bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of Amorphous Silicon Materials and Devices with Improved Stability
Authors: Dalai Vikram L. , Ping E. X. , Kaushal Sanjeev , Leonard Mark , Bhan Mohan K. , Han K.
Published: April 2011

We discuss the growth of a-Si:H Materials and devices using a low pressure remote ECR plasma. We show that by using this plasma in an etching mode with a high H flux, we can grow high quality a-Si:H films at high temperatures (325–375 C). These films have significantly improved stability compared to standard a-Si:H films deposited using glow discharge. We can further improve the stability of these films by incorporating minute (sub ppm levels) of boron during growth. We also report on the fabrication of devices at these temperatures using this very reactive plasma. We discuss the precautions taken to obtain good devices, and discuss how the devices can be further improved.
Built-In Potentials Via Electroabsorption Measurements in a-Si:H p-i-n Solar Cells: a Critical Assessment
Authors: Wang Qi , Schiff E. A. , Hegedus Steven S.
Published: April 2011

We have measured electroabsorption (EA) in a-Si:H p-i-n solar cells in order to estimate their built-in potentials Vbi. This Method was pioneered by the Osaka University group; in simple cases Vbi is identified with a parameter V0 obtained by a simple linear fit to the dependence of EA on external bias voltage. Using signal averaging techniques we are able to Measure V0 with a reproducibility of better than 2%. In one sample from the Institute of Energy Conversion with an a-SiC:H p+ layer we estimate Vbj = 0.97 ± 0.06 V, which is in good agreement with previous JVT Measurement. The reason that the error estimate is larger than the reproducibility error is the presence of several small effects not accounted for by the original EA theory: in particular V0 depends slightly on the laser wavelength. We attribute these effects to the small portion of Vbi dropped in the a-SiC:Hp+ layer, which has a different electroabsorption than a-Si:H. We discuss models for the wavelength dependence.
Analysis of the Physical Origin of the blue shift of the Optical Bandgap of a-Si:H based Multilayers
Authors: Bernhard Norbert , Bauer Gottfried H.
Published: April 2011

The physical origin of the blue shift of the optical Taue bandgap of compositional multilayers of a-Si:H and its alloys with Ge, C or N is analysed. It is shown that for multilayers with bandgap differences up to 0.7 eV between well and barrier Material, the effect can be understood completely classical in terms of the effective medium approximation, when the mean composition of the multilayer films is not kept constant. For the variation of both the electronic well and barrier widths a shift of the Taue bandgap is theoretically expected. It is of the same order of magnitude as the effect which is experimentally observed. Interfacial transition layers can account for a blue shift also for higher bandgap differences, as usually the case in a-Si:H/a-SiNx:H Multilayers, and when the mean composition of the multilayers is kept constant.
Mobility-Lifetime Products in Glow Discharge and RF Sputter Deposited A-Si:H
Authors: Farias M. H. , Roche A. , Weisz S. Z. , Jia H. , Shinar J. , Lubianiker Y. , Balberg I.
Published: April 2011

A comparative study of the deposition temperature (Ts) dependence of the Mobility-lifetime (μτ) products of the charge carriers in glow-discharge and rf sputter-deposited a-Si:H is described and discussed. The Ts-dependence of the μτ's the majority carrier light-intensity exponents of the two types of films are strikingly similar. These observations lead to the conclusion that the structure of the recombination levels as well as the recombination processes are in accord with the “defect pool” Model, in contrast to previous suggestions. The differences between the two types of films thus appear to be limited to the differences in the concentrations of dangling bonds.
The Growth, Steady State and Decay of the Photocarrier Population at low Temperatures
Authors: Tran Minh Q. , Stradins P. , Fritzsche H.
Published: April 2011

We used the transient infrared photoconductivity to measure the rise and fall of the non-equilibrium photocarrier concentration n at helium temperatures and the conditions for recombination. The growth rate of n was found to be only a few percent of the electron-hole pair generation rate G in agreement with LESR data of Street and Biegelsen. The saturation value of n is about 1017cm−3 and nearly independent of G. After turning off the generation light, the residual n requires an hour to decrease by a factor 2 but it can be made to recombine in seconds by infrared light.
The Time-of-Flight Technique Applied to Amorphous Silicon Pin Solar Cells
Authors: Brummack Hanna , Bernhard N. , Eberhardt K. , Schubert M. B.
Published: April 2011

Fast transient photocurrent measurements have been performed on a-Si:H based pin diodes with thicknesses down to 0.5 μm. On a thick sample drift mobilities derived in either the small-signal or the space-charge limited current mode are compared. On real solar cell devices in SCL voltage (integral) Mode the electron lifetimes τ are determined from the extraction time of the photo-generated charge in dependence on the degradation state of the sample. A clear and reproducible correlation between lifetime and degradation state has experimentally been established. Lifetimes τ, for which an intensity dependence has been observed in the SCL voltage Mode, are compared to the μτ-product from a small-signal charge collection Measurement. The influence of the real absorption profile on the measurements is discussed.
Hydrogenated Amorphous Silicon Germanium Alloy for Stable Solar Cells
Authors: Terakawa A. , Shima M. , Sayama K. , Tarui H. , Nishiwaki H. , Tsuda S.
Published: April 2011

The film properties and solar cell performance of a-SiGe:H samples with the same optical gap and different combinations of hydrogen content (CH) and germanium content (CGe) have been compared. The optimum composition for the initial properties, such as the tail characteristic energy, defect density and conversion efficiency of the solar cell, was determined, and the differences could be explained by the difference in H bonding configuration. The degradation ratio of the conversion efficiency becomes larger in higher CH samples. This suggests that hydrogen or Si-H2 participates in light-induced degradation. As a result, the optimum CH for an efficient solar cell is believed to shift to the lower CH region after light soaking. Based on these findings, the stabilized conversion efficiency of 3.3% under red light (γ>650nm) for an a-SiGe:H single-junction solar cell (1cm2) and 10.6% under lsun light for an a-Si/a-SiGe double-junction stacked solar cell (1cm2) have been achieved. The degradation ratio is only 8.6% for the double-junction solar cell.
Hole Drift Mobility in a-Si1−xCx:H
Authors: Gu Qing , Wang Qi , Schiff E. A. , Li Yuañ-Min , Malone Charles T.
Published: April 2011

We present a summary of our recent measurements on hole drift mobilities in hydro-genated amorphous silicon-carbon alloys (a-Si1−xCx:H). Increasing the bandgap has a vastly smaller effect for the hole mobility than for electrons. In conjunction with previous drift Mobility Measurements in a-Si1−xCx:H and a-Si1−xGex:H, these hole measurements complete a simple pattern for the effects of bandgap modification on drift Mobilities: electron mobilities decline as the bandgap is increased beyond 1.72 eV or decreased below 1.72 eV, but hole mobilities are relatively unaffected.
Electronic and Optical Properties of a-Si1−xCx:H Films Produced From Admixtures of Silane and Ditertiarybutylsilane
Authors: Gaughan K. , Viner J.M. , Taylor P.C.
Published: April 2011

We investigated the optical and electronic properties of amorphous silicon carbide (a-Si1−xCx:H) films produced by plasma enhanced chemical vapor deposition from admixtures of silane and ditertiarybutylsilane [SiH2 (C4H9) 2 or DTBS] using photothermal deflection spectroscopy, electrical conductivity and its temperature dependence as well as photoconductivity. These a-Si1−xCx:H films exhibit low Urbach energies and high photoconductivities similar to films produced with other carbon feedstock sources. We also present our results for hydrogen diluted a-Si1−xCx:H films using DTBS as the carbon feedstock source.
Ambipolar Diffusion Lengths, Lamb, and Steady-State Photoconductivity, σph, in B2H6 Doped Μc-Si
Authors: Cho S.M. , He S.S. , Lucovsky G.
Published: April 2011

We have compared the photo-transport properties of thin films of B-compensated Μc-Si and device-grade a-Si:H prepared by remote plasma-enhanced chemical-vapor deposition (PECVD). The steady state photocarrier grating technique was used to determine the ambipolar diffusion lengths, Lamb. The conductivity of the μc-Si:B thin films changed from n-type to p-type as the B2H6 fraction in the B2H6/SiH4 source gas mixture was increased. The steady state photoconductivity, σph, decreased as B2H6 was initially introduced and the material changed from n-type to intrinsic; σph then increased as the material converted to p-type. Lamb displayed a complementary behavior with a maximum value at the approximate compensation point between the n-type and p-type conductivity regions. The steady-state photoconductivity and Lamb did not show any significant photo-induced degradations under intense illumination. Finally, the photoconductivity and Lamb displayed a strong dependence on sample thickness which is associated with Fermi level pinning at the surface.
Process-Property Relationships For a-Si1-xCx:H Deposition: Excursions in Parameter Space Guided by Real Time Spectroellipsometry
Authors: Lu Yiwei , Kim Sangbo , Gunes Mehmet , Lee Yeeheng , Wronski C.R. , Collins R.W.
Published: April 2011

Real time spectroellipsometry (RTSE) has been applied to study the growth of a-Si1-xCx:H alloys (x∼0.1; Eg=1.90–2.00 eV) for applications as i- and p-type layers in wide band gap solar cells. Two important material parameters, the optical gap and the relative bond-packing density (or void volume fraction), can be estimated from RTSE data collected during the growth of a sequence of layers onto the same substrate using different plasma-enhanced CVD conditions. In this way, large regions of parameter space have been scanned expeditiously, and an improved understanding of the effects of H2-dilution, substrate temperature (Ts), plasma power, gas pressure, and gas flow on the film properties has been obtained.
Amorphous Silicon Alloy Photovoltaic Technology - from R&D to Production
Authors: Guha S. , Yang J. , Banerjee A. , Glatfelter T. , Hoffman K. , Ovshinsky S.R. , Izu M. , Ovshinsky H. C. , Deng X.
Published: April 2011

The key requirements for photovoltaic modules to be accepted for large-scale terrestrial applications are (i) low material cost, (ii) high efficiency with good stability, (iii) low manufacturing cost with good yield and (iv) environmental safety. Thin films of amorphous silicon alloy are inexpensive; the products are also environmentally benign. The challenge has been to improve the stable efficiency of these modules and transfer the R&D results into production. Using a Multijunction, Multi-bandgap approach to capture the solar spectrum more efficiently, we have developed one-square-foot modules with initial efficiency of 11.8%. After 1000 h of one-sun light soaking, a stable efficiency of 10.2% was obtained. Both the efficiency values were confirmed by National Renewable Energy Laboratory. The technology has been transferred to production using an automated roll-to-roll process in which different layers of the cell structure are deposited in a continuous manner onto stainless steel rolls, 14” wide and half a mile long. The rolls are next processed into modules of different sizes. This inexpensive manufacturing process produces high efficiency modules with subcell yields greater than 99%. The key features of the technology transfer and future scope for improvement are discussed.
The Effect of H2 Dilution on the Stability of a-Si:H based Solar Cells
Authors: Yang Liyou , Chen Liang-Fan
Published: April 2011

We have systematically investigated the effect of H2 dilution on the stability of a-Si:H based solar cells. The results clearly show that the device stability against light soaking improves substantially with increasing H2 dilution until a threshold is reached. Beyond this threshold which depends on the substrate temperature, the stability no longer changes with further increase in H2 dilution. On the other hand, at a given ratio of H2 to the reactant gases, the device stability generally improves with increasing substrate temperature. Multi-step light soaking experiments have shown that devices made with H2 dilution saturate much faster (∼100 hours) under one-sun illumination and exhibit little overshoot effect in the recovery process, in sharp contrast to devices made without H2 dilution. Based on the simple two-component model for defect kinetics, these observations and the fact that the apparent saturation time coincides with the time constant of the “fast” defects strongly suggest that negligible amount of “slow” defects exist in materials made with H2 dilution. While H2 dilution generally suppresses the formation of microstructure giving rise to dihydride bonding and microvoids, the differences in the kinetics of light induced degradation cannot always be traced to obvious differences in these structural properties.
Stability Test Of 4 Ft2 Triple-Junction a-Si Alloy PV Production Modules
Authors: Deng X. , Izu M. , Narasimhan K. L. , Ovshinsky S. R.
Published: April 2011

We report results of stability tests of 4 ft2 triple-junction a-Si alloy photovoltaic (PV) Modules. These Modules were produced in ECD's 2 Megawatt (MW) continuous, roll-to-roll PV Manufacturing line during the early stage of optimization. The stable module efficiency after 600 hours of 1 sun light soaking at approximately 50°C under load, is 8%. This is the highest stable efficiency for large area (≥4 ft2) a-Si alloy PV Modules Made in a production line.
Accurate Light Absorption Profile in Tandem A-SI:H Solar Cells on Textured TCO Substrates
Authors: Tao G. , Makaro Zs. , Zeman M. , Metselaar J.W.
Published: April 2011

While a-Si:H tandem solar cells deposited on textured TCO substrates have already shown high efficiency and good stability [1], the light absorption profile in such cells is still one of the important quantities to know. An accurate absorption profile is required when we do solar cell analysis, design, and optimization, or when we do computer simulations.

With the computer program GENPRO2D [2] which was developed in our laboratory, and was based on the incoherent Multi-rough-interfaces (scattering) Model, we are able to calculate the light absorption profile in a tandem a-Si:H solar cell for different light spectra and different light incident angles, provided that the scattering of light at every interface in the cell is known. In this paper, we will present our calculated results with comparison to the measured results of a real tandem cell.
A New Method for the Derivation of the Output Characteristics of Amorphous Silicon Thin-Film Transistors.
Authors: Mittiga A. , Mariucci L. , Carluccio R. , Pecorai A. , Fortunato G.
Published: April 2011

A novel method to derive the output characteristics of a-Si:H thin film transistors from the channel conductance curve is presented. The Method well reproduces the experimental data both in the linear and saturation regimes without using any adjustable parameter. The Method is simple and fast enough to be used in a circuit simulator.
The Kinetics of Removal of Defects in a-Si:H TFTs Made with PECVD Oxide Gate Insulator Material
Authors: Morgan P. N. , Milne W. I. , Deane S. C. , Powell M. J.
Published: April 2011

AMorphous silicon thin film transistors may be manufactured using a variety of gate insulator Materials. The sign and magnitude of the fixed charge, Qf, in the gate insulator material determines the as-deposited density of states in the a-Si:H as predicted by the defect pool Model [1]. For the case of PECVD nitride Qf is positive giving rise to a defect peak in the lower part of the bandgap. In thermal oxide, which has small negative Qf the states are in the upper part of the bandgap. Using the technique of low temperature bias stress or high temperature bias anneal it is possible to create further defects in the bandgap on top of those already present, facilitating the study of upper (Dh) and lower (De) gap states. In a previous work we studied the removal kinetics of such defects using TSDR (Thermally Stimulated Defect Removal) in both PECVD nitride and thermal oxide devices [2]. Here we repeat the experiments on thin film transistors made with PECVD helium diluted oxide as the gate insulator Material. PECVD helium diluted oxide is interesting as its Qf May be varied during Manufacture. Thus TFTs with characteristics similar to either thermal oxide or PECVD nitride can be obtained.
The Power Law Dependence of Electroluminescence Intensity on Forward Current in a-Si:H p-i-n Devices
Authors: Wang Keda , Han Daxing , Silver Marvin
Published: April 2011

Both total electroluminescence intensity and spectrum have been measured as a function of applied voltage at various temperatures on p-i-n devices with i-layer thickness from 0.2 μm to 2.0 μm. At constant temperature the luminescence intensity shows a power-law dependence on forward bias current with an exponent, γ. As the temperature increases from 80 K to 300 K, γ decreases from 1.5 to 0.9 in thin (≤ 0.5 μm) samples. Thick, 2.0 μm, samples on the other hand, show γ ≈ 1 over the same temperature range. Each electroluminescence spectrum has been decomposed into two gaussian functions corresponding to the main band and the defect band luminescence, respectively. We find that the integral intensity of the high energy luminescence band versus the current obeys a power-law with exponent γ1, while the integral intensity of the low energy luminescence band versus the current obeys a power-law with exponent γ2· γ1 > γ2 for all samples at all temperatures in these Measurements.
Manufacturing Considerations for VLSI Interconnect Systems
Authors: Thomas Michael E.
Published: April 2011

In the next decade, it is expected that integrated circuits having 5 to 7 levels of metal will be common in VLSI technologies with linear interconnect densities approaching 200 meters/cm2/level. Multilevel interconnect technology needs are presently generating processing and structural issues which will dominate the future manufacturing yield and performance of these integrated circuits. The challenge of meeting these needs will require a concurrent improvement in design and manufacturing simplicity and cleanliness. This presentation will examine the architectural needs of future multilevel metal systems in light of the lithography, materials, and electrical requirements which must be addressed by the interconnect engineer. A comparison of interconnect systems based on different conductor materials will be presented.
Comparative Cu Diffusion Studies in Advanced Metallizations of Cu and Al-Cu Based Thin Films
Authors: Gupta D.
Published: April 2011

Availability of diffusion data is important in the evaluation of the prospect of substituting Cu for Al-Cu metallization for improving electrical and electromigration performance. Measurements have been made of 67Cu radioactive tracer diffusion in Cu, Cu-0.4Zr and several Al-Cu thin films of commonly used compositions. Grain boundary self diffusion in Cu is described by δDb= 1.5xl0-9 exp( — 0.92eV/kT) cm3/ sec. The activation energy for Cu diffusion in Al, Al-l%Cu and Al-0.5Cu-0.15Ti thin films depends on the amount of Cu present and varies in the 0.4 - 1.0 eV range. The measured diffusion parameters in the two alloy systems are compared and contrasted with those available from electromigration studies.
The Stability of TiH2 Used as Diffusion Barrier on SiO2 Substrates
Authors: Murarka Shyam P. , Ko Sen-Hou , Ding Pei-Jun , Lanford William A.
Published: April 2011

TiH2 has been considered as a diffusion barrier and adhesion promoter between oxide and Cu. This phase is formed by reaction of Ti with hydrogen during rapid thermal annealings. In this investigation the stability of TiH2 on PECVD and thermal oxides has been studied during Ar anneal at 400 and 500°C. X-ray diffraction, sheet resistance measurements, RBS, and nuclear reaction technique to profile hydrogen have been used in this study. The results indicate that the stability of TiH2 is dependent on the nature of the oxide, for example, the water concentration and the density of the oxide and on the temperature of the anneal. These results will be discussed in view of the applicability of TiH2 which has a low thin film electrical resistivity of about 100 μΩ-cm.
Refractory Metal Encapsulation in Copper Wiring
Authors: Palleau J. , Oberlin J.C. , Braud F. , Torres J. , Mermet J. L. , J Mouche M- , Ermolieff A. , Piaget J.
Published: April 2011

The thermal stability at the Cu / SiO2 interface has been studied as a function of the annealing atmosphere composition. Using either good vacuum conditions or refractory metal encapsulation, no copper diffusion into SiO2 has been found even for thermal treatments at 500°C for l0h. Moreover, a noticeable accumulation of the refractory metal, ( Cr, Ti ), at the Cu / SiO2 interface has been observed. The diffusion phenomena allows the self-aligned formation of a refractory metal barrier layer at the SiO2 surface.
W/Pt and Ti/Pt Based Contacts to Algaas/Gaas Heterojunction Bipolar Transistors
Authors: Kalkur T.S. , Wright P.D.
Published: April 2011

Ti/Pt and W/pt was used form contacts on hevily doped InAs and InGaAs emitter layers of heterojunction Bipolar transistors (HBTs) . The as deposited contacts were ohmic for Ti/Pt on InAs and W/Pt on InGaAs. The rapid thermal annealing was performed in the temperature range of 300-600 C. The contact characteristics of Ti/Pt and W/Pt were compared with Au/Cr contacts.
Correlation Between the Microstructures and the Electrical Properties of Ni/Au/Te/Au Contacts on n-GaAs
Authors: Lin X. W. , Watté J. , Wuyts K. , Swider W. , Silverans R.E. , Liliental-Weber Z. , Washburn J.
Published: April 2011

The structural evolution of Ni/Au/Te/Au contacts on n-GaAs (001) was examined, in correlation with their electrical properties as a function of rapid thermal annealing in the temperature range 350 - 600°C. It was found that heating at temperatures ≥ 550°C results in the formation of ohmic contacts, while contacts annealed at lower temperatures remain nonohmic. Transmission electron microscopy revealed that heating ≥ 450°C leads to extensive reactions between Ni/Au/Te/Au and GaAs and deep spike formation into the GaAs. The major reaction products were identified as NiAs and β-AuGa. Ga2Te3 grains, growing epitaxially on GaAs, were detected only in 550°C annealed samples. Heating to 600°C caused considerable Ga2Te3 loss. Implications of these results concerning the ohmic contact formation mechanism are discussed.
Ohmic Contacts To p+-GaAs and Al0.26Ga0.74As
Authors: Han W. Y. , Cole M. W. , Casas L. M. , DeAnni A. , Wade M. , Jones K. A. , Lapore A. , Lu Y. , Yang L. W.
Published: April 2011

Ohmic contacts, with metallization scheme of Pd/Ge/Ti/Pt, were formed on heavily carbon doped GaAs and AlxGa1-xAs. The lowest specific contact resistances were 4.7x10-7 and 8.9x 10-6 Ω-cm2 for the p+-GaAs and Al0.26Ga0.74As. The p+-GaAs and Al0.26Ga0.74As were doped with carbon to 5x1019 and 2x1019 cm-3 respectively. Interfacial reactions and elemental diffusion of the contacts were investigated via transmission electron microscopy and Auger electron spectrometry with depth profiles.
A Proposed Regrowth Mechanism for the Enhancement of Schottky Barrier Height to N-GAAS
Authors: Chen C-P. , Chang Y. A. , Kuech T.F.
Published: April 2011

A systematic study of the enhancement of Schottky barriers to n-GaAs diodes has been carried out using the Ni-Al binary system. The diodes, Ni2Al3/n-GaAs, Ni2Al3/Ni/n-GaAs, Ni/Al/Ni/n-GaAs and NiAl/Al/Ni/n-GaAs, have been realized by sputter deposition at a base pressure ∼2xl0-7 Torr. A high Schottky barrier height ranging from 0.95 to 0.98 eV (deduced from current-voltage measurements) was observed for all the annealed contacts except for Ni2Al3/n-GaAs contacts. The enhancement of the Schottky barrier height in all the contacts was attributed to the formation of a high Al content (Al,Ga)As layer at the metal/semiconductor interface. The formation of this (Al,Ga)As layer was explained in terms of a regrowth mechanism. In this mechanism, Ni reacts with GaAs initially at low temperatures, forming NixGaAs. The NixGaAs layer is believed to react with the Ni-Al layer to form the (Al,Ga)As layer when subjected to a high temperature annealing. A (200) dark field XTEM image of the annealed contact was used to demonstrate the existence of this (Al,Ga)As phase.
Substrate Dependence of Electrical Properties of Contacts on p-InP
Authors: Park Moon-Ho , Yeh C.L. , Wang L.C. , Deng F. , Liu Q. Z. , Clawson A.R. , Lau S. S.
Published: April 2011

Pd and Ni contacts on various p-InP substrates which were grown by liquid-encapsulation Czochralski (LEC) and metal organic chemical vapor deposition (MOCVD) were investigated. Pd contacts on the substrates supplied by one manufacturer were found to be ohmic contacts with a minimum contact resistivity of ∼ 5xl0-5Ω-cm2 for annealing temperature between 420°C and 500°C. However, ohmic behavior was not observed for Pd contacts on other substrates. Hall measurement and double-crystal x-ray diffractometer were used to evaluate the substrates. It was speculated that existence of intrinsic defects in p-InP grown by LEC method may be responsible for the observed ohmic behavior. This defect-assisted tunneling mechanism is potentially usefully for making ohmic contacts on other compound semiconductors.
Current Transport in Cryogenic Processed Metal/InP and GaAs Interfaces
Authors: He L. , Shi Z.Q. , Anderson W.A.
Published: April 2011

Schottky contacts to n type InP and GaAs have been made by deposition on substrates cooled to low temperature (LT=77K) in a vacuum close to 10-7 Torr.The Schottky barrier height, ФB, was found to be as high as 0.96eV with Pd/InP and 0.95eV for Au/GaAs. This indicated a significant increase in ФB compared with the room temperature (RT=300K) deposition. For diodes fabricated at room temperature, the reverse saturation current density, JO, decreased sharply with decrease in measuring temperature. For the RT InP diodes, the conduction mechanism was controlled by thermionic emission (TE). For the LT InP diodes, the value of JO was about six orders smaller than for the RT diode at the same temperature. As testing temperature decreased, the barrier height was increased from 0.96 to 1.15eV, with a temperature coefficient of -3.2 x 10-4 eV/K. The forward transport mechanism was controlled by thermionic field emission (TFE). For the GaAs diodes, thermionic emission (TE) dominated in the current transport at room temperature for both RT and LT diodes. At low testing temperature, RT diodes exhibited an excess current component at low forward bias.
Metallizing and Die Attaching to Cvd Diamond
Authors: Iacovangelo CD , DiConza PJ , Jerabek EC , Zarnoch KP
Published: April 2011

The high thermal conductivity of diamond (four times that of copper) and its low dielectric constant (less than alumina or aluminum nitride) makes it a desirable material for electronic substrates. The advent of CVD methods for depositing diamond in large areas at reasonable cost has spurred numerous applications for metallized CVDD. This paper describes several processes developed to provide reliable and stable metallization on CVDD including bond coats, diffusion barriers, vias, and solder die attach. Transition metals were found to provide well-adhered bond coats through carbide formation at the metal/CVDD interface. XPS depth profiles and conductivity measurements of three metallization systems: Ti/Pt/Au, WTi/Au, and Nb/Au after various heat treatments show WTi/Au to be the most stable system. Via filling was accomplished by LPCVD-W and electrolytic Cu for high and low aspect ratio holes respectively. The low thermal expansion coefficient of CVDD, -1.5 ppm/°C, presents a major challenge for reliable die attach of GaAs (5.85 ppm/°C). A novel concept for a compliant interface on CVDD which can overcome this problem will be presented.
Thermal Stability of Ti/Pt/Au Non-Alloyed Ohmic Contacts on InN
Authors: Ren F. , Abernathy C. R. , Pearton S. J. , Wisk P. W.
Published: April 2011

Extremely low contact resistance of non-alloyed Ti/Pt/Au metallization on n-type InN is demonstrated. The contacts were annealed at different temperatures up to 420 °C to investigate their thermal stability. A low contact resistivity of 1.8 x 10-7 ohm-cm2 was measured at room temperature using the transmission line method. This was due to the extremely high doping level (5 x 1020 cm-3) in the InN. After 300 °C annealing, the contact resistivity increased to 2.4 x 10-7 ohm-cm2- For 360 °C annealing, the contact morphology showed some degradation, but the contact resistivity was almost the same as at 300 °C. There was serious degradation of the contacts after 420 °C annealing. The morphology became very rough, and the contact and sheet resistances increased by factors of 3-5 times. This degradation is believed due to the decomposition of the InN film. The contact resistivities between n-type epitaxial GaAs and InN were also investigated, and showed values around 10-4 ohm-cm2.
Epitaxial Growth of CoSi2/Si Hetero-Structure by Solid State Interaction of Co/Ti/Si Multilayer
Authors: Li Bing-zong , Wu Wei-Jun , Shao Kai , Gu Zhi-Guang , Jiang Guo-Bao , Huang Wei-Ning , Fang Hua , Sun Zhen , Liu Ping , Zhou Zu-Yao
Published: April 2011

A new method of epitaxial growth of CoSi2 film on Si substrate by ternary solid state interaction is investigated. XRD, RBS and TEM show that single-crystalline CoSi2 can be formed on both Si (111) and (100) substrates by using Co/Ti/Si or TiN/Co/Ti/Si multilayer. The evolution of multilayer structure and its resistivity is studied and epitaxy mechanism is discussed. Experimental results indicate strong affinity between Co and Si. During the ternary interaction the epitaxial CoSi2 can be grown directly on Si and its growth may behave as a diffusion controlled process. The thickness of Ti layer and the annealing procedure have important effect on CoSi2 epitaxial growth.
The Effect of Titanium Silicidation on Type II End-of-Range Dislocation Loops
Authors: Herner S.B. , Krishnamoorthy V. , Robinson H.G. , Jones K. S.
Published: April 2011

The shrinkage in type II end-of-range dislocation loops was used to determine the relative flux of vacancies from the silicidation of titanium on silicon (100) wafers. A low temperature anneal (700°C 20 min.) in a forming gas ambient formed the initial silicide (approximately 750 Å thick), and several higher temperature anneals with the silicide intact and etched off followed to study the diffusion of the vacancies. The concentration of vacancies captured by the loops after a 900°C 60 minute post silicidation anneal was approximately 7.8 x 1013 /cm2 while the concentration after a 700°C 60 minute post silicidation anneal was only 9 x 1012 /cm2. Removal of the silicide prior to the high temperature post silicidation anneals resulted in fewer vacancies captured by the loops.
In-Situ Tem Observation of Interfacial Reactions in the Zr/Si System
Authors: Tanaka Htroyuki , Konno Toyohiko J. , Sinclair Robert
Published: April 2011

The interfacial reactions in the Zr/Si system were studied by in-situ cross-section TEM including high resolution mode. The reactions consisted of formation of an amorphous interlayer followed by the nucleation and growth of crystalline ZrSi2- The development of the amorphous layer was found to involve two different stages. The ZrSi2 was also found to grow layer-by-layer into the Si via a ledge mechanism.
Comparison of Cosi2- and Tisi2-Polycide Interconnections Tested by Conventional and High Accelerated Reliability Tests
Authors: Depta Dirk , Hollenbeck Ingo
Published: April 2011

Based on 2μm-wide CoSi2-n+- and TiSi2-n+-polycide structures with a l00nm-thick silicide and a standard AlSi-metallization a comparison between conventional and the high accelerated SWEAT-test was carried out. Supported by simulations different parameters (e.g. activation energie EA) were determined by time-to-failure-measurements. Because of comparable results out of both different tests the SWEAT-test will be prefered due to short time-to-test. Also it will be shown that both silicide systems have an about three times higher activation energy for the inducing of EM-based “open”-failures than the tested standard AlSi-metallization. The failure-rate was less than 100 FIT for both polycides but because of process advantages the CoSi2-polycide should be a promissing metallization to improve the reliability of single and/or multilevel-metallization.
Stress Migration in Aluminum Lines in Integrated Circuits
Authors: Okabayashi H.
Published: April 2011

This paper reports on two types of voiding which occur in Al lines in integrated circuits.

The first type of voiding occurs in high-temperature processes during chip fabrication, in which the thermal stress is expected to be compressive. Ultrahigh voltage electron microscopy (UHVEM) observations of the voids and voiding process show interrelations between the evolution and morphology of voids and grain-boundaries.

The other type of voiding occurs at low temperatures where highly tensile thermal stress develops in Al lines. This type of voiding occurs in accelerated life tests and actual operation. The results of accelerated life tests of intentionally oxygen-contaminated samples are described. Voids observed in low-oxygen samples are mostly large-angle-wedge-shaped and induce essentially no open failures in the early-failure period. In high-oxygen samples, crack-like voids occur, and parallel-slit-like voids also occur. These narrow voids result in high open-failure rates in the early-failure period.
Reliable Metallization and Wet Etch Process for Waveguide Formation on InP/InGaAs Mqw Modulator Structures
Authors: Thirstrup Carsten , Clausen Thomas
Published: April 2011

A simple process for making reliable InP/InGaAs multiple quantum well (MQW) modulator waveguide devices optimized with respect to electro-refractive modulation has been developed. The main concern of this study is the surface properties of the InP surface prior to metallization and etching. A new protective surface passivation technique combining vacuum procurement (∼5xl0-7 Torr) to reduce the water content in the native oxides with an in situ rf-sputter deposition of reactive SiOx onto the surface of InP is reported. This procedure provides smooth surfaces and good optical properties of GaInAs/InP based strip-loaded waveguides.
Anisotropy of Aluminum Porous Anodization Process for Vlsi Planar Metallization
Authors: Lazarouk S. , Baranov I. , de Cesare G. , Maiello G. , Proverbio E. , Ferrari A.
Published: April 2011

In this work factors affecting the anisotropy (i.e., difference in vertical and lateral anodization rates) of the aluminum anodization process are investigated. By varying the electrochemical process parameters, a degree of anisotropy of about 0.6 was obtained. The structure of the aluminum porous oxide was determined by a Scanning Electron Microscope. The difference in the anodization conditions for porous aluminum oxide growth along lateral and vertical direction was determined. The developed processing technique was used for forming multilevel VLSI metallization with feature sizes of about 1.2 µm.
Depth-Selective Investigation of Fe-Silicides Formed After Molecular Beam Epitaxy, Using Conversion Electron MÖSsbauer Spectrometry.
Authors: Degroote S. , Kobayashi T. , Dekoster J. , Vantomme A. , Langouche G.
Published: April 2011

Fe-Silicides were formed by annealing MBE-deposited thin Fe layers with a thickness in the range of 24 Å on (7x7) reconstructed Si(l11) substrates. Samples suitable for depth-selective investigations by CEMS (Conversion Electron Mössbauer Spectrometry) were prepared by using only the 57Fe isotope for a few monolayers of the total Fe film, and depositing these selectively right at the interface or separated from it. During the growth the substrate was held at room temperature. The silicide formation upon annealing to temperatures up to 900°C was monitored in situ with RHEED. From the CEMS studies a drastically different sample composition was inferred as a function of monolayer distance from the interface for the as-deposited samples and for annealing temperatures up to 400°C. Analysis of these spectra indicates the presence of metastable and stable iron silicides.
Chemical Mechanical Polishing for Planarization in Manufacturing Environment
Authors: Desai Mukesh , Jairath Rahul , Stell Matt , Toiles Robert
Published: April 2011

Global Planarization requirements of the deep sub-micron technology generation requires use of CMP as preferred planarization technique. In the past, CMP has been used extensively in the polishing of silicon wafers. However , there has been some reluctance to utilize this technology in the planarization of oxide films during IC manufacture. This has been driven primarily by issues regarding manufacturability , and therefore cost of ownership of CMP processes. Here the key process integration issues in CMP planarization of oxide films are outlined.

An effect of consumable set is shown to be critical in achieving repeatable CMP performance via removal rate & non-uniformity. Various defects induced as a result of CMP are explained. Cost of ownership model is used to demonstrate the importance of minimizing such defects.
Electronic Structures of β-SiC(001) Surfaces and Al/β-SiC(001) Interface
Authors: Hu Xiao , Yan Hong , Ohuchi Fumio S.
Published: April 2011

Surface electronic structures of β-SiC reconstructed (001) surfaces and the Al/β-SiC(001) interface have been investigated by employing a tight-binding method. Distinct surface electronic characteristics corresponding to different surface reconstructions are discussed based on the interpretation of surface density of states. The calculations of the Al/β-SiC (001) interface indicate that aluminum deposition on β-SiC(001) surface may induce the substrate to return to the ideal unreconstructed surface and that Al-C interaction is stronger than Al-Si interaction. Al deposition on C-rich surfaces may form a better bonded interface than that on the Si-rich surfaces. Our findings are in good agreement with available experimental and theoretical results.
Computer Simulation of Si and C Atoms on SiC Surfaces
Authors: Matthai C C , Moran G J , Morrison I
Published: April 2011

The molecular dynamics method employing an empirical potential energy function to describe the Si-C interaction has been used to determine the minimum energy sites for Si and C adatoms on C-terminated SiC (001) substrates. It is found that whereas a single C adatom lies on the carbon dimer bond, this site only becomes energetically favourable for silicon adatoms when they interact to form a dimer pair.
Diamond Chemical Vapor Deposition: Gas Compositions and film Properties
Authors: Bachmann Peter K. , Hagemann Hans-Jürgen , Lade Hartmut , Leers Dieter , Picht Frederike , Wiechert Detlef U. , Wilson Howard
Published: April 2011

Rate, crystallinity and phase purity of vapor-grown diamond deposits are discussed. Emphasis is on microwave plasma CVD of diamond from C/H-, C/H/O-, C/H/F-, C/H/CI- and C/H/N-gas mixtures.

The manufacture of wear-resistant diamond thin films, diamond vacuum window membranes and thick diamond heat spreader plates are used as examples to outline the influence of various deposition parameters on the performance of finished products and to describe the use of ternary gas phase compositional diagrams as tools for minimization of deposition technology and product optimization efforts.
Deposition of Flame Grown Diamond Films in an Enclosed Chamber
Authors: Doverspike Kathleen , Shamamian Vasgen A. , Freitas Jaime A.
Published: April 2011

Polycrystalline diamond films were synthesized using an oxy-acetylene flame in the open atmosphere and in an enclosed chamber. In the present work, we have shown that the 2.16eV defect band seen in the photoluminescence spectra from the central portion of the films grown in the open atmosphere show a dependence on the growth temperature. Films grown in the open atmosphere all exhibit a decrease in the crystalline quality when moving to the outside edge most likely due to the entrainment of nitrogen into the films.

The present study was done in the enclosed chamber using an oxygen atmosphere via an oxygen flow around the torch. Films have been grown in the enclosed chamber that show only trace amounts of the 2.16eV band. Both the Raman and the photoluminescence spectra show that the films grown in the enclosed chamber are very uniform over the deposition area, which suggests that the degradation of the outer portion of the open atmosphere films may be the result of room air entrainment, and not a temperature variation across the substrate. In addition, when either lower purity oxygen is used or lower growth temperatures, we easily observe the 2.16eV band which may be the result of nitrogen impurities in the source gases.
Effects of Methane Concentration and Hydrogen Treatment on Preferred Orientation in Diamond Films Grown by Chemical Vapor Deposition
Authors: Ganesan D. , Sharma S. C.
Published: April 2011

We have conducted x-ray diffraction, Raman spectroscopy, and scanning electron microscopy analyses of diamond films grown by hot filament assisted chemical vapor deposition (HFCVD). We present results on the relative abundance of the (111), (220) and (400) faces in polycrystalline diamond films as functions of CH4 concentration. The intensity of the (111) peak can be varied from about 20% to 60% by adjusting CH4 in CH4/H2 mixtures. We also present results on preferred orientation in films grown under varying hydrogen treatments. We discuss correlations between the preferred orientation, FWHM of the diamond peak in the Raman spectrum, and surface morphology of the films.
Structural Study of SIC/AIN Bilayers and Trilayers on SI and 6H-SIC
Authors: Prasad Beesabathina D. , Fekade K. , Wongchotigul K. , Spencer M. G. , Salamanca-Riba L.
Published: April 2011

The growth morphology and microstructure of SiC/AlN/6H-SiC, SiC/AlN/SiC/Si, and SiC/AlN/Si heterostructures grown by LPCVD were studied using transmission electron microscopy. The SiC/AIN bilayers grown on 6H-SiC substrates were single crystalline and comprised of 3C-SiC and 2H-AlN. The epitaxial relationship between 2H-AlN and 6H-SiC is [0001]AlN//[0001]SiC. The SiC/AlN/SiC trilayers and the SiC/AIN bilayer grown on (001)Si were composed of 3H-SiC and 2H-AlN. However, the 2H-AlN layer was polycrystalline even though the (001)3C-SiC was single crystalline. The preferred orientation of the AlN layers in SiC/AlN/SiC/Si and SiC/AlN/Si are [0112] and [0002], respectively. The AlN/3C-SiC interface is relatively sharp compared to the AIN/Si interface in which an amorphous layer close to the interface was observed. In general, the polycrystalline AlN structure has two distinct layers: (1) nucleation layer and (2) bulk layer. High resolution lattice images of the polycrystalline AlN showed amorphous areas and small misoriented crystallites in the nucleation layer. The bulk layer consists of preferentially oriented large columnar grains.
Electron Cyclotron Resonance Plasma Chemical Vapour Deposition of Silicon Carbide Thin Films Using Ditertiary Butyl Selane
Authors: Boumerzoug Mohamed , Boudreau Marcel , Mascher Peter , Jessop Paul E.
Published: April 2011

Silicon carbide films were deposited by electron cyclotron resonance plasma chemical vapour deposition, using Ditertiary Butyl Silane (SiH2(C4H9)2), a non-corrosive organic compound, liquid at room temperature and stable in air, as precursor. Depositions were carried out in an Ar/H2 plasma at relatively low temperatures, below 400 °C. The influence of deposition parameters such as substrate temperature, gas flow rates, pressure, and microwave power, was systematically investigated and related to the Si:C ratios and the refractive index. The film composition was measured by Auger electron spectroscopy and the surface morphology was examined by scanning electron microscopy. The deposition rates and refractive indexes were extracted from the conventional ellipsometric functions, psi and delta. The results show that high quality silicon carbide of variable Si:C ratios and with very low levels of impurities are obtained.
Exposure of Diamond to Atomic Hydrogen: Secondary Electron Emission and Conductivity Effects
Authors: Malta D. P. , Posthill J. B. , Humphreys T. P. , Thomas R. E. , Fountain G. G. , Rudder R. A. , Hudson G. C. , Mantini M. J. , Markunas R. J.
Published: April 2011

Secondary electron (SE) yield was enhanced by a factor of ∼30 and surface conductance increased up to 10 orders of magnitude when O-terminated or non-terminated natural diamond (100) surfaces were exposed to atomic H. The SE yield from atomic H-exposed surfaces was spatially dependent on near-surface microcrystalline perfection enabling defect-contrast imaging in the conventional SE mode of the scanning electron microscope (SEM). Ultraviolet photoelectron spectroscopy (UPS) on atomic H-exposed surfaces revealed an intense low energy peak attributed to photoexcitation of secondary electrons into unoccupied hydrogen-induced states near the conduction band edge and their subsequent escape into vacuum. The low energy photoemission peak, enhanced SE yield and enhanced surface conductivity were completely removed via high temperature annealing or exposure to atomic O creating the denuded or O-terminated surfaces, respectively.
CVD-Growth of Low-Doped 6H SIC Epitaxial Films
Authors: Kordina O. , Henry A. , Hallin C. , Glass R. C. , Konstantinov A. O. , Hemmingsson C. , Son N. T. , Janzén E.
Published: April 2011

We present a method for growing low-doped 6H SiC films using chemical vapour deposition in a hot-wall system. The study discusses the influence of temperature, growth rate and C/Si ratio on the purity of the layers. Furthermore, we make a comparison between methane and propane as carbon source, and investigate the influence of bake-out prior to growth. The films are characterised using low temperature photoluminescence. The relative intensity of the free exciton related luminescence as compared to impurity related bound exciton recombination is discussed in terms of material purity. A capacitance-voltage technique is used to determine the doping concentration.
Combined Structural and Optical Assessment of CVD Grown 3C-SiC/Si
Authors: Feng Z. C. , Tin C. C. , Yue K. T. , Hu R. , Williams J. , Liew S. C. , Foo Y. G. , Choo S. K. L. , Ng W. E. , Tang S. H.
Published: April 2011

A combined structural and optical assessment of cubic (3C-) SiC thin films grown on Si (100) substrates by chemical vapor epitaxy (CVD) is presented. The CVD growth was performed at both atmospheric and low (100 Torr) pressure, using a vertical reactor. The CVD-grown 3C-SiC films with different growth time were characterized by X-ray diffraction, Raman scattering and Fourier transform infrared (FTIR) spectroscopy to be single crystalline with a high degree of crystal perfection. The film thickness was determined from FTIR spectra. Variations of X-ray, FTIR and Raman spectra with different growth conditions and film thicknesses are studied comparatively. Related problems are discussed.