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Combined nanoscale KPFM cha ac e iza ion and de ice
simula ion o he e alua ion o he MOSFET a iabili y
ela ed o me al ga e wo k unc ion luc ua ions
A. Ruiz, N. Seoane, S. Cla amun , A. Ga cía-Lou ei o, M. Po i and M. Na ia
Ve sion: accep ed a icle
A. Ruiz, N. Seoane, S. Cla amun , A. Ga cía-Lou ei o, M. Po i and M. Na ia (2019) Combined
nanoscale KPFM cha ac e iza ion and de ice simula ion o he e alua ion o he MOSFET a iabili y
ela ed o me al ga e wo k unc ion luc ua ions. Mic oelec onic Enginee ing, 216, 111048.
Doi: h ps://doi.o g/10.1016/j.mee.2019.111048
How o ci e:
Copy igh in o ma ion:
Combined nanoscale KPFM cha ac e iza ion and de ice simula ion o he e alua ion o he
MOSFET a iabili y ela ed o me al ga e wo k unc ion luc ua ions
A. Ruiz1, N. Seoane2, S. Cla amun 1, A. Ga cía-Lou ei o2, M. Po i1, M. Na ia1
1Elec onic Enginee ing Depa men , Uni e si a Au ònoma de Ba celona, Ba celona 08193, Spain
2 CITIUS, Uni e sidade de San iago de Compos ela, San iago de Compos ela 15782, Spain
Elec onic add ess: ana.[email p o ec ed]
1. Summa y
In his wo k, a mo e ealis ic app oxima ion based
on 2D nanoscale expe imen al da a ob ained on a
me al laye is p esen ed o in es iga e he impac o
he me al ga e polyc ys allini y on he MOSFET
a iabili y. The nanoscale da a (ob ained wi h a
Kel in P obe Fo ce Mic oscope, KPFM) we e
in oduced in a de ice simula o o analyze he e ec
o a TiN me al ga e wo k unc ions (WF) luc ua ions
on he MOSFET elec ical cha ac e is ics. The esul s
demons a e ha he de ice cha ac e is ics a e
a ec ed no only by he WF luc ua ions, bu also
hei spa ial dis ibu ion, which is specially ele an in
e y small de ices. The e ec on hese cha ac e is ics
o he spa ial dis ibu ion on he ga e a ea o such
luc ua ions is also e alua ed.
2. In oduc ion
Ex ensi e s udies ha e been de o ed o in es iga e
a iabili y sou ces a ec ing ul a-scaled MOSFET
echnologies, as Random Dopan Dis ibu ions, Line
Edge Roughness, high-k dielec ic polyc ys alliza ion
[1–5], in e ace aps [6–8] and me al
polyc ys alliza ion [9–11]. Cha ges cap u ed in aps
loca ed a he semiconduc o /insula o in e ace can
lead o luc ua ions in he h eshold ol age (VT) and
he on-cu en [12,13] in oducing, he e o e, de ice-
o-de ice a iabili y. Such VT luc ua ions also
depend on he posi ion o he aps along he channel
[13]. Rega ding me al ga es, he me al
polyc ys alliza ion esul s in g ains wi h di e en
sizes and o ien a ions, which ha e associa ed di e en
WFs. The andom dis ibu ion o g ains (and he
co esponding WF) esul s in VT a iabili y (TVV)
[9–11]. Some wo ks ha e al eady analyzed he impac
o he WF luc ua ions on he a iabili y o MOSFETs
[9,10]. Howe e , he s a is ical models ha we e used
make assump ions ha migh no be ep esen a i e o
eal de ices.
In his wo k, he impac o me al
polyc ys alliza ion on he elec ical pa ame e s o
MOSFETs is s udied, based on KPFM expe imen al
WF maps. These esul s a e compa ed o hose
ob ained using he app oxima ed WF dis ibu ions
no mally used in cus oma y app oaches o his kind
o a iabili y sou ce. An analysis o he in luence o
he loca ion o he WF luc ua ions along he channel
is also s udied.
3. Expe imen al se -up.
A 100 nm hick TiN laye g own o e a H O2/Si
subs a e was used o ob ain he expe imen al da a.
The laye was ab ica ed by con inuous e-gun
e apo a ion o me allic TiN. The TiN o ma ion was
ensu ed by passing he Ti a oms h ough a eac i e
ni ogen-en iched a mosphe e (ni ogen pa ial
p essu e o 8×10-4 mba s). X-Ray Di ac ion (XRD)
was used o de e mine he s uc u e o he TiN laye .
The XRD spec um shows a polyc ys alline s uc u e
wi h wo peaks [14], ha co espond o he [111] and
[200] o ien a ions [9]. being he [111] o ien a ion
dominan o e he [200] one.
The nanoscale mo phological and elec ical
p ope ies o he TiN laye we e measu ed wi h a
Nano-Obse e AFM om Concep Scien i ic
Ins umen s. This echnique allows bimodal single
pass AM-KPFM measu emen s, so ha i is possible
o ob ain du ing he same scan opog aphical and
sample- ip con ac po en ial di e ence (CPD) 2D
maps wi h nanome e esolu ion [15,16]. Compa ed o
a li mode based AM-KPFM (no mally wi h a wo se
esolu ion [17–19], ou bimodal single pass AM-
KPFM can p o ide a simila esolu ion o ha
ob ained wi h a FM-KPFM [17,20] and minimizes
c oss- alk be ween opog aphy and he CPD da a
[18,21]. Since he CPD image co esponds o he WF
di e ence be ween he ip and he sample, assuming a
cons an alue o he ip WF du ing he es , he
measu ed CPD luc ua ions can be ela ed o he WF
a ia ions o he TiN laye . The e o e, CPD maps gi e
in o ma ion o he local alue o he WF o he
sample. KPFM images we e ob ained wi h highly
doped Si ips o ge a be e esolu ion.
4. Expe imen al esul s.
Fig. 1a co esponds o a 520 nm × 240 nm
opog aphical image o he TiN laye . I shows a
g anula s uc u e, whe e he G ains (Gs) a e
su ounded by g ain bounda ies (GBs), which
co espond o he dep essions in he image. Fig. 1b
shows he measu ed WF map o he same su ace
egion. No e ha GBs end o show lowe WFs (WF <
4.1 eV) han nanoc ys als.
We used he open-sou ce so wa e Gwyddion o
iden i y he Gs and ob ain he TiN g anula pa e n
(Fig. 1c), whe e he GBs ha e been neglec ed. When
only nanoc ys als a e conside ed, Gs wi h di e en
maximum WF alues a e measu ed, as shown in Fig.
2, which co esponds o a 2D-his og am ha ela es
he maximum WF and he maximum heigh (wi h
espec o he mean heigh alue o he opog aphical
image shown in Fig. 1a) o each g ain in Fig. 1c. No e
ha al hough a con inuous dis ibu ion o maximum
WFs is ob ained, WFs a e mos ly concen a ed a ~4.3
eV and, wi h less equency, a ound ~4.5 eV,
sugges ing wo p edominan WFs and indica ing a
much highe numbe o nanoc ys als wi h low WF
han wi h high WF. This esul , con i med by XRD
[14], is compa ible wi h he p esence o wo g ain
o ien a ions in he TiN laye ([111] and [200]) whose
WFs a e sepa a ed by 200 mV [9] .
Fig. 1. Topog aphy (a) and WF (b) maps ob ained wi h
KPFM on a TiN laye . Bina y mask (c) o he g ains
iden i ied in he opog aphical map and an example
gene a ed WF map (d) om he bina y mask. O ange colo
co esponds o 4.5 eV and pu ple colo o 4.3 eV.
Fig. 2. 2D-his og am showing he maximum WF s
maximum heigh o he g ains, ob ained om Fig. 1c. In he
X axis, he heigh o each g ain is de e mined wi h espec
o he mean alue o he opog aphical image (Fig. 1a).
The da a ob ained om KPFM images add new
in o ma ion on he p ope ies o he polyc ys alline
me al laye , no aken in o accoun in p e ious wo ks.
Besides he dispe sion in he WF o he nanoc ys als
(no only wo disc e e alues a e measu ed), GBs wi h
lowe WF han Gs a e also obse ed, which could also
a ec he a iabili y o de ices. The e o e, all hese
ea u es should be aken in o accoun when s udying
he MOSFET a iabili y and when conside ing he
WF luc ua ions as a iabili y sou ce.
5. Simula ions
In o de o e alua e he de ice a iabili y
associa ed o he WF luc ua ions o he TiN laye ,
di e en WF dis ibu ions ep esen ing he me al ga e
o a MOSFET we e conside ed. WF maps as hose
shown in Fig. 1 ha e been di ided o gene a e 100
non-o e lapping 50 nm × 50 nm ga e WF p o iles.
Nex , hese p o iles we e in oduced in a 3D in-house-
buil d i -di usion de ice simula o [22] as me al
ga e, o e alua e he de ice elec ical cha ac e is ics o
MOSFETs wi h a ga e a ea o 50 × 50 nm2. In o de
o compa e he esul s ob ained wi h ou
me hodology, based on nanoscale expe imen al da a,
wi h hose shown in he li e a u e, we p oposed he
s udy o wo cases: (i) he ac ual WF dis ibu ion (as
in Fig. 1b, wi h GBs and a con inuous dis ibu ion o
Gs WF), and (ii) an app oxima ed WF dis ibu ion,
wi h wo disc e e alues o he WF, as in Fig. 1d.
No e ha he las is he cus oma y app oach o his
kind o TVV sou ce [9]. To gene a e he
app oxima ed WF maps (Fig. 1d), he g ain pa e n in
Fig. 1c is he s a ing poin . We gene a ed an
app oxima ed WF maps whe e GBs ha e been
neglec ed and, o he Gs in Fig. 1c, wo disc e e and
cons an alues, co esponding o he [111] and [200]
o ien a ions (con i med om XRD analysis), we e
only conside ed. We ha e assigned 4.3 eV o he
nanoc ys als wi h WF lowe han 4.4 eV and 4.5 eV o
hose wi h highe alues, leading o WF maps as ha
shown in Fig. 1d. The MOSFET beha io o de ices
wi h me al ga e WF dis ibu ions ob ained om he
WF maps as in Fig. 1b and 1d ha e been compa ed.
Fig. 3. Dis ibu ions o IOFF ( op), VT (middle) and ION
(bo om) ela ed o WF luc ua ions in 50 nm × 50 nm Si
MOSFETs (a a d ain bias o 50 mV) when using ac ual WF
da a (le column) an app oxima ed WF ( igh column) om
maps as hose shown in Fig. 1b and 1d espec i ely. The
mean alue (< >) and s anda d de ia ion (σ) o he
s a is ical ensembles a e shown.
Fig. 3 shows he o -cu en (IOFF), h eshold
ol age (VT) and on-cu en (ION) dis ibu ions
ob ained o hese wo cases. No e ha , he
app oxima e case (i. e., dis ega ding he GBs and he
WF con inuous dis ibu ion), in he igh column,
leads o a ~10% and ~18% educ ion in σV
T and
σlog(IOFF), espec i ely, and o a conside able shi
(~0.12 V in he case o he VT) in he mean alue o
he dis ibu ions.
To be e unde s and hese esul s, he e ec o he
spa ial loca ion o he Gs in he MOSFET me al ga e
has also been e alua ed. As an example, Fig. 4 shows
he ga e o wo de ices in which only one nanoc ys al
has been included. The a e age WF o he g ains is
4.3 eV o g ain (a) and 4.18 eV o g ain (b). Since,
in his sec ion, we wan o e alua e only he impac on
VT o he posi ion o he g ains in he channel, he WF
o he po ion o he ga e no co e ed by he
nanoc ys al has been se o same a e age alue, ha
is, 4.3 eV o Fig. 4a and 4.18 eV o Fig. 4b. The G
has been swep along he de ice ga e, om he sou ce
end (X=0 nm) o he d ain end (X=50 nm), and o
each posi ion o he g ain, he de ice was simula ed
and he co esponding VT ex ac ed. Fig. 5 shows he
VT a ia ion wi h espec o he homogeneous case
when he g ain posi ion is swep , a bo h low and high
d ain biases. No e ha , al hough he dis ibu ion o
WF is he same in all cases, he speci ic loca ion o
he G may ha e a di e en impac on he VT alues
(depending on i s posi ion along L), leading o bo h
posi i e and nega i e h eshold ol age shi s wi h
espec o he g ain a e age WF alue. In addi ion, he
de ice is clea ly mo e sensi i e o WF a ia ions a
he sou ce end han a he d ain end (as seen in Fig. 5
o bo h g ains). A he d ain end, he p esence o he
g ain does no ha e any in luence on VT. The d ain
bias also has an in luence on he TVV, as seen on Fig.
5. Howe e , when he g ains we e swep along he y-
di ec ion (i.e. along he wid h o he ga e a ea), no
signi ican changes a e obse ed in VT.
Fig. 4. Two examples o isola ed nanoc ys als (enclosed in
pink ec angles), wi h a e age WF alues <WF> o 4.3 eV,
g ain (a), and 4.18, g ain (b). The la ge g een squa es
show he eal dimensions o he 50 × 50 nm de ice ga e.
The e o e, he esul s demons a e ha , no only he
WF alues o he g ains in he me al ga e can impac
on he MOSFET a iabili y, bu also VT depends on
how hose luc ua ions a e dis ibu ed along he
channel di ec ion. This dependence o VT on he G
posi ion can be explained aking in o accoun he
impac o he WF luc ua ions on he elec os a ics o
he de ice. Depending on he G loca ion, he po en ial
dis ibu ion in he channel is a ec ed di e en ly,
leading o a ia ions o VT. A simila e ec was
obse ed o o he sou ces o a iabili y, as is he case
o in e ace aps in ul a-scaled MOSFETs [6].
Fig. 5. VT spa ial sensi i i y o a TiN g ain WF luc ua ions
when i s posi ion is swep along he channel o he Si
MOSFET a bo h low and high d ain biases like hose
shown in Fig 4a and 4b ha e seen conside ed o he
simula ion. ΔVT is calcula ed as he di e ence be ween he
VT o a de ice wi h a ga e WF equal o he <WF> o he G
and he VT o he de ice ha includes he nanoc ys al.
6. Conclusion
When analyzing he impac o he WF luc ua ions o
polyc ys alline me al ga es on he MOSFET
a iabili y, he p esence o GBs and he WF
con inuous dis ibu ion o he Gs need o be
conside ed o ob ain mo e ealis ic da a. Mo eo e ,
he de ice cha ac e is ics and a iabili y a e also
a ec ed by he spa ial dis ibu ion o such
luc ua ions: in small de ices, whe e ew nanoc ys als
may be p esen in he ga e a ea, hei loca ion should
also be conside ed in o de o co ec ly es ima e he
a iabili y a de ice le el.
Acknowledgmen s
This wo k has been pa ially suppo ed by he
Spanish AEI and ERDF (TEC2016-75151-C3-1-R,
TEC2014-53909-REDT and RYC-2017-23312).
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