Electronic Engineering

Epitaxy and chemical reactions during thin-film formation from low-energy ions: new kinetic pathways, new phases, and new properties

by Nicole Herbots

Nicole Herbots, O.C. Hellman
ARIZONA STATE UNIVERSITY, Departmentof PhysicsandAstronomy, Tempe AZ 85287
0. Vancauwenberghe* MASSACHUSETTS INSTITUTE OFTECHNOLOGY, DepartmentofMaterialsScience & Engineering,Cambridge, MA 02139

Ref: Mat. Res. Soc. Symp. Proc. Vol. 235. pp. 749-762 (1992)

ABSTRACT
Three important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of... more ABSTRACT
Three important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of material into a substrate, the enhancement of atomic mobility in the subsurface, and the modification of growth kinetics it creates. All lead to a significant lowering of the temperature necessary to induce epitaxial growth and chemical reactions. The fundamental understanding and new applications of low temperature kinetics induced by low energy ions in thin film growth and surface processing of semiconductors are reviewed. It is shown that the mechanism of IBD growth can be understood and computed quantitatively using a simple model including ion induced defect generation and sputtering, elastic recombination, thermal diffusion, chemical reactivity, and desorption. The energy, temperature and dose dependence of growth rate, epitaxy, and chemical reaction during IBD is found to be controlled by the net recombination rate of interstitials at the surface in the case of epitaxy and unreacted films, and by the balance between ion beam decomposition and phase formation induced by ion beam generated defects in the case of compound thin films. Recent systematic experiments on the formation of oxides and nitrides on Si, Ge/Si(100), heteroepitaxial SixGe1−x/Si(100) and GaAs(lOO) illustrate applications of this mechanism using IBD in the form of Ion Beam Nitridation (IBN), Ion Beam Oxidation (IBO) and Combined Ion and Molecular beam Deposition (CIMD). It is shown that these techniques enable (1) the formation of conventional phases in conditions never used before, (2) the control and creation of properties via new degrees of freedom such as ion energy and lowered substrate temperatures, and (3) the formation of new metastable heterostructures that cannot be grown by pure thermal means.

RBS STUDY OF THE EFFECT OF ARSENIC AND PHOSPHORUS INTERFACIAL SEGREGATION UPON THE SINTERING OF CONTACTS BETWEEN IMPLANTED POLYCRYSTALLINE SILICON AND ALUMINUM -SILICON(1%)

by Nicole Herbots

Nicole HERBOTS *, Maurice LOBET and Femand Van de WIELE
Microekxtronics Lab, Uniwrsite Catholique de Lmamin, 3, place du Levant. B - 1348 Louvain -la - Neuve, Belgium
Nuclear Instruments and Methods in Physics Research B7/8 (1985) 278-286 North-Holland, Amsterdam

The sintering behavior of the interface between Al :Si(l%) alloy and polycrystalline Si (poly-Si) was studied as a... more The sintering behavior of the interface between Al :Si(l%) alloy and polycrystalline Si (poly-Si) was studied as a function of the poly-Si implantation dose by combining RBS, SEM, TEM and X-ray microanalysis. Two different N-dopants were used: arsenic and phosphorus. The dopants were implanted in the poly-Si layer and thermal annealing was used to obtain dopant segregation towards the poly-Si interfacea.
After sir&ring, two main effects were detected: (1) Al-Si eutectic phase precipitates and Si crystallites are formed at the interface. (2) The density of precipitates is a function of the implantation dose. For doses above 1 x lOI5 at./cm2. segregated arsenic and phosphorus are found to completely inhibit this precipitation process, provided that the segregation peak of the dopant profile is preserved before metallization.
Several conclusions can be drawn: for surface concentrations higher than 8~10’~ at./cm3, arsenic and phosphorus inhibit the precipitation of the Al-Si eutectic phase, and thus inhibit interactions between the films at the interface. Moreover, argon gas, usedfor sputtering deposition of aluminum, segregated at the poly-Si/Al: Si(l%) interface and may also inhibit the metal-semiconductor interdiffusion.

All-polymer microfluidic particle size sorter for biomedical applications

by Javier G. Fernandez

Co-authored with Christopher A. Mills and Josep Samitier, Published in "Physica Status Solidi"

The design and method for the production of an all-polymer microfluidic particle sorter, for use in biomedical... more The design and method for the production of an all-polymer microfluidic particle sorter, for use in biomedical applications, is described. The sorter is made from biocompatible materials with properties, such as high optical transparency, that make it useful in a biological laboratory. The method of sorting is designed to be gentle on biological species, using a method of guiding the particles towards the filter, and has been successfully used to separate latex beads depending on their diameters. Preliminary qualitative experiments have been able to separate beads of 45 and 90 μm in diameter from a mixture of the two. These dimensions are on the same scale as those of some eukaryotic cells

Thin film formation from low energy ions: new kinetic paths, new properties, new phases

by Nicole Herbots

N Herbots (Massachusetts Institute of Technology, USA)

MATERIALS & DESIGN Vol. 13 No. 2 APRIL 1992

MRS fall meeting: A selective review

Advances in the science and technology of communication and computing devices (electronics and optoelectronics... more Advances in the science and technology of communication and computing devices (electronics and optoelectronics devices) have relied heavily during the second half of the 20th century upon the scaling down of device dimensions. These dimensions are now close to the average distance between atoms in solid matter. More specifically, the very operation of new devices depends critically on the arrangement of atoms at interfaces, ie the junction of two different materials, as shown in Fig. 3. Interfaces are now often confined within one single atomic plane. In addition to the decrease in spatial dimen- sions, the complexity of the material structure has increased significantly as well. For instance, the number of interfaces found in a device has multiplied. This has led to the name of 'artificially structured materials', to emphasize the remoteness of atomic arrangement found in such structures with respect to those found as 'naturally occurring in nature'.
These structures can be described as a succession of ultra- thin solid films. These films are often epitaxial - from the Greek epi-, skin or surface, and -taxos, order - which means that each atomic layer is organized as in a periodic crystal, even at heterointerfaces where different materials join,

A quantitative model of point defect diffusivity and recombination in ion beam deposition and combined ion and molecular deposition

by Nicole Herbots

O. Vancauwenberghe, N. Herbots, and O. C. Hellman MassachusettsInstituteo/Technology, 77MassachusettsAvenue. Cambridge. jWassachusetts02139
(Received 18 October 1990; accepted 12 February 1991)
J. Vac. Sci. Techno!. B 9 (4), JullAug 1991, p.2027-2033 0134-211X/911042027-07$01.00 @ 1991 American Vacuum Society 2027

We are investigating the use of low energy ions (< 1 keV) in low temperature thin film growth techniques, ion beam... more We are investigating the use of low energy ions (< 1 keV) in low temperature thin film growth techniques, ion beam deposition (IBD) and combined ion and molecular deposition (CIMD). In IBD, a thin film is directly grown from a low energy ion beam as the only source of material, while in CIMD, low temperature growth of thin films is achieved by depositing materials simultaneously from a low energy ion beam and one or several molecular beams. A simple model of the IBD process has been developed and accounts for atomic collisions and thermal diffusion during thin film growth. Computer simulation of IBD of Si on Si have been conducted as a function of ion energy to support more quantitatively this physical description of IBD. The results show that the IBD growth mechanism is mediated by the fast diffusing interstitials and establish a low energy limit to achieve epitaxial growth by IBD that depends on the point defect diffusivities. The defect generation has to be confined in the subsurface region in order to favor interstitial recombination with the surface, leading to net thin film growth, and vacancy annihilation to prevent amorphization. The effect of point defect diffusivities on the IBD growth process is also investigated. It is found that a model including fast moving interstitials can account for various experimental observations specific to IBD.

Ion-solid interactions during ion beam deposition of 74Ge and 30Si on Si at very low ion energies (0-200 eV range)

by Nicole Herbots

ION-SOLID INTERACTIONS DURING ION BEAM DEPOSITION OF 74Ge AND 30Si ON Si AT VERY LOW ION ENERGIES (O-2OO eV RANGE)*
N. HERBOTS, B.R. APPLETON, T.S. NOGGLE, R.A. ZUHR and S.J. PENNYCOOK
Solid State Division, Oak Ridge National Laboratory, PO Box X, Oak Ridge, TN 37831, USA
Nuclear Instruments and Methods in Physics Research B13 (1986) 250-258 North-Holland, Amsterdam

Atomic collisions in solids in the 40-200 eV energy range have been studied both theoreticalIy and experimentaIiy to... more Atomic collisions in solids in the 40-200 eV energy range have been studied both theoreticalIy and experimentaIiy to determine the feasibility of the ion beam deposition (IBD) of amorphous and/or epitaxial layers. IBD was first modeled by a rate equation including the target sputtering yield and the ion self-sputtering, range and range straggling. To obtain preliminary values of those parameters, Monte Carlo simulations with TRIMSPUT were used. The surface binding energy (SBE) appeared to be an important parameter of the simulation for sputtering yields under 200 eV. By fitting the SBE with available sputtering data for Ar on Si below 1 keV, a very good agreement waso obtained between simulations and sputtering data of other ion-target combinations. Experimentally, 30Si and 74Ge ions were deposited on Si( 100) at 300 K and 700 K. Cross-section TEM combined with ion scattering and ion channeling showed that IBD can provide very thin (3 nm) though perfectly continuous films with sharp interfaces (<l nm). IBD damage to the substrate saturates as a function of dose, is negligible below 4OeV, and presents an interesting annihilation/long range diffusion behavior as a
function of the temperature during irradiation.

Heteroepitaxial properties of SiGeC on Si (100) grown by combined ion-and molecular-beam deposition

by Nicole Herbots

Author(s): Jacobsson, H (Jacobsson, H); Xiang, J (Xiang, J); Herbots, N (Herbots, N); Whaley, S (Whaley, S); Ye, PH (Ye, PH); Hearne, S (Hearne, S)
Source: JOURNAL OF APPLIED PHYSICS Volume: 81 Issue: 7 Pages: 3081-3091 DOI: 10.1063/1.364352 Published: APR 1 1997

The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1-x-yGexCy on Si(100), has been... more The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1-x-yGexCy on Si(100), has been investigated. The epitaxial quality of Si1-x-yGexCy is found to be inferior to that of Si1-xGex with similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank-van der Merve to Stranski-Krastanov type growth. We suggest that the very large mismatch between the average bond length in the Si1-x-yGexCy material, as determined by Vegard's law, and the equilibrium Si-C bond length, weakens the Si-C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier for island formation or indirectly through the formation of defects. A decrease in Ge incorporation in the Si1-x-yGexCy films with increasing C incorporation suggests a repulsive Ge-C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 degrees C, whereas at 450 degrees C no such phase can be observed. The temperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to detect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fraction and its substitutionality is emphasized. (

Long range ordered semiconductor interface phase and oxides

by Nicole Herbots

Herbots; Nicole (Tempe, AZ), Atluri; Vasudeva P. (Scottsdale, AZ), Bradley; James D. (Gilbert, AZ), Swati; Banerjee (Chandler, AZ), Hurst; Quinton B. (Tempe, AZ), Xiang; Jiong (Tempe, AZ)

A semiconductor processing method capable of producing highly ordered, ultra thin dielectrics, including gate oxide... more A semiconductor processing method capable of producing highly ordered, ultra thin dielectrics, including gate oxide and other semiconductor dielectrics, and interphase phases with low defect density. The process includes a degrease step, an etch, primary oxidation and then a passivation step which utilizes hydrofluoric acid to passivate the cleaned silicon surface with hydrogen. Dielectric layers may then be formed with low interface defect density, low flat band voltages and low fixed charge on semiconductor substrates.

ATOMIC TRANSPORT KINETICS ACROSS Al/Si INTERFACES

by Nicole Herbots

Teaching-learning environments and student learning in electronic engineering

by Adrian Bromage

Entwistle, N. A., Nisbet, J. and Bromage, A. (2004) Paper presented at the Third Workshop of the European Network on Powerful Learning Environments, Brugge, 30 September to 2 October 2004

This paper presents early findings from the ETL project, a national study in Britain which is investigating teaching... more This paper presents early findings from the ETL project, a national study in Britain which is investigating teaching and learning across five contrasting subject areas in higher education. The focus here is on electronic engineering and, in particular on analogue electronics. Staff in six course units have collaborated with the researchers to enable data to be collected from their students, and in four of the units changes were made
on the basis of the evidence presented to the them. The effects of these ‘collaborative initiatives’ were investigated using data obtained from the following year groups derived from questionnaires and interviews with both students and staff. On this basis, a clearer idea has been developed about the nature of teaching and learning in the subject with implications for ways of enhancing the teaching-learning environments provided for students in future.

Infrared spectroscopic analysis of an orderedSi/SiO2 interface. Appl. Phys. Lett., 84 (4), pp. 493-496.

by Nicole Herbots

Queeney, K.T., Herbots, N., Shaw, J.M., Atluri, V. & Chabal, Y.J. (2004).

Source: APPLIED PHYSICS LETTERS Volume: 84 Issue: 4 Pages: 493-495 DOI: 10.1063/1.1644030 Published: JAN 26 2004

Infrared spectroscopy is used to compare the Si/SiO2 interfaces created by thermal oxidation of a standard Si(100)... more Infrared spectroscopy is used to compare the Si/SiO2 interfaces created by thermal oxidation of a standard Si(100) substrate and of an ordered, (1x1) Si(100) substrate. The thermal oxides (approximately 25 Angstrom) examined in this study are etched in dilute hydrofluoric acid and the resulting films analyzed spectroscopically. The behavior of the dominant optical phonon modes as a function of film thickness provides strong evidence that the ordered Si(100) substrate provides a template for an Si/SiO2 interface with a higher degree of homogeneity in the Si-O bonding environment of the intervening substoichiometric SiOx layer than does the standard Si(100) substrate. (C) 2004

Genesis of our discovery of ordered interphases of SiO2, a journalist's perspective

by Nicole Herbots

This article was written by a reporter for the Research Corporation Bulletin in 1999 after he interviewed me following a Research Opportunity Award in the amount of $25 k from the Research Corp. ASU and ARBOR matched the award with another $25k.

Dr. Herbots, Belgian-born, Ph.D. graduate in applied physics of Catholic University of Louvain and a microelectronics... more Dr. Herbots, Belgian-born, Ph.D. graduate in applied physics of Catholic University of Louvain and a microelectronics specialist, made progress in the course of three years as an Oak Ridge Re- search Associate and four years as an MIT professor (1987-1991). At MIT she developed new methods for synthesizing thin film layers on chips at low temperatures, and for creating films that can’t be grown using thermal processes.

She joined Arizona State University in 1991,  to further develop a novel invention she had made at MIT. Called Combined Ion and Molecular Beam Deposition or CIMD, it is a  tech- nique for depositing materials on semiconductors that combines a so- phisticated evaporation system (molecular beam deposition) with an easily controlled ion beam.
But a life-threatening accident curtailed her research
After building a CIMD clean room at Arizona State University and getting research off to a good start, Nicole Herbot’s work, almost her life, came to an abrupt end in May 1994.  This is where the history of her research in ordered nanophases of SiO2 on Si(100) began. She had to rebuild her scientific understanding of matter,  interfaces, phase structures and nanophases after losing her short memory and developing "petit mal" (a milder form of epilepsy characterized by short or longer "absences" where the patient loses awareness of surroundings without loss of consciousness). The episodes increase with fatigue, mild illnesses and colds, to several a day.  They result in post-"absences" exhaustion, typical of epilepsy, where the patient needs to sleep for a period of time concomittant with the duration of the absences to recover.  The condition precludes driving.
The long hours spent on bed rest recovering from the petit mal absences gave her the time to reflect on the continuing mystery of SiO2/Si(100) extraordinary properties in microelectronics.  This is how her "Tsunami" model of structural collapse as Si(100) crystals oxidizes into an amorphous film came to be, and a new concept to prevent structure loss and thus grow heteroepitaxial SiO2 on Si(100) was conceived, and led to several patents (2003, 2010), PhD theses and papers.

Tuning Schottky diodes at the many-layer-graphene/ semiconductor interface by doping

by Sefaattin Tongay

Ultrapure multilayer graphene in bromine-intercalated graphite

by Sefaattin Tongay

Polymer stabilized chiral nematic liquid crystals for fast switching and high contrast electro-optic devices

by Flynn Castles

Published in 'Applied Physics Letters' [copyright (2009) American Institute of Physics].

D. J. Gardiner, S. M. Morris, F. Castles, M. M. Qasim, W.-S. Kim, S. S. Choi, H.-J. Park, I.-J. Chung, and H. J.... more D. J. Gardiner, S. M. Morris, F. Castles, M. M. Qasim, W.-S. Kim, S. S. Choi, H.-J. Park, I.-J. Chung, and H. J. Coles

Official link: http://link.aip.org/link/doi/10.1063/1.3605597
PDF: http://www.eng.cam.ac.uk/~fc252/APL_98_263508_2011.pdf

A fast switching electro-optic device, based upon the in-plane addressing of very short pitch polymer stabilized chiral nematic liquid crystals, is presented. Polymer stabilization of the standing helical arrangement is essential to prevent the appearance of defects above the in-plane electrodes. Response times as short as 50 ls are observed at room temperature along with contrast ratios greater than 3000:1 owing to the high optical extinction at visible wavelengths in the “Off” state. The combination of these fast response times with such high contrast ratios is of great importance for next generation electro-optical elements.

Electronic Properties of SnO2-Based Ceramics with Double Function of Varistor and Humidity Sensor

by Benjamin Jones

A. B. GLOT, A. P. SANDOVAL-GARCIA, A. V. GAPONOV, R. BULPETT, B. J. JONES and G. JIMENEZ-SANTANA
Advances in Technology of Materials and Materials Processing 10 (2009) 21

Tin dioxide based varistor ceramics SnO2-Co3O4-Nb2O5-Cr2O3-xCuO (x=0; 0.05; 0.1 and 0.5) were made and their... more Tin dioxide based varistor ceramics SnO2-Co3O4-Nb2O5-Cr2O3-xCuO (x=0; 0.05; 0.1 and 0.5) were made and their electrical properties were studied. The highest nonlinearity coefficient and electric field (at current density 10-3 A cm-2) were obtained for 0.1 mol.% CuO addition. It was observed that low-field electrical conductivity is increased with relative humidity, therefore, materials obtained exhibit double function of varistor and humidity sensor. The highest humidity sensitivity coefficient is found for SnO2-Co3O4-Nb2O5-Cr2O3 ceramics (without CuO). Observed varistor and humidity-sensitive properties are explained in the frames of grain-boundary double Schottky barrier concept as a decrease of the barrier height with electric field or relative humidity. Using suggested simple theory and data obtained on isothermal capacitance relaxation, the energy of the grain-boundary monoenergetic trapping states were estimated. These values are less than found for activation energy of electrical conduction (as a measure of the barrier height). These observations confirm the barrier concept.

tin oxide; tin dioxide; varistor; electronic material; sensor; humidity; grain boundary; interface; surfaces; non linear resistance; non ohmic; tin; copper; cobalt; chromium; niobium

Biomechanical Fracture Healing Simulation for Smart Implants Using Telemetry

by Benjamin Jones

J.L. Nemchand, A.W. Anson, B.J. Jones, D. Wilson, S. Taylor
Journal of Biomechanics 43S1 (2010) S69

Electro-thermal coupling analysis methodology for RF circuits

by Didac Gómez

Didac Gómez, Cédric Dufis, Josep Altet, Diego Mateo, José Luis González
Accepted for publication in Microelectronics Journal.
(expanded version of the work presented at THERMINIC 2010).

In this paper an electro-thermal co-simulation methodology suitable for RF circuits is presented. It circumvents... more In this paper an electro-thermal co-simulation methodology suitable for RF circuits is presented. It circumvents traditional transient simulation drawbacks that arise when signals or magnitudes whose frequencies are separated orders of magnitude are present simultaneously in the simulated circuit. The accuracy of the proposed technique is verified experimentally by comparing simulation and measurements of the thermal coupling between an integrated Power Amplifier (PA) and a differential temperature sensor embedded in the same silicon die, using a 65 nm CMOS technology.

DESIGN OF A 2.5-GHz QVCO ROBUST AGAINST HIGH FREQUENCY SUBSTRATE NOISE

by Didac Gómez

M. Molina, D.Gomez, X.Aragones, D.Mateo and J. L.Gonzalez
Microwave And Optical Technology Letters

This work presents the design procedure followed to obtain a low-power voltage-controlled oscillator (VCO) robust... more This work presents the design procedure followed to obtain a low-power voltage-controlled oscillator (VCO) robust against high-frequency substrate noise, using as a demonstrator a 2.5 GHz VCO with quadrature outputs (QVCO) based on a 5-GHz LC tank resonant VCO (LC-VCO) and frequency divider. A simple, intuitive, and easy to handle analytical model is proposed to identify the design parameters that contribute to the performance degradation of LC-VCOs due to the effect of high frequency substrate noise. The guidelines obtained have been applied in the design of the low-power QVCO. Finally, the work discusses several trade-offs that can be used to maximize the immunity of a LC-VCO against substrate noise.

Development of Digital Vehicle Distance Monitoring System

by Mohd Helmy Abd Wahab