Table Of ContentTibor Grasser E ditor
Bias
Temperature
Instability for
Devices and
Circuits
BiasTemperature Instability for Devices and Circuits
Tibor Grasser
Editor
Bias Temperature Instability
for Devices and Circuits
123
Editor
TiborGrasser
InstituteforMicroelectronics
TechnischeUniversita¨tWien
Wien,Austria
ISBN978-1-4614-7908-6 ISBN978-1-4614-7909-3(eBook)
DOI10.1007/978-1-4614-7909-3
SpringerNewYorkHeidelbergDordrechtLondon
LibraryofCongressControlNumber:2013948914
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Editorial
First observations of a threshold voltage instability in MOS transistors which
was found to be very sensitive to bias and temperature were made in the 1960s.
However,thisbiastemperatureinstability(BTI)hasremainedarelativelyobscure
and unimportant phenomenon until the routine introduction of nitrogen into the
oxide around the year 2000. Since then, particularly the negative BTI (NBTI) in
pMOSFETs has received a considerable amount of attention, both from industry
andfromacademia.With theadventof high-kgatestacks, thepresumablyrelated
phenomenon of the positive BTI (PBTI) in nMOSFETs has been attracting a
comparableamountofinterest.
Despiteitsnearly50-year-longhistory,BTIhasremainedahighlycontroversial
issue,andmanyfundamentalquestionsmaybeconsideredunresolved.Theplethora
ofobservations,explanations,aswellaspossiblephysicalmodelsfoundinliterature
isoftenhighlyconfusing.Oneaspectoftheconfusionisrelatedtotheexponentially
growingnumberofpublicationsonthetopic,whichcontainnumerouscontradictory
claims. Furthermore, viewpoints within the same research group evolve as new
aspectsofthephenomenonarerevealed.Inordertoresolveatleastthispartofthe
confusion,Ihaveattemptedtobringtogetherworld-leadinggroupsworkingonthat
topic to review, define, and summarize their currentunderstanding of a particular
aspect of the phenomenon more clearly and in greater detail than is possible in
regularjournalandconferencepublications.
The book is structured in four chapters and encompasses characterization,
defect/device modeling, technological impact, and circuit aspects. The opening
chapter looks into the primary challenges we face in our understanding of BTI,
namely characterization issues. The most prominentexample is given by the fact
that the degradation induced by BTI recovers once the stress bias is removed,
an issue already discussed in the earliest papers. However, it was only realized
about10yearsagothatthisrecoveryhasadramaticimpactonallcharacterization
attempts. The first contribution by Kerber and Cartier (GF/IBM) discusses the
most frequently used characterization methods, starting from standard stress and
sense schemes, over on-the-fly techniques, to fast voltage ramp stresses, which
are particularly useful during technology qualification. Since BTI is a strongly
v
vi Editorial
temperature-dependent phenomenon, a lot can be learned from fast and well-
controlled switches of the device temperature. This is possible by using local
polysiliconwiresplacedaroundthedevicesasdiscussedandexploitedbyAichinger,
Pobegen,andNelhiebel(Infineon/KAI)inthenextcontribution.
As devicesarescaled downinto the nanometerregime,discrete chargecapture
and emission events can be monitored and studied. Just like in random telegraph
noise (RTN), it was observed that the discrete changes in the threshold voltage
caused by single defect discharging events show a very wide distribution. Wang,
Chiu, and Liu (National Chiao Tung University) discuss this phenomenon in
detail using statistics of threshold voltage steps and emission times and give an
interpretationoftheirdatabasedonathermallyassisteddispersivechargetunneling
model. Along similar lines, Reisinger (Infineon) discusses a recently suggested
analysis method named the “time-dependent defect spectroscopy,” pointing out
various experimental pitfalls as well as providing a glimpse at the numerous
resultsobtainedfromthistechnique.Recently,ithasbeensuggestedthatthetraps
responsibleforRTNmayalsoplayanimportantroleinBTI.TheresearchonRTN
hasbeengoingonforseveraldecadesandthestateoftheartissummarizedinthe
contributionofFrankandMiki(IBM/Hitachi).
Oneofthemostimportantconsequencesofdeviceminiaturizationisthatfuture
deviceswill only containa countablenumberof defects,resulting in considerable
variabilityduringdegradation.Rauch(IBM)givesadetailedstudyofintrinsicand
extrinsic variability, properties of the distributions, scaling issues, as well as the
impactofthisvariabilityonanaloganddigitalcircuitssuchasSRAMcells.Inthe
nextcontribution,Kaczer,Toledano-Luque,Franco,andWeckx(IMEC)discusstheir
defect-centricviewonthistime-dependentvariability,withaparticularfocusonthe
singledefectthresholdvoltagedistribution,itsimpactonthetotalthresholdvoltage
shift,anditsconnectionwithtime-zerovariability.
An extremely important aspect in our understanding of BTI is the correct
identificationofthedefectsunderlyingthedegradation.Oneofthefewtechniques
whichcanrevealthechemicalnatureofthosedefectsutilizessomeformofelectron
spinresonance(ESR).CampbellandLenahan(NIST/PennStateUniversity)review
(cid:2)
their work in this field and discuss their observation of P, E , and K centers
b
in response to negative bias temperature stress in SiO , SiON, and high-k gate
2
stacks.Inthesubsequentcontribution,Afanas’ev,Houssa,andStesmans(University
of Leuven) give their perspective on the topic but put a strong emphasis on the
importance of hydrogen-related defects in a wide range of technologies. Zhang
(LiverpoolJohn Moores University),on the other hand, summarizes his efforts in
identifyinga widerangeofpossible defectsin SiO , SiON, andhigh-kdielectrics
2
using electrical measurements. Finally Ang (Nanyang Technological University)
discusses observations which indicate the importance of hole trapping and trap
transformationsduring cyclic bias temperature stress, which are inconsistent with
theconventionalreaction–diffusionformalism.
The second chapter is focused on theoretical and modeling aspects. In the
openingcontributionbyEl-SayedandShluger(UCLondon),theoreticalproperties
(cid:2)
of the most commonly observed oxide defects such as E centers are discussed
Editorial vii
usingdensityfunctionaltheory.Whensuchdefectsarecharged,theyinteractwith
thediscretedopandsinsidethedevice,leadingtopotentiallyenormouschangesof
the device characteristics, as discussed in detail by Amoroso, Gerrer, and Asenov
(UniversityofGlasgow).OneofthefirstpopularmodelsforNBTIisthereaction–
diffusionmodel,originallysuggestedin1977,butcontinuouslyrefinedusingmore
recent findings. The latest developmentsalong these lines of thought are summa-
rizedbyMahapatra(IITBombay).Expressingacontraryview,thefoundationsand
the applicability of reaction–diffusion theory are then examined using stochastic
chemicalkineticsbySchanovskyandGrasser(TUWien).Inthenextcontribution,
Goes,Schanovsky,andGrasser(TUWien)developarigorousformulationofcharge
trapping based on nonradiative multiphonon theory using additional metastable
states in order to explain experimental data obtained from time-dependent defect
spectroscopy.Finally,Grasser(TUWien)discussesarecentlysuggestedformalism
for an approximate description of BTI as a collection of independent first-order
reactionsusingcapture/emissiontimemaps.
Thethirdchapterfocusesontheimpactofvarioustechnologicalprocessingsteps
on BTI. One of the most prominent actors frequently linked to the phenomenon
in various theories is hydrogen and the wealth of literature together with recent
findings are summarized by Pobegen, Aichinger, and Nelhiebel (KAI/Infineon).
Next,theimpactofvariousprocessingstepsisdiscussedindetailbyMahapatra(IIT
Bombay),includingtheimpactofnitrogen,fluoride,andhydrogenversusdeuterium
innitridedaswellashigh-kgatestacks.While mostmoderntechnologiesemploy
very thin dielectric layers, power MOS transistors typically require thick layers
of SiO . Experimentalchallenges together with other peculiarities related to such
2
devicesarediscussedinthecontributionofStojadinovic´ etal. (UniversityofNisˇ).
Inordertosuppressexcessiveleakagethroughultrascaledinsulatinglayers,high-k
materials have to be used in these technologies. Unfortunately, in these materials
PBTIinnMOSFETsbecomesacriticalissue.Differencesandsimilaritiesbetween
NBTI and PBTI, includingprocessingissues and static versusdynamicstress, are
discussedbyZhao,Krishnan,Linder,andStathis(IBM)inthefirsthigh-kcontribu-
tion.ThefollowingcontributionbyYoungandBersuker(UTDallas/SEMATECH)
is particularly devoted to experimental issues, fast transient charging, electron
trapping, and concurrent defect generation. Finally, Toledano-Luque and Kaczer
(IMEC)discussrecentexperimentalresultsobtainedonnanoscaledhigh-kdevices,
withafocusonstochasticchargetrappingandstatisticallifetimeprediction.
In order to overcome various scaling issues, alternative channel materials and
device topologies have been suggested to replace conventional planar silicon
technology. Franco and Kaczer (IMEC) present recent results obtained on SiGe
channel devices, which show considerably improved reliability compared to their
Si channel counterparts. Huang, Wang, and Li (Peking University) discuss the
reliabilityofSinanowiresincomparisonwithplanartechnologies,withaparticular
focus on stochastic charge capture and emission in nanoscaled devices. Finally,
Fleetwoodetal.(VanderbiltUniversity)discussbiastemperatureinstabilitiesin4H-
SiCdevicesandsuggestBTItobeofadifferentorigininthesedevices.
viii Editorial
ThefinalchapterisfocusedontheimpactofBTIoncircuits.First,Keane,Wang,
Jain,andKim(Intel/UniversityofMinnesota)discussodometersforthedirecton-
chip assessment of BTI on circuits for a better measurement and timing control.
A bottom-to-topapproachof reliability analysis from device levelto system level
agingisdescribedbySutaria,Velamala,Ravi,andCao(ArizonaStateUniversity).
Then, Wirth et al. (UFRGS) summarize latest attempts in statistical modeling
of charge trapping in the context of RTN and BTI from a circuit perspective.
Finally,Martin-Martinez,Rodriguez,andNafria(UABarcelona)addressdifferent
alternativestotranslatetheeffectsofNBTIdegradationontheelectricalproperties
ofdevicesintocircuitperformanceandreliability.
I sincerely hope that the information provided in these chapters proves useful
to scientists and engineers working in this rapidly changing field by accurately
capturing the state of the art and that it triggers further research into this elusive
phenomenon.
Wien,Austria TiborGrasser
Contents
PartI
1 BiasTemperatureInstabilityCharacterizationMethods.............. 3
AndreasKerberandEduardCartier
2 ApplicationofOn-ChipDeviceHeatingforBTIInvestigations....... 33
ThomasAichinger,GregorPobegen,andMichaelNelhiebel
3 StatisticalCharacterizationof BTI-Induced High-k
DielectricTrapsinNanoscaleTransistors ............................... 53
TahuiWang,Jung-PiaoChiu,andYu-HengLiu
4 TheTime-DependentDefectSpectroscopy .............................. 75
HansReisinger
5 AnalysisofOxideTrapsinNanoscaleMOSFETsusing
RandomTelegraphNoise.................................................. 111
DavidJ.FrankandHiroshiMiki
6 BTI-InducedStatisticalVariations ....................................... 135
StewartE.RauchIII
7 StatisticalDistributionofDefectParameters............................ 161
B.Kaczer,M.Toledano-Luque,J.Franco,andP.Weckx
8 Atomic-ScaleDefectsAssociatedwiththeNegativeBias
TemperatureInstability.................................................... 177
JasonP.CampbellandPatrickM.Lenahan
9 Charge Properties of Paramagnetic Defects
inSemiconductor/OxideStructures...................................... 229
V.V.Afanas’ev,M.Houssa,andA.Stesmans
10 OxideDefects................................................................ 253
JianF.Zhang
ix
