Defects in SiO2 and Related Dielectrics: Science and Technology

618 Pages·2000·27.414 MB·English

by  Adrian C. Wright (auth.), G. Pacchioni, L. Skuja, D. L. Griscom (eds.)

Defects in Si0 and Related Dielectrics:
2
Science and Technology
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Series II: Mathematical and Physical Chemistry - Vol. 2
Defects in SiÜ2 and Related
Dielectrics:
Science and Technology
edited by
G. Pacchioni
Dipartimento di Scienza dei Materiali,
Universitä Milano-Bicocca,
Milano, Italy
L. Skuja
Institute of Solid State Physics,
University of Latvia,
Riga, Latvia
and
D. L Griscom
Naval Research Laboratory,
Washington DC, U.S.A.
Springer Science+Business Media, B.V.
Proceedings of the NATO Advanced Study Institute on
Defects in SiÜ2 and Related Dielectrics: Science and Technology
Erice, Italy
April 8-20, 2000
A C.I.P. Catalogue record for this book is available from the Library of Congress.
ISBN 978-0-7923-6686-7 ISBN 978-94-010-0944-7 (eBook)
DOI 10.1007/978-94-010-0944-7
Printed on acid-free paper
All Rights Reserved
©2000 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 2000
Softcover reprint of the hardcover 1st edition 2000
No part of the material protected by this copyright notice may be reproduced or utilized in
any form or by any means, electronic or mechanical, including photocopying, recording
or by any information storage and retrieval system, without written permission from the
copyright owner.
CONTENTS
Preface ............................................................................................................................................... vii
Structure and topology
Defect-free vitreous networks: The idealised structure of Si0 and related glasses
2
A. C. Wright .............................................................................................. , ............................ .
Topology and topological disorder in silica
L. W Hobbs and X Yuan ............ ............ ...................... ........ ................................ ................. 37
Bulk defects
Optical properties of defects in silica
L. Skuja ................................................................................................................................ 73
The nature~ of point defects in amorphous silicon dioxide
D. L. Griscom ...... .................................................. ............................ .......................... ...... 117
Ab initio theory of point defects in Sial
G. Pacchioni ....................................................................................................................... 161
A demi-century of magnetic defects in a-quartz
J A. Weil ............................................................................................................................. 197
Interaction of Sial glasses with high energy ion beams and vacuum UV excimer laser pulses
H. Hosono and K. Kawamura ............................................................................................. 213
Excitons, localized states in silicon dioxide and related crystals and glasses
A. N. Trukhin ....................................................................................................................... 235
Gamma rays induced conversion of native defects in natural silica
FM. Gelardi and S. Agnello ................................................................................................ 285
Ge and Sn doping in silica: structural changes, optically active defects, paramagnetic sites
A. Paleari ............................................................................................................................ 307
Computational studies of self-trapped excitons in silica
L.R. Corrales, J Song, R.M. VanGinhoven and H. Jonsson ............................................... 329
Surface defects
Defects on activated silica surface
VA. Radzig ........................................................................................................................ 339
vi
Ab-initio molecular dynamics simulation of amorphous silica surface
M Bernasconi .................................................................................................................... 371
Bragg grating
Periodic UV -induced index modulations in doped-silica optical fibers:
formation and properties of the fiber Bragg grating
C. G. Askins ....................................................................................................................... 391
Bulk silicas prepared by low pressure plasma CVD: formation of structure and point defects
K M Golant ....................................................................................................................... 427
Change of spectroscopic and structural properties of germanosilicate glass under
mechanical compression and UV irradiation
V. M Mashinsky ............................................................................................................... 453
UV photoinduced phenomena in oxygen-deficient silica glasses
A. Rybaltovskii .................................................................................................................. 471
One-and two-quantum UV photo-reactions in pure and doped silica glasses.
2. Germanium oxygen deficient centers (GODC)
V. N Bagratashvili, S. l Tsypina, P. V. Chernov, A. 0. Rybaltovskii,
Yu. S. Zavorotny ................................................................................................................. 499
Photoinduced refractive index change and second harmonic generation in MCVD
germanosilicate core fibres fabricated in reduced (nitrogen and helium) atmospheres
E. M Dianov, A. N Guryanov, V. F Khopin, V. M Mashinsky, 0. l Medvedkov,
0. D. Sazhin, S. A. Vasiliev, N N Vechkanov, Yu. P. Yatsenko ....................................... 515
SilSiO interface and gate dielectrics
l
Molecular hydrogen interaction kinetics of interfacial Si dangling bonds in thermal
(111)Si/Si02. An electron spin resonance saga
A. L. Stesmans ................................................................................................................... 529
Ultrathin oxide films for advanced gate dielectrics applications
Current progress and future challenges
E. P. Gusev ....................................................................................................................... 557
SiC/Si0 interface defects
2
V. V. Afanas'ev .................................................................................................................. 581
Point defects in Si-Si0 systems: current understanding
2
s.p Karna, H.A. Kurtz, A.C. Pineda, W.M Shedd and R.D. Pugh ..................................... 599
Index ................................................................................................................................................ 617
PREFACE
Silicon dioxide plays a central role in most contemporary electronics and photonics
technologies. Indeed, its amorphous form (a-Si02) is present in the cores and claddings of
fiber optics for communications and medical applications, comprises the gate and
passivation oxide layers in 90% of all metal-oxide-semiconductor (MOS) devices (e.g.,
computer chips), is used to fabricate windows, photomasks, and transmissive optics for
excimer-Iaser microchip lithography, and is commonly one of the components of the
multi-layer coatings used to produce highly reflective mirrors or highly transmissive lenses
for laser optics. The crystalline a-quartz form of silicon dioxide is fabricated into
frequency standards (e.g., for digital watches) and accelerometers. In many of these
applications, point defects introduced during the manufacturing process, generated by
stressful operating conditions (e.g., by focussing of ultraviolet photons), or resulting from
ambient exposures to ionizing radiations (e.g., in satellite deployments or near nuclear
reactors) can degrade the otherwise excellent optical, insulating, and/or mechanical
properties of a-Si02 or a-quartz, leading to potential device failures. In other cases, such
as holographically written fiber Bragg gratings, selectively created point defects form the
bases for completely new technologies.
A half century of spectroscopic examinations of point defects in glassy silica and a-quartz
have led to the identification and characterization of about a dozen intrinsic defect types
(those constructed of silicon and/or oxygen atoms or ions) and around ten times as many
defect varieties involving the presence of impurities. Thus it should not be surprising that
scientists working in different countries, using forms of Si02 fabricated by unusual
methods, and employing widely differing experimental and theoretical approaches, have
often arrived at seemingly contradictory model interpretations of the point defects
responsible for various spectroscopically recorded phenomenologies. Until the lifting of
the "iron curtain", east-versus-west dichotomies were particularly commonplace, although
strong disagreements among scientists within a single country were certainly not unheard
of. But during the last decade of the twentieth century researchers in this field from all
comers of the globe began to fraternize with their former rivals and, like the "blind men
and the elephant", have gradually come to the realization that the surest path to deeper
knowledge lies in improved communication and collegial efforts to resolve apparent
imbroglios.
It was in this spirit that the NATO Advanced Study Institute "Defects in Si02 and Related
Dielectrics: Science and Technology" was convened in Erice, Italy, April 8-20, 2000. 14
invited speakers summarized the states of the art of electron paramagnetic resonance (EPR)
Vll
Vlll
and optical spectroscopy of point defects both on the surfaces and in the interiors of pure
and doped a-Si02 in bulk, thin-film and fiber forms, of ab initio calculations of the models
proposed for these defects, of devising model structures for "defect free" forms of a-Si02,
and of the "ground truth" of point-defect structures in a-quartz crystals unambiguously
determined by EPR. By the end of the Institute there was a sense that some of the most
vexing controversies of the past few decades were beginning to evaporate in the heat and
light of collegial exposition, debate, and synthesis. But, by the same token, some new
mysteries emerged, some of which may eventually be solved by some of the about 80
students from 24 different countries in attendance.
The editors gratefully acknowledge the very generous support provided by NATO, which
made it possible for several participants from NATO countries and from former "East
block" countries to be present at the meeting. Without this support, neither the course nor
the production of this book would have been possible. NATO was not the sole sponsor of
the meeting. Significant contributions came also from the US Office of Naval Research
Europe, from UNESCO, and from the National Science Foundation. A special thanks goes
to the other members of the Scientific Committee, Victor Radzig (Moscow) and Shashi
Kama (Albuquerque) who also helped us in editing this book.
Finally, we are indebted to the staff of the E. Majorana Centre for Scientific Culture in
Erice for their hospitality, efficiency, attention to detail, and unfailing good humor that
contributed making the school the successful and highly enjoyable occasion that it was.
Gianfranco Pacchioni
Milan, Italy
Linards Skuja
Riga, Latvia
David L.. Griscom
Washington DC, USA
DEFECI'-FREE VITREOUS NETWORKS:
The Idealised Strocture 0/Si0 and Related Glasses
2
Adrian C. WRIGlIT
J.J. Thomson Physical Laboratory, University ofR eading,
Whiteknights, Reading, RG6 6AF, U.K
1. Introduction
"Randomness and disorder are almost
synonymous with uncertainty and ignorance. "
G.S. Rushbrooke
Whereas, for crystalline materials, the concept of a defect is easy to defme, the same is not
true for amorphous solids·, due to the statistical fluctuations which are an inherent feature
of their structure. Thus, before it is possible to identify defects in an amorphous structure,
it is frrst necessary to establish what is meant by the ideal defect-free structure into which
they are to be introduced and, in particular, the extent of such fluctuations which can be
considered to be a normal and integral part of that structure. It should also be noted that,
since the ideal structure is disordered, departures from normality can occur in the
direction of both decreased and increased order, the former leading to what are commonly
known as defects.
Vitreous Si0 is the archetypal oxide glass former and hence it is perhaps surprising
2
just how little is really known, as opposed to merely postulated, about its structure and
those of the related AX2 glasses summarised in Table ]. The present chapter, therefore,
will attempt to define these ideal structures and will briefly summarise the results of
experimental techniques for their quantitative characterisation.
Si0 exists as a variety of crystalline polymorphs [2] which, with the exception of one
2
high-pressure form (stishovite), comprise networks of Si0 tetrahedra. In the case of
4
crystalline networks, the perfect structure is defmed by the crystallographer's unit cell plus
translational symmetry, the latter leading to the sharp Bragg peaks typical of a crystalline
solid. A complete specification of the perfect (infmite) structure, therefore, requires
relatively few parameters (i.e. the lattice parameters together with the fractional co-
• In this chapter the teons vihwllIS and gltISS will be reserved for materials covered by the ASTM definition of a
glass as "an inorganic product of fusion which has cooled to a rigid condition without crystallising."
G. Pacchioni et at. (eds.), Defects in Si02 and Related Dielectrics: Science and Technology, 1-35.
© 2000 Kluwer Academic Publishers.
2
ordinates and thermal parameters for the atoms in the asymmetric unit) and hence, given
accurate diffraction data over a reasonable region of reciprocal space, it is in practice
relatively straightforward to uniquely determine the structure ofa simple crystalline solid.
AJS
TABLE 1. Glass Fonners (II
AJS T, (K.) Till (K.) T, ITm ,eD(C.U. A·3)
Si02 1463 1996 0.73 0.02206
8eF2 598 813 0.74 0.02562
Ge02 853 1389 0.61 0.02098
ZnC~ 388 591 0.66 0.01198
GeSe2 703 1013 0.69 0.01103
An amotphous solid, on the other hand, has a structure which lacks periodicity,
extended symmetry and long range order and it is the absence of the last of these that
leads to a diffraction pattern which is a continuous and relatively slowly varying function
of the scattering vector magnitude,
=
Q (41tU) sin 0, (1)
where A. is the incident X-ray or neutron wavelength and 20 the scattering angle, in
contrast to the sharp Bragg peaks of a crystalline material. Hence, in order to completely
defme the structure of an amotphous solid, it would be necessary to specify the c0-
ordinates and thermal parameters of every atom present, which is clearly impossible for a
real sample. In addition, because amotphous solids are normally isotropic on a
macroscopic scale, the maximum that can be obtained from a diffraction experiment on
an amotphous solid is a one-dimensional correlation function, from which the
regeneration of the underlying three-dimensional structure can never be unique. It is for
this reason that modelling plays such an important role in structural studies of amotphous
solids and why the choice between possible models involves a wide range of
experimental techniques and not just X-ray and/or neutron diffraction. The maximum that
can be achieved in an experimental study is a structural model which is consistent with all
the known data but, even if perfect agreement were to be obtained between model and
experiment, this is no guarantee that other models could not be generated which would fit
equally well.
1.1. CRYSTALLITE THEORY
The first structural theory of glasses was the early crystaOite theory which envisaged
glass as an aggregate of extremely small crystals, termed crystallites, with fairly sharp
external boundaries. Although it is generally attributed to Lebedev [3], the crystallite
theory was in fact first proposed in 1835 by Frankenheim [4], thus predating the frrst