave can be understood from the structural evolution during sol-gel processing.
Microwave Sintering of Pure and Doped Nanocrystalline Alumina Compacts
Authors: Bruce R. W. , Fliflet A. W. , Kurihara L. K. , Chow G.-M. , Schoen P. E.
Published: April 2011

A single-mode cavity microwave furnace, operating in the TE103 mode at 2.45 GHz is being used to investigate sintering of pure and doped nanocrystalline alumina. The purpose of these experiments is to determine the effect of additives on the sintering process in the nanocrystalline regime. Using the sol-gel method, high purity Al2O3 nanocrystalline powders were synthesized. These powders were calcined at 700°C and then CIP'ed to 414 MPa, producing 0.4 in. diameter, 0.25 in. high cylindrical compacts. The compacts were heated in the microwave furnace to temperatures between 1100°C to approximately 1800°C and were then brought back to room temperature using a triangular heating profile of about 30 minutes duration. A two-color IR pyrometer was used to monitor the surface temperature of the workpiece. The additives tested in this work lowered the temperature needed for densification but this effect was offset by increased grain growth. Initial grain growth from < 5 nm to ∼ 50 nm was closely correlated with the γ to α-alumina phase transition.
The use of Microwave-Assisted Processing for the Production of High Tc Superconductors
Authors: Rowley A. T. , Wroe F. C. R.
Published: April 2011

High critical temperature superconducting (HTcS) bulk ceramics with the high values of critical current densities (Jc) necessary for practical applications, are only achieved through careful control of the material microstructure. Consequently, many stages in the production of HTcSs are extremely time consuming; often taking a number of days to proceed to completion, and usually requiring precise control of sample temperature.

The volumetric nature of microwave heating will clearly have an impact on the processing of large quantities of these materials, particularly when it is balanced with the simultaneous application of radiant heating. In this way, the production of thermal gradients can be avoided, even when relatively fast heating rates (for these materials) are used.

Perhaps more interesting, is the possibility of non-thermal microwave effects (due to the presence of an electric field) enhancing the processing times and even the material properties of HTcSs.

This work assesses the impact of microwave-assisted processing on a number of stages involved in the production of bulk pieces of Bi-2212 and Y-123 based superconductors, and demonstrates quite clearly that non-thermal as well as thermal microwave effects are relevant to these materials.
In—Line Measurement Of High Temperature Dielectric Constant In The Process Of Sintering
Authors: Jian Zhou , Jiping Cheng , Yuling Tang , Jinyu Qiu
Published: April 2011

In this paper, a resonant cavity method is developed and some experimental results for measuring dielectric constants of ceramic samples (e. g. Al2O3) under different sintering temperatures are reported. The experiments show that this method has higher precision and good prospects of in—line monitoring the high temperature dielectric constant in the process of raising the temperature of the samples. These results provide some scientific experimental basis for physical research of ceramic materials.
The Dielectric Properties Of Porous Zinc Oxide Ceramics
Authors: Calame J. P. , Carmel Y. , Gershon D. , Birman A. , Martin L. P. , Dadon D. , Rosen M.
Published: April 2011

Measurements of the complex dielectric constant of microwave sintered, porous ZnO at 2.45 GHz are presented. The dielectric properties as a function of porosity do not obey the standard Maxwell-Garnet dielectric mixing law with the ceramic material as the major phase, but instead behave as if the ceramic grains always remain in relatively poor electrical contact even at very high densities. Electromagnetic simulations, carried out for a variety of microstructure geometries, are performed to explore this observation. A model which treats the ceramic as an array of grains and pores, with the grains separated from each other by nonor slightly-percolating, fractal-geometry surfaces, provides a good description of the experimental results.
FDTD Simulation of Microwave Sintering in Large (500/4000 Liter) Multimode Cavities
Authors: Subirats Marta , Iskander Magdy F. , White Mikel J , Kiggans Jim
Published: April 2011

To help develop large-scale microwave-sintering processes and to explore the feasibility of the commercial utilization of this technology, we used the recently developed multi-grid 3D Finite-Difference Time-Domain (FDTD) code and the 3D Finite-Difference Heat-Transfer (FDHT) code to determine the electromagnetic (EM) fields, the microwave power deposition, and temperature-distribution patterns in layers of samples processed in large-scale multimode microwave cavities.

This paper presents results obtained from the simulation of realistic sintering experiments carried out in both 500 and 4000 liter furnaces operating at 2.45 GHz. The ceramic ware being sintered is placed inside a cubical crucible box made of rectangular plates of various ceramic materials with various electrical and thermal properties. The crucible box can accommodate up to 5 layers of ceramic samples with 16 to 20 cup-like samples per layer. Simulation results provided guidelines regarding selection of crucible-box materials, cruciblebox geometry, number of layers, shelf material between layers, and the fraction volume of the load vs. that of the furnace.

Results from the FDTD and FDHT simulations will be presented and various tradeoffs involved in designing an effective microwave-processing system will be compared graphically.