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DOI: 10.2478/msp-2019-0083
S e eome ic analysis o Ta2O5 hin ilms
DINARA SOBOLA1, PAVEL KASPAR1,∗, JINDRICH OULEHLA1, ¸STEFAN ¸T˘
ALU2, NIKOLA PAPEŽ1
1B no Uni e si y o Technology, Facul y o Elec ical Enginee ing and Communica ion, Physics Depa men , Technická 8,
616 00 B no, Czech Republic
2Technical Uni e si y o Cluj-Napoca, The Di ec o a e o Resea ch, De elopmen and Inno a ion Managemen (DMCDI),
Cons an in Daico iciu S ee , no. 15, Cluj-Napoca, 400020, Cluj coun y, Romania
The pu pose o his wo k is he s udy o he co ela ion be ween he hickness o an alum pen oxide hin ilms and hei
h ee-dimensional (3D) mic omo phology. The samples we e p epa ed on silicon subs a es by elec on beam e apo a ion. The
di e ences in su ace s uc u e o he p ocessed and e e ence samples we e in es iga ed. Composi ional s udies we e pe o med
by ene gy-dispe si e X- ay spec oscopy. S e eome ic analysis was ca ied ou on he basis o a omic o ce mic oscopy (AFM)
da a, o an alum pen oxide samples wi h 20 nm, 40 nm, 60 nm, 80 nm and 100 nm hicknesses. These me hods a e equen ly
used in desc ibing expe imen al da a o su ace nanomo phology o Ta2O5. The esul s can be used o alida e heo e ical
models o p edic ion o co ela ion o nano ex u e su ace pa ame e s.
Keywo ds: a omic o ce mic oscopy; s e eome ic analysis; Ta2O5, opog aphy
1. In oduc ion
Tan alum pen oxide (Ta2O5) inds use in many
elec ical and op ical applica ions. In he elec ical
ield i is o en employed as a dielec ic insula o
in me al-insula o -me al (MIM) o me al-insula o -
semiconduc o (MIS) s uc u es [1]. These de ices
a e used o example in scaled-down e sions o
ul a-la ge scale in eg a ed de ices (ULSI), such as
dynamic andom access memo y ca ds o com-
pu ing, o h ee-dimensional capaci o s uc u es,
such as he enched- ype capaci o (TTC) [2]. Be-
cause o i s p ope ies Ta2O5is also employed in
in eg a ed senso s o hyd ogen ion sensing mem-
b anes o p o ein de ec ion, making i sough a -
e in he ield o biological and biochemical sen-
so s [3]. Tan alum pen oxide, due o i s high e ac-
i e index and e y low abso p ion coe icien [4],
is also sui able o he ab ica ion o hin ilms
o he pu poses o an i e lec i e coa ings o sola
cells o CCD de ices, and o p o ec ion o ma e-
ial su aces agains co osion because o i s high
chemical s abili y [5]. P epa a ion o Ta2O5has
been a challenging issue, bu he e a e a numbe
∗E-mail: [email p o ec ed].cz
o possible me hods o c ea e hin Ta2O5laye s,
wi h a ying deg ee o success and speci ic p op-
e ies o he p epa ed laye . Some o he mos o en
used me hods a e s anda d echniques o hin- ilm
p epa a ion, like chemical apo deposi ion (CVD)
o magne on spu e ing, bu because o he chem-
ical na u e o Ta2O5, a mo e specialized p ocesses,
like pulse lase abla ion o sol-gel me hod should
be employed [6]. The possible uses o Ta2O5a e
nume ous, and he men ioned examples a e only
some o he be e explo ed ones. Because o he
wide a ie y o possible applica ions, he ma e ial
p ope ies o an alum pen oxide a e con inuously
explo ed. This pape in es iga es he changes o
chemical composi ion and op ical p ope ies and
also p esen s, so a only b ie ly explo ed s e e-
ome ic analysis o Ta2O5su aces wi h he ilm
hickness o 20 nm, 40 nm, 60 nm, 80 nm and
100 nm. Imaging by AFM can b ing ou s anding
esul s in he ield o nanos uc u ed su ace e-
sea ch and analysis, especially when hin ilms a e
conce ned [7–11]. In e p e a ion o AFM esul s
is usually educed o plain su ace desc ip ion –
oughness and peak- alley a io, hough. A com-
p ehensi e desc ip ion o su ace mo phology o
s udied ma e ials is an ongoing challenge necessa y
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DINARA SOBOLA e al.
(a) (b) (c)
(d) (e)
Fig. 1. 2-D AFM images o he su ace mic o ex u e o Ta2O5o samples, o scanning squa e a eas o 1 µm×
1µm. Sample hickness: (a) 20 nm; (b) 40 nm; (c) 60 nm; (d) 80 nm; (e) 100 nm.
Fig. 2. Re lec ion spec a o Ta2O5 ilms.
o unde s anding hei p ope ies and hei po en-
ial o echnological exploi a ion [12–16]. In he
p esen ed wo k, he opog aphy o Ta2O5has been
s udied in co ela ion wi h ilm hickness. S uc-
u al and op ical p ope ies ha e been desc ibed
using EDX and e lec ome y spec a. Fo he 3D
Fig. 3. EDX spec a o Ta2O5 ilms wi h di e en hick-
nesses.
cha ac e iza ion o sample su ace, AFM imaging
has been used and a ac al analysis has been pe -
o med on he acqui ed da a.
2. Ma e ials and me hods
Ta2O5 ilms g own by elec on beam e apo-
a ion, we e chosen o he expe imen . A omic
o ce mic oscopy (AFM) cha ac e iza ion was
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S e eome ic analysis o Ta2O5 hin ilms
(a) (b) (c)
(d) (e)
Fig. 4. Heigh dis ibu ion his og am wi h he in eg a ion cu e o he his og am compu ed o images o Fig. 1.
Sample hickness: (a) 20 nm; (b) 40 nm; (c) 60 nm; (d) 80 nm; (e) 100 nm.
ca ied ou o he quan i a i e analysis o spe-
ci ic mic os uc u al ea u es o samples. Images o
scanned squa e o 1 µm×1µm we e chosen o
u he p ocessing (Fig. 1). The scanning was ca -
ied ou in apping mode, a oom empe a u e and
no mal humidi y. The ele an 3-D AFM images
o he Ta2O5su ace mic o ex u e o samples wi h
20 nm, 40 nm, 60 nm, 80 nm and 100 nm hickness,
ob ained using AFM o a 1 µm×1µm squa e a ea
a e shown in Fig. 1a o Fig. 1e.
Fig. 2shows e lec ance spec a o he ilms a -
e calib a ion on silicon s anda d. Shi ing o max-
ima and minima is he esul o he di e ence in he
ilms hickness.
The dep h o EDX analysis depends on pa am-
e e s o elec on beam and includes ew mic ons o
nea -su ace a ea. The spec a ob ained a 20 keV
elec on beam a e shown in Fig. 3.
3. Resul s and discussion
Pu e imaging o su ace opog aphy in his
case is insu icien and nume ical p ocessing is de-
manded o desc ip ion o di e ences in he sam-
ples [17–22]. The s e eome ic analysis was ca -
ied ou on he basis o AFM da a, because i gi es
eal 3D in o ma ion abou su ace ex u e [23–28].
The su ace opog aphy was desc ibed in e ms
o s e eome ic analysis using he SPIPTM 6.7.4
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DINARA SOBOLA e al.
(a) (b) (c)
(d) (e)
Fig. 5. The Abbo -Fi es one cu e compu ed o images o Fig. 1. Sample hickness: (a) 20 nm; (b) 40 nm; (c)
60 nm; (d) 80 nm; (e) 100 nm.
so wa e [29], acco ding o ISO 25178-2:2012 [30]
and ASME B46.1-2009 [31]. The heigh dis-
ibu ion his og am wi h he in eg a ion cu e
o he his og am compu ed o images om Fig. 1
is shown in Fig. 4. The heigh dis ibu ion his-
og am o e s in o ma ion abou he la ness o su -
ace. The maximum o he high ange is ypical o
he 100 nm hick ilm.
G aphical ep esen a ion o Abbo -Fi es one
cu e compu ed o images om Fig. 1is shown
in Fig. 5. Ma hema ically, he bea ing a io cu e
is a cumula i e p obabili y densi y unc ion o he
su ace p o ile heigh and can be compu ed by in-
eg a ing he p o ile ace [29].
G aphical ep esen a ion o ma e ial p obabili y
cu e compu ed o images om Fig. 1is shown
in Fig. 6. The ma e ial p obabili y cu e is a ep-
esen a ion o he ma e ial a io cu e, whe e he
heigh s a e plo ed in uni s o s anda d de ia ions
o a no mal (Gaussian) dis ibu ion wi h he same
mean and s anda d de ia ion as he heigh da a. I
is known ha a no mal dis ibu ion o his ype o
plo is ep esen ed by a s aigh line. This cha is
use ul in s udying how close o a no mal dis ibu-
ion is he dis ibu ion o heigh s o he analyzed
su ace [29].
Iso opic a ea powe spec al densi y (IAPSD)
unc ion compu ed o images om Fig. 1is shown
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S e eome ic analysis o Ta2O5 hin ilms
(a) (b) (c)
(d) (e)
Fig. 6. Ma e ial p obabili y cu e compu ed o images o Fig. 1. Sample hickness: (a) 20 nm; (b) 40 nm; (c)
60 nm; (d) 80 nm; (e) 100 nm.
in Fig. 7. The IAPSD unc ion is he a ea o
powe spec al densi y (APSD) unc ion in eg a ed
o all angles o gi en equencies (in e se wa e-
leng h) [29]. This unc ion is simila o all he
s udied samples.
The in eg a ed adial spec um unc ion com-
pu ed o images om Fig. 1is shown in Fig. 8.
Acco ding o he calcula ion, he spec al dep hs
g ows o he su aces o he ilms wi h la ge
hickness.
The ac al dimension, D has been com-
pu ed o a ious angles by analyzing he Fou ie
ampli ude spec a o a ious angles. The ampli-
ude Fou ie p o ile was ex ac ed and he loga-
i hm o equency and ampli ude coo dina es we e
compu ed. The ac al dimension, D, o each di-
ec ion was hen compu ed as D =(6 +s)/2, whe e
s is he (nega i e) slope o he log-log cu es. The
compu ed ac al dimension is he a e age o all
di ec ions [29]. In Table 1, he alues o he ac al
dimension, D calcula ed o he images om Fig. 1
a e shown.
In Table 2, s a is ical pa ame e s o he AFM
images, acco ding wi h ISO 25178-2: 2012 and
ASME B46.1-2009 a e shown. The alue D
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DINARA SOBOLA e al.
(a) (b) (c)
(d) (e)
Fig. 7. IAPSD unc ion compu ed o images om Fig. 1. Sample hickness: (a) 20 nm; (b) 40 nm; (c) 60 nm; (d)
80 nm; (e) 100 nm.
Table 1. The ac al dimension, D, o Ta2O5samples wi h 20 nm, 40 nm, 60 nm, 80 nm and 100 nm hickness
associa ed wi h images om Fig. 1.
The ac al Ta2O5sample hickness
dimension, D 20 nm 40 nm 60 nm 80 nm 100 nm
Values 2.73±0.01 2.70±0.01 2.68±0.01 2.66±0.01 2.65±0.01
∗S a is ically signi ican di e ence: P <0.05.
sys ema ically dec eases wi h he g ow h o ilm
hickness. I could be explained by dec easing he
amoun o ea u es (hills and dep hs) on he su -
ace. In spi e o inc easing he nume ical alues o
highs and alleys, he g ow h o he hickness leads
o dec easing o su ace i egula i y.
The ac al dimension was ound o dec ease
om D =2.73±0.01 o D =2.65±0.01 o
he hickness inc ease o 20 nm o 100 nm. The
quali a i e obse a ions h ough s a is ical pa am-
e e s o he 3-D su ace ex u e e ealed ha he
smoo hes su ace has been ob ained o he sample
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S e eome ic analysis o Ta2O5 hin ilms
(a) (b) (c)
(d) (e)
Fig. 8. In eg a ed adial spec um unc ion compu ed o images om Fig. 1. Sample hickness: (a) 20 nm; (b)
40 nm; (c) 60 nm; (d) 80 nm; (e) 100 nm.
wi h 20 nm hickness (Sa, Sq, Sz, S10z, S , Sp ha e
he lowe alues), while he mos i egula opog a-
phy has been ound o he same sample wi h 20 nm
hickness ( he ac al dimension D =2.73±0.01).
1D FFT ( as Fou ie ans o m) line a e age unc-
ions desc ibe Fou ie ampli ude spec a o each
X line o Y column and he co esponding a e age
ampli ude spec um. In ou cases, hese ha e been
compu ed o images om Fig. 1and a e shown
in Fig. 9.
4. Conclusions
In his s udy, he co ela ion be ween hick-
nesses o indi idual Ta2O5 hin ilms and hei 3D
su ace cha ac e is ics was analyzed using AFM.
We demons a ed ha bo h op ical p ope ies and
opog aphy o he ilms change wi h hei hick-
ness as a as quan i a i e cha ac e is ics o su -
ace nanomo phology a e conce ned. F ac al ana-
lysis was used o es ima ion o ex u e e olu ion
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DINARA SOBOLA e al.
Table 2. S a is ical pa ame e s acco ding o ISO 25178-2: 2012 and ASME B46.1-2009 o a 1 µm×1µm squa e
a ea o he Ta2O5samples wi h 20 nm, 40 nm, 60 nm, 80 nm and 100 nm hickness, associa ed wi h
images om Fig. 1.
S a is ical pa ame e s Symbol Ta2O5samples
20 nm 40 nm 60 nm 80 nm 100 nm
Ampli ude pa ame e s
A i hme ic mean heigh Sa [nm] 0.191 0.208 0.222 0.240 0.2536
Roo mean squa e heigh Sq [nm] 0.240 0.262 0.279 0.301 0.318
Su ace skewness Ssk [–] 0.022 0.030 0.011 0.019 –0.0001
Su ace ku osis Sku [–] 3.034 3.021 3.024 3.005 3.033
Maximum heigh Sz [nm] 2.276 2.307 2.622 2.694 3.16
Ten poin heigh S10z [nm] 2.164 2.222 2.467 2.609 2.864
Maximum alley dep h S [nm] 1.116 1.127 1.261 1.311 1.543
Maximum peak heigh Sp [nm] 1.1 1.180 1.362 1.383 1.617
Hyb id pa ame e s
Mean summi cu a u e Ssc [1/nm] 0.199 0.199 0.199 0.200 0.203
Roo mean squa e g adien Sdq [–] 0.198 0.198 0.200 0.202 0.206
A ea oo mean squa e slope Sdq6 0.159 0.160 0.162 0.165 0.169
Su ace a ea a io Sd [%]1.947 1.955 1.985 2.03 2.118
P ojec ed a ea S2A [nm2]1E+06 1E+06 1E+06 1E+06 1E+06
Su ace a ea S3A [nm2]1E+06 1E+06 1E+06 1E+06 1E+06
Func ional pa ame e s
Su ace bea ing index Sbi0.3425 0.352 0.310 0.340 0.290
Co e luid e en ion index Sci1.578 1.589 1.581 1.575 1.564
Valley luid e en ion index S i0.1144 0.111 0.115 0.1128 0.1158
Reduced summi heigh Spk [nm]0.2611 0.2858 0.3092 0.3266 0.3536
Co e oughness dep h Sk [nm] 0.6186 0.6731 0.7178 0.7783 0.8184
Reduced alley dep h S k [nm] 0.2226 0.2357 0.2593 0.2725 0.3013
Spa ial pa ame e s
Densi y o summi s Sds
[1/µm2]3E+04 2.8E+04 2.8E+04 2.6E+04 2.5E+04
Tex u e di ec ion S d [°]15.06 58.61 42.98 7.984 140.8
Tex u e di ec ion index S di [–]0.8663 0.8691 0.8497 0.8586 0.8723
Dominan adial wa eleng h S w [nm]64.19 106.3 144 81.86 181.1
Radial wa e index S wi [-]0.2571 0.3235 0.2582 0.2433 0.259
Mean hal wa eleng h Shw [nm]19.23 21.28 22.73 23.81 23.81
Co ela ion leng h a 20% Scl20 [nm]4.942 6.59 6.59 8.237 8.237
Co ela ion leng h a 37% Scl37 [nm]3.295 4.942 4.942 4.942 4.942
Tex u e-aspec a io a 20% S 20 [–]0.75 1111
Tex u e-aspec a io a 37% S 37 [–]0.6667 1110.75
C oss ha ch angle Sch [°]54.78 106.5 50.54 10.76 9.388
∗S a is ically signi ican di e ence o all alues: P <0.05.
wi h he ilm g ow h. The applica ion o s e eo-
me ic analysis enabled cha ac e iza ion o opog-
aphy and e alua ion o nano ex u e su ace pa am-
e e s. These pa ame e s o he nanoscale ilms a e
connec ed wi h mechanical s esses caused by la -
ice misma ch wi h he subs a e. The calcula ion
app oach allows nume ical es ima ion o changes
caused by g ow h o he ilms.
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S e eome ic analysis o Ta2O5 hin ilms
(a) (b) (c) (d)
(e) ( ) (g) (h)
(i) (j)
Fig. 9. The a e age X-Fou ie p o ile, o sample hickness: (a) 20 nm; (b) 40 nm; (c) 60 nm; (d) 80 nm; (e)
100 nm; and he a e age Y-Fou ie p o ile, o sample hickness: ( ) 20 nm; (g) 40 nm; (h) 60 nm; (i)
80 nm; (j) 100 nm.
Acknowledgemen s
Resea ch desc ibed in he pape was inancially suppo ed
by he Na ional Sus ainabili y P og am unde G an LO1401.
Fo he esea ch, in as uc u e o he SIX Cen e was used.
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