bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Impurities on Diffusion and Activation of ion Implanted Boron in Silicon
Authors: Robertson L. S. , Brindos R. , Jones K. S. , Law M. E. , Downey D. F. , Falk S. , Liu J.
Published: April 2011

The interaction between boron and silicon interstitials caused by ion implant damage is a physical process which hinders the formation of ultra-shallow, low resistivity junctions. The possibility of mitigating the effective interstitial point defect population via introduction of nonmetallic impurities in ion implanted silicon has been investigated. Amorphization of a n-type Czochralski wafer was achieved using a series of Si+ implants of 40 keV and 150 keV, each at a dose of 1×1015/cm2. The Si+ implants produced a 2800Å deep amorphous layer, which was then implanted with 8 keV 1×1014/cm2 B+. The samples were then implanted with high doses of either carbon, oxygen, sulfur, chlorine, selenium, or bromine. The implant energies of the impurities were chosen such that the damage and ion profiles of the impurity were contained within the amorphous layer. This allowed for the chemical species effect to be studied independent of the implant damage caused by the impurity implant. Post-implantation anneals were performed in a tube furnace at 750° C. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Hall effect measurements were used to study the dopant activation. Transmission electron microscopy (TEM) was used to study the end-of-range defect evolution. The addition of carbon and chlorine appear to reduce the boron diffusion enhancement compared to the boron control. Carbon and chlorine also appear to prevent boron out-diffusion during annealing compared to the control, which exhibited 20% dose loss following annealing.
A Molecular Dynamics Study of Low-Energy Argon and Boron Implants on Silicon (100) Vicinal Surfaces Stepped Surface
Authors: Mazzone A.M. , Lamel C.N.R.
Published: April 2011

The purpose of this study is to illustrate the effects of the structure of the silicon surface on low-energy implants commonly used in current silicon technology. T o this aim Molecular Dynamics simulations with classical forces are used to study implantation of argon and boron with a kinetic energy in the range from 5eV to 30 eV into a silicon stepped surface. In addition to these calculations, the binding energy of boron atoms embedded in small clusters with a step shape hav e been studied with a quantum mechanical method of a semiempirical type. The purpose of these calculations is to compare the stable sites generated by theimplan ts with the ones attained during thermal treatments under near-equilibrium conditions.
Reaction of Excess Silicon Interstitals in the Presence of Arsenic and Germanium
Authors: Brindos R. , Keys P. H. , Griglione M. , Jones K. S. , Law M. E. , Agarwal Aditya , Andideh Ebrahim
Published: April 2011

CVD grown boron marker layers were used to monitor the release of silicon interstitials from an arsenic doped surface region that was subsequently implanted with silicon. These structures were annealed for various times at 750°C under a nitrogen gas flow. A comparison of boron spike enhancement and defect dissolution is made. It is shown that enhancement values from the Si+ implant were reduced at short times for samples containing arsenic compared to samples implanted with Si+ alone or As+ alone. The TEM results showed that defect densities were dramatically reduced for the samples containing As. These results imply that the previously reported reduction in {311} formation observed in As doped wells is most likely not a Fermi level effect and is consistent with the formation of As interstitial clusters (AsIC's). The data shows that AsIC's form and control extended defect formation and slow the enhanced diffusion.
Antimony Clustering due to High-dose Implantation
Authors: Shibahara Kentaro , Onimatsu Dai
Published: April 2011

Antimony implantation is a promising technique for fabricating ultra-shallow n+/p junctions for extensions of sub-100-nm n-MOSFETs. By increasing the Sb+ implantation dose to 6×1014 cm−2, sheet resistance (Rs) of an implanted layer was reduced to 260 /sq. for rapid thermal annealing (RTA) at 800°C. The obtained junction depth of 19 nm is suitable for sub-100-nm MOSFETs. However, the reduction in the sheet resistance showed a tendency to saturate. No pileup at the Si-SiO2 interface, which was the major origin of dopant loss in lower dose cases was, observed in Sb depth profiles in this case. However, in the case of 900°C RTA, Sb depth profiles indicated that Sb was nearly immobile in the region where Sb concentration exceeded 1×1020 cm−3. These results imply that the major limiting factor of Rs reduction under the highdose condition is Sb precipitation, which is different from the lower dose cases.
In-situ Growth and Growth Kinetics of Epitaxial (100) CoSi2 Layer on (100) Si by Reactive Chemical Vapor Deposition
Authors: Rhee Hwa Sung , Lee Heui Seung , Park Jong Ho , Ahn Byung Tae
Published: April 2011

Uniform epitaxial CoSi2 layers have been grown in situ on a (100) Si substrate at temperatures near 600 °C by reactive chemical-vapor deposition of cyclopentadienyl dicarbonyl cobalt, Co(η5-C5H5)(CO)2. The growth kinetics of an epitaxial CoSi2 layer on a Si (100) substrate was investigated at temperatures ranging from 575 to 650 °C. In initial deposition stage, platelike discrete CoSi2 spikes were nucleated along the <111> directions in (100) Si substrate with a twinned structure. The discrete CoSi2 plates with both {111} and (100) planes grew into an epitaxial layer with a flat interface on (100) Si. For epitaxial CoSi2 growth on (100) Si, the activation energy of the parabolic growth was found to be 2.80 eV. The growth rate seems to be controlled by the diffusion of Co through the CoSi2 layer.
Development of a Post-Spacer Etch Clean to Improve Silicide Formation
Authors: Yeh Edward K. , Sengupta Samit S. , Gabriel Calvin T.
Published: April 2011

The formation of a uniform, low-resistance silicide is dependent on the contamination level of the silicon surface upon which the Ti or Co is deposited. Contamination may be in the form of embedded carbon and fluorine residues from previous processing steps, such as the LDD spacer etch. The extent to which the spacer etch contributes impurities can be determined by making contact angle measurements; that is, measurement of the angle formed by a droplet of water placed on the wafer surface. A clean silicon surface provides a contact angle of > 70°, whereas a contaminated silicon surface produces contact angles down to only a few degrees. By using contact angle as a metric, a post-spacer etch clean was developed to remove impurities from the silicon surface without significant silicon loss. The clean procedure entails the use of a CF4/H2O plasma to treat the wafer directly after spacer etch. The clean process was then evaluated by the formation of a blanket Ti silicide followed by sheet resistance measurement. By using this cleaning process, a Ti silicide sheet resistance comparable to that formed on virgin silicon wafers was obtained on wafers that experienced the spacer etch. By comparison, wafers that were subjected to the spacer etch but not the post-spacer clean yielded a higher sheet resistance. Additional study of the post-spacer etch clean process revealed that oxide on the wafer (even the small amount formed during an O2-based resist ash process) can prevent the CF4/H2O plasma from cleaning the surface, perhaps by blocking H in the cleaning plasma from extracting C and other contaminants from the silicon surface. Co silicide formation is even more sensitive to surface impurities than Ti silicide. Using the same post-spacer etch clean, uniform, low-resistance Co silicide formation has been demonstrated.
In situ and Ex situ Measurements of Stress Evolution in the Cobalt-Silicon System
Authors: Lucadamo G. , Lavoie C. , Cabral C. , Carruthers R. A. , Harper J.M.E.
Published: April 2011

The biaxial stress in Co thin-films has been investigated in situ by measuring changes in substrate curvature that occurred during deposition and annealing.Films of Co, 35 to 500 nm in thickness, were deposited by UHV magnetron sputtering at room temperature on Si (100) and poly-Si substrates.Results show that during Co deposition the bending force increased linearly with film thickness; a signature of constant stress.In addition, the stress evolution during silicide formation was measured under constant heating rate conditions from room temperature up to 700°C. The stress-temperature curve was correlated with Co2Si, CoSi, and CoSi2 phase formation using in situ synchrotron X-ray diffraction measurements.The room temperature stress for the CoSi2 phase was found to be ∼0.8 GPa (tensile) in the films deposited on Si (100) and ∼1 GPa (tensile) on the films deposited on poly-Si.The higher tensile stress in the poly-Si sample could be a result of Si grain growth during annealing.
The Physical and Electrical Properties of Polycrystalline Si1−xGex as a Gate Electrode Material for ULSI CMOS Structures
Authors: Kang Sung-Kwan , Ko Dae-Hong , Ahn Tae-Hang , Joo Moon-Sik , Yeo In-Seok , Whoang Sung-Jin , Yang Doo-Young , Whang Chul-Joo , Lee Hoo-Jeong
Published: April 2011

Poly Si1−xGex films have been suggested as a promising alternative to the currently employed poly-Si gate electrode for CMOS technology due to lower resistivity, less boron penetration, and less gate depletion effect than those of poly Si gates. We investigated the formation of poly Si1−xGex films grown by UHV CVD using Si2H6 and GeH4 gases, and studied their microstructures as well as their electrical characteristics. The Ge content of the Si1−xGex films increased linearly with the flux of the GeH4 gas up to x=0.3, and saturated above x=0.45. The deposition rate of the poly Si1−xGex films increased linearly with the flux of the GeH4 gas up to x=0.1, above which it is slightly changed. The resistivity of the Si1−xGex films decreased as the Ge content increased, and was about one half of that of poly-Si films at the Ge content of 45%. The C-V measurements of the MOSCAP structures with poly Si1−xGex gates demonstrated that the flat band voltage of the poly Si1−xGex films was lower than that of poly-Si films by 0.2V.
Silicidation of Titanium-Rich Titanium Boride Deposited by Co-Sputtering on Si (100)
Authors: Sade G. , Pelleg J.
Published: April 2011

Titanium boride is known as a good diffusion barrier, in particular against copper, however outdiffusion of boron might deteriorate the semiconductor device. A TiSi2 sublayer prevents effectively boron penetration into the Si substrate. In this study the intention was to form a TiB2/TiSi2 bilayer film by silicidation of a titanium-rich titanium boride deposited by magnetron co-sputtering from elemental targets. The TiSi2 formation as well as the redistribution of titanium in the boride layer has been investigated by X-ray diffraction (XRD), Auger depth profiling and cross-sectional transmission electron microscopy (XTEM). Contact structure with Cu metallization was prepared to characterize this structure electrically.

The Ti-rich titanium boride film was completely amorphous by XRD up to 700 °C. Crystallization of Ti-rich silicides (Ti3Si, Ti5Si3) have started at 750 °C, but already at 800 °C crystallization of C54 TiSi2 was completed. TiB2 begins to crystallize at 800 °C. Sheet resistance measurements confirmed these results. The sheet resistance of the as-deposited film was about 16 ω/□ and no significant change was detected up to 700 °C. Then, a remarkable drop in the sheet resistance to ∼1 Ω/□ was obtained after 800 °C, and this value was actually unchanged up to 925 °C. Cross-sectional TEM revealed the formation of the C54 TiSi2 layer between TiB2 and Si and additionally, a second C54 TiSi2 layer was observed within the boride film. Current-voltage measurements of the prepared contact structure showed that it was a Schottky diode with very high leakage current.
Controlling CoSi2 nucleation : the effect of entropy of mixing
Authors: Detavernier C. , Van Meirhaeghe R.L. , Maex K. , Cardon F.
Published: April 2011

It is generally known that nucleation effects strongly influence the CoSi to CoSi2 phase transition. According to classical nucleation theory, the small difference in Gibbs free energy between the CoSi and CoSi2 phase is responsible for the nucleation barrier. Adding elements that are soluble in CoSi and insoluble in CoSi2 will influence the entropy of mixing, and thus change ΔG. In this way, the height of the nucleation barrier may be controlled.

By depositing Fe or Ge (respectively replacing Co and Si in the CoSi lattice) in between the Co and the Si substrate, we were able to increase the nucleation barrier. In the presence of Ni, the nucleation barrier is lowered, and low-resistive disilicide is formed at lower temperatures.
Study of CoSix Spike Leakage for 0.1-um CMOS
Authors: Goto Ken-ichi
Published: April 2011

We have clarified a new leakage mechanism in Co salicide process for the ultra-shallow junctions of 0.1-um CMOS devices and revealed the optimum Co salicide process conditions for minimizing the leakage current. We found that leakage currents generate from many localized points that are randomly distributed in the junction area, and not from the junction edge. We successfully verified our localized leakage model using Monte Carlo simulation. We identified abnormal CoSix spiking growth under the Co silicide film, as being the origin of the localized leakage current. These CoSix spikes grow rapidly only during annealing between 400°C and 450°C when Co2Si phase is formed. These spikes never grow during annealing at over 500°C, and decrease with high temperature annealing over 500°C. A minimum leakage current can be achieved by optimized annealing at between 800°C and 850°C for 30 sec. This is because a trade-off between reducing the CoSix spikes and preventing the Co atom diffusion from Co silicide film to Si substrate, which begins at annealing above 900°C.
The Effect of Wafer Shape on Slurry Film Thickness and Friction Coefficients in Chemical Mechanical Planarization
Authors: Lu Joseph , Coppeta Jonathan , Rogers Chris , Manno Vincent P. , Racz Livia , Philipossian Ara , Moinpour Mansour , Kaufmanc Frank
Published: April 2011

The fluid film thickness and drag during chemical-mechanical polishing are largely dependent on the shape of the wafer polished. In this study we use dual emission laser induced fluorescence to measure the film thickness and a strain gage, mounted on the polishing table, to measure the friction force between the wafer and the pad. All measurements are taken during real polishing processes. The trends indicate that with a convex wafer in contact with the polishing pad, the slurry layer increases with increasing platen speed and decreases with increasing downforce. The drag force decreases with increasing platen speed and increases with increasing downforce. These similarities are observed for both in-situ and ex-situ conditioning. However, these trends are significantly different for the case of a concave wafer in contact with the polishing pad. During ex-situ conditioning the trends are similar as with a convex wafer. However, in-situ conditioning decreases the slurry film layer with increasing platen speed, and increases it with increasing downforce in the case of the concave wafer. The drag force increases with increasing platen speed as well as increasing downforce. Since we are continually polishing, the wafer shape does change over the course of each experiment causing a larger error in repeatability than the measurement error itself. Different wafers are used throughout the experiment and the results are consistent with the variance of the wafer shape. Local pressure measurements on the rotating wafer help explain the variances in fluid film thickness and friction during polishing.
Improvement of Wafer Edge Profile and Cmp Performance Through The Floating Head Design
Authors: Wang Huey-Ming , Moloney Gerry , Stella Mario , Deguzman Sesinando
Published: April 2011

The dependence of IC fabrication on the Chemical Mechanical Planarization (CMP) process increases as the device features go down to 0.25 micron or beyond. Due to the tighter CMP process spec, it is very important to reduce the within wafer non-uniformity (WIWNU%) to achieve higher process yield. The symmetrical increment of linear velocity at wafer edge is not sufficient to change wafer edge profile by breaking the matched speed rule. A better solution is through the change of head design for a fixed platen from the polisher design point of view. This study demonstrates the improvement of the CMP process performance, especially at the wafer edge, from the modification of the floating type polish head. The best WIWNU% from a single air chamber head is about 5.12% at 6-mm edge exclusion (EE). In order to obtain better pad deformation control, the retaining-ring pressure chamber is separated from that of the sub-carrier. The average WIWNU% is about 4% for 3-mm and 5-mm EE from two-pressure-chamber head. Due to the limitation of retaining-ring pressure effect, a third pressure chamber is further added that can be extended the edge control up to 1 inch from the wafer edge. The WIWNU% is about 3.8% at 5-mm edge exclusion with low down forces. The slurry and insert types also show effect on the wafer edge profile. It has been also proven that this three-pressure-chamber head is able to reduce the post-CMP thickness variation from the ILD production wafer, especially at wafer edges. More detailed information and CMP mechanism will be discussed in this paper.
A New Poly-Si CMP Process with Small Erosion for Advanced Trench Isolation Process
Authors: Miyashita Naoto , Uekusa Shin-ichiro , Nishioka Takeshi , Iwami Satoko
Published: April 2011

Chemical-Mechanical Polishing has been revealed as an attractive technique for poly-Si of trench planalization. Major issue of the process integration is pattern erosion after over polishing. A new process with silica slurry containing organic surfactant is reported in this paper. A patterned wafer after conventional CMP process is eroded by over polishing, however, the new process conducts small erosion for wide trenches. The organic surfactant is well known as a inhibitor for the protection of poly-Si from alkaline, and the new slurry shows a large pH dependency of the viscosity. The experimental work has been focused on the viscosity, and the mechanism of the small erosion is discussed. This new process should be useful for recessing poly-Si by CMP, because it keeps the erosion level very low.
Technique of surface control with the Electrolyzed D.I.water for post CMP cleaning
Authors: Shirakashi Mitsuhiko , Itoh Kenya , Katakabe Ichiro , Kamezawa Masayuki , Kihara Sachiko , Tsujimura Manabu , Saitoh Takayuki , Yamada Kaoru , Miyashita Naoto , Kodera Masako , Matsui Yoshitaka
Published: April 2011

Chemical mechanical planarization (CMP) has been widely used for planarization of ILD, STI, plug and wiring processes. Wafer has several surfaces of materials, such as wiring materials, barrier materials, dielectric materials etc., that must be cleaned at the same time. In post metal CMP cleaning processes, in addition to cleaning several surfaces, it is very important that the oxidization level of metal materials, such as wiring, is held and controlled to maintain its resistance. Especially copper, that is began to use for wiring, is very easy to be oxidized. We have confirmed that the Electrolyzed D.I.water is effective in post Cu CMP cleaning for controlling the surface condition of Cu during cleaning and leaving a robust surface after CMP. We describe the Electrolyzed D.I.water system and present some result of analysis of Cu surface by treated with the Electrolyzed D.I.water.
Magnetoresistive properties of 1st AFM Co/Cu multilayers sputtered in an Ar+O2 atmosphere
Authors: Kubinski D. , Parsons M. , Hangas J.
Published: April 2011

Sputter-deposited Co/Cu multilayers at the 1st antiferromagnetic maximum (tCu= 9Å) exhibit large magnetoresistance and low relative hysteresis and are attractive for use in many position sensor applications. Unfortunately, their large magnetoresistance values can be hard to reproduce, perhaps a consequence of the difficulties in growing flat, pin-hole free layers. In this study we demonstrate that their magnetoresistive properties can be improved with the addition O2 to the Ar sputtering gas. A sequence of [Co(15Å)/Cu(9Å)]20 multilayers were made using magnetron sputtering in a 2mTorr Ar+O2 atmosphere, with the O2 concentration ranging from <1 ppm to 10,000 ppm. For films sputtered in our purest Ar, the magnetoresistance was typically less than 10%. Adding small amounts of O2 to the Ar improved the magnetoresistance, and at 1000 ppm O2 concentration it reached an optimal value of ∼45% and was found to be quite reproducible. The largest saturation fields were also achieved at 1000 ppm O2. Increasing the O2 concentration beyond 1000 ppm degraded the magnetoresistance and reduced the saturation fields. Magnetic measurements indicate that the improved magnetoresistance for films sputtered in Ar + O2 is primarily a consequence of more complete antiferromagnetic ordering at low fields. Auger depth profiling revealed no evidence for the O2 incorporation into the films, even for those fabricated in 10,000 ppm O2. Influence of the O2 on the microstructure of the multilayers is discussed.
CVD of Thin Films of Copper and Cobalt from Different Precursors: Growth Kinetics and Microstructure
Authors: Mane Anil , Shalini K. , Devi Anjana , Lakshmi R. , Dharmaprakash M.S. , Paranjape Mandar , Shivashankar S.A.
Published: April 2011

We have investigated the growth of thin films of Cu and Co by CVD using the β-diketonate complexes of the metals, viz., the respective acetylacetonates, dipivaloylmethanates, and ketocarboxylates. Film growth rate was measured as a function of CVD parameters such as substrate temperature and reactor pressure. Film microstructure was examined by optical microscopy, XRD, SEM, and STM. Electrical resistivity was measured as a function of temperature and film thickness. It was found that film microstructure is a function of the molecular structure of the precursor and of the other growth parameters. For example, Cu films from Cu(II) ethylacetoacetate comprise uniform, fine grains which result in bulk electrical conductivity at a thickness as small as 75nm. Though grown under nearly the same conditions, Cu films from Cu(II) dipivaloylmethanate are porous, with faceted, large crystallites. Cobalt films from Co(II) acetylacetonate are x-ray amorphous even at a deposition temperature of 450°C. It is possible, by choosing CVD parameters, to obtain metal films with microstructures appropriate to devices and to structures of very small dimensions.
X-ray Probes of Magnetic Multilayer Structure
Authors: Tanner B.K. , Hase T.P.A. , Fulthorpe B.D. , Clarke J. , Luo G.M. , Halder S.K. , Rozatian A.S.H. , Wilkins S.B.
Published: April 2011

We discuss the application of x-ray scattering and fluorescence to the problem of unravelling the relationship between the structural and magnetic properties of magnetic multilayers. Particular attention is paid to the use of grazing incidence diffuse scatter to determine the compositional gradient, out-of-plane roughness amplitude, in-plane correlation length and fractal parameter of buried interfaces. Anomalous scattering provides information on the local environment of specific atoms and grazing incidence fluorescence is a depth -sensitive probe of chemical composition. We present examples indicating the sensitivity limits and the reproducibility of the techniques, all from multiple layer structures of magnetic metals.
Grain Boundary Curvature in Polycrystalline Metallic Thin Films
Authors: King Alexander H. , Mangat Rakesh , Owusu-Boahen Kwame
Published: April 2011

Well-annealed thin films are typically observed to exhibit mean grain diameters that are approximately equal to the film thickness. The standard explanation of this “sheet thickness effect” is that it results from a balance of grain boundary curvature in two different directions which, in turn, results from pinning at grain boundary grooves. TEM experiments have been performed to assess this model, and it is found that the predicted curvature about axes in the film plane is absent. Alternate explanations of the sheet thickness effect are considered.
Shape Transition of InAs Islands on InP (111)A
Authors: Li Hanxuan , Daniels-Race Theda , Hasan Mohamed-Ali
Published: April 2011

Atomic force microscopy (AFM) reveals that InAs islands grown on InP (111)A, as they grow in size, undergo a shape transition. Below a critical size of around 30 nm, round-shaped quantum dots form, while above this size they grow in the shape of triangles, reflecting the symmetry of the (111) substrates. The edges of triangular islands are aligned along the three equivalent {110} directions of the InP (111) surface. The triangular islands grow laterally much faster than vertically, indicating the aspect ratio decrease of the islands with increasing InAs coverage. Our results provide a better understanding of the self-organization behaviors of InAs on InP (111)A.
Carbon-Induced Ge Islands on Si(001) Grown by LPCVD
Authors: Goryll M. , Vescan L. , Lüth H.
Published: April 2011

The formation of carbon-induced Ge islands has been studied using low-pressure chemical vapour deposition (LPCVD) of Ge on Si(001) at temperatures between 600°C and 700°C. Propane (C3 H8 ) diluted in He was used as a carbon source. The experiments show that the influence of carbon was most significant for deposition at low growth temperature of the Ge island layer. Small-sized islands with a narrow size distribution could be achieved using a carbon adsorption layer. Compared to a sample grown without this layer, the size distribution was significantly smaller. An enhancement of the growth rate of Ge, as seen from Rutherford backscattering spectroscopy (RBS) will be discussed.
Stability of Ensembles of Ge/Si(100) Islands
Authors: Zhang Y. , Drucker Jeff
Published: April 2011

We have investigated the stability of ensembles of Ge/Si(100) islands by annealing at their growth temperature. Islands grown by molecular beam epitaxy at temperatures of 450, 550, 600 and 650°C were annealed for times between 5 and 120 minutes. Small, pure Ge hut clusters, bound by {105} facets appear to be extremely stable structures, surviving the longest anneals with no apparent coarsening. Dome clusters, however, coarsen. Large alloyed hut clusters, apparent in as-grown samples only for growth temperatures greater than 600°C, appear during annealing at 450 and 550°C. During anneals at 550 and 650°C, we observe novel coarsening behavior. Arrays of crystallographically oriented, alloyed hut clusters are formed which result from the dissolution of large, alloyed dome clusters.
The Effect of Indium Surfactant on the Optoelectronic and Structural Properties of MBE Grown Gallium Nitride
Authors: Zhu C.F. , Fong W.K. , Leung B.H. , Cheng C.C. , Surya C. , Sundaravel B. , Luo E.Z. , Xu J.B. , Wilson I.H.
Published: April 2011

Gallium nitride films were grown by rf-plasma assisted molecular beam epitaxy. A small indium flux was used as surfactant during the growth. The optical and electrical properties of the films grown with and without In surfactant were characterized by investigating the photoluminescence (PL), high resolution x-ray diffraction (HRXRD) and low-frequency noise power spectra. The sample grown in the presence of In surfactant showed a suppressed yellow luminescence (YL) compared to the one grown without In surfactant. Significant reduction in the full width at half maximum of the GaN (0002) x-ray diffraction peak, indicating a better film quality, was obtained when In surfactant was used during growth. Atomic force microscopy studies show that the root mean squared surface roughness for films grown with and without the In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. This is attributed to the enhanced 2-dimensional growth by In surfactant. A smaller Hooge parameter was obtained from the low-frequency noise measurement for the sample grown with In surfactant indicating that application of In surfactant led to significant reduction in the trap density of the material.
Real-Time Pseudodielectric Function of Low-Temperature-Grown GaAs
Authors: Gajewski D.A. , Guyer J.E. , Kopanski J.J. , Pellegrino J.G.
Published: April 2011

We present the real-time pseudodielectric function <ε(E)> of low-temperature-grown GaAs (LT-GaAs) thin films during the growth as a function of growth temperature Tg and thickness. We obtained accurate measurements of the real-time <εc(E)> by using in situspectroscopic ellipsometry (SE) in conjunction with active feedback control of the substrate temperature using diffuse reflectance spectroscopy. We show that for epitaxial LT-GaAs layers, the peak in the imaginary pseudodielectric function <ε2(E)> decreases in amplitude and sharpness systematically with decreasing Tg. We also revealed an abrupt change in <εc(E)> near the critical epitaxial thickness hepi, the value of which decreases with decreasing Tg. Above hepi, the LT-GaAs grows polycrystalline (amorphous) above (below) Tg ∼ 190°C. We also simultaneously monitored the surface roughness and crystallinity by using real-time reflection high-energy electron diffraction (RHEED). These results represent progress in obtaining real-time control over the composition and morphology of LT-GaAs
Determine the Three-Dimensional Crystallographic Misorientation in Heterostructures by Selected Area Diffraction (SAD) in TEM
Authors: Guo X. J. , Wen C.-Y. , Huang J. H. , Shih H. C.
Published: April 2011

We proposed a concise and novel scheme to determine the crystallographic misorientation of heteroepitaxial structures. In addition to subtle high-resolution transmission electron microscope images, the information revealed from selected-area diffraction patterns at the interfaces offers another path to determine the angles of misorientations. The principle is to extract the basically three-dimensional misorientation information from a two-dimensional selected-area diffraction pattern through the employment of the Laue circle
Highly Ordered Uniform Quantum Dots Induced by Ion Sputtering
Authors: Kurz H. , Facsko S. , Bobek T. , Dekorsy T.
Published: April 2011

Self-organized hexagonally ordered quantum dot patterns are produced on GaSh (100) and InSb (100) surfaces by low energy Ar+-ion sputtering at normal angle of incidence. The QDs are crystalline, exhibiting narrow size distributions with diameters from 17–80 nm depending on sputter conditions, densely packed with densities as high as 2 × 1011 cm−2. The origin of the QD formation is attributed to the interplay of two surface processes during ion bombardment: ion induced surface roughening, provoked by the curvature dependent sputter yield and balanced by surface diffusive processes. The observed QD patterns obtained at different sputter conditions show that the formation mechanism can be described by the Kuramoto-Sivashinsky equation. The dominant diffusive process emerges to be effective ion induced without any mass transport on the surface, inherent to the sputtering process.
Formation of Gallium Nitride (GaN) Transition Layer by Plasma Immersion Ion Implantation and Rapid Thermal Annealing
Authors: Kwok D. T. K. , Ho A. H. P. , Zeng X. C. , Chan C. , Chu P. K. , Wong S. P.
Published: April 2011

Recent advances in the preparation of gallium nitride (GaN) and related compounds have made possible the production of blue semiconductor laser. Conventional preparation involves growing GaN thin films on lattice-mismatching sapphire using metal-organic chemical vapor deposition (MOCVD). In this article, we describe an alternative method to produce a lattice-matching strained layer in GaAs for subsequent GaN growth by plasma immersion ion implantation (PIII) followed by rapid thermal annealing. Our novel approach uses broad ion impact energy distribution and multiple implant voltages to form a spread-out nitrogen depth profile and an amorphous surface layer. This approach circumvents the retained dose and low nitrogen content problems associated with ion beam implantation at fix energy. Based on our Raman study, the resulting structure after PIII and rapid thermal annealing is strained and contains some GaN possibly in crystal form
Epitaxial Growth of Co3O4 Films by Low Temperature, Low Pressure Chemical Vapor Deposition
Authors: Shalini K. , Mane Anil U. , Lakshmi R. , Shivashankar S.A. , Rajeswari M. , Choopun S.
Published: April 2011

The growth of strongly oriented or epitaxial thin films of metal oxides generally requires relatively high growth temperatures or infusion of energy to the growth surface through means such as ion bombardment. We have grown high quality epitaxial thin films of Co3O4 on different substrates at a temperature as low as 450°C by low-pressure metal-organic chemical vapor deposition (MOCVD) using cobalt(II) acetylacetonate as the precursor. With oxygen as the reactant gas, polycrystalline Co3O4 films are formed on glass and Si(100) in the temperature range 350-550°C. Under similar conditions of growth, highly oriented films of Co3O4 are formed on SrTiO3(100) and LaAlO3(100). The film on LaAlO3(100) grown at 450°C show a rocking curve FWHM of 1.61°, which reduces to 1.32° when it is annealed in oxygen at 725°C. The film on SrTiO3(100) has a FWHM of 0.330 (as deposited) and 0.29° (after annealing at 725°C). The ø-scan analysis shows cube-on-cube epitaxy on both these substrates. The quality of epitaxy on SrTiO3(100) is comparable to the best of the pervoskite-based oxide thin films grown at significantly higher temperatures.
Structure Characterization of Epitaxial Strain Relaxation in YBa2Cu3O7−x/PrBa2Cu3O7 Superlattices
Authors: Varela María , Arias Diego , Sefrioui Zouhair , León Carlos , Ballesteros Carmen , Santamaría Jacobo
Published: April 2011

The structure of c-axis oriented [YBa2Cu3O7−(YBCO) N / PrBa2Cu3O7 (PBCO)M/1000Å superlattices with N ranging between 1 and 12 and M=5 unit cells, grown by high oxygen pressure sputtering on (100) SrTiO3 substrates, is analyzed by x-ray diffraction (XRD) and highresolution transmission electron microscopy (HREM). The XRD spectra refinement shows epitaxial strain for YBCO thickness below 4 unit cells. For larger YBCO layer thickness, stress relaxes and step disorder builds up. HREM observations show sharp and flat interfaces between substrate and superlattice stack. The only observable defects are isolated steps or a-axis oriented domains in relaxed samples. The results of both structural tools are compared.
Epitaxial Growth of Cerium Oxide Buffer Layers on MgO, YSZ and Sapphire Substrates
Authors: Thorley A. , Gnanarajan S. , Katsaros A. , Savvides N.
Published: April 2011

We studied the epitaxial growth of CeO2 thin films deposited onto MgO(100), YSZ(100) and Al2O3(1102 ) (r-plane sapphire) substrates by reactive dc magnetron sputtering of a Ce metal target in an Ar/O2 plasma. The crystalline quality and biaxial alignment of the films was determined using x-ray diffraction techniques (θ-2θ, ω-scans, pole figures, ø-scans). The CeO2/MgO(100) and CeO2/Al2O3(1102) epitaxy was evident at 600°C and developed to nearly perfect biaxial alignment at 850°C with Δø = 5° and 9° respectively. The CeO2/YSZ (100) epitaxy occurred below 300°C while deposition at ≥ 650°C led to single-crystal quality CeO2 films with Δø = 0.2°.
Observation of a New Ordered Structure of Oxygen on W(110)
Authors: Muzzall D. E. , Chiang S.
Published: April 2011

Using both low energy electron diffraction (LEED) and scanning tunneling microscopy (STM), we have made the first observation of a new ordered surface structure of oxygen on W(110). This structure is characterized by the matrix relative to the (1×1) W(110) structure, in which 15 tungsten atoms make up the rectangular unit cell. Based on high resolution STM images, a model for the structure is proposed which includes 6 adsorbed oxygen atoms and has a coverage of 0.40 ML.
A Novel Method for True Work Function Determination of Metal Surfaces by Combined Kelvin Probe and Photoelectric Effect Measurements
Authors: Lägel Bert , Baikie Iain D. , Dirscherl Konrad , Petermann Uwe
Published: April 2011

We have developed a novel method for in-situ measurements of the true work function (ø) of metal surfaces by combined ultra-high vacuum compatible Kelvin Probe and photoelectric effect measurements. The work function is an extremely sensitive parameter of surface condition and can be used to study oxidation and thin film growth on metal surfaces. For example, the increase in ø due to oxidation of polycrystalline rhenium is 1.9eV.

The Kelvin Probe measures local work function differences between a conducting sample and a reference tip in a non-contact, truly non-invasive way over a wide temperature range. However, it is an inherently relative technique and does not provide an absolute work function if the work function of the tip (øtip) is unknown.

We present a novel approach to measure øtip with the Kelvin Probe via the photoelectric effect, using a Gd foil as the photoelectron source, hereby combining the advantages of both methods to provide the absolute work function of the sample surface. We demonstrate the application of the technique by in-situ work function measurements during oxidation of polycrystalline rhenium. The extended Kelvin Probe method therefore has potential applications as a characterisation tool for thin film epitaxy and work function engineering of surfaces.
Isothermal I-V Characteristics of 4H-SiC p-n Diodes with Low Series Differential Resistivity at Avalanche Breakdown
Authors: Vassilevski Konstantin V. , Zekentes Konstantinos , Zorenko Alexandr V. , Romanov Leonid P.
Published: April 2011

4H-SiC p+-n-n+ diodes of low series resistivity were fabricated and packaged. The diodes exhibited a homogeneous avalanche breakdown at voltage Ub=260V. These diodes were capable to dissipate a pulsed power density of 7.4 MW/cm2 at avalanche current. Isothermal I-V characteristics of fabricated diodes were measured at forward bias and at avalanche breakdown. An experimental determination of the electron saturated drift velocity along the c-axis in 4H-SiC was performed for the first time. It was found to be 7.7×106cm/s at room temperature.
Temperature Dependence and Current Transport Mechanisms in AlxGa1−xN Schottky Rectifiers
Authors: Zhang A.P. , Cao X.A. , Dang G. , Ren F. , Han J. , Chyi J.-I. , Lee C.-M. , Chuo C.-C. , Nee T.E.
Published: April 2011

GaN and Al0.25Ga0.75N lateral Schottky rectifiers were fabricated either with (GaN) or without (AlGaN) edge termination. The reverse breakdown voltage VB (3.1 kV for GaN with both p+ guard rings and metal overlap edge terminations; 4.3 kV for Al0.25Ga0.75N without edge termination) displayed a negative temperature coefficient of −6.0 ± 0.4 V·K−1 for both types of rectifiers. The reverse current originated from contact periphery leakage at moderate bias, while the forward turn-on voltage at a current density of 100A·Cm−2 was ∼5 V for GaN and ∼7.5 V for AlGaN. The on-state resistances, RON, were 0.13 Δcm2 for GaN and 2.3 Δcm2 for AlGaN, producing figures-or-merit (VRB)2/RON of 73.9 and 8.2 MW.Cm−2, respectively. The activation energy of the reverse leakage was 0.13 eV at moderate bias.
Design and Performance of Nitride-based UV LEDs
Authors: Crawford M. H. , Han J. , Shul R. J. , Banas M. A. , Figiel J. J. , Zhang L.
Published: April 2011

We overview several of the challenges in achieving high efficiency nitride-based UV (< 400 nm) LEDs. The issue of optical efficiency is presented through temperature-dependent photoluminescence studies of various UV active regions. These studies demonstrate enhanced optical efficiencies for active regions with In-containing alloys ( InGaN, AlInGaN). We compare the performance of two distinct UV LED structures. GaN/AlGaN quantum well LEDs with λ < 360 nm emission have demonstrated output powers > 0.1 mW, but present designs suffer from internal absorption effects. InGaN/AlInGaN quantum well LEDs with 370 nm< λ < 390 nm emission and > 1 mW output power are also presented.
DLTS study of 3C-SiC grown on Si using hexamethyldisilane
Authors: Kato M. , Ichimura M. , Arai E. , Masuda Y. , Chen Y. , Nishino S. , Tokuda Y.
Published: April 2011

n-type 3C-SiC was heteroepitaxially grown on n-type Si(100) substrates using HMDS (hexamethyldisilane) and characterized by DLTS (deep level transient spectroscopy) measurements. In order to investigate relationship of defect density with epilayer thickness, epilayers with various thicknesses were grown. Relatively thin (<1.0μm thick) epilayers were found to contain defects with energy levels distributed in a wide energy range, while relatively thick (>2.2μm thick) epilayers contain a defect with an activation energy of 0.25eV. This defect level is slightly shallower than that in 3C-SiC grown by SiH4 and C3H8 (∼0.3eV).
Non-Contact Characterization of Recombination Processes in 4H-SiC
Authors: Matocha K. , Chow T.P. , Gutmann R.J.
Published: April 2011

Carrier decay transients in 4H-SiC n-type and p-type epilayers have been charac-terized using a non-destructive, non-contact microwave photoconductivity technique. Decay transients show a two-stage exponential decay with first decay constants as high as 400 ns in 10 νm p-type epilayers. The second decay constant increases with temperature and is dominated by interface recombination.
Lateral and Vertical Growth Study in the Initial Stages of GaN Growth on Sapphire with ZnO Buffer Layers by Hydride Vapor Phase Epitaxy
Authors: Gu Shulin , Zhang Rong , Zhang Ling , Kuech T. F.
Published: April 2011

The initial stage of hydride vapor phase epitaxy GaN growth on ZnO-buffered sapphire is reported. A high supersaturation in the growth ambient was used to favor a rapid initial growth on the substrate. A subsequent step with high lateral growth rate was chosen to promote coalescence of the initial islands and provide optimal material properties. The specific mole fractions of the GaCl and NH3 control these vertical and lateral growth rates. The use of a two- step growth process in the GaN growth has led to improved and controlled morphology and high quality GaN materials have then been grown on sapphire substrate with and without ZnO buffer layers.
Achievements and Characterizations of GaN With Ga-Polarity in Radio-Frequency Plasma-Assisted Molecular Beam Epitaxy
Authors: Shen X.Q. , Ide T. , Cho S.H. , Shimizu M. , Hara S. , Okumura H.
Published: April 2011

Lattice polarities and film qualities of GaN grown by rf-MBE were investigated concentrating on the use of different buffer layer processes at the initial stage. Direct clarifying by coaxial impact collision ion scattering spectra technique, together with RHEED and chemical wet etching, were applied to identify the lattice polarity of GaN films. XRD rocking curve and photoluminescence results showed that the qualities of GaN films with Ga-polarity were dramatic improved compared to those with N-polarity. Hall effect measurement results indicated that the mobility of the Ga-face film was increased to one order higher (568 cm2/Vs in maximum at room temperature) than that of N-face one.
Short gate length AlGaN/GaN HEMTs
Authors: Breitschädel O. , Kley L. , Gräbeldinger H. , Kuhn B. , Scholz F. , Schweizer H.
Published: April 2011

We report on our progress on the fabrication of AlGaN/GaN HEMTs with extremely short gate length. AlGaN/GaN HEMTs with different gate length from 6 νm down to 60nm were fabricated to investigate DC- and high frequency behavior as well as short channel effects. We have found that the transistors with gates in the 100 nm range can be improved in the device performance with respect to transconductance and high frequency but shows also short channel effects as the loss of saturation in the output characteristics and a strong dependency of the threshold voltage on the gate length.
Pendeo Epitaxy Of 3C-SiC on Si Substrates
Authors: Carter G.E. , Zheleva T. , Melnychuck G. , Geil B. , Jones K. , Saddow S. E.
Published: April 2011

Pendeo Epitaxy is a type of Lateral Epitaxial Overgrowth (LEO) that instead of using a dielectric buffer layer, uses an etched substrate to grow laterally without an interface layer. We report the first successful growth of 3C-SiC on Si using Pendeo epitaxy. Rectangular stripes of 3C-SiC on (100) Si substrates were fabricated, along both the [110] and [100] directions. Pendeo epi was only observed for columns parallel to [001], indicating a preferred growth facet for Pendeo epi of 3C-SiC on Si. SEM and TEM investigations were performed to assess the material quality of the Pendeo 3C-SiC material. Films were grown for 60 min at 1310°C and film coalescence was achieved without evidence of voids where the growth fronts joined. TEM data indicate not only the growth of vertical and lateral 3C-SiC on the 3C-SiC seed layer but direct nucleation of 3C-SiC on the exposed Si columns side wall and trench bottom, despite the lack of a carbonization procedure. The quality of the Pendeo 3C-SiC film appears to be of high quality indicating that Pendeo epi of 3C-SiC on low-cost, large-diameter Si substrates may prove to be a cost effective way to grow device-grade SiC layers on Si substrates for device applications.
Microstructure and Thermal Stability of Transition Metal Nitrides and Borides on GaN
Authors: Jasiński Jacek , Kamińska Eliana , Piotrowska Anna , Barcz Adam , Zieliński Marcin
Published: April 2011

Microstructure and thermal stability of ZrN/ZrB2 bilayer deposited on GaN have been studied using transmission electron microscopy methods (TEM) and secondary ion mass spectrometry (SIMS). It has been demonstrated that annealing of the contact structure at 1100°C in N2 atmosphere does not lead to any observable metal/semiconductor interaction. In contrast, a failure of the integrity of ZrN/ZrB2 metallization at 800°C, when the heat treatment is performed in O2 ambient has been observed.
Hall effect measurements at low temperature of arsenic implanted into 4H-silicon carbide
Authors: Senzaki J. , Fukuda K. , Ishida Y. , Tanaka Y. , Tanoue H. , Kobayashi N. , Tanaka T. , Arai K.
Published: April 2011

The arsenic dose dependence of electrical properties for implanted samples at 500°C and subsequently annealed at 1600°C for 30min has been investigated to derivate the activation energies of the arsenic donors in silicon carbide. Hall effect measurements were performed between 20K and 773K. Hall carrier concentration of implanted sample with high dose of 7×1015 cm−2 is independence of temperature, which indicates the formation of implanted layer with metallic conduction. For the sample with low dose of 1×1014 cm−2, the experimental Hall mobility varies directly as T3/2 below 80K and as T−3/2 above 150K. The activation energies of arsenic donors determined from the implanted sample with low dose using a least-squares fit of the charge neutrality equation are 66.8 meV for hexagonal site and 127.0 meV for cubic site, respectively.
Hydrothermal Preparation of Ba(Ti,Zr)O3 Thin Films From Ti-Zr Metallic Alloys on Silicon Substrate
Authors: Xia Chang-Tai , Fuenzalida V. M. , Zarate R. A.
Published: April 2011

Ba(Ti,Zr)O3 thin films were grown hydrothermally on silicon substrates coated with sputtered a Ti-34 at.%Zr metallic alloy thin film. To ensure the formation of Ba(Ti,Zr)O3 under the hydrothermal conditions at 150°C, the concentration of the Ba(OH)2 had to be greater than 0.25 M. Preliminary capacitance measurement revealed a dielectric constant of 200 in Ba(Ti,Zr)O3 films of approximately 320 nm. The formation mechanism is discussed.