bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Electrical Properties of Microcrystalline Silicon Films Using AC Measurements
Authors: Dirani Ely A. T. , Nardes Alexandre M. , Andrade Adnei M. , Fonseca Fernando J. , Muccillo Reginaldo
Published: April 2011

Hydrogenated amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon films are indispensable materials for large area electronic devices like solar cells, image sensors and thin film transistors (TFTs). The interest of the µc-Si:H films arise from the fact that they combine the high optical absorption of a-Si:H and the electrical transport properties close to those of crystalline silicon. In this work we show the correlation between substrate deposition temperature, crystallinity and electrical properties of a-Si:H and µc-Si:H films. The films were prepared by a conventional PECVD (13.56 MHz) RF system from PH3/SiH4/H2 gas mixtures in the temperature range of 100 to 250°C. While phosphorus doped (n) a-Si:H are deposited yielding conductivity values no better than 10−2 S/cm, (n) µc-Si:H layers deposited at substrate temperature of 250°C show conductivity values higher than 101 S/cm, crystalline fraction up to 80% and Hall mobility of about 0.9 cm2. V−1.s−1. It was observed that a change in the dark conductivity behavior occurs around 140°C, with a large increase in the conductivity values. A corresponding increase is not seen in the average grain size and in the crystalline volume fraction, which shows an almost linear increase with the deposition temperature. This stronger influence of the temperature in the electrical characteristics of the µc-Si:H films may be related to the phosphorus activation, which occurs in higher degree at higher deposition temperatures. The correlation among Raman spectroscopy, Hall effect and AC conductivity measurements (frequency range 6 Hz to 13 MHz) shows that the crystalline phase dominates the electrical transport mechanism in µc-Si:H films. Preliminary results of AC measurements indicate that the electrical resistivity of each phase of this material can be determined.
Effects of low-temperature annealing on the initial and stabilized performance of amorphous silicon solar cells
Authors: Carlson D. , Ganguly G. , Lin G.
Published: April 2011

We have recently observed that the initial performance of amorphous silicon (a-Si) solar cells can be improved by up to several % by annealing the cells at successively lower temperatures for successively longer times. For some devices, we also observed an improvement in performance after light soaking that was statistically significant. We have also observed an improvement in the stabilized performance of cells that were subjected to reverse bias annealing after light soaking. This effect was clearly evident in single-junction p-i-n cells with amorphous silicon-carbon (a-SiC) i-layers where the density of metastable centers is very high (> 1018cm-3). When we light-soaked a-SiC cells and then subjected them to low-temperature reverse bias annealing, they exhibited clear evidence of improved short-wavelength response after a second light soaking. These annealing effects are explained in terms of hydrogen motion within the a-Si network and within microvoids.
A Novel Poly-Si Solar Cell using Grain Boundary Etching Treatment and Transparent Conducting Oxide
Authors: Lim Dong Gun , Lee Wook Jae , Yi Junsin
Published: April 2011

This paper deals with a novel structure of polycrystalline silicon (poly-Si) solar cell for terrestrial applications. Grain boundary (GB) in poly-Si degrades a conversion efficiency of poly-Si solar cell. To reduce the GB side-effect, we investigated various parameters such as the preferential GB etch, etchtime, ITO electrode, heat treatment, and emitter layer effect. Among various preferential etchants such as Sirtl, Yang, Secco, and Schimmel, a Schimmel etchant illustrated an excellent preferential etching property. We observed a 10μm deep trench along grain boundaries and randomly textured grain surface with pyramid structure. We used rf magnetron sputter grown tin doped indium oxide (ITO) film as a top contact metal. ITO films showed a resistivity of 1.14 ×10-4 Ω-cm and transmittance of 90.5% for the wavelength of 594 nm. ITO films served as a top electrode as well as an effective AR coating layer. ITO film properties were strongly influenced by the preparation temperatures. Substrate temperature of 400oC gave the highest conversion efficiency of poly-Si solar cell. With well-fabricated poly-Si solar cells, we were able to achieve conversion efficiency as high as 16% at the input power of 20 mW/cm2.
Density of States in a-Si:H from SCLC and Its Application in Modeling a Vertical TFT
Authors: Sedghi Naser , Eccleston Bill
Published: April 2011

Steady-state space-charge limited current (SCLC) measurements are used to investigate the density of states (DOS) in the mobility gap of hydrogenated amorphous silicon (a-Si:H). The density of states is calculated by different methods based on both continuous DOS and discrete traps assumptions. The density of states found by the SCLC measurements is used to set the trap densities and trap energy levels to model a vertical a-Si:H thin-film transistor (TFT) using the Medici device simulation package. The effect of different sets of traps in the bulk of a-Si:H and variation of the physical dimensions of the device on the characteristics of the vertical TFT is studied. The simulation on the space-charge limited current is performed to verify the validity and accuracy of the SCLC method.
Metastable changes of the electrical conductivity in microcrystalline silicon
Authors: Nickel N. H. , Rakel M.
Published: April 2011

The temperature dependence of the dark conductivity, σD, of as-grown and H depleted µproportional σc-Si was measured. While σD of the H depleted samples did not exhibit any influence of thermal treatment prior to the measurements, in as-grown σproportional µc-Si the dark conductivity increased by 2 orders of magnitude below 300 K upon rapid thermal quenching. The frozen-in state is reversible and an anneal at 440 K followed by a slow cool completely restores the initial state. The time and temperature dependence of the relaxation of the quenched-in state reveals two competing processes. At short times σD increases due to the activation of a donor complex and at long times σD decreases due to the dissociation of bond-center H complexes.
Radical Species Distributions in Hot-Wire Chemical Vapor Deposition Probed Via Threshold Ionization Mass Spectrometry and Direct Simulation Monte Carlo Techniques
Authors: Holt Jason K. , Swiatek Maribeth , Goodwin David G. , Atwater Harry A. , Muller R.P. , Goddard W.A.
Published: April 2011

Monte Carlo simulations of hot-wire chemical vapor deposition (HWCVD) gas ambients indicate different flux ratios (SiH3/Si and H/SiHx) under conditions for amorphous or polycrystalline silicon growth. Gas-phase reactions of Si with ambient SiH4studied usingabinitiomethods reveals that collisional stabilization of the adduct (H3SiSiH) is unlikely under typical HWCVD growth pressures, but an energetically favorable, low-pressure pathway has been identified that leads to the formation of Si2H2and H2. Threshold ionization mass spectrometry has revealed significant quantities of the radical SiH2at HWCVD growth pressures, indicative of heterogeneous pyrolysis. Mass spectrometry at low pressures suggests that incident silane dissociatively adsorbs at the wire and undergoes sequential H elimination to produce subhydrides. Disilicon species were not detected in significant quantities at HWCVD growth pressures. Finally, hot wire operation in a pure H2ambient yields SiH4as the dominant etching product from the silicon-coated walls of the growth chamber.
Material properties and growth process of microcrystalline silicon with growth rates in excess of 1 nm/s
Authors: Hamers E.A.G. , Smets A.H.M. , Smit C. , Hoefnagels J.P.M. , Kessels W.M.M. , Sanden M.C.M. van de
Published: April 2011

The expanding thermal plasma (ETP) has been used to deposit microcrystalline silicon (µc-Si:H) with rates up to 2.7 nm/s. Typical material properties of well crystallised material are crystallite sizes of 20 nm, photo- and dark conductivity of 2×10−5 and 2x10−7 S/cm respectively, and an activation energy of 600 meV. The radical densities of SiH3, SiH, and Si present in the gas phase have been quantified. In conditions where [.proportional µc-Si:H is deposited the atomic hydrogen flux towards the surface is of the same magnitude or higher as the flux of deposited radicals. Furthermore, the abundance of radicals such as SiH and Si is large and may contribute several tens of percent to the deposition rate.
A New Field-Aided Germanium-Induced Lateral Crystallization of Silicon
Authors: Naeli Kianoush , Mohajerzadeh Shamsoddin , Khakifirooz Ali , Haji Saber , Soleimani Ebrahim A.
Published: April 2011

The effect of an electric field on germanium-seeded lateral crystallization of a-Si is studied for the first time and compared to this effect in Ni-induced lateral growth. While the crystallization rate is lower when Ge is used as the nucleation seed and annealing should be done at higher temperatures, filed-aided crystallization shows a similar behavior to that observed for Ni-induced crystallization. Optical microscopy results indicate that grain growth starting from the negative electrode occurs in Si films at annealing temperatures higher than 480°C, while the applied electric field ranges form 200 to 1400V/cm. SEM was also used to confirm the crystallinity of the films.
The Effect of H2 Dilution On Thin Film SiN Deposited by Hot Wire Cvd Using SiH4 and NH3 Gas Mixtures
Authors: Dillon A. C. , Gedvillas L. , Williamson D. L. , Thiesen J. , Perkins J. D. , Mahan A. H.
Published: April 2011

The structure of thin film SiN, deposited by the hot wire chemical vapor deposition (HWCVD) technique using SiH4 and NH3 gas mixtures, has been examined as a function of the amount of H2 dilution of the gas mixture. For NH3/SiH4 gas ratios > 0.5/1, all films are a-SiN:H. While H2 dilution does not change the basic film structure, in that the films are amorphous with all dilutions, H2 dilution does increase the efficiency of NH3 dissociation in the gas phase, and causes a further reduction in the already small amount of N-H bonding in a-SiN:H films deposited by HWCVD. For NH3/SiH4 gas ratios typically <0.5/1 and with high H2 dilution, the first deposition of µc-SiN is demonstrated. X-ray diffraction (XRD) measurements demonstrate that the structure of these films consists of silicon crystallites embedded in an a-SiN:H matrix. An upper limit for N incorporation with the preservation of microcrystallinity was found, beyond which the films again became amorphous. The existence of this limit is explained in terms of structural disorder in the a-SiN:H tissue brought about by N incorporation.
The Effect of Moderate Hydrogen Dilution on Stability and Structure of Amorphous Silicon Deposited by Hot-Wire CVD
Authors: Weber Urban , Schroeder Bernd
Published: April 2011

The effect of moderate hydrogen dilution of the process gas, F(H2)/F(SiH4) = 0 to 3, on the properties of amorphous silicon is discussed for material and solar cells deposited by Hot-Wire CVD. Dielectric properties were obtained from spectroscopic ellipsometry and are related to stability and hydrogen bonding configuration of films deposited with varying hydrogen dilution at different substrate temperatures. The stability was determined by comparing defect densities obtained from photoconductivity spectroscopy in the constant photocurrent mode (CPM) before and after pulsed-light soaking. At low substrate temperatures, which are relevant for the prepara- tion of pin-type solar cells (160-200°C), moderate hydrogen dilution (∼0.3) improves material quality regarding density and network disorder (oscillator bandwidth) as obtained from spectro-scopic ellipsometry, resulting in a higher stability. At higher substrate temperatures (300°C), stability and hydrogen bonding configurations are generally better, but moderate hydrogen dilu-tion already deteriorates these properties compared to material prepared without dilution. The incorporation of Hot-Wire-a-Si:H into pin-type solar cells is also discussed and a good correlation of ellipsometric results with bulk-related properties of solar cell performance is observed. The optimum hydrogen dilution is found to be 0 to 0.3 for i-layer deposition yielding initial efficiencies of up to 8.9% for solar cells entirely fabricated by Hot-Wire CVD.
Effect of CdCl2 Treatment on the Interior of CdTe Crystals
Authors: Price Kent J.
Published: April 2011

An essential processing step in CdTe/CdS polycrystalline solar cells is heat treatment in CdCl2. We present photoluminescence results from single crystals of CdTe that have been exposed to CdCl2 treatments at 387 C similar to those used in actual cell fabrication. Using sub band gap excitation from a tunable diode laser, we probe states in the interior of the crystal. We show that high-purity (99.998 percent) CdCl2 treatment results in the appearance of a 1.45 eV donor-acceptor transition that is likely due to a Cl-Cu center. Low purity (99.7 percent) CdCl2treatment results in the appearance of the 1.45 eV line and a 1.555 eV Cu-related emission. These results indicate that the CdCl2 treatment has an effect on the interior of CdTe grains, in addition to its already well established effect on grain boundaries in polycrystalline CdS/CdTe devices. They also imply that CdCl2 treatment may result in the incorporation of Cu into the CdTe grains. The results will be related to the effects of CdCl2 on polycrystalline CdS/CdTe devices that have been observed by other groups.

This work is supported by NREL
Influence of proton irradiation and development of flexible CdTe solar cells on polyimide
Authors: Romeo A. , Bätzner D.L. , Zogg H. , Tiwari A.N.
Published: April 2011

CdTe/CdS solar cells of ∼10% efficiency, developed with a vacuum deposition method were irradiated with high-energy protons of different fluences. The Voc and f.f. of irradiated cells increase or decrease depending on the fluence. The normal soda lime glass substrate darkens under the irradiation; therefore low Isc is measured. Measurements suggest that CdTe solar cells are highly stable under proton flux. Flexible and lightweight solar cells were developed in a superstrate configuration on polymer substrates. 8.6 % efficiency cells with Voc∼770 mV and Isc of 20.3 mA/cm2 were achieved.
CdTe Thin Film Solar Cells: The CdS/SnO2 Front Contact
Authors: Fritsche J. , Gunst S. , Thiβen A. , Gegenwart R. , Klein A. , Jaegermann W.
Published: April 2011

Tin dioxide (SnO2) coated glass is the commonly used substrate for thin film solar cells based on CdTe absorbers. We have investigated the properties of the CdS/SnO2 interface by X-ray and ultraviolet photoelectron spectroscopy. SnO2 coated glass substrates as used for solar cell preparation were cleaned by different procedures such as derinsing, sputtering, heating and annealing in oxygen atmosphere. Different surface properties with a strongly dependent number of defects in the SnO2 band gap are identified. CdS films were deposited stepwise by thermal evaporation to determine the electronic interface properties for different surface preparation conditions. Comparative barrier heights at the CdSSnO2 contact are found for most surface pretreatments. The Fermi level position in these cases is situated in the SnO2 band gap. A different interface behaviour is determined for sputter cleaned SnO2 surfaces, which is attributed to the formation of oxygen vacancies during sputtering and subsequent formation of an interfacial SnOxSy compound.
How do Buffer Layers Affect Solar Cell Performance and Solar Cell Stability?
Authors: von Roedern Bolko
Published: April 2011

Buffer layers are commonly used in the optimization of thin-film solar cells. For CuInSe2-and CdTe-based solar cells, multilayer transparent conductors (TCOs, e.g., ZnO or SnO2) are generally used in conjunction with a CdS heterojunction layer. Optimum cell performance is usually found when the TCO layer in contact with the CdS is very resistive or almost insulating. In addition to affecting the open-circuit voltage of a cell, it is commonly reported that buffer layers affect stress-induced degradation and transient phenomena in CdTe- and CuInSe2-based solar cells. In amorphous silicon solar cells, light-induced degradation has a recoverable and a nonrecoverable component too, and the details of the mechanism may depend on the p-type contact layer. Because of the similarity of transients and degradation in dissimilar material systems, it is suggested that degradation and recovery are driven by carriers rather than by diffusing atomic species. The question that must be addressed is why, not how, species diffuse and atomic configurations relax differently in the presence of excess carriers. In this paper, I suggest that the operating conditions of a cell can change the carrier transport properties. Often, excess carriers may enhance the conductance in localized regions (“filaments”) and buffer layers; limiting current flow into such filaments may therefore control the rate and amount of degradation (or recovery).
Laser Light Scattering in-situ Studies on the Growth of Chalcopyrite Thin Films
Authors: Scheer R. , Pietzker Ch. , Bräunig D.
Published: April 2011

The method of diffuse laser light scattering (LLS) has been tested for process monitoring of simultaneous and sequential chalcopyrite film formation. Characteristic LLS features are observed which can be assigned to morphological and optoelectronic film modifications. The surface roughness development as a function of time of CuInS2 and CuInSe2 epilayers grown on Si(111) substrates is monitored. It is found that the critical thickness of a smooth surface without islands depends on the film composition (Cu/(Cu+In) ratio). LLS transients for sequential film formation depict a series of characteristic features which are connected with, e.g., precursor transformation, surfacial sulfurization, and secondary phase transformation.
A Comparative Study of CdS Thin Films Grown by Chemical-Bath Deposition and Close-Spaced Sublimation
Authors: Moutinho H.R. , Albin D. , Yan Y. , Dhere R.G. , Perkins C. , Li X. , Al-Jassim M.M.
Published: April 2011

In this work we study the properties of cadmium sulfide thin films grown by chemicalbath deposition and close-spaced sublimation, on SnO2/borosilicate glass and SnO2/silicon substrates, before and after treatment in vapor CdCl2 at 400°C for 5 minutes. The as-deposited CBD CdS films had cubic structure, poor crystallinity, and high density of planar defects. After the CdCl2 treatment, these films recrystallized to the hexagonal structure, with improved crystallinity and a decrease in the density of planar defects. The as-deposited CSS films had hexagonal structure, better crystallinity, and lower density of planar defects. The main effect of the CdCl2 treatment was a decrease in the intragrain strain in the films. The CBD films had smaller grains and provided a good conformal coverage over the SnO2 films. In contrast to these films, CSS CdS did not have any oxygen or chlorine in its bulk.
Improved Routes to Nanocrystalline Metal Oxide Films for Dye-Sensitised Solar Cells and Related Applications
Authors: O'Hare Iain P. , Govender Kuvasani , O'Brien Paul
Published: April 2011

Nanoporous metal oxide thin films are currently attracting interest for a wide range of electronic applications, including sensors and dye-sensitised photovoltaic cells. However, limited, and poorly controlled, film fabrication routes represent a key factor impeding the development of such devices. To date, device applications have largely been limited to sol-gelfabricated nanocrystalline films of titanium dioxide (TiO2). Such studies have recently been extended to the application of an alternative film fabrication technique, notably that of chemical bath deposition (CBD), for the growth of zinc oxide (ZnO). One interesting feature of CBDfabricated films of ZnO is that, under specific conditions of supersaturation, highly reticulated layers may be obtained, such an observation suggesting that control of morphology is possible. Thick nanoporous films of ZnO have been deposited, upon conducting glass substrates, under both acidic and alkaline conditions, from a solution containing the metal ion, added acid or base, and either a chelating agent, such as ethylenediamine or triethanolamine, or a buffer, hexamethylenetetraamine (HMT). The deposition rate is controlled by systematic adjustment of both temperature and pH, together with the nature, and relative concentration, of the reactants in the solution (chelating agent or metal ion). The material properties of the resulting films have been characterised through the use of a range of techniques, including Scanning Electron Microscopy (SEM), X-Ray Powder Diffraction (XRD) and Energy Dispersive Analysis by XRays (EDAX), and the results are discussed within the context of the suitability of the deposited films for incorporation within nanocrystalline devices.
Effects of Surface Termination on CuIn1−XGaXSe2 Prepared from Mixed Cu-In-Ga-Se Precursors
Authors: Beck Markus E. , Alleman Jeff , Swartzlander-Guest Amy , Matson Rick , Noufi Rommel
Published: April 2011

Thin film CuIn(Ga)Se2 samples were prepared by a two-stage method starting from amorphous or nano-crystalline precursor structures. Deposition of individual Cu+Se and In+Se layers as a function of substrate temperature revealed the onset of detectable crystal structures at Tsub = 100°C and Tsub. ≥200°C, respectively. For the quaternary system the formation of CuInSe2 was observed at 400°C and evidence was found for liquid CuxSe assisted growth.

Further focus was on surface termination schemes with the objective to enhance the opencircuit voltage. Ga+Se, In+Se, Ga+Se/In+Se, and In+Se/Ga+Se terminating layers with varying amounts of Ga and In are addressed. Schemes studied to date have resulted in an increase in Voc at the expense of short-circuit current. The use of Ga containing termination layers resulted in the formation of large voids in the CIGS which could be explained by the volume changes during formation of the quaternary material and a Cu2Se free surface in these instances.
Reduction of Whisker-Originated Short between W Polymetal and Contact Plug
Authors: Akasaka Yasushi , Suzuki Hiroshi , Yokoyama Yuji , Yasutake Nobuaki , Yasutake Hitomi , Yoshikawa Susumu , Kohyama Yusuke , Ozawa Yoshio , Hieda Katsuhiko , Suguro Kyoichi , Nakanishi Toshihiro
Published: April 2011

Whisker-originated short in the self-aligned contact (SAC) W polymetal gate was directly observed for the first time. Short points between gate electrodes and poly-Si plugs in the test structure were identified by emission microscope and cross-sectional TEM samples of those points were made by using focused ion beam (FIB).

Whiskers are formed during high-temperature processing such as LP-CVD SiN. We have proposed that NH3 de-oxidation step inserted in the SiN deposition sequence is effective for suppressing whisker growth. [1] In this study it was also confirmed that 600°C NH 3 pre-flow improved leakage current between gate electrode and contact plugs.
Constrained Diffusional Creep in Thin Copper Films
Authors: Weiss D. , Gao H. , Arzt E.
Published: April 2011

The mechanical properties of thin metal films have been investigated for many years. How- ever, the underlying mechanisms are still not fully understood. In this paper we give an overview of our work on thermomechanical properties and microstructure evolution in pure Cu and dilute Cu-Al alloy films. Very clean films were produced by sputtering and annealing under ultra-high vacuum (UHV) conditions. We described stress-temperature curves of pure Cu films with a constrained diffusional creep model from the literature. In Cu-1at.%Al alloy films, Al surface segregation and oxidation led to a “self-passivating” effect. These films showed an increased high- temperature strength because of the suppression of constrained diffusional creep; however, under certain annealing conditions, these films deteriorated due to void growth at grain boundaries.
Dislocation Dynamics Simulations of Dislocation Interactions in Thin Fcc Metal Films
Authors: Pant Prita , Schwarz K.W. , Baker S.P.
Published: April 2011

Mesoscopic simulations of dislocation interactions in thin, single crystal FCC metal films were carried out. Interactions between threading-misfit and threading-threading dislocation pairs were studied and the strength of the interactions determined. Threading-threading interactions were found to be significantly stronger than threading-misfit interactions. Dislocations with different possible combinations of Burgers vectors were studied under cyclic loading. Only annihilation of dislocations was seen to result in residual dislocation structure after complete unloading. No differences were observed in the nature of threading-misfit interactions in 111 and 001 oriented films.
Observations of Dislocation Motion and Stress Inhomogeneities in a Thin Copper Film
Authors: Balk T. John , Dehm Gerhard , Arzt Eduard
Published: April 2011

In situ transmission electron microscopy has been utilized to study dislocation plasticity in a 200 nm thick copper film. The behavior of dislocations in a [111]-oriented grain was recorded during a thermal cycle. During cooling, it was observed that dislocations were emitted from a grain boundary triple junction in regular intervals of 30°C to 40°C. Subsequent glide occurred on a (111) plane parallel to the film surface, despite the expectation of zero resolved shear stress on such planes. The initial emitted dislocations remained close to the triple junction, avoiding contact with another [111] grain rotated by 17°. Glide into the opposite end of the grain was initiated only after the injection of several additional dislocations, which induced strong curvature in all dislocations near the active triple junction. Post mortem examination of dislocation curvature revealed that an inhomogeneous stress state existed within the grain.
A Kinetic Model for the Strain Relaxation in Heteroepitaxial Thin Film Systems
Authors: Zhang Y.W. , Wang T.C. , Chua S.J.
Published: April 2011

A kinetic model is presented to simulate the strain relaxation in the GexSi1−x/Si(100) systems. In the model, the nucleation, propagation and annihilation of threading dislocations, the interaction between threading dislocations and misfit dislocations, and surface roughness are taken into account. The model reproduces a wide range of experimental results. The implications of its predictions on the threading dislocation reduction during the growth processes of the heteoepitaxial thin film systems are discussed.
Misfit Dislocations in Epitaxial Ni/Cu Bilayer and Cu/Ni/Cu Trilayer Thin Films
Authors: Yamamoto Tadashi , Misra Amit , Hoagland Richard G. , Nastasi Mike , Kung Harriet , Hirth John P.
Published: April 2011

Misfit dislocations at the interfaces of bilayer (Ni/Cu) and trilayer (Cu/Ni/Cu) thin films were examined by plan-view transmission electron microscopy (TEM). In the bilayers, the spacing of misfit dislocations was measured as a function of Ni layer thickness. The critical thickness, at which misfit dislocations start to appear with the loss of coherency, was found to be between 2 and 5 nm. The spacing of the misfit dislocations decreased with increasing Ni layer thickness and reached a plateau at the thickness of 30 nm. The minimum spacing is observed to be about 20 nm. A g·b analysis of the cross-grid of misfit dislocations revealed 90° Lomer dislocations of the <110>{001} type lying in the (001) interface plane at a relatively large thickness of the Ni layer, but 60° glide dislocations of the <110>{111} type at a relatively small thickness of the Ni layer. In the trilayers, misfit dislocations formed at both interfaces. The spacing of the misfit dislocation is in agreement with that of the bilayers with a similar Ni layer thickness. The misfit dislocation arrays at the two interfaces, having the same line directions, are 60° dislocations with edge components with opposite signs but are displaced with respect to each other in the two different interface planes. This suggests that interactions of the strain fields of the dislocations have a strong influence on their positions at the interface.
Local Microstructure and Stress in Al(Cu) Thin Film Structures Studied by X-Ray Microdiffraction
Authors: Valek B.C. , Tamura N. , Spolenak R. , MacDowell A.A. , Celestre R.S. , Padmore H.A. , Bravman J.C. , Brown W.L. , Batterman B. W. , Patel J. R.
Published: April 2011

The microstructure of materials (grain orientation, grain boundaries, grain size distribution, local strain/stress gradients, defects, …) is very important in defining the electromigration resistance of interconnect lines in modern integrated circuits. Recently, techniques have been developed for using submicrometer focused white and monochromatic x-ray beams at synchrotrons to obtain local orientation and strain information within individual grains of thin film materials. In this work, we use the x-ray microdiffraction beam line (7.3.3) at the Advanced Light Source to map the orientation and local stress variations in passivated Al(Cu) test structures (width: 0.7, 4.1 μm) as well as in Al(Cu) blanket films. The temperature effects on microstructure and stress were studied in those same structures by in-situ orientation and stress mapping during a temperature cycle between 25°C and 345°C. Results show large local variations in the different stress components which significantly depart from their average values obtained by more conventional techniques, yet the average stresses in both cases agree well. Possible reasons for these variations will be discussed.
Plasma Induced Chemical Changes at Silica Surfaces During Pre-Bonding Treatments
Authors: Hansen Darren M. , Albaugh C.E. , Moran Peter D. , Kuech T. F.
Published: April 2011

Plasma-treated and DI H2O rinsed oxide layers are commonly used in wafer bonding applications. Borosilicate glass (BSG) layers deposited by low-pressure chemical vapor deposition (LPCVD) treated with an O2 plasma in reactive ion etching (RIE) mode at 0.6 W/cm2 and rinsed with DI H2O readily bond to GaAs and Si. The chemical role of this pre-bonding treatment was investigated using attenuated total reflection Fourier transform infrared (ATR- FTIR) spectroscopy. The peak intensities for both the Si-O and B-O absorbance bands decreased in intensity as a result the plasma treatment consistent with the uniform sputter etching of BSG. The effect of changing the total plasma treatment time was investigated in terms of the total amount of material removed. Polarization-dependent ATR-FTIR revealed that the H2O/OH absorbance bands decreased in peak intensity with the OH groups preferentially oriented perpendicular to the sample surface after the plasma treatment. The subsequent DI H2O rinse restores the water to the surface while changing the surface BSG composition. ATR-FTIR studies suggest that for oxide compositions greater than 10 mole % B2O3, the top 4 nm of B2O3 was removed or leached from the oxide layer during the DI H2O rinse.
A Novel Method of Fabricating SiC-On-Insulator Substrates for Use in MEMS
Authors: Kuo Hung-I , Zorman Christian , Mehregany Mehran
Published: April 2011

This paper reports on a novel, bonding-free method to fabricate silicon carbide-on-insulator (SiCOI) substrates. The process bypasses wafer bonding by using a high deposition rate polysilicon process in conjunction with wet chemical etching to produce wafer-thick polysilicon layers that serve as substrates for the SiCOI structures. Because wafer bonding is not used, insulators of various material types and thickness can be used. Using this method, transfer percentages over 99% are readily achievable. Various applications could benefit from this technology, including high temperature SiC-based microelectromechanical systems (MEMS) and SiC electronic devices.
Packaging Of Ultrathin Semiconductor Devices Through The ELO Packaging Process
Authors: Sickmiller Mike
Published: April 2011

The trend in semiconductor packaging is moving toward thinner and thinner packages. Likewise, chip profile is moving toward thinner and thinner chips. Presented here is a technique used to obtain a semiconductor package containing chips as slim as one micron in thickness. The ELO Packaging Process yields ultrathin chips for applications such as advanced heat sinking, high-efficiency optoelectronics, multiple stacked chips in a single package, and thin mechanically flexible semiconductor circuits. This technology is being developed around both the fab and packaging house so as not to interfere with the conventional semiconductor fabrication process flow.

Through a combination of back-grinding and chemical etch techniques, chips have been thinned to as little as 1 µm and bonded to a variety of new host substrates[1]. Several bonding methods have been utilized – including thin solder or epoxy layers – to bond these functional chips to a variety of new substrates. Ultrathin microwave power amplifiers have been bonded to heat sinks and optoelectronic devices have been bonded to transparent substrates. In both cases, the ultrathin chip configuration coupled with the desired substrate can increase performance of the chip by a factor of 10X.
A Novel Ultra-miniature catheter tip pressure sensor fabricated using silicon and glass thinning techniques
Authors: Allen Henry , Ramzan Kamrul , Knutti Jim , Withers Stan
Published: April 2011

A novel subminiature pressure sensor for blood pressure measurement has been fabricated. The device is only 250 microns wide and 70 microns thick. It is 1.1 mm in length. The sensor is housed in a guide-wire lead for use in measuring coronary artery blood pressure. The device has a 5 micron thick silicon diaphragm and senses pressure using a 1/2 bridge piezoresistive network. Glass is processed to provide depressions above the sensing area as well as above the connection area of the device. A full-thickness silicon wafer is processed using standard micromachining techniques. V-Groove notches are micro-machined on the top surface of the silicon to provide locators/guides for the lead-wires. Diaphragm windows are patterned on the back of the silicon wafer and the wafer is etched down to form the 5 micron diaphragm, using electro-chemical etch-stop techniques. The Glass and Silicon wafers are aggressively cleaned prior to bond. The glass and silicon wafers are then precisely aligned to better than 10 microns and bonded using anodic bonding techniques.

The glass/silicon wafer sandwich then has the silicon thinned from 400 microns to 37 microns using both grinding and polishing. Then the full-thickness glass wafer is etched in HF to a thickness of 37 microns as well, for a composite 74-micron thick structure. The wafer is then diced to form the micro-mechanical structure.
Atomic-Layer Cleaving and Non-contact Thinning and Thickening for Fabrication of Laminated Electronic and Photonic Materials
Authors: Current Michael I. , Farrens Shari N. , Fuerfanger Martin , Kang Sien , Kirk Harry R. , Malik Igor J. , Feng Lucia , Henley Francois J.
Published: April 2011

An innovative suite of layer transfer technologies, collectively called the NanoCleaveTM Process, includes a non-porous cleave plane utilizing a compressive strain layer, growth of a high purity, crystalline device layer, plasma activation coupled with vacuum bonding, room-temperature cleaving along an atomically flat plane and a variety of post-cleave CVD processes to thicken or thin the device layer to a desired final thickness is described. Applications of this process include fabrication of SOI wafers containing Si and SiGe alloy device layers.
Characterization & Analysis of Sub-Grain Boundaries in Sequential Lateral Solidification Processed SOI Films
Authors: Crowder M. A. , Limanov A. B. , Turk B. A. , Im James S.
Published: April 2011

The nature of the formation of sub-grain boundaries within sequential lateral solidification (SLS) processed thin silicon films has been examined using single crystal Si films as a pre- cursor material. Experimental details include the use of an excimer laser projection system and straight-slit beamlets to produce directionally solidified microstructures. Within the SLS processed silicon-on-insulator (SOI) films, three microstructurally distinct regions are identi-fied: (1) an initial planar defect-free area (the extent of which can depend on laser fluence and orientation); (2) a transitional area within which the sub-grain boundaries appear and propagate in a well-defined direction relative to the crystallographic orientation; and (3) a final area characterized by sub-grain boundaries aligning approximately to the scan direction, and the in-plane texture becoming more random. We discuss the results within the context of a plastic deformation model of sub-grain boundary formation.
Oxidation of Molybdenum Thin Films and its Impact on Molybdenum Field Emitter Arrays
Authors: Chalamala Babu R. , Reuss Robert H. , Wei Yi , Bernhard John M. , Sosa Edward D. , Golden David E. , Aggarwal Sanjeev , Ramesh R.
Published: April 2011

Oxidation of emitter surfaces can be a serious problem for Mo field emitter arrays. We studied the oxidation and related changes in the electronic properties of Mo thin films as a function of annealing temperature. Experiments were done on Mo thin films prepared on Si and sodalime glass substrates. These films were thermally oxidized and characterized using a variety of techniques including x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and thermal desorption spectroscopy (TPD) methods. For films oxidized below 400°C, partial oxidation was observed, with MoO3(110) being the principal oxide phase. However, at a temperature of 500°C and above, oxidation of the film was complete. Electrical characteristics of the films undergo a rapid transition from semiconductive to highly insulating at temperatures between 475 to 500°C. Temperature programmed desorption spectra showed that the oxides are stable at elevated temperature with only a principal O2 desorption peak at approximately 786°C.
Porous Silicon Coated with Ultra-Thin Diamond-Like Carbon Film Cathodes
Authors: Evtukh Anatoli A. , Litovchenko Volodimir G. , Litvin Yurii M. , Fedin Dmitrii V. , Rassamakin Yurii V. , Sarikov Andrey V. , Chakhovskoi Andrei G. , Hunt Charles E. , Felter Thomas E.
Published: April 2011

The main requirements to electron field emission cathodes are their efficiency, stability and uniformity. In this work we combined the properties of porous silicon layers and diamond-like carbon (DLC) film to obtain emission cathodes with improved parameters. The layered structures of porous silicon and DLC film were formed both on flat n-Si surface and silicon tips created by chemical etching. The conditions of the anodic and stain etching of silicon in HF containing solution under the illumination have been widely changed. The influence of thin (≤10nm) DLC film coating of the porous silicon layer on electron emission has been investigated. The parameters of emission efficiency such as field enhancement coefficient, effective emission areas and threshold voltages have been estimated from current-voltage dependencies to compare and characterize different layered structures. The improvement of the emission efficiency of silicon tip arrays with porous layers coated with thin DLC film has been observed. These silicon-based structures are promising for flat panel display applications.
Effect of Deposition Condition of Precursor Amorphous Silicon Thin Films on the Behavior of Milc
Authors: Yoon Y.-G. , Kim G.-B. , Park H.-H , Lee S.-W , Joo S.-K.
Published: April 2011

We studied on the effect of a deposition condition of precursor a-Si thin films on the shape and micro-structure of MILC. The a-Si thin films were prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) with silane and hydrogen as a source gas and the deposition temperature was varied from 100 to 400∼. The a-Si films deposited at a lower temperature showed a tendency to (111) crystals and leaving some a-Si residues in MILC region, while those with higher deposition temperature tended to be crystallized to (110). These differences were explained in terms of original hydrogen content and following structural changes by the dehydrogenation during annealing.
Analysis of ITO Films Deposited on Various Polymer Substrates for High-Resolution Plastic Film LCDs
Authors: Han Jeong In , Park Sung Kyu , Lee Chan Jae , Kim Won Keun , Kwak Min Gi
Published: April 2011

The electrical and mechanical properties in indium-tin-oxide films deposited on polymer substrate were examined. The materials of substrates are polyethersulfone(PES), polycarbonate(PC), polyethylene terephthalate(PET) which have gas barrier layer and anti-glare coating for plastic-based devices. The experiments were performed by rf-magnetron sputtering using a special instrument and buffer layers. Therefore, we obtained a very flat polymer substrate deposited ITO film and investigated the effects of buffer layers, in addition to the instrument. Moreover, the influences of an oxygen partial pressure and post-deposition annealing in ITO films deposited on polymer substrates were clarified. X-ray diffraction observation, measurement of electrical property, and optical microscope observation were performed for the investigation of micro-structure and electro-mechanical properties. They indicated that as-deposited ITO thin films are amorphous and become quasi-crystalline after adjustment of oxygen partial pressure and thermal annealing above 180 °C. As the results, we obtained 20-25 Ω/ of ITO films with a good transmittance (above 80%) under 0.2 % oxygen contents and vacuum annealing. Furthermore, using organic buffer layer, we obtained ITO films which have rather high electrical resistance (40-45 Ω/ ) but have improved optical (more than 85%) and mechanical characteristics compared to the counterparts.
Varistor Beahavior in Lead Based Perovskite Comounds
Authors: Sharma Seema , Choudhary R.N.P.
Published: April 2011

Polycrystalline samples of Pb(Cd1/2W1/2)O3 and Pb(Mo1/2W1/2)O3 were synthesized by a high-temperature solid-state reaction technique. Preliminary crystal structure and microstructure of the compounds at room temperature were studied using X-ray diffraction (XRD) technique and Scanning electron microscopy (SEM), respectively. The dielectric permittivity (⊏) and losstangent (tan ⊏) of the compounds were obtained both as a function of frequency(103-104Hz) atroom temperature and temperature (30-3200C) at 10 kHz. Both the ac and dc conductivity have been studied over a wide range of temperature. The current– voltage (I-V) characteristics of the compound studied at different temperatures reveal that the Pb(Cd1/2W1/2)O3 also has excellent varistor behavior. A PTCR effect and NTCR effect was exhibited by Pb(Cd1/2W1/2)O3 and Pb(Cd1/2Mo1/2)O3 respectively.
Diffusion Behavior of Ion-Implanted n-type Dopants in Silicon Germanium
Authors: Eguchi S. , Leitz C. W. , Fitzgerald E. A. , Hoyt J. L.
Published: April 2011

The diffusion behavior of ion implanted arsenic and phosphorus in relaxed-Si0.8Ge0.2 is investigated. Both dopants exhibit enhanced diffusivities in SiGe compared to those in Si under equilibrium conditions. The ratio of the effective diffusivity in SiGe relative to that in Si is found to be approximately seven for arsenic, and roughly two for phosphorus at high concentrations. Under transient diffusion conditions, arsenic diffusion in SiGe is retarded while arsenic diffusion in Si is enhanced by the ion implant damage. The transient retardation of arsenic diffusion in SiGe is observed at temperatures ranging from 900 to 1050°C. These results suggest that using arsenic, it is possible to form n+/p junctions in relaxed-Si0.8Ge0.2 as shallow as those in Si, by optimizing the implant annealing conditions.
Electrical Properties of Ultra Shallow p Junction on n type Si Wafer Using Decaborane Ion Implantation
Authors: Song Jae-Hoon , Choi Duck-Kyun , Oh Min-Seok , Choi Won-Kook
Published: April 2011

The junction depth should be less than 0.05 microns to fabricate sub 0.1 micron devices. This requires implanting boron with energy of less than 1 keV. One drawback in a low energy ion source is low throughput due to low ion beam current. At present, boron known for a major p-type dopant for PMOSFET has problem to easily diffuse into Si wafer even in rapid thermal processing by high diffusivity. To resolve this problem, decaborane (B10H14) molecules are implanted to make p+/n junction on n-type Si wafers for low-energy boron dopant source. Ionized decaborane is accelerated at 1∼10 kV and implanted up to dosages from 1×1012/cm2 to 5×1013/cm2. Afterwards, Decaborane implanted Si wafers were post-annealed for 10 sec at 800, 900 and 1000°C, respectively. From RBS results on as-implanted n-type Si wafer implanted at 5 kV, it is observed there are amorphous Si layers with 4 nm in depth and boron ions are implanted up to 1∼5 nm in depth from SIMS analysis. The electrical properties of these p-n junctions are 127∼130 ω/sq. as sheet resistance, +0.3 V turn-on voltage and −1.1 V breakdown voltage obtained from I-V measurement.
Growth and Characterization of UHV/CVD Si/SiGe Strained-Layer Superlattices on Bulk Crystal SiGe Substrates
Authors: Sheng S.R. , Dion M. , Mcalister S.P. , Rowell N.L.
Published: April 2011

High-quality short-period Si/SiGe strained-layer superlattices have been grown on bulk single-crystal SiGe substrates using a commercial low-temperature ultrahigh vacuum chemical vapor deposition (UHV/CVD) reactor. These superlattices were characterized by high-resolution x-ray diffraction (HRXRD), Auger electron spectroscopy (AES), atomic force microscopy (AFM), cross-sectional transmission electron microscopy (XTEM) and photoluminescence (PL). HRXRD, AES, and XTEM results confirm that the materials deposited are high crystal-quality superlattice layers with abrupt interfaces and excellent thickness and composition uniformity across superlattices of 5 periods. AFM images show similar surface RMS roughness of much less than 1 nm for both the top layer surface and the starting substrate surface, indicating very smooth surfaces. PL measurements further confirm material quality and composition, and show sharp, well-resolved near band-edge BE and FE PL and strong broad sub-gap PL perhaps related to direct-gap superlattice transitions. The materials grown here are very promising for applications of both high-speed electronic devices and high-efficiency optoelectronic devices.
Poly-SiGe TFTs Fabricated by Low Temperature Chemical Vapor Deposition at 450°C
Authors: Shimizu Kousaku , Zhang Jianjun , Lee Jeong-woo , Hanna Jun-ichi
Published: April 2011

Low temperature growth of poly-SiGe has been investigated by reactive thermal chemical vapor deposition technique, which is a newly developed technique for preparing polycrystalline materials with using redox reactions in a set of source materials, Si2H6 and GeF4.. In order to prepare high uniformity and reproducibility of Si-rich poly-SiGe, total pressure, gas flow ratio, and residence time are optimized at 450°C of substrate temperature. Through optimizing the conditions, poly-Si1−xGex (x<0.04) films have been prepared in the reproducibility more than 90% and uniformity more than 88%. Bottom gate type of n-channel thin film transistors has been fabricated in various grain size of poly-Si1−xGex on SiO2 (100nm)/Si substrates. 5-36 cm2/Vs of field effect mobility of thin film transistors (L/W = 50μm/50μm) have been achieved after hydrogenation, whose threshold voltage is around 2±0.5V, and on/off ratio is more than 104.