bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Ion Metal Plasma (IMP) Titanium Deposition on Ti Silicide Formation
Authors: Sabbadini A. , Cazzaniga F. , Brambilla M. , Bresolin C. , Cusi V. , Marangon T. , Queirolo G.
Published: April 2011

Titanium disilicide obtained by direct interaction between Si and a deposited Ti layer is a choice for low- resistance gate interconnections and source and drain areas. The properties of the TiSi2 film can be influenced by many factors; such as substrate nature and doping, the depositing Ti layer, structure dimensions [1][2][3][4]. This work is addressed to study the properties of TiSi2 film as obtained from titanium deposited by Ion Metal Plasma (IMP), which has recently been introduced in high aspect ratio contact and via applications.

Its suitability for titanium silicide formation is investigated here in comparison to standard PVD deposition. The study was carried out on flat and patterned samples. Titanium silicide formed on mono- Si substrates were characterized as a function of RTP temperature in terms of sheet resistance, tilm morphology, crystallography and phase evolution. It was found that the TiSi2 film obtained from IMP- Ti is very similar to the one obtained from PVD standard deposition. However, for annealing below 700°C, an increase in the sheet resistance of the TiSi2 C49 phase from IMP- Ti compared to the one from PVD- Ti was found, and is explained by different silicide grain size. Analyses performed on patterned samples with doped silicon and poly- Si lines show similar electrical results for TiSi2 from IMP and PVD deposition; however, fbr p+ poly-Si lines, the IMP samples displayed correct TiSi2 formation down to 0.18µm line width, while the PVD wafers showed discontinuous results at these minimum feature sizes.
Agglomeration Of Cu Electroplating Seed Layers On Ultra-Thin Ta, Ta1-xNx, Tal-xOx, Contaminated Ta, and Composite Ta/Ta1-xNx Diffusion Barriers
Authors: Hartman J. W. , Yeh Helen , Atwater H. A. , Hashim Imran
Published: April 2011

The agglomeration of thin (10 nm) Cu films suitable for use as electroplating seed layers has been investigated on ultrathin (<4 nm) Ta, Ta1-xNx, Tal-xOx, and composite Ta/Ta1-xNx, diffusion barriers. Copper films on clean 3.6nm Ta barriers deposited by ultrahigh vacuum sputter deposition at up to 120°C are stable against agglomeration during 30 minute anneals at 360°C and display strong (022) crystallographic texture. Similar Cu films deposited on thinner Ta, Ta0 85N0 15, Ta0.95O0 05, and residual gas contaminated (∼ 1 Langmuir) Ta barriers agglomerate during annealing, and Cu films on Ta0 85N0 15 and contaminated Ta have random biaxial crystallographic texture. The density of agglomerated regions in Cu films on SiO2 and Ta0 85N0 15 is characterized as a function of thickness of an ultrathin Ta adhesion layer.
The Effect Of Surface Oxides On Cu/Ta Interfacial Interactions
Authors: Chen L. , Ekstrom B. , Kelber J.
Published: April 2011

We report results of Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) studies under ultra high vacuum (UHV) conditions which demonstrate that even submonolayer coverages of oxygen on Ta significantly degrade the strength of Cu/Ta chemical interactions, and affect the kinetics of Cu diffusion into bulk Ta. On clean Ta, monolayer coverages of Cu will de-wet only above 600 K. A partial monolayer of adsorbed oxygen (3L O2 at 300 K) results in a reduction of the de-wetting temperature to 500 K, while saturation oxygen coverage (10 L O2, 300 K) results in de-wetting at 400 K. Diffusion of Cu into the Ta substrate at 1100 K occurs only after a 300-second induction period at this temperature. The induction period increases to 600 sec for partially oxidized Ta and to 1200 sec for saturation oxygen coverage. TPD studies indicate no desorption of Cu for temperatures below 1300 K. The higher desorption temperature of Cu (compared to the 1150 K sublimation temperature) indicates that all the Cu originally deposited is now chemically bound to Ta.
Prevention of Corner Voiding in Selective CVD Deposition of Titanium Silicide on SOI Device
Authors: Maa Jer-shen , Ulrich Bruce , Stecker Lisa , Stecker Greg , Hsu Sheng Teng
Published: April 2011

In the application of selective CVD of titanium silicide to SOI devices, voids were observed at the bottom corner of the spacers, which caused reduction of drain current and in extreme cases formed an open circuit. Test structures were constructed to monitor void formation. It was found the voiding became serious when the thickness of the Si film was reduced. Adjusting the deposition condition by reducing the TiCi4 flow rate or by using a two-step deposition process was able to significantly reduce the chance of void formation. On very thin Si films, voiding can be prevented by depositing a selective Si layer prior to silicide deposition.
Diffusion Barriers for Copper Metallization: Predicting Phase Stability and Reactivity using Equilibrium Thermodynamics
Authors: Ramberg C. E. , Blanquet E. , Pons M. , Ghetta V. , Bernard C. , Madar R.
Published: April 2011

The guidelines for designing a conductive, amorphous material, capable of thermodynamic equilibrium with copper, are defined using readily available thermodynamic information. The tradeoff between desired properties – equilibrium at the interfaces, amorphous microstructure, and electronic conductivity – are described, along with trends in relevant binary systems that result in these properties. These guidelines defined systems for experimental study, for which preliminary results are presented.
Characterization of PECVD Wnx for Copper Barrier Application
Authors: Vijayendran A. , Danek M.
Published: April 2011

We evaluated PECVD WNx as a potential copper barrier. Ultrathin (100 Å) PECVD WNx films were deposited utilizing WF6/N2/H2 chemistry. Films with N/W stoichiometries ranging from 0.1 to 1.0 and resistivities between 200 – 1000 μΩ-cm were deposited by varying pressure, deposition temperature, N2 flow, and H2 flow. The thermal stability of the films was evaluated by annealing Si/WNx /Cu stacks for 1 hour at temperatures up to 700°C. Barrier failure was detected by sheet resistance change and surface SIMS. The thermal stability was correlated with N/W ratio and free fluorine content as determined by temperature programmed desorption mass spectroscopy. The tests showed that films with N/W ratios between 0.3 and 0.4 had optimal barrier properties, while fluorine was seen to have a detrimental effect on barrier stability. Moreover, tests showed that the substrate affects fluorine concentration as WNx deposited on silicon dioxide has a higher interfacial fluorine content than WNx on silicon. Thus, fluorine contamination at the WNx /Si02 interface led to poor electrical reliability as measured by leakage current vs. time on MOS capacitors.
Classification of the Modes of Dissociation in Immiscible Cu-Alloy Thin Films
Authors: Barmak K. , Lucadamo G. A. , Cabral C. , Lavoie C. , Harper J. M. E.
Published: April 2011

We have found the dissociation behavior of immiscible Cu-alloy thin films to fall into three broad categories that correlate most closely with the form of the Cu-rich end of the binary alloy phase diagrams. The motivation for these studies was to use the energy released by the dissociation of an immiscible alloy, in addition to other driving forces commonly found in thin films and lines, to promote grain growth and texture evolution. In this work, the dissociation behavior of eight dilute (3.3 ± 0.5 at% solute) binary Cu-systems was investigated, with five alloying elements selected from group VB and VIB, two from group VillA, and one from group 1B. These alloying elements are respectively V, Nb, Ta, Cr, Mo, Fe, Ru and Ag. Several experimental techniques, including in situ resistance and stress measurements as well as in situ synchrotron x-ray diffraction, were used to follow the progress of solute precipitation in approximately 500 nm thick films. In addition, transmission electron microscopy was used to investigate the evolution of microstructure of Cu(Ta) and Cu(Ag). For all eight alloys, dissociation occurred upon heating, with the rejection of solute and evolution of microstructure and texture often occurring in multiple steps that range over several hundred degrees between approximately 100 and 900°C. However, in most cases, substantial reduction in resistivity of the films took place at temperatures of interest to metallization schemes, namely below 400°C.
Barrier Effect on Electroplated Cu Films
Authors: Faust R. , Jiang Q.
Published: April 2011

The effect of various barrier materials on the microstructure of electroplated Copper films was investigated. Analysis of the Cu was performed at the as-deposited, room temperature stabilized, and annealed states. It shows that the barrier material can have a dramatic effect on the properties of electroplated Cu.
Electroplated Cu Recrystallization in Damascene Structures at Elevated Temperatures
Authors: Jiang Qing-Tang , Thomas Michael E. , Bersuker Gennadi , Foran Brendan , Mikkola Robert , Carpenter Brad , Ormando John
Published: April 2011

Transformations in electroplated Cu films from a fine to course grain crystal structure (average grain sizes went from ∼0.1 µm to several microns) were observed to strongly depend on film thickness and geometry. Thinner films underwent much slower transformations than thicker ones. A model is proposed which explains the difference in transformation rates in terms of the physical constraint experienced by the film since grain growth in thinner films is limited by film thickness. Geometrical constraints imposed by trench and via structures appear to have an even greater retardation effect on the grain growth. Experimental observations indicate that it takes much longer for Cu in damascene structures to go through grain size transformations than blanket films.
Improved Al-Via Fill Process Technology for Sub-0.251µm Interconnect
Authors: Sengupta S. S. , Narasimhan M. , Lee S. , Abburi M. , Yao G.
Published: April 2011

In this paper, a simple and improved method for Al via fill is demonstrated. The ALPS (Aluminum Low Pressure Seed) technique was used to deposit a smooth, highly conformal Al seed layer over an all-IMP (ionized metal plasma) Ti/TiN/Ti stack. Subsequent warm Al deposition was carried out in a conventional warm Al chamber. The ALPS method was compared to standard hot Al deposition. Physical SEM characterization and electrical data showed lower via resistances, with better yield for ALPS. No voiding was observed even within unlanded vias. With the ALPS seed layer, the IMP Ti/TiN/Ti liner stack provided a superior wetting surface compared to an IMP Ti-only liner which resulted in voids within unlanded vias. Electrical data obtained for ALPS- and hot Al-deposited Kelvin vias and via chains with various via/metal underlaps were compared with conventional CVD W plugs (using IMP TiN as the glue layer). Both Al fill methods gave lower via resistance compared with W plugs, as expected.
A Study on the Effect of Post Metal Etching Polymer Strip Process on Via Resistance
Authors: Koh Leong-Tee , Chooi Simon Y. M. , Chok Kho-Liep , Li He-Ming , Gn Fang-Hong
Published: April 2011

Corrosion of the titanium glue layer in a Ti/TiN/Al(Cu) /TiN ARC metal stack is observed during post metal etching polymer stripping in an alkaline chemical stripper. This novel corrosion only occurs when the underlying tungsten via plug is exposed, and leads to high resistance in vias. Investigation of the mechanism is attempted through variation of the polymer stripping duration, the deposition of the titanium and the polymer stripper, and the nitridization of the titanium layer. The high via resistance effect is solved by using analternate polymer stripper which is considered to be an inactive electrolyte for the galvanic reaction between the titanium glue layer and the exposed tungsten via.
In-Situ Study of Ti/TiN Stability under Nitrogen Anneal
Authors: DeHaven P. W. , Rodbell K. P. , Gignac L.
Published: April 2011

The effectiveness of a TiN capping layer to prevent the conversion of α-titantium to titanium nitride when annealed in a nitrogen ambient has been studied over the temperature range 300–700°C using in-situ high temperature diffraction and transmission electron microscopy. Over the time range of interest (four hours), no evidence of Ti reaction was observed at 300°C. At 450°C. nitrogen was found to diffuse into the Ti to form a Ti(N) solid solution. Above 500°C the titanium is transformed to a second phase: however this reaction follows two different kinetic paths, depending on the annealing temperature. Below 600°C. the reaction proceeds in two stages, with the first stage consisting of Ti(N) formation, and the second stage consisting of the conversion of the Ti(N) with a transformation mechanism characteristic of short range diffusion (grain edge nucleation). Above 600°C, a simple linear transformation rate is observed.
The Formation of C54 TiSi2 in The Presence of Implanted or Deposited Molybdenum
Authors: Roux M. , Mouroux A. , Zhang S.-L.
Published: April 2011

The presence of Mo, either implanted in Si substrate prior to Ti deposition or deposited at the interface between Ti and Si, leads to the formation of C54 TiSi2 at 600 °C. Without Mo, the C54 TiSi2 does not form below 700 °C. It is shown that the C54 TiSi2 formed with the implanted Mo of a nominal dose of 5x1014 at./cm2 and that formed with the deposited Mo of 0.09 nm average thickness, display similar microstructure properties. The preferential orientation of the C54 TiSi2 is <110> in the samples with implanted Mo or with 0.09 nm Mo interlayer, as well as in the reference sample without any Mo. It becomes <010> when the Mo interlayer is 0.73 nm thick. The silicide surface and Si/silicide interface are appreciably rougher for the silicides formed with 0.09 nm Mo interlayer, with implanted Mo or in the absence of Mo, than for the silicide formed with 0.73 nm Mo interlayer. The experimental results indicate that the enhanced formation of C54 TiSi2 is caused by the same effect, i.e. template mechanism, irrespective of the means of Mo addition to the Ti-Si system.
Diffusion Barriers for Fluorinated Low-k Dielectrics
Authors: DelaRosa M. , Kumar A. , Bakhru H. , Lu T.-M.
Published: April 2011

The fluorinated low-k dielectrics SiO:F and Teflon AF were investigated for process integration with aluminum and copper interconnects. To minimize fluorine diffusion, several potential barrier materials were deposited onto the fluorinated dielectrics and characterized after heat treatment at temperatures up to 450°C. The barrier layers studied include conventional materials such as Ta, TaN, and TiN, in addition to several novel materials. Barrier layer materials were deposited using evaporation, and sputtering. The materials were characterized using nuclear reaction analysis (NRA) to determine the fluorine concentration profile. A reaction zone was noted at the dielectric-barrier interface on several samples, corresponding to the formation of a fluoride complex. hI some instances, this fluoride layer was self-limiting and prevented further fluorine diffusion through the remainder of the barrier layer.
Reliability Characterization of Moisture-Induced Degradation of Low-K Dielectric Behavior for Advanced Interconnects
Authors: Ionescu A. M. , Mondon F. , Blachier D. , Morand Y. , Reimbold G.
Published: April 2011

This paper reports degradation characteristics of low-k dielectric (FOX) in multi-level metal structures (comb-type capacitors) submitted to moisture stress. A large increase of leakage current (>105) and capacitance (up to ×3) is observed after moisture stress when only FOX is used as lateral dielectric, while moderate degradation takes place when an oxide liner is placed between FOX and metal lines. Enhanced moisture induced degradation is found on previously probed dices with respect to virgin devices. Systematic electrical measurements, combined with SEM analysis, are performed to find out the moisture diffusion path. When contact pads are damaged by previous probing (owing to the mechanical weakness of FOX in the pad stack), they provide a direct entry path for enhanced humidity intake. Humidity is also shown to enter through wafer border. Using a SiO2 liner combined with FOX improves considerably the resistance to moisture degradation.
The Effects of Environment and Fatigue on the Adhesion and Subcritical Debonding of Dielectric Polymers
Authors: Snodgrass J. M. , Pantelidis D. , Bravman J. C. , Dauskardt R. H.
Published: April 2011

The adhesion of thin film polymers will be critical in the integration of low-κ materials into microelectronic processing. This study describes the adhesion of two promising low-κ polymers (polyimide and benzocyclobutene) to a silicon dioxide surface. Critical adhesion values were measured using interface fracture mechanics samples in a double cantilever beam geometry. The effect of subcritical (time-dependent) delamination was also evaluated for these systems. Subcritical debonding data are important in understanding the effect of environment and temperature on interface reliability. To that end, experiments were conducted over a range of humidities to elucidate the effect of moisture on interface delamination. The important effect of the acceleration of debond growth rates due to cyclic loading is also described. In addition, XPS studies are presented to characterize the debond path in these layered systems.
Evaluation of Copper Penetration in Low-κ Polymer Dielectrics by Bias-Temperature Stress
Authors: Loke Alvin L. S. , Wong S. Simon , Talwalkar Niranjan A. , Wetzel Jeffrey T. , Townsend Paul H. , Tanabe Tsuneaki , Vrtis Raymond N. , Zussman Melvin P. , Kumar Devendra
Published: April 2011

The industry is strongly interested in integrating low-κ dielectrics with Damascene copper. Otherwise, with conventional materials, interconnects cannot continue to scale without limiting circuit performance. Integration of copper wiring with silicon dioxide (oxide) requires barrier encapsulation since copper drifts readily in oxide. An important aspect of integrating copper wiring with low-κ dielectrics is the drift behavior of copper ions in these dielectrics, which will directly impact the barrier requirements and hence integration complexity.

This work evaluates and compares the copper drift properties in six low-κ organic polymer dielectrics: parylene-F; benzocyclobutene; fluorinated polyimide; an aromatic hydrocarbon; and two varieties of poly(arylene ether). Copper/oxide/polymer/oxide/silicon capacitors are subjected to bias-temperature stress to accelerate penetration of copper from the gate electrode into the polymer. The oxide-sandwiched dielectric stack is used to overcome interface instabilities occurring when a low-κ dielectric is in direct contact with either the gate metal or silicon substrate. The copper drift rates in the various polymers are estimated by electrical techniques, including capacitance-voltage, current-voltage, and current-time measurements. Results correlate well with timeto-breakdown obtained by stressing the capacitor dielectrics. Our study shows that copper ions drift readily into fluorinated polyimide and poly(arylene ether), more slowly into parylene-F, and even more slowly into benzocyclobutene. A qualitative comparison of the chemical structures of the polymers suggests that copper drift in these polymers may possibly be retarded by increased crosslinking and enhanced by polarity in the polymer.
Diffusion Barriers For Fluorinated Low-k Dielectrics
Authors: DelaRosa M. , Kumar A. , Bakhru H. , Lu T.-M.
Published: April 2011

The fluorinated low-k dielectrics SiO:F and Teflon AF were investigated for process integration with aluminum and copper interconnects. To minimize fluorine diffusion, several potential barrier materials were deposited onto the fluorinated dielectrics and characterized after heat treatment at temperatures up to 450°C. The barrier layers studied include conventional materials such as Ta, TaN, and TiN, in addition to several novel materials. Barrier layer materials were deposited using evaporation, and sputtering. The materials were characterized using nuclear reaction analysis (NRA) to determine the fluorine concentration profile. A reaction zone was noted at the dielectric-barrier interface on several samples, corresponding to the formation of a fluoride complex. In some instances, this fluoride layer was self-limiting and prevented further fluorine diffusion through the remainder of the barrier layer.
The Study of Fluorinated Amorphous Carbon as Low-K Dielectric Material and its Interface with Copper Metallization
Authors: Ariel N. , Eizenberg M. , Tzou E. Y.
Published: April 2011

In order to achieve better performance of devices, the interconnects RC delay time, the limiting factor of the device speed today, must be reduced. This calls for a new interconnect stack: lower resistivity Copper and low k materials (k<3) as dielectrics.

Fluorinated amorphous carbon (a-F:C) prepared by HDP- CVD is an attractive candidate as a low-k material. In this work we have studied the film, its stability and its interface with Copper metallization. The high density plasma CVD process resulted in a film which contains C and F at a ratio of 1:0.6 as determined by Nuclear Reactions Analysis. XPS analysis of the Cls transition indicated four types of bonds: C-C, C-CF, CF, and CF2. X-ray diffraction as well as high resolution TEM analyses proved that the film was amorphous at least up to 500°C anneal. For various applications, the advantage of adding a thin bi-layer of a-SiC/SiOx for adhesion promotion purposes was demonstrated. In addition, the interface of a-F:C and the adhesion promoter layer with Ta, TaN and Cu was studied. No interdiffusion was observed by SIMS after 400°C annealing. 500°C annealing caused F outdiffusion from the film and Cu diffusion into the adhesion promoter layer.
Phenyl Silica Glass for Formation of Porous Dielectric Film
Authors: Endo Kazuhiko , Shinoda Keisuke , Tatsumi Toru
Published: April 2011

Phenyl and alkyl groups were introduced into silica glass in order to prevent the formation of a Si-O network and reduce its density and to reduce the dielectric constant of the glass. In this regard, the phenyl group was more effective than the alkyl group. The measured Si-O intensity of FTIR spectrum of the glass with introduced phenyl was only 14% of thermal SiO2 film, however, the thermally stable carbon component prevented further reduction in density after 400°C annealing.
Low-K Porous Spin-On-Glass
Authors: Kohl Paul A. , Padovani Agnes , Wedlake Michael , Bhusari Dhananjay , Ann Sue , Allen Bidstrup , Shick Robert , Rhodes Larry
Published: April 2011

Previously, the fabrication of air-gap structures for electrical interconnections was demonstrated using a sacrificial polymer encapsulated in conventional dielectric materials. The air-gaps were formed by thermally decomposing the sacrificial polymer and allowing the by-products to diffuse through the encapsulating dielectric. The diffusivity of the polymer decomposition products is adequate at elevated temperatures to allow the formation of air-gaps. This process was extended to form low dielectric constant, porous silica from commercially available methylsilsesquioxane (MSQ) by the addition of the sacrificial polymer to the MSQ. The porous MSQ film was thermally cured followed by decomposition of the NB at temperatures above 400°C. The dielectric constant of the MSQ was lowered from 2.7 to 2.3 by creating 70 nm pores in the MSQ. The voids created in the MSQ appeared to exhibit a closed-pore structure.
Film Properties of Low-Density and Ultra-Low-Dielectric-Constant Material
Authors: Muraguchi Ryo , Egami Miki , Arao Hiroki , Tounai Atsushi , Nakashima Akira , Komatsu Michio
Published: April 2011

We studied the effect of pore diameter on the film properties of low-density porous material with special interest in the pore diameter range below 5nm. A novel low-density material, Interpenetrated SOG (IPS), was designed to realize such porous character. It is composed of a pyrolic template, which is an organic olygomer, and framework, made from SOG polymer and silica sol, forming an interpenetrated structure. Thermal decomposition of the organic component successfully resulted in films with pore diameter range below 5nm. It is found that the dielectric constant and the pore diameter depended on the density and the film strength was affected by the average pore diameter. Practically, films with the average pore size below 5nm possessed dielectric constants as low as 2.2–2.0 and sufficient strength.
Calculation of Pore Size Distribution in the Ellipsometric Porosimetry: Method and Reliability
Authors: Mogilnikov K. P , Polovinkin V. G , Dultsev F. N , Baklanov M. R
Published: April 2011

Ellipsometric porosimetry allows measurement of the pore size distribution in a thin porous film deposited on top of any solid substrate. The most important concept of this technique is the use of in-situ ellipsometry to determine the amount of adsorbate adsorbed/condensed in the film. Changes in refractive index and film thickness are used for calculation of the amount of adsorbate. A room temperature porosimetry based on adsorption of vapours of some organic solvents has been developed. In this paper, a method of calculation of the pore size distribution and reliability of the ELP results is discussed and the validity of the Gurvitsch rule for organic adsorbates (toluene, heptane, CCl4) is examined. Porous silica films on top of Si wafers were used for this analysis.
Uniform Quantum Wire and Quantum Dot Arrays by Natural Self-Faceting on Patterned Substrates
Authors: Nötzel Richard , Fricke Jörg , Niu Zhichuan , Jahn Uwe , Friedland Klaus-Jürgen , Ramsteiner Manfred , Schönherr Hans-Peter , Trampert Achim , Ploog Klaus H.
Published: April 2011

The combination of self-organized growth on high-index substrates with lithographic patterning and atomic hydrogen assistance allows the fabrication of GaAs quantum wires and quantum dots as well as coupled wire-dot arrays with superior structural and electronic properties by molecular beam epitaxy. The selectivity of patterned growth on high-index substrates differs qualitatively from that on low-index ones thus producing quantum wire and quantum dot structures which fulfill the stringent criteria on the geometrical features to be met for useful devices.
Connection between Structure and Electronic Properties in Epitaxial Magnetic Layers
Authors: Altmann K. N. , Foo J. A. Con , Himpsel F. J. , Kelly J. F. , Lagally M. G. , MacKay J. F. , O'Brien W. L. , Ortega J. E. , Petrovykh D. Y.
Published: April 2011

This study explores the consequences of structure on the electronic properties of magnetic multilayers. Epitaxial layers of Co and Cu are grown on Cu(100) in a new deposition system that couples sputter-deposition with MBE and contains a wide range of characterization tools, including RHEED, LEED, and Kerr effect. This system can be coupled in situ to spin-polarized, angle-resolved photoemission and to resonant, magnetic X-ray scattering, both employing synchrotron radiation. The interface structure turns out to be critical in determining the coercivity and the presence of quantum well states, which determine oscillatory magnetic coupling.
Transmission Electron Microscopy Study of Ingaas/Gaas Structural Evolution Near the Stranski-Krastanow Transformation
Authors: Wellman J. , George T. , Leon R. , Fafard S. , Zou J. , Cockayne D. J. H.
Published: April 2011

An experimental study of the microstructure during formation and evolution of MOCVD-grown In0.6Ga0.4As/GaAs quantum dots (QDs) was undertaken to provide a more thorough understanding of the underlying growth principles. Transmission Electron Microscopy (TEM) was used to examine the evolution of the In0.6Ga0.4As/GaAs system in order to correlate photoluminescence (PL) spectra with structural data. In particular, we have examined the QD size evolution, capped and uncapped, and its possible contribution to the slight QD PL blueshift observed before QD saturation. TEM studies in the QD coalescence regime clarify the microstructural origins of the sharp decrease in QD PL due to large, incoherent islands observed in AFM and TEM images.
Compliant Substrate Processes
Authors: Doolittle W. A. , Brown A. S.
Published: April 2011

Recent results indicate that compliant substrates offer significant promise as a new approach for strain management in semiconductors. The potential applications include 1) the growth of device-quality highly mismatched materials on dissimilar substrates, and 2) the lateral control of material properties resulting from the effects of strain on bandstructure and/or growth dynamics. A significant amount of research in this area is dedicated to the reduction of extrinsic processing effects resulting from compliant substrate fabrication, and the development of simple models for understanding the observed reduction in defect density and/or strain in the epitaxial films grown on compliant substrates. A recent focus in our work has been on the growth of GaN on a novel and easily removable substrate -lithium gallate- for the regrowth on a bonded GaN template. The first step in this approach is the optimization of the growth of GaN on lithium gallate. In addition, this approach requires the use of an appropriate bonding layer to reduce the strain or defect production during growth due to coefficient of thermal expansion mismatches between the GaN sample and the handle wafer. Our work in this area will be highlighted in the context of an overview of various compliant substrate approaches and current results that indicate their efficacy.
Observation of Surfactant Properties of Thallium in the Epitaxial Growth of Indium Arsenide on Gallium Arsenide
Authors: Storm D.F. , Lange M.D.
Published: April 2011

Because of the large lattice mismatch between InAs and GaAs, the growth of the former on the (001) surface of the latter undergoes a well-known transition from a layer-by-layer mode to an island mode at an equivalent coverage of 1–2 monolayers (ML). We have observed a suppression of this transition when growth proceeds under a simultaneous thallium flux. The thallium is not significantly incorporated into the InAs layer; however, approximately I ML may remain at the interface. The effect of the thallium on the electronic properties of the InAs is investigated.
Localized Doping Enhancement by Photon-Assisted Chemical Beam Epitaxy
Authors: Shi B.Q. , Tu C.W.
Published: April 2011

Doping results from Ar+-laser-assisted chemical beam epitaxy with triethylgallium, tris(dimethylamino) arsenic and silicon tetrabromide as group-HI, group-V and dopant precursors respectively are reported. Enhancements in the n-type doping concentration are observed with laser irradiation in the investigated substrate-temperature range 390°C – 500°C. With a 300 W/cm2 irradiation power density, an increase in the carrier concentration by 70 times is obtained at 390°C substrate temperature. A numerical model developed by us for epitaxial growth and doping with the above precursors is used to assess the contribution of laser-induced thermal heating to the observed doping increase. A reaction scheme for photo-induced decomposition of physisorbed silicon tetrabromide is proposed. A kinetic rate equation for the photolysis is derived and used to estimate the absorption cross section required to reproduce the observed concentration enhancements resulted from laser irradiation. The possibility is established that dramatic increases in carrier concentration at low growth temperatures are due to photolysis of physisorbed silicon tetrabromide.
Self-Consistent Rate-Equation Approach to Nucleation and Growth in Point/Extended Island Models of 1-D Homoepitaxy
Authors: Amar Jacques G. , Popescu Mihail N. , Family Fereydoon
Published: April 2011

A self-consistent rate equation (RE) approach to submonolayer growth on a one-dimensional surface is presented. This approach explicitly takes into account the existence of gaps between clusters and can successfully predict the coverage dependence of the average densities of monomers N1, and clusters, N. It also implies an unusual dependence for the monomer-monomer capture number σ1 as a function of monomer density. To obtain the island size-distribution, a second set of mean-field equations is used describing the evolution of the size-dependent capture zones and leading to explicit size- and coverage-dependent capture numbers. The solution of this fully self-consistent RE approach is then compared with kinetic Monte Carlo results
Lateral InxGa1−x, P Heterostructures Obtained by Single Step Growth on Pre-Patterned Substrate by Chemical Beam Epitaxy
Authors: de Castro M.P.P. , Betitni J. , Ribeiro C.A. , Carvalho M.M. , Frateschi N.C.
Published: April 2011

We present an investigation on the spatial compositional variation in InGaP layers grown by chemical beam epitaxy (CBE) on pre-patterned substrates. Neighboring regions with 190 meV bandgap discontinuity are observed with the growth at 500°C. The development of laser structures on V-grooves that incorporate these lateral heterostructures is achieved by controlling the growth temperature during growth
A Kinetic Monte Carlo Model for Ga Desorption from Chemisorbed and Physisorbed States During High Temperature GaAs MBE
Authors: Mahalingam K. , Dorsey D. L. , Taferner W. T. , Eyink K. G.
Published: April 2011

A kinetic Monte Carlo model is developed to examine the influence of As/Ga flux ratio on the Ga desorption kinetics during molecular beam epitaxy of (100)-GaAs, based on data reported in desorption mass spectrometry experiments. A good match to experimental results is obtained when a mechanism involving desorption from a physisorbed state is included, in addition to desorption from a chemisorbed state. Analysis of the results revealed that the dependence of the Ga desorption energy on the As/Ga flux ratio, observed in growth experiments, is explained in terms of the component due to desorption from the physisorbed state. The Ga desorption energy associated with the chemisorbed state is independent of the As/Ga flux ratio. These predictions are similar to results reported in a recent study of In desorption during molecular beam epitaxy of InGaAs
Elevated Temperature Silicon Carbide Chemical Sensors
Authors: George M. A. , Ayoub M. A. , Ila D. , Larkin D. J.
Published: April 2011

In this study, the (I-V) properties of the sensors were measured as a function of hydrogen, propylene and methane exposure at temperatures up to 400° C and sensor responses were observed for each gas. The response to hydrogen and propylene had a rapid increase and leveling off of the current followed by the subsequent decrease to the baseline when the gas was switched off. However, exposure to methane resulted in a rapid spike in the current followed by a gradual increase with continued exposure. X-ray photoelectron (XPS) studies of methane exposed SiC sensors revealed that this behavior is attributed to the oxidation of methane at the Pd surface.
Characterization of Thick 4H-SiC Hot-Wall CVD Layers
Authors: Paisley M. J. , Irvine K. G. , Kordina O. , Singh R. , Palmour J. W. , Carter C. H.
Published: April 2011

Epitaxial 4H-SiC layers suitable for high power devices have been grown in a hot-wall chemical-vapor deposition (CVD) system. These layers were subsequently characterized for many parameters important in device development and production. The uniformity of both thickness and doping will be presented.

Doping trends vs. temperature and growth rate will be shown for the p-type dopant used. The n-type dopant drops in concentration with increasing temperature or increasing growth rate. In contrast, the p-type dopant increases in concentration with decreasing temperature or increasing growth rate. A simple descriptive model for this behavior will be presented.

The outcome from capacitance-voltage and SIMS measurements demonstrate that transitions from n to n−, or p to p−, and even n to p levels can be made quickly without adjustment to growth conditions. The ability to produce sharp transitions without process changes avoids degrading the resulting surface morphology or repeatability of the process. Avoiding process changes is particularly important in growth of thick layers since surface roughness tends to increase with layer thickness.

Device results from diodes producing two different blocking voltages in excess of 5 kV will also be shown. The higher voltage diodes exhibited a breakdown behavior which was near the theoretical limit for the epitaxial layer thickness and doping level grown.
Homo-Epitaxial and Selective Area Growth of 4H and 6H Silicon Carbide Using a Resistively Heated Vertical Reactor
Authors: Eshun Ebenezer , Taylor Crawford , Spencer M. G. , Kornegay Kevin , Ferguson Ian , Gurray Alex , Stall Rick
Published: April 2011

Silicon carbide technology is rapidly developing into a production process. This is due to rapid progress in the development of high quality epitaxy and substrates. We report on the development of a resistively heated vertical reactor and it's application to homo-epitaxy and selective area growth. Epitaxial growth of 4H and 6H-SiC requires high temperatures (in excess of 1500°C). In this work we investigate resistive heating which offers advantages in cost, temperature uniformity and power efficiency of heating. However, resistive heating presents major technological challenges. Due to the power efficiencies possible with resistive heating we are able to obtain temperatures in excess of 1750°C. Using this system we have grown “state of the art” 4H and 6H-SiC. At 1580°C our background doping is p-type at a level of 3–5×1015cm−3 as measured by capacitance techniques in agreement with earlier results presented by investigators from Siemens Corp using a similar system. The background concentration increases by about an order of magnitude at 1680°C. This system has also been used to perform experiments with selective area growth of SiC using a graphite mask. This masking technology allows for the growth of SiC in specific regions at elevated temperature in excess of 1600°C.
Experimental and Theoretical Analysis of the Hall-Mobility in N-Type Bulk 6H- and 4H-SiC
Authors: Müller S. T. G. , Hofmann D. , Winnacker A.
Published: April 2011

The electrical properties of nitrogen doped n-type 6H- and 4H-SiC bulk crystals grown by the Lely- or modified Lely-method have been characterized by Hall-measurements. The doping densities were determined by a fit of the neutrality equation to the experimental data, accounting for in-equivalent lattice sites and the temperature dependence of the effective density-of- states-mass extracted from recent results of ab-initio-calculations of the 6H- and 4H-SiC bandstructure [1]. The theoretical analysis of the Hall-mobility is based on an extended form of the Rode-Nag iteration algorithm [2]. The calculation scheme considers all relevant elastic and inelastic scattering mechanisms. the anisotropy of the crystal modifications and the possible effect of spatial inhomogeneities in the distribution of donors, acceptors or in the related electron system. Within these concepts it is possible to achieve a quantitative agreement between theoretical and experimental mobility data in 4H- and 6H-SiC over the whole temperature range of band conduction. New values for the acoustic deformation potentials Eac [15.0±0.5 eV (6H), 14.8±0.5 eV (4H)] and the coupling constants for intervalley phonon scattering Dint [2.3 ± 0.1 × 109eV/cm (6H), 2.6 ± 0.1 × 109eV/cm (4H)] are given.
Effect of N/Ga Flux Ratio in GaN Buffer Layer Growth by MBE on (0001) Sapphire on Defect Formation in the GaN Main Layer
Authors: Ruvimov S. , Liliental-Weber Z. , Washburn J. , Kim Y. , Sudhir G. S. , Krueger J. , Weber E. R.
Published: April 2011

Transmission electron microscopy was employed to study the effect of N/Ga flux ratio in the growth of GaN buffer layers on the structure of GaN epitaxial layers grown by molecular-beamepitaxy (MBE) on sapphire. The dislocation density in GaN layers was found to increase from 1×1010 to 6×1010 cm−2 with increase of the nitrogen flux from 5 to 35 sccm during the growth of the GaN buffer layer with otherwise the same growth conditions. All GaN layers were found to contain inversion domain boundaries (IDBs) originated at the interface with sapphire and propagated up to the layer surface. Formation of IDBs was often associated with specific defects at the interface with the substrate. Dislocation generation and annihilation were shown to be mainly growth-related processes and, hence, can be controlled by the growth conditions, especially during the first growth stages. The decrease of electron Hall mobility and the simultaneous increase of the intensity of “green” luminescence with increasing dislocation density suggest that dislocation-related deep levels are created in the bandgap.
Reproducibility and Uniformity of MOVPE Planetary Reactors® for the Growth of GaN Based Materials
Authors: Heuken M. , Protzmann H. , Schoen O. , Luenenbuerger M. , Juergensen H. , Bremser M. , Woelk E.
Published: April 2011

Production scale MOVPE reactors such as the AIXTRON 2000HT Planetary Reactor® offer unique possibilities to fabricate highly efficient GaN based devices at a low cost of ownership. The scope of this investigation is to understand the dependence of wavelength, thickness and doping uniformity on parameters such as total gas flow, temperature distribution in the reactor and purity of the precursors. Wafer to wafer uniformity in the 7×2” wafer configuration as well as run to run reproducibility will be discussed. We obtained a wafer to wafer standard deviation of 2.7% for the sheet resistance of Si-doped GaN/InGaN/GaN double heterostructures. The wafer to wafer standard deviation of the main PL emission wavelength at 412.3 nm is 1.8 nm. The run to run reproducibility of the main emission wavelength is <3 nm. We obtained reproducible resistivities of GaN:Mg layers of less than 1 Ωcm which corresponds to 5−10×1017cm−3. Statistical data of p-type doping taking 20 runs into account gave an average hole concentration of 5.5×1017cm−3. Together with the wafer to wafer thickness uniformity of <1% the most sensitive layer properties are well controlled to allow a cost-effective mass production process. Structures such as SQW and MQW structures were grown to understand the performance of a production system with respect to interface properties.
The Effects of Damage on Hydrogen-Implant-Induced Thin-Film Separation from Bulk Silicon Carbide
Authors: Gregory R. B. , Holland O. W. , Thomas D. K. , Wetteroth T. A. , Wilson S. R.
Published: April 2011

Exfoliation of SiC by hydrogen implantation and subsequent annealing forms the basis for a thin-film separation process which. when combined with hydrophilic wafer bonding, can be exploited to produce silicon-carbide-on-insulator, SiCOI. SiC thin films produced by this process exhibit unacceptably high resistivity because defects generated by the implant neutralize electrical carriers. Separation occurs because of chemical interaction of hydrogen with dangling bonds within microvoids created by the implant, and physical stresses due to gas-pressure effects during post-implant anneal. Experimental results show that exfoliation of SiC is dependent upon the concentration of implanted hydrogen, but the damage generated by the implant approaches a point when exfoliation is, in fact, retarded. This is attributed to excessive damage at the projected range of the implant which inhibits physical processes of implantinduced cleaving. Damage is controlled independently of hydrogen dosage by elevating the temperature of the SiC during implant in order to promote dynamic annealing. The resulting decrease in damage is thought to promote growth of micro-cracks which form a continuous cleave. Channeled H_ implantation enhances the cleaving process while simultaneously minimizing residual damage within the separated film. It is shown that high-temperature irradiation and channeling each reduces the hydrogen fluence required to affect separation of a thin film and results in a lower concentration of defects. This increases the potential for producing SiCOI which is sufficiently free of defects and, thus, more easily electrically activated.
Conducting (Si-Doped) Aluminum Nitride Epitaxial Films Grown by Molecular Beam Epitaxy
Authors: Kim J. G. , Moorthy Madhu , Park R. M.
Published: April 2011

As a member of the III-V nitride semiconductor family, AlN, which has a direct energygap of 6.2eV, has received much attention as a promising material for many applications. However, despite the promising attributes of AlN for various semiconductor devices, research on AlN has been limited and n-type conducting AlN has not been reported. The objective of this research was to understand the factors impacting the conductivity of AlN and to control the conductivity of this material through intentional doping. Prior to the intentional doping study, growth of undoped AlN epilayers was investigated. Through careful selection of substrate preparation methods and growth parameters, relatively low-temperature molecular beam epitaxial growth of AlN films was established which resulted in insulating material. Intentional Si doping during epilayer growth was found to result in conducting films under specific growth conditions. Above a growth temperature of 900°C, AlN films were insulating, however, below a growth temperature of 900°C, the AlN films were conducting. The magnitude of the conductivity and the growth temperature range over which conducting AlN films could be grown were strongly influenced by the presence of a Ga flux during growth. For instance, conducting, Si-doped, AlN films were grown at a growth temperature of 940°C in the presence of a Ga flux while the films were insulating when grown in the absence of a Ga flux at this particular growth temperature. Also, by appropriate selection of the growth parameters, epilayers with n-type conductivity values as large as 0.2 Ω−1 cm−1 for AlN and 17 Ω−1cm−1 for Al0.75Ga0.25N were grown in this work for the first time.
Fast and Slow UV-Photoresponse in n-Type GaN
Authors: Rocha R. , Koynov S. , Brogueira P. , Schwarz R. , Chu V. , Topf M. , Meister D. , Meyer B. K.
Published: April 2011

The photocurrent decay in n-type GaN films prepared by low-pressure chemical vapor deposition (LPCVD) was measured in the ms-to-s time range using steady-state UV light and in the μs time regime using short high-power pulses from higher harmonics of a Nd:YAG laser. A power law time dependence is observed with exponents ranging from −0.1 to −0.3, which is an indication of a broad distribution of trapping states inside the band gap. Combining Hall effect results and the magnitude of the initial slope of the photocurrent decay we estimate a mobility-lifetime product of 2.1×10−4 cm2/V for photogenerated electrons at times below a few μs. Slow transients might be a handicap for applications of GaN in UV detectors.