bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Preparation Technique Termed “Chemical Annealing” to make a Rigid and Stable Si-Network
Authors: Shirai Hajime , Hanna Jun-Ichi , Shimizu Isamu
Published: March 2011

A novel preparation technique termed “Chemical Annealing (CA)” was developed with aim of making a stable and rigid structure of Si-network. The a-Si:H films were made by the alternate deposition of several tens angstrom thick a-Si:H and the treatment with atomic hydrogen or excited novel gases such as Ar* and He*. Hydrogen contents (CH) and optical gap (Eg) in the film prepared by this tecnique were able to reduced by CH of 1.5at%, and Eg of 1.5eV, respectively at substrate temperature:300C. All of them exhibited high photoconductivities in the level of 10-5 10-4 S/cm under illumination of 100mW/cm2. In the films with CH of 3at% or less, in particular, marked improvement was confirmed in the stability after light soaking. In addition, the time-of-flight measurement revealed a non-dispersive transport and a significant enhancement in the drift mobility of holes up to 0.2cmm2/Vs at room temperature in the film with CH : 5at% and Eg:1.65eV prepared at 300C. Advantages of the CA process are summarized together with the discussion of role of atomic hydrogen, excited novel gases such as Ar* and He* in the growing surface.
Film Deposition Process in Pulse Discharge CVD
Authors: Yoshida T. , Fujisawa H. , Hokaya T. , Ichikawa Y. , Sakai H.
Published: March 2011

To understand the deposition process of pulse discharge (PD) CVD, we studied spatial distribution and decay of plasma parameters and those of SiH LIF signals. In addition, we studied film properties of a-SiC:H and a-SiGe:H deposited by the PD-CVD. It was found that the quality of p-type a-SiC:H films deposited by the PD-CVD from SiH4+CH4+B3 was better than those of conventional p-type a-SiC:H films. The p-type a-SiC:H films were applied to the p-layer of p-i-n a-Si solar cells, and a conversion efficiency of 12. 3% was obtained for a 1cm2.
Deposition of Device Quality, Low H Content a-Si:H by the Hot Wire Technique
Authors: Mahan A. H. , Nelson B. P. , Salamon S. , Crandall R. S.
Published: March 2011

We report measurements of the Urbach edge, optical bandgap, and ambipolar diffusion length on a series of hydrogenated amorphous silicon (a-Si:H) films deposited by hot-wire-assisted chemical vapor deposition (HW). We compare the properties of these films to those of a series of a-Si:H films deposited by the traditional radio frequency (rf) glow discharge (GD) technique, where we varied the substrate temperature to change the bonded H content (CH). We show for the first time that, as CH is decreased below the value traditionally associated with device quality GD a-Si:H (∼10 at.%), the electronic properties of the GD films deteriorate in the traditional manner while those for the HW samples remain device quality. Properties of these low CH HW samples will be presented and compared to those of GD films containing comparable CH. Because several indications exist that the structure of the HW films is different than that of the GD films, Raman and Small Angle X-Ray Scattering (SAXS) measurements are presented to illustrate structural differences.
Correlation Between Freeze-In Temperature of Defect Density and Hydrogen Concentration in a-Si:H
Authors: Xu X. , Isomura M. , Yoon J. H. , Wagner S. , Abelson J. R.
Published: March 2011

We measured the freeze-in temperature of the dangling-bond density in a-Si:H in nine samples with hydrogen concentrations ranging from 7.0 to 31 at.%. The measurements were made by determining the defect density of samples quenched from successively higher temperature. We determined the defect densities with the constant photoconductivity method. The freeze-in temperature is 211±10 °C, and is independent of hydrogen concentration.
Amorphous Silicon Selenium Alloy Film Deposited Under Hydrogen Dilution
Authors: He Muzhi , Lin Guang H. , Bockris J. O'M.
Published: March 2011

Amorphous silicon selenium alloy films were prepared by plasma enhanced chemical vapor deposition with hydrogen dilution. The flow rate ratio of hydrogen to silane was about 8:1. Amorphous silicon selenium alloy was found to have an optical bandgap ranging from 1.7 eV to 2.0 eV depending on the selenium concentration in the films. The light to dark conductivity ratios of the alloy films are ∼ 104. The optical and electrical properties, Urbach tail energy and sub-bandgap photo response spectroscopy of the alloy film were investigated. The film quality of the alloy deposited with hydrogen dilution is greatly improved comparing to that of the alloy film deposited without hydrogen dilution. The electron spin resonance experiment shows that selenium atom is a good dangling bond terminator.
Deposition of Fluorinated Silicon Nitride using Plasma Enhanced Chemical Vapor Deposition Technique
Authors: Khan Ibrahim , Naseem H. A. , Ang S. S. , Brown W. D.
Published: March 2011

High hydrogen content of ammonia/silane deposited silicon nitride films has been linked to instability in electronic devices such as MOSFET's MNOSFET's and TFT's. Fluorine has been proposed to help reduce the hydrogen content of these films. In this work, NF3 was used as a fluorinating agent. Optical and electrical properties were studied as a function of NF3 flow rate. A maximum optical gap of 5.3 eV was obtained with NF3 as compared to 3.2 eV without. The dielectric strength improved from 4 to 10 MV/cm with the addition of NF3. FTIR data show that the Si-N peak shifts to higher wave numbers and the Si-H peak drops below the detection limit with the addition of NF3. Also, the broad Si-N peak at 850 cm-1 is composed of many individual peaks which become discernable when a stainless steel screen is placed in front of the substrate. As the NF3 concentration is increased, a new peak at 1030–1060 cm-1 appears. This may be associated with a N-F vibration (1030 cm-1).
Effects of Hydrogen Radical Annealing on Electrical Properties of Amorphous Silicon
Authors: Jang Jin , Kim Tae Gon , Koh Song Ok , Song Hyon Kyun , Park Kyu Chang , Chung Moon Hyun , Kim Sung Chul
Published: March 2011

We studied the layer by layer deposition technique of a-Si:H film, where the hydrogen radicals are exposed between the deposition of each layer. The effects of each layer thickness and hydrogen radical exposure time on the electrical and optical properties were studied. With the decrease of the each layer thickness, more hydrogen is involved in the network if the structure is still amorphous, but the hydrogen content is very small for microcrystal Si formed by long exposure to hydrogen radicals in between the depositions of thin layers.
a-SiC:H Doped with Reactive Gases and with Ion Implantation
Authors: Demichelis F. , Pirri C. F. , Tresso E. , Della Mea G. , Rigato V. , Rava P. , Amato G.
Published: March 2011

Boron doped a-SiC:H samples have been obtained both by gas phase doping during film growth and by using ion implantation. All the implanted samples were annealed under vacuum to remove the damage introduced by ion implantation and to produce a dopant diffusion. Physical properties deduced by optical, electrical and structural characterization of the two sets of samples have been compared. Ion implantation technique allows a better control of the dopant dose but increases the compositional disorder and the obtained conductivity values are one order of magnitude lower than those of gas doped samples.
Etching Properties of Hydrogenated Amorphous Silicon
Authors: Tsuo Y. S. , Xu Y. , Baker D. W. , Deb S.K
Published: March 2011

We have studied wet-chemical and dry etching properties of doped and undoped hydrogenated amorphous silicon (a-Si:H) films with bonded hydrogen content varying from 0 to 20 at.%. Etching processes studied include (1) wet-chemical etching using solutions of KOH, isopropyl alcohol (IPA), and H2O, (2) hydrogen plasma etching, and (3) XeF2 vapor etching.
The Slope Etching of a-Si:H Film using CF4 + O2 Gas
Authors: Sung Kang Hyun , Park B. W. , Kim J. J. , Kim C. Y. , Choi J. I. , Bae H. K. , Park Y. H. , Hur C. W.
Published: March 2011

The slope etching technology of hydrogenated amorphous silicon film (a-Si:H) has been very useful for its devices; thin film transistor, contact image sensor and other large area electronic components. To obtain a good step coverage slope etching was performed by RIE using CF4 gas and optimum amount of O2 gas after modification of photoresist(PR) patterns by thermal treatment. In this experiment, primary factors were

1) thermal treatment temperature and time of PR.

2) CF4 gas flow rate, etch rate of a-Si:H film and ash rate of PR in proportion to O2 gas flow rate.

As a result, the slope angle of 11° was obtained when CF4 gas flow rate was 46 SCCM, O2 gas flow rate was 7 SCCM and thermal treatment temperature and time was 140°C and 30 minutes respectively.
Propagating Shear Waves in Liquid Pentachlorobiphenyl
Authors: Bezot P. , Hesse-Bezot C. , Pruzan P.
Published: March 2011

A depolarized light scattering study of pressure supercooled Pentachlorobiphenyl is presented. Fram the analysis of propa gative depolarized shear doublets, the shear modulus G∞ at infinite frequency is measured for various temperatures. The pressure range is from atmospheric pressure to pressures whem the liquid is in a glassy state : G∞ (p) is found to vary linearly at each measured temperature.
Fatigue Life Analysis and Tensile Overload Effects with High Strength Steel Notched Specimens
Authors: Underwood J. H.
Published: March 2011

Pressure vessels often have notches or other stress concentrations present. Considering further that pressure vessels are nearly always subjected to some cyclic loading, fatigue cracking at notches is an important problem. The objective here is to describe some fatigue life testing and analysis which was performed with notched specimens in order to determine the effects of notch overload on fatigue life of pressure vessels.
Fatigue Crack Growth in Autofrettaged Thick-Walled High Pressure Tube Material
Authors: Stacey A. , Webster G.A.
Published: March 2011

Fatigue crack growth studies have been made on C-shaped and ring specimens taken from as-received and autofrettaged 4333 M4 thick-walled tubing. The ring specimen was chosen because it enables cracks to be propagated through the same residual stress distribution as that present in the tubing. It is shown that the reduced crack growth rates measured close to the bore in autofrettaged tubing can be attributed to the presence of compressive residual stresses there and can be explained in terms of the contribution of these stresses to the stress intensity factor range applied.
On the Determination of Stress Intensity Factors for Cracked Thick Cylinders
Authors: Parker A P , Andrasic C P
Published: March 2011

The authors have previously published stress intensity (K) solutions for singly and multiply cracked thick cylinders with internal pressure and autofrettage stress fields. In this paper a method of obtaining K values for intermediate radii ratios is proposed. The method involves an approximate superposition procedure which models the removal (or addition) of cylinder material and is based on the nearest available radii ratio. The procedure is exact for very short crack lengths, and generally gives answers within 5% at crack lengths up to 20% of wall thickness (wherein most of the fatigue lifetime is expended) after removal of 20% of the wall thickness. A simple expression is given for the anticipated change in fatigue lifetime resulting from material removal.
Two-Parameter Semiconductor Transducer for Measuring High-Pressure and Temperature
Authors: Wlodarski W.
Published: March 2011

The paper presents the results of studies on the application of semiconductor p-n junctions as two-parameter transducers of high-hydrostatic pressure and of temperature in the area of the pressure. A block diagram of an electronic circuit intended to collaborate with a two-parameter transducer has been given.
Design of Blind End Closures for High Pressure Vessels
Authors: Chaaban A. , Leung K. , Pick R. J. , Burns D. J.
Published: March 2011

The finite element method has been used to investigate the stress fields in blind end closures of thick-walled pressure vessels. A design curve for choosing end thickness has been developed by elastic analysis of a range of geometries and by elastic-plastic analysis of several geometries. The effects of inner corner radius of the blind end and a small
central hole in the end are discussed.
The Growth Rate of Semi-Elliptic Fatigue Cracks in Thick-Walled Cylinders
Authors: Lees W. A. , Crofton P. S. J.
Published: March 2011

The rate of growth of fatigue cracks originating at the bore and at the outside surface of thick-walled low alloy steel cylinders has been measured for cylinders subjected to fluctuating internal pressure.

Analysis of the results using linear elastic fracture mechanics relationships shows that crack growth rates found in air adequately predict the behaviour of cracks growing from the outside surface of a cylinder.

Fatigue cracks growing from the bore of a cylinder subjected to fluctuating internal pressure are found to advance at a consistently higher rate than that predicted from crack growth rate tests carried out in air.

These findings are discussed in relation to the proposed adoption of existent strain-life fatigue data for pressure vessel design.
Effect of Hydrostatic Pressure on Geometry of Slip in Silicon Iron Single Crystals
Authors: Dobromyslov A.V. , Dolgikh G.V. , Talutz N.I. , Shmatov V.T. , Beresnev B. I.
Published: March 2011

The effect of the pressure 550MPa on the choice of the acting slip plane in the single crystals of Fe−2,9%Si was studied. It was established that the presence of pressure resulted in the increase of the slip asymmetry. The effect of pressure is attributed to the action of normal stresses and to the special structure of screw dislocations.
Study on Taylor Criterion for Complete Fracture of the Casing Packed with High Explosive
Authors: Danian Chen , Desheng Wang
Published: March 2011

The criterion for complete fracture of the casing by detonation of packed high explosive was first presented by G.I.Taylor. Thereafter Taylor criterion has been reviewed and extended by many authors. This paper is intended to present a clear understanding of the fragmentation mechanism, and to study the influence of stress waves on the fracture of the casing using finite difference calculation of elastic-plastic flow. The results show that Taylor criterion is correct to a certain extent.
Equation of State of Helium and Polybutene and Raman Spectrum of Water at High Shock Pressures and Temperatures
Authors: Nellis W. J. , Holmes N. C. , Mitchell A. C. , Trainor R. J. , Boslough M. B. , Ree F. H. , Walrafen G. E.
Published: March 2011

Liquid helium was shock-compressed in Hugoniot equation-of-state measurements at pressures of 1.2 and 16 GPa (12 and 160 kbar) using a two-stage light-gas gun [1]. Specimens were initially at a temperature of 4.3 K and a molar volume of 32 cm3/mole. Specimen holders were a refinement of the cryogenic targets used for liquid H2 and D2 experiments [2]. The data are in good agreement with the published theoretical prediction of Young, et al.[3] The high shock temperatures test the repulsive pair potential to an interatomic spacing approaching 1 Å, which is comparable to a solid volume at a temperature of 0 K of about 0.5 cm3/mole.
Measurement of Liquid Compressibility in a Gasketed Diamond Anvil Cell by a Modified Piston-Displacement Method
Authors: Chang-Sheng Zha
Published: March 2011

The compressibility of liquids was measured in a gasketed diamond anvil cell using a modified piston displacement method. A pair of metal markers was fixed on the diamonds. The gasket thickness at different pressures was measured by monitoring the distance change between the markers using a micrometer microscope. The area of the gasket hole was measured by means of microphotography. Then the product of the average area and thickness of the gasket hole determined the sample volume. Using this method we obtained the compressibility of a 4:1 v/v methanol-ethanol liquid mixture at hydrostatic pressures up to 8 GPa and found that the liquid volume at 8 GPa decreases to 51.5% of the initial volume. By the least-squares method, we fitted the experimental data to the Tait equation and obtained C=0.4055, B=0.5436 GPa. The relative error is estimated to be about 1.7%. This simple and convenient method could significantly extend the pressure range of liquid compressibility measurements.
Surface Accumulation of Boron During Si Molecular Beam Epitaxy
Authors: Parry C. P. , Kubiak R. A. A. , Newstead S. M. , Parker E. H. C. , Whall T. E.
Published: March 2011

A high temperature, elemental boron evaporation source has been used for the study of the boron doping behaviour in Si as a function of growth temperature and doping level. Significant profile smearing of boron at doping levels below 5×1018cm−3 is observed. Profile smearing is more severe in higher doped samples for growth temperatures above 600°C at a growth rate of 0.28 nms−1. This is interpreted as arising from the formation of a surface phase of boron at higher doping levels. The marked improvement in profile abruptness at low temperatures suggests significant benefits associated with the use of an elemental boron source for the growth of high resolution Si/Si1−xGex device structures.
X-Ray Characterisation of Boron Delta Layers in Si and SiGe
Authors: Powell A. R. , Kubiak R. A. , Whall T. E. , Parker E. H. C. , Bowen D. K.
Published: March 2011

We demonstrate the growth, by MBE, of high sheet density B delta layers in both Si and SiGe epitaxial layers. Double Crystal X-Ray Diffraction is shown to be a non-destructive method of characterising the width of very narrow (0.3 nm) delta layers and the sheet density of the activated B. The ability of delta layers to withstand high temperature anneals is considered and it is found that a 750 °C anneal for 1 hour broadens the delta layer to beyond the width required for carrier confinement.
MBE Alloy Clustering Kinetics - A Stochastic Model Study
Authors: Venkatasubramanian R. , Khoie Rahim
Published: March 2011

A theoretical study of alloy clustering in an hypothetical diamond cubic alloy, 00.560.5 in which thermodynamics favors phase separation is performed based on a master equation approach. The a-b atom pair interaction is assumed weaker and repulsive (-0.25 eV). It is shown that below 375°C, due to negligible surface migration, there is no clustering of the alloy, but, the surface roughness is very large. In the intermediate temperature range of 300 – 625°C, with increasing temperature, surface migration increases, resulting in more clustering and decreased surface roughness. Above 500°C, due to very high surface migration, complete phase separation and smooth surface result. It is shown that the conventional MBE growth techniques are incompatible with the growth of good quality heterostructures which consist of alloys having large poistive enthalpy of mixing.
Low Temperature In-Situ Processing for Si-MBE
Authors: Ramm Juergen , Beck Eugen , Zueger Albert
Published: March 2011

A basic process sequence for low temperature in-situ processing of metal-insulator-semiconductor (MIS) structures in an ultra-high vacuum (UHV) multichamber system is presented. It includes conditioning of the process chamber by plasma heating, in-situ cleaning of silicon wafers, and conventional silicon molecular beam epitaxy (Si-MBE). The in-situ cleaning is achieved by an argon/hydrogen plasma treatment of the wafer surface at temperatures well below 400° C. The native oxide as well as carbon compounds are removed from the silicon surface. Etch rates for SiO2 are determined for various plasma parameters. Without additional cleaning procedures, silicon films are deposited in another process step using a quadrupole mass spectrometer controlled electron beam evaporator. Epitaxial films are obtained for substrate temperatures as low as 500°C on (100) and 600°C on (111) silicon for deposition rates of 0.05 nm/s.
Structural Characterization of Short-Period SimGEn Superlattices by Transmission Electron Microscopy and X-Ray Diffraction
Authors: Jäger W. , Leifer K. , Ehrhart P. , Kasper E. , Kibbel H.
Published: March 2011

High resolution and analytical transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize short-period strained-layer Sim-Gen superlattices ( m monolayers Si, n monolayers Ge, total number of periods N≤ 145, total thickness ≃ 200 nm). The superlattices were grown by low-temperature molecular beam epitaxy (T = 300–400°C) on different SiGe alloy buffer layers on Si (100)substrates. The combination of these two methods shows that detailed informations can be obtained about superlattice periodicity, interface roughness, strain, and average composition.
Very Thick Coherently Strained GexSi1−x Layers Grown in a Narrow Temperature Window
Authors: Chern C. H. , Wang K. L. , Bai G. , Nicolet M. -A.
Published: March 2011

Strain relaxation of GexSi1−x layers is studied as a function of growth temperature. Extremely thick coherently strained layers whose thicknesses exceed more than fifty times of the critical thicknesses predicted by Matthews and Blakeslee's model were successfully grown by MBE. There exits a narrow temperature window from 310 °C to 350 °C for growing this kind of high quality thick strained layers. Below this temperature window, the layers are poor in quality as indicated from RHEED patterns. Above this window, the strain of the layers relaxes very fast accompanied with a high density of misfit dislocations as the growth temperature increases. Moreover, for samples grown in this temperature window, the strain relaxation shows a dependence of the residual gas pressure, which has never been reported before.
Strain-Free GexSi1−x Layers with Low Threading Dislocation Densities Grown on Si Substrates
Authors: Fitzgerald E. A. , Xie Y. H. , Green M. L. , Brasen D. , Kortan A. R. , Mii Y. J. , Michel J. , Weir B. E. , Feldman L. C. , Kuo J. M.
Published: March 2011

We have grown linearly compositionally graded GexSi1−x structures at high temperatures (700–900°C) on Si substrates to form a surface which resembles a GexSi1−x substrate. We have obtained completely relaxed structures with x≤0.50 and threading dislocation densities in the 105cm−2 - 106cm−2 range. Because of the very low threading dislocation densities, the structures appear dislocation free in conventional transmission electron microscopy (TEM) cross-section and plan view. Employing the electron beam induced current technique (EBIC), we were able to consistently measure these low threading dislocation densities. A direct comparison of two x=0.35 films, one graded in Ge content and one uniform in Ge content, shows that compositional grading decreases the dislocation density by a factor of 100–1000. These. higher quality graded buffers have been used as templates for the subsequent growth of InGaP light emitting diodes (LED) and GexSi1−x/Si two-dimensional electron gas (2DEG) structures. Room temperature operation of orange-red LEDs were obtained at current densities of =600A/cm, and mobilities as high as 96,000 cm2/V-s were achieved at 4.2K in the 2DEG structures.
Kinetics of Ge Segregation in the Presence of Sb During Molecular Beam Epitaxy
Authors: Fukatsu S. , Fujita K. , Yaguchi H. , Shiraki Y. , Ito R.
Published: March 2011

Kinetics of Ge segregation during molecular beam epitaxial growth is described. It is shown that the Ge segregation is self-limited in Si epitaxial overlayers due to a high concentration effect when the Ge concentration exceeds 0.01 monolayer (ML). As a result, segregation profiles of Ge are found to decay non-exponentially in the growth direction. This unusual Ge segregation was found to be suppressed with an adlayer of strong segregant, Sb, during the kinetic MBE growth. We develop a novel scheme to realize sharp Si/Ge interfaces with strong segregante. Lower limit of the effective amount of Sb for this was found to be 0.75 ML.
Characterization of Si1−xGex/Si Heterostructures Using Optically-Detected Magnetic Resonance
Authors: Kennedy T. A. , Glaser E. R. , Trombetta J. M. , Wang K. L. , Chern C. H. , Arbet-Engels V.
Published: March 2011

Si1−xGex/Si heterostructures with varying layer-thicknesses have been characterized using photoluminescence and magnetic resonance detected on photoluminescence. Three of the four samples studied exhibit sharp photoluminescence bands at different energies. For a 120 Å Si/40 Å Si1−xGex heterostructure, magnetic resonance of an electron in the Si and of a hole in the Sil. xGex layers were observed. These results indicate cross-interface, or Type II, excitonic recombination. Further, anisotropie magnetic resonance spectra indicate the presence of dangling-bonds defects in the heterostructures.
Growth of Si1−xGex, Strained Layers Using Atmospheric-Pressure CVD
Authors: Namavar F. , Manke J. M. , Kvam E. P. , Sanfacon M. M. , Perry C. H. , Kalkhoran N. M.
Published: March 2011

The objective of this paper is to demonstrate the epitaxial growth of SiGe strained layers using atmospheric-pressure chemical vapor deposition (APCVD). We have grown SiGe layers with various thicknesses and Ge concentrations at temperatures ranging from 800–1000°C. The samples were studied using a variety of methods, including transmission electron microscopy (TEM), high resolution X-ray diffraction (HRXRD) and Raman spectroscopy (RS). Both HRXRD and RS results indicate that samples with about 10% Ge and a thickness of about 1000 Å are almost fully strained. TEM analyses of these samples indicate a film defect density less than 105/cm2. SIMS results indicate that the oxygen concentration in the epitaxial layers is lower than that found in CZ substrates.

Our analyses also indicate that as-grown epitaxial Ge layers several microns thick have a defect density less than 107/cm2. The relatively low defect density in both SiGe and Ge layers grown on Si has been attributed to far higher dislocation glide velocity at the relatively elevated growth temperatures employed in CVD and to very good growth cleanliness.
Fabrication of Bond and Etch Back Silicon on Insulator Using SiGe-MBE and Selective Etching Techniques
Authors: Godbey D. , Palkuti L. , Leonov P. , Krist A. , Wang J. , Twigg M. , Hughes H. , Hobart K.
Published: March 2011

Undoped thin layer silicon on insulator has been fabricated using wafer bonding and selective etching techniques using an MBE grown Si0.7Ge0.3 layer as an etch stop. Defect free, undoped 200–350 nm silicon layers are routinely fabricated using this procedure. A new selective silicon-germanium etch has been developed that significantly improves the ease of fabrication of the BESOI material.
Si/Ge Superlattices for Optical Applications: Possibilities, Problems, and Prospects
Authors: Zachai R.
Published: March 2011

Si/Ge superlattices offer the possibility to study the influence of various effects on the electronic band structure. Strain, quantization, zone folding, and wave vector mixing effects are expected to create novel optical properties in these Si-based multilayer structures. New optical transitions were observed by various experimental methods like photoluminescence and modulation spectro-scopy. In this article we will review the present state of knowledge of the optical properties of short period strained layer Si/Ge superlattices and discuss the problems and prospects for optical applications.
Well-Resolved Band-Edge Photoluminescence from Strained Si1–xGex Layers Grown by Rapid Thermal Chemical Vapor Deposition
Authors: Sturm J. C. , Schwartz P. V. , Manoharan H. , Mi Q. , Lenchyshyn L. C. , Thewalt M. L. W. , Rowell N. L. , Noël J. -P. , Houghton D. C.
Published: March 2011

Well resolved band-edge luminescence of excitons in silicon-germanium alloy strained layers, quantum wells, and superlattices has been observed in films grown by Rapid Thermal Chemical Vapor Deposition. The signal is due to bound excitons at low temperatures and free excitons at higher temperatures, and has a strong no-phonon signal which is caused by alloy scattering. Bandgaps inferred from photoluminescence agree well with those measured by absorption spectroscopy, inferring that a no-phonon process dominates the band-edge absorption.
GexSi1−x Waveguides Grown by Rapid Thermal Processing Chemical Vator Deposition
Authors: Jung K. H. , Mayer R. A. , Hsieh T. Y. , Campbell J. C. , Kwong D. L.
Published: March 2011

We report the growth and characterization of GexSi1−x films for optical waveguiding. GexSi1−x/Si waveguides were grown by rapid thermal processing chemical vapor deposition. An average attenuation of 3.3 dB/cm was achieved for a 1 μm thick Ge0.04Si0.96 layer patterned into rib waveguides 2000 Å deep with widths of 5 μm. Directional couplers were also fabricated. Average coupling efficiencies of 85% were achieved for 1.5 μm interwaveguide separation.
Modulation Doped Si/SiGe Heterostructures
Authors: Schäffler F. , AG Daimler-Benz
Published: March 2011

An overview of SiGe-based, modulation doped heterostructures is given. Strained layer handling, a prerequisite for realizing both n- and p-type devices, Is treated in terms of band engineering. The main emphasis is put on recent results obtained with high-electron mobility n-type Si/SiGe structures. Hall, Shubnikov-deHaas, and cyclotron resonance measurements are presented. The thermal stability of the heterostructures and the dopant distribution are treated with respect to device applications. Room temperature and 77K dc-measurements on very recent modulation doped field effect transistor (MODFET) implementations using implanted source/drain contacts are discussed. Device concepts with n- and p-type MODFETs combined in a superior complementary layout (CMODFET) are proposed.
Simulations of Ge+ and C+ Implantations to form SiGe/Si HBT and Characterization of SiGe and SiGeC Diodes
Authors: Gupta Ashawant , Waters Jeffrey W. , Cook Carmen , Yang Cary Y. , Fukamia Akira , Shoji Ken-Ichi , Nagano Takahiro
Published: March 2011

Simulations of Ge+ and C+ implantations in Si were performed to study bandgap grading in the SiGeC/Si heterojunction bipolar transistor (HBT). Although no bandgap discontinuity was observed at the base-emitter junction, it was found that a wide-bandgap emitter and a narrow-bandgap base with proper bandgap grading were obtainable with implantation. Electrical characterization of SiGe and SiGeC diodes formed by Ge+ and C+ implantations in Si was carried out. Current-voltage (I-V) measurement results confirm that carbon doping improves the crystalline quality of the germanium-implanted layer. On the other hand, capacitance-voltage (C-V) measurements indicate that both germanium and carbon implantations result in considerable dopant deactivation.
Fabrication of CoSi2 Gate Si Permeable Base Transistor Using Si-MBE
Authors: Nakagawa K. , Ohshima T. , Nakamura N. , Miyao M.
Published: March 2011

A permeable base transistor (PBT) with submicron grating is fabricated using a Si/COSi2/Si double heterostructure. The high-quality Si/COSi2/Si double heterostructure is formed by two-step moleculer beam epitaxy (i.e. low-temperature MBE and successive high-temperature MBE). The Si and COSi2 interfaces observed by a cross-sectional transmission electron microscope are smooth and atomically abrupt. A new method of patterning COSi2 films is developed. This method uses the difference in surface energies between different crystal orientations. The mutual conductance and cutoff frequency of the PBT are 50 mS/mm and 6 GHz, respectively. These agree with the results of computer simulations. In addition, computer simulations indicate a potential of Si PBT for high frequency application, and a cutoff frequency as high as 90 GHz can be obtained by optimizing the device structure.
Epitaxial Growth of Silicon on CoSi2 (001)/Si (001)
Authors: Xiao Q. F. , Jimenez J. R. , Schowalter L. J. , Luo L. , Mitchell T. E. , Gibson W. M.
Published: March 2011

Epitaxial Si layers have been grown under a variety of growth conditions on CoSi2 (001) by molecular beam epitaxy (MBE). The structural properties of the Si overgrowth were studied by in-situ Reflection High Energy Electron Diffraction (RHEED), as well as ex-situ MeV4He+ ion channeling and High Resolution Transmission Electron Microscopy (HRTEM). Strong influences of the CoSi2 surface reconstruction on the Si overgrowth have been observed. RHEED studies show islanding growth of Si on the CoSi2 (001) (3/√2 × √2)R45 reconstructed surface, but smooth growth of Si on the CoSi2 (001) {√2 × √2)R45 reconstructed surface, under the same growth conditions. The growth of Si on thin layers of CoSi2 (2nm-6nm) with (√2 × √2)R45 reconstructed surface at 460°C results in high crystalline quality for the Si top layer, as indicated by good channeling minimum yield (Xmin < 6%), but cross-sectional TEM shows that the CoSi2 layers are discontinuous. We also report preliminary results on Si grown on a 2 × 2 reconstructed CoSi2 (001) surface.
RTP-CVD of Si Materials and Devices for ULSI Applications
Authors: Kwong D. L. , Hsieh T. Y. , Jung K. H.
Published: March 2011

Rapid thermal processing chemical vapor deposition (RTP-CVD) has received considerable attention because of its ability to reduce many of the processing problems associated with thermal exposure in conventional chemical vapor deposition, while still retaining the ability to grow high quality epitaxial layers. In this paper, the principles of the RTP-CVD system are described, followed by results of experiments on in-situ cleaning, undoped Si epitaxy and in-situ doped Si epitaxy, and selective Si deposition using oxide masks. Our results show that RTP-CVD is capable of growing high quality, epitaxial layers with sharp, dopant transition profiles. Selective deposition was achieved without the use of HC1. We also studied the growth and characterization of GexSi1−x films for optical waveguiding.
Growth of A β-SiC Filli on a Si Substrate by a Direct Carbonization Method
Authors: Hirano Yasuaki , Inada Taroh
Published: March 2011

Single crystal β-SiC films have been fabricated on (100)Si substrates through a thermal reaction between the substrate and carbon atoms sublimed from a high purity graphite source. The substrate temperature during the deposition ranged from 600 to 1100°C. The film properties were analyzed by RHEED and x-ray diffraction measurements. RBS measurements and TEM observations have also been made to investigate the film properties. The single crystal β-SiC films grow at and above 1000°C on (100) substrates. The activation energy is found to be around 1.1 eV for the crystallization process.
The Synthesis and Stability of Si1−yQy Alloys and Strained Layer Superlattices
Authors: Iyer S. S. , Eberl K. , Goorsky M. S. , Legoues F. K. , Cardone F. , Ek B. A.
Published: March 2011

We have synthesized Si1−yQy layers and strained layer superlattices on Si (100) with C concentrations of up to a few percent using Solid Source Molecular Beam Epitaxy. The presence of C even in small quantities is known to disrupt the epitaxy of Si. We show that under conditions of high Si flux for a given C/Si flux ratio, defect-free epitaxy results. However, exceeding a critical C/Si flux ratio leads to disruption of epitaxy, initially via twinning and subsequently by amorphous growth. Growth temperature also plays a significant role in preventing twinning and islanding. Low growth temperature also suppresses the precipitation of β-SiC and leads to the formation of pseudomorphic Si1−yQy random alloys. The layers are characterized by X-ray diffraction, Secondary Ion Mass spectroscopy, and Transmission Electron Microscopy. We have also studied the thermal stability of strained layer superlattices and find that the layers are stable to about 800°C (for y = 0.003). Between 800°C and 1000°C, the layers relax by interdiffusion. Above 1000°C, silicon carbide precipitation occurs and the carbide layers nucleate and grow at high C content regions of the film.
Electronic Structures for (Si)m (GaP)n Superlattices
Authors: Lin-Chung P. J.
Published: March 2011

This paper reports on a tight-binding calculation of the band structures of the Si-GaP superlattice (SL) systems with emphasis on the results of the band gap properties. This calculation finds that the SLs grown onto the [110] or [111] oriented substrate do not produce direct gap materials. On the other hand, some of the [001] oriented SLs become direct gap materials when either an interface (IF) state is created at the P and Si IF, or a confined state in the Si occurs with only Ga and Si atoms forming all the IF.
Electrical and Optical Properties of Si and Si1−xGex, Alloy Grown by the Ultra-High Vacuum Vapour Phase Epitaxy Method
Authors: Leong W. Y. , Robbing D. J. , Glasper J. L. , Canham L. T. , Carline R. , Calcott P.
Published: March 2011

Epitaxial growth and p-type doping in Si and Si1−xGex alloy by the ultra-high vacuum vapour phase epitaxy (UHV-VPE) method using SiH4/GeH4/B2H/H2 mixture is reported. Growth temperatures as low as 610°C were studied for Ge contents between x=0 to 0.25. Secondary Ion Mass Spectroscopy (SIMS) data of boron dopant profiles in si and Si1−xGex structures are presented. Strong luminescence attributed to the strained Si1−xGex alloy is obtained. The bandgap in the alloy layer obtained from our luminescence data is compared with published data. Unambiguous electroluminescence from a Si1−xGex multiple quantum well p-n structure grown by UHV-VPE, supported by the photoluminescence and photoconductivity measurement, is reported for the first time.
An Overview of Doping Strategies in Si:MBE
Authors: Kubiak Richard , Parry Carl
Published: March 2011

This paper reviews the diverse methods used to achieve doping during MBE of Si and SiGe, and the incorporation processes involved. The optimum choice of dopant and methodology depends on the most appropriate growth conditions for a given structure. At growth temperatures exceeding 750°C, Potential Enhanced n-type doping of coevaporated Sb is capable of achieving high resolution structures, at doping levels up to mid-1019 cm−3. At lower temperatures, such as those most suited to SiGe growth, Sb-doping becomes a formidable challenge, due to the high accumulated equilibrium coverages required. Low energy ion implantation appears to be the favoured route for good control, p-type B-doping can readily be achieved by coevaporation of compounds or, to avoid oxygen incorporation at low temperatures, the element. A “designer” chart for B-doping of Si is presented.
An Investigation of Boron Incorporation in SiGe MBE
Authors: Parry C. P. , Kubiak R. A. , Newstead S. M. , Whall T. E. , Parker E. H. C.
Published: March 2011

The performance of many Si/SiGe devices, particularly those involving modulation doped quantum wells, will depend on the quality of the matrix and doping interfaces involved. These may be adversely affected by profile smearing of Ge and the dopant. A study of boron incorporation in SiGe, as a function of substrate temperature and Ge fraction, shows a marked difference in profile smearing for boron in Si and in the SiGe alloy. This is shown to be associated with a reduction in the temperature for transition from equilibrium to kinetically limited accumulation in the alloy.
In-Situ TEM Observation of Electromigration Damage by Surface or Interface Diffusion in Al and Al Alloy Films
Authors: Chang C. Y. , Vook R. W.
Published: March 2011

In-situ transmission electron microscope (TEM) electromigration damage (EMD) tests were performed on pure Al films which were thermally evaporated onto oxidized silicon wafers under different deposition conditions. Three different aluminum alloy films, Al-2wt%Cu, Al-8wt%Cu, and Al-2wt%Cu-lwt%Si were also examined. TEM images were recorded photographically and by a video camcorder. The sample stripes were stressed by a high DC current density (≈1.5 MA/cm2). A linear temperature ramp (5°C/min) was supplied by an external, computer controlled heater. The morphology of EMD-induced voids was found to be strongly dependent on microstructure. In small grain size Al stripes, EMD occurred by the formation of void “fingers” which propagated in an almost random manner. In large grain size Al and Al alloy stripes, the EMD-elongated voids propagated approximately parallel to each other and along the field direction. They were preceded with clearly identifiable local thinning. The thinned regions often had crystallographic edges. Contrary to the commonly held belief that EMD occurs only by a grain boundary diffusion mechanism, the present study clearly shows that surface or interface diffusion was the dominant, latter stage EMD failure mode in large grain size films.
A Statistical Characterization of Electromigration-Induced Open Failures in 2-Level Metal Structures
Authors: Kahn H. , Thompson C. V.
Published: March 2011

A new electromigration test structure has been designed and fabricated which allows statistical characterization of current-induced open failures at vias, under varying current flow geometries. Results for a 2-level Al-Cu metallization system with W-filled 1.0 μm vias reveal no differences in via lifetimes for parallel, anti-parallel, or perpendicular current flows. However, a factor of 7 improvement in the total average via resistance produces an order of magnitude improvement in lifetimes. Line reliability remains superior to the reliability of the vias, indicating that the vias are the “weak links” in the system.

A model for evaluating temperature and current density effects which incorporates the atomic flux equation has been developed and used to make reliability predictions for extrapolations to operating conditions. The model suggests that the median time to failure of a 2-level ietal structure with an average via resistance of two ohms will be 2.7×1017 hours for operating conditions of 2×105 A/cm2 and 125°C.
The Effect of a Passivation Over-Layer on Tile Mechanisms of Stress Relaxation in Continuous Films and Narrow Lines of Aluminum
Authors: Paszkiet C. A. , Korhonen M. A. , Li Che-Yu
Published: March 2011

Stress relaxation was studied in bare and nitride-covered continuous films and narrow lines of aluminum. The rate of relaxation in unpassivated metallizations is shown to be consistent with a dislocation-controlled mechanism. Relaxation in passivated lines appears to depend on grain boundary diffusion-controlled void growth. In passivated continuous films, two rate-controlling mechanisms appear to operate in sequence.
Mechanical Modeling of Stress Generation During Cure of Encapsulating Resins
Authors: Lagasse R. R. , Chambers R. S. , Guess T. R. , Plazek D. J. , Bero C.
Published: March 2011

We have developed a numerical model for calculating stresses generated during cure of shrinking encapsulating resins. Mechanical modeling of polymer encapsulated electronic devices usually focusses on stress generated during cooling after cure. The stress developed during cure, due to shrinkage of the encapsulant, is normally neglected. That assumption is valid if both the shear and bulk moduli of the encapsulant at the cure temperature are negligible with respect to the moduli at lower temperatures. Our measurements on a model epoxy encapsulant show that the shear modulus during cure, varying from 0 to 6 MPa, is at least 100 times smaller than that at ambient temperature. In contrast, the bulk modulus at the cure temperature is only 2.5 times smaller. Since the bulk modulus during cure cannot be neglected, significant stress can be produced if volume shrinkage is constrained by a stiff mold or embedded elements. In fact, mechanical failure of encapsulating materials during cure has been evident in some of our experiments. Using measurements of shear and bulk moduli plus volume shrinkage as inputs to a finite element model, we have successfully predicted the shrinkage strains and stresses developed during cure of a model epoxy resin inside a cylindrical tube. Consideration of cure shrinkage stress has led to a process modification that appears to reduce mechanical failures in a real encapsulated device.
Texture and Microstructure Effects on Electromigration Behavior of Aluminum Metallization
Authors: Knorr D. B. , Rodbell K. P. , Tracy D. P.
Published: March 2011

Pure aluminum films are deposited under a variety of conditions to vary the crystallographic texture. After patterning and annealing at 400°C for 1 hour, electromigration tests are performed at several temperatures. Failure data are compared on the basis of t50 and standard deviation. Microstructure is quantified by transmission electron microscopy for grain size and grain size distribution and by X-ray diffraction for texture. A strong (111) texture significantly improves the electromigration lifetime and decreases the standard deviation in time to failure. This improvement correlates with both the fraction and sharpness of the (111) texture component.
Computer Simulation of Grain Growth in Thin-film Interconnect Lines
Authors: Walton D. T. , Frost H. J. , Thompson C. V.
Published: March 2011

Microstructural evolution in thin-film strips is of interest due to the direct effect of grain structure on integrated circuit interconnect reliability and resistance to electromigration-induced failure. We have explored the evolution of interconnect grain structure via a two-dimensional grain growth simulation. We focus on the strip's transformation to the bamboo structure, in which individual grains traverse the width of the strip. We find that the approach to a fully bamboo structure is exponential, and that the rate of transformation is inversely proportional to the square of the strip width. When the simulation is extended to model grain boundary pinning due to grooving at grain boundary – free surface intersections, we find that there exists a maximum strip width to thickness ratio beyond which the transformation to the bamboo structure does not proceed to completion. By using our simulation results in conjunction with a “failure unit” model for electromigration-induced failure [4] we are able to reproduce the experimentally observed abrupt increase in time-to-failure below a critical strip width, and also model the reliability as a function of annealing conditions.
High-Energy Backscattered Electron Imaging of Voids in Aluminum Metallizations
Authors: Follstaedt D. M. , Van Den Avyle J. A. , Romig A. D. , Knapp J. A.
Published: March 2011

Backscattered electron imaging of microcircuits in scanning transmission electron microscopes at 120 kV is shown to produce improved images of voids in passivated Al metallization lines relative to those obtained with scanning electron microscopes at ≤ 40 kV. At 120 kV, resolutions of about 0.1 μm are achieved for voids imaged beneath 1.0 μm glass overlayers. This technique allows improved characterization of microstructures for basic investigations of void formation and more accurate counting of voids in microcircuits without removing glass overlayers. Smaller voids should also be detectable with the higher voltage.
Intermetallic Reactions Between Copper and Magnesium as an Adhesion / Barrier Layer
Authors: Arcot Binny , Cabral C. , Harper J. M. E. , Murarka S. P.
Published: March 2011

The reliability of copper multilevel interconnections requires good adhesion and the prevention of copper diffusion into the interlevel dielectric. Magnesium is a candidate for an adhesion layer and diffusion barrier for copper due to the high heats of formation of magnesium oxides, fluorides and sulfides and the formation of low resistivity compounds of Mg with copper. An investigation of the interactions in thin films of copper and magnesium has been carried out in the temperature range of 25°C to 500°C. The results of these reactions leading to phase formation in Cu/Mg bilayers deposited on Si3N4 or SiO2 using X-ray diffraction, in situ sheet resistance, and Rutherford backscattering measurements are presented in this paper. It was found that the Mg-rich phase CuMg2 is the first phase to form on annealing to approximately 215°C, followed by the formation of the Cu-rich phase Cu2Mg at about 380°C in the presence of excess Cu.