Recei ed: 3 Feb ua y 2023
|
Re ised: 8 Ma ch 2023
|
Accep ed: 14 Ma ch 2023
DOI: 10.1002/ppap.202300019
RESEARCH ARTICLE
Syn hesis o hin‐ ilm ma e ials using non he mal plasma
a a highe deg ee o dissocia ion
Vladimi Cech
1
|Ma in B anecky
2
1
Ins i u e o Ma e ials Chemis y, Facul y
o Chemis y, B no Uni e si y o
Technology, B no, Czech Republic
2
Applied and In eg a ed Pho onics,
Ins i u e o Scien i ic Ins umen s o he
CAS, B no, Czech Republic
Co espondence
Vladimi Cech, Ins i u e o Ma e ials
Chemis y, Facul y o Chemis y, B no
Uni e si y o Technology, Pu kyno a 118,
CZ‐612 00 B no, Czech Republic.
Email: [email p o ec ed]
Funding in o ma ion
Technology Agency o he Czech
Republic, G an /Awa d Numbe :
TA01010796; G an o á Agen u a Ceské
Republiky, G an /Awa d Numbe :
16‐09161S; Minis e s o Škols í, Mládeže
a Telo ýcho y, G an /Awa d Numbe :
LM2015056
Abs ac
Lowe low a es o p ecu so molecules a e a o able o he syn hesis o hin‐
ilm ma e ials using non he mal plasma a a highe deg ee o dissocia ion and
su icien ly high deposi ion a e. These deposi ion condi ions can be used o
bo h con inuous wa e (CW) and pulsed plasmas and esul in highe
consump ion o p ecu so molecules, which is bene icial o indus ial
applica ions due o cos educ-
ion. A wide ange o powe
can be used o con ol he
chemical and physical p ope -
ies o hin‐ ilm ma e ials
based on powe ‐dependen
plasma chemis y. Hyd oge-
na ed amo phous silicon ca -
bide ilms deposi ed in CW
and pulsed plasma a e used as
an example. The di e en
kine ics o ilm g ow h and
he ole o sel ‐bias ol age in
bo h ypes o plasma a e
discussed.
KEYWORDS
deg ee o dissocia ion, non he mal plasma, o ganosilicon p ecu so s, plasma‐enhanced
chemical apo deposi ion (PECVD), s icking coe icien , hin ilms
1|INTRODUCTION
Low‐p essu e plasma‐enhanced chemical apo deposi-
ion (PECVD) is known as a hin‐ ilm echnology o
syn hesize ma e ials wi h a iable chemical and physical
p ope ies using non he mal plasma. The p inciple o he
echnology was desc ibed in de ail by Jansen.
[1]
This
plasmachemical p ocess is con olled by many pa ame-
e s such as powe , low a e o p ecu so molecules,
p ocess p essu e, p ecu so molecule chemical cha ac e ,
subs a e empe a u e, and eac o ype. Among hese
p ocess pa ame e s, powe and low a e appea o be
e y impo an . Le us see how hese pa ame e s a ec
he mechanical p ope ies o he syn hesized ma e ial.
Hyd ogena ed amo phous ca bon (a‐C:H, diamond‐
like ca bon) was syn hesized om cyclohexane
(200 sccm) dilu ed wi h hyd ogen gas (50 sccm), and
inc easing he powe densi y om 0.10 o 0.36 W cm
−2
Plasma P ocess Polym. 2023;20:e2300019 www.plasma-polyme s.com
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© 2023 The Au ho s. Plasma P ocesses and Polyme s published by Wiley‐VCH GmbH.
led o an inc ease in Young's modulus om 120 up o
170 GPa.
[2]
The low a e is gi en in s anda d cubic
cen ime e s pe minu e (sccm). Simila ly, a‐C:H ilms
deposi ed om pu e me hane (100 sccm) showed an
inc ease in ha dness om 11.9 o 16.5 GPa wi h
inc eased adio equency (RF) powe o 100–300 W.
[3]
Hyd ogena ed amo phous silicon ca boni ide (a‐
SiCN:H) ilms we e p epa ed om ime hylsilane in a
mix u e o ni ogen and 20 sccm a gon by Pe e e al.
[4]
The o al low a e o hese p ecu so s was 180 sccm.
Inc easing he ime hylsilane low a e om 10 o
50 sccm a cons an discha ge powe had no e ec on
Young's modulus o app oxima ely 135 GPa. F ischmu h
e al.
[5]
poin ed o hyd ogena ed amo phous silicon
ca bide (a‐SiC:H) ilms deposi ed om me hane
(13.5 sccm), silane (6.5 sccm), and a gon (50 sccm),
whe e Young's modulus (137–196 GPa) o he ilms was
con olled by powe (750–2000 W). A Young's modulus
anging om 113 o 126 GPa due o inc easing RF powe
(100–1600 W) was de e mined o silicon‐ ich a‐SiC:H
ilms deposi ed om a Si
2
H
6
/CH
4
/He/A mix u e o
4400 sccm.
[6]
The abo e‐men ioned s udies used low a es o ens
o housands o sccm and he e o e changes in powe
allowed mechanical p ope ies o be changed only by
ens o pe cen . Signi ican changes in mechanical
p ope ies can be achie ed by changing he powe while
using a much lowe low a e. Using 3.8 sccm e a-
inylsilane in a pulsed plasma, Young's modulus o a‐
SiC:H ilms was inc eased om 10 o 143 GPa, while
inc easing he e ec i e powe in he ange o 2–150 W.
[7]
The Yasuda pa ame e , W/FM [J g
−1
](W,F, and Ma e
he powe , low a e, and molecula weigh o he
p ecu so ), ep esen s he inpu ene gy deli e ed o he
plasma pe uni mass o he p ecu so .
[8]
This pa ame e
is expec ed o be p opo ional o he concen a ion o he
ac i a ed plasma species used o he syn hesis o he hin
ilm ma e ial and he deposi ion a e is he e o e
inc eased by inc easing he powe a a cons an low
a e.
[9]
This idea applies o highe low a es, whe e only
abou 1% o he p ecu so molecules a e ac i a ed by
elec ons o o m chemically eac i e agmen s.
[1]
Deposi ion condi ions cha ac e ized by limi ed agmen-
a ion o p ecu so molecules a e called by Inagaki
p ecu so ‐su icien condi ions,
[9]
in which he p ocess
p essu e app oxima ely co esponds o he p ese p es-
su e be o e he igni ion o he plasma. Inagaki poin ed
ou ha he inc ease in he deposi ion a e wi h
inc easing powe (Yasuda pa ame e ) is ollowed by i s
dec ease due o he lack o p ecu so molecules wi h
espec o mo e p onounced p ecu so agmen a ion,
and he called hese deposi ion condi ions p ecu so ‐
de icien condi ions. Howe e , when using a low low
a e, he p ocess p essu e d ops om he p ese alue
e en o he powe ange whe e he deposi ion a e
inc eases, indica ing a highe deg ee o p ecu so
agmen a ion.
[7]
A low low a e o p ecu so molecules
means a low concen a ion o gas molecules in he
plasma p ocess, i a low sys em is used, whe e he
plasma eac o is con inuously pumped.
In his s udy, he d op in p ocess p essu e is analyzed
and ela ed o he deg ee o dissocia ion o he p ecu so
molecules. A con inuous wa e (CW) plasma o e a inylsi-
lane a a low low a e was used o deposi a‐SiC:H ilms.
He e, he plasma species and he chemical and physical
p ope ies o he hin ilms a e cha ac e ized as a unc ion o
he powe supplied o he discha ge. The plasma and hin
ilm cha ac e is ics a e compa ed wi h hose ob ained in a
p e ious s udy
[7]
o pulsed plasma unde simila deposi ion
condi ions. The di e en kine ics o ilm g ow h in CW and
pulsed plasma is also discussed.
2|EXPERIMENTAL SECTION
2.1 |Thin ilm deposi ion
Capaci i ely coupled non he mal plasma was used o
he deposi ion o hin ilms in a deposi ion sys em
equipped wi h asymme ic plana pa allel elec odes as
p e iously desc ibed.
[10]
The RF (13.56 MHz) plasma was
ope a ed in CW mode. Double‐sided polished (100)
silicon wa e s (0.8 × 10 × 10 mm
3
; ON Semiconduc o )
we e loaded in o he smalle powe ed elec ode. The
plasma eac o was e acua ed o a base p essu e o
2×10
−4
mTo and he silicon subs a e was p e ea ed
wi h a gon plasma (10 sccm, 43 mTo , 5 W) o 10 min o
emo e physiso bed molecules om i s su ace, ollowed
again by e acua ion o he base p essu e. Te a inylsilane
(TVS; Si(–CH═CH
2
)
4
; Sigma‐Ald ich) as a p ecu so was
in oduced in o he eac o a a low a e o 3.8 sccm and
a p essu e o 20 mTo was se by he bu e ly con ol
al e (VAT 615 DN 63). The plasma eac o is equipped
wi h Leybold Vacuum CTR90 and CTR91 capaci i e
senso s. A powe ange o 10–70 W was used o deposi a‐
SiC:H ilms. The lowe limi is de e mined by he
minimum ou pu powe o he RF gene a o (CESAR
1310; Ad anced Ene gy) and he uppe limi co esponds
o he maximum powe esul ing in a s able and
ep oducible plasma. A ma ching ne wo k was used o
educe he e lec ed powe o ze o. A e hin ilm
deposi ion, he TVS apo was emo ed om he
deposi ion sys em wi h a gon gas (10 sccm, 43 mTo )
o 60 min. The sample was hen le unde he base
p essu e o ano he 12 h be o e being ans e ed o
a mosphe ic p essu e.
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2.2 |Analy ical echniques
The HPR‐30 P ocess and Residual Gas Analyze (Hiden
Analy ical) made i possible o check low le els o
esidual gases (oxygen, ni ogen, and wa e molecules) in
he deposi ion chambe be o e and du ing he plasma
p ocess o a oid con amina ion o he a‐SiC:H ilms wi h
oxygen and ni ogen a oms. The emo e loca ion o he
mass spec ome e inpu ensu es ha only neu al
species en e he mass spec ome e . Du ing he deposi-
ion p ocess, he mass spec ome e enables he moni o -
ing o neu al subs ances in he deposi ion chambe
depending on he applied RF powe . The de aul elec on
ene gy o 70 eV was used. The sys em can analyze ions
om 0.4 o 510 amu (a omic mass uni ) wi h a minimum
s ep o 0.01.
The Tande on 4130 MC (HVEE) is a linea accele a-
o ha was used o Ru he o d backsca e ing spec-
ome y and elas ic ecoil de ec ion analysis (ERDA)
measu emen s o cha ac e ize he elemen al composi ion
in he bulk o he ilm. The silicon a oms in he ilms
we e analyzed wi h 2.73 MeV alpha pa icles, while he
ligh e ca bon a oms we e measu ed wi h 2.4 MeV
p o ons; bo h ypes o pa icles inciden pe pendicula
o he ilm su ace and hose sca e ed pa icles we e
de ec ed a an angle o 170°. Fo he cha ac e iza ion o
hyd ogen a oms, an ERDA wi h an inciden beam o
2.75 MeV alpha pa icles a 75° o he no mal o he ilm
su ace was used. Hyd ogen a oms ecoiled a 30° we e
de ec ed by a su ace ba ie de ec o co e ed wi h a
12 µm hick Myla s opping oil.
Fou ie ‐ ans o m in a ed spec oscopy (FTIR) using
a VERTEX 80 (B uke Op ics) was employed a 160 Pa
o cha ac e ize he chemical s uc u e o he a‐SiC:H
ilms a e 12 h unde he base acuum. Two hund ed
i y‐six scans we e collec ed wi h a scan esolu ion o
4cm
−1
o ob ain ansmission spec a in he ange o
400–4000 cm
−1
. The in a ed spec um o he ilm was
de e mined by sub ac ing he spec um o he ba e
silicon wa e and in e e ence e ec s
[11]
om he
eco ded spec um.
The Young's modulus and ha dness o he a‐SiC:H
ilms we e in es iga ed using a 2D T iboScope TS75
(B uke Hysi on) a ached o an NTeg a P ima Scanning
P obe Mic oscope (NT‐MDT). Fo cyclic nanoinden a-
ion,
[12]
a h ee‐sided py amidal Be ko ich inden e wi h
a adius o cu a u e o 50 nm was used o de e mine he
dep h p o ile o he mechanical p ope ies up o 20% o
he ilm hickness. Dep h p o iles o Young's modulus
and ha dness we e ex apola ed o ze o con ac dep h
( ilm su ace) o de e mine he co ec mechanical
pa ame e s o he ilm una ec ed by he silicon
subs a e.
[12]
The hickness and densi y o he a‐SiC:H ilms we e
analyzed using high‐ esolu ion X‐ ay e lec ome y wi h
a con en ional coppe X‐ ay ube, a pa abolic mul ilaye
mi o collima o , and a Ge 220 Ba els‐ ype monoch o-
ma o . The in ensi y pa e n was measu ed by a
scin illa ion de ec o using a sli .
The op ical p ope ies and hickness o he deposi ed
ilms we e e alua ed by a phase‐modula ed spec oscopic
ellipsome e UVISEL (Ho iba Scien i ic). The measu e-
men s we e pe o med a an incidence angle o 70° and a
spo size o 100 × 300 μm
2
using a wa eleng h o
250–830 nm in s eps o 5 nm. The dispe sion dependence
o he dielec ic unc ion was i ed using he i e‐
pa ame e Tauc–Lo en z o mula, which was de i ed o
he pa ame e iza ion o he op oelec onic esponse o
amo phous dielec ics.
[13]
The deposi ion a e was
calcula ed as he a io be ween he ilm hickness
de e mined by ellipsome y and he deposi ion ime.
3|RESULTS AND DISCUSSION
3.1 |Rela i e p essu e d op
By in oducing he p ecu so in o he deposi ion
chambe a a gi en low a e, a s eady‐s a e p essu e is
eached a e a ce ain ime depending on he pumping
speed. The pumping speed o he acuum pump sys em
is ypically limi ed by he bu e ly con ol al e ha
allows he p essu e o he p ecu so molecules o be
p ese o a gi en alue, p
o
, be o e he plasma is igni ed
(plasma o egime). The gene al gas equa ion can be
con e ed in o he o m
pnkT=
,
B
o o (1)
whe e he p essu e, p
o
, is ela ed o he concen a ion o
p ecu so molecules, n
o
,k
B
is he Bol zmann cons an ,
and Tis he gas empe a u e. Analogous o Equa ion (1),
a e he plasma is igni ed (plasma on egime), he
p ocess p essu e s abilizes a p
on
, which is ela ed o he
concen a ion o plasma species, n
on
, ha can be
exp essed as
nn nnn=+++
,
on undis bp in ad (2)
whe e n
undis
is he concen a ion o p ecu so molecules
ha we e no dissocia ed, n
bp
is he concen a ion o by‐
p oduc s, n
in
is he concen a ion o in e media es, and
n
ad
is he concen a ion o adicals; all hese componen s
a e cons an a he s eady‐s a e plasma o a gi en RF
powe . Du ing he plasma p ocess, p ecu so molecules
a e agmen ed in o ee adicals in he p ocesses o
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elec on‐impac dissocia ion and dissocia i e elec on‐
impac ioniza ion. As a esul o ecombina ion p ocesses
in he bulk plasma (associa ion o plasma species in o
oligome s) and on he su ace o he g owing ilm
(chemiso p ion), hose chemically eac i e species ( adi-
cals) o m by‐p oduc s (e.g., H
2
,CH
4
) o in e media es
con aining a double o iple bond (e.g., H
2
C═CH
2
,
HC≡CH) o a e chemically bound o he su ace o he
g owing ilm. A he same ime, i is ue ha
nn n=+
,
o undis dis (3)
whe e n
dis
is he concen a ion o dissocia ed molecules.
Highe low a es, which esul in only abou 1% o
dissocia ed p ecu so molecules,
[1]
do no signi ican ly
a ec he p ocess p essu e, and hus p
on
≈p
o
since
n
on
≈n
undis
≈n
o
; concen a ions, n
dis
,n
bp
,n
in
, and n
ad
,
a e small compa ed o n
undis
. Howe e , a a deg ee o
p ecu so agmen a ion highe han 1%, a change in
p ocess p essu e can be expec ed. E e y dissocia ed
molecule is spli in o wo o mo e agmen s, meaning
ha n
on
>n
o
and he p ocess p essu e inc eases a e
he plasma is igni ed. Plasma deposi ion is a dynamic
p ocess, whe e eac i e plasma species a e gene a ed bu
also ecombined, and he s eady‐s a e concen a ion o
plasma species, n
on
, is con olled by he gene a ion and
ecombina ion a es. The esul ing p ocess p essu e, p
on
,
can he e o e be highe , lowe , o , in a special case, equal
o he p ese p essu e, p
o
.
I he ecombina ion p ocess is as enough, he
p ocess p essu e is lowe han he p ese p essu e and
he ela i e p essu e d op can be exp essed as
∆ppp
p
nn
n
=−=−
.
o on
o
o on
o (4)
The deg ee o dissocia ion,
dis
, is exp essed as he
ac ion o he p ecu so molecules ha ha e dissocia ed,
hus wi h espec o Equa ion (3)
n
nn
nn
n
=+=−
.
dis
dis
dis undis
o undis
o
(5)
Since n
on
>n
undis
and using Equa ions (2), (4), and
(5) we ge
∆p <
.
dis
(6)
The ela i e p essu e d op, he e o e, exp esses he lowe
limi o he deg ee o dissocia ion and mul iplied by 100%
indica es he minimum consump ion o he p ecu so in
pe cen . This means ha he ac ual deg ee o dissocia ion is
highe han his alue, Δp
. The las ela ion (Equa ion 6)is
alid o neu al as well as cha ged (ionic) plasma species,
al hough he cha ged species may ha e a highe p ocess
empe a u e, T
on
>T
o
.
As an example, he p ocess p essu e (black symbol)
dependen on he RF powe o CW plasma (10–70 W) and
pulsed plasma (2–150 W)
[7]
a a TVS low a e o 3.8 sccm
and a p ese p essu e o 20 mTo , as shown in Figu e 1.
E ec i e powe is used o he pulsed plasma, de ailed in he
s udybyB aneckye al.
[7]
The co esponding ela i e
p essu e d op is shown as a ed symbol (Figu e 1). A
smoo hing B‐spline (O igin; O iginLab Co po a ion) was
used o i he da a only o cap u e he dependence end. I
is e iden ha he deg ee o dissocia ion is highe o a CW
plasma han o a pulsed plasma a a gi en RF powe . While
o he pulsed plasma, he ela i e p essu e d op inc eases
om 0.04 o 0.33, in he case o he CW plasma, he ela i e
p essu e d op a ies om 0.41 o 0.57. E en highe p essu e
d opso up o0.81we e ound o a ubula plasmasys em
using a TVS low a e anging om 1.4 sccm (p ese p essu e
29–114 mTo ) o 7.0 sccm (29 mTo ).
[14]
Se e al TVS low
a es we e es ed o obse e he p essu e d op in he plan‐
pa allel plasma sys em
[10]
used in his s udy. A p essu e d op
was obse ed o a low a e o 1.9 sccm and a p ese p essu e
o 20–162 mTo and 3.8 sccm and 20–81 mTo , bu no
p essu e d op was no ed o a low a e o 7.6 sccm and a
p ese p essu e o 41–81 mTo . In he nex sec ion, we will
look a how he CW plasma leading o a highe deg ee o
dissocia ion a ec s he deposi ion p ocess.
3.2 |Plasma chemis y
The powe ‐dependen (CW mode, 10–70 W) mass spec a
o neu al species in TVS plasma oge he wi h he
spec um co esponding o ze o powe (plasma o ) a e
FIGURE 1 Powe ‐dependen p ocess p essu e and he
co esponding ela i e p essu e d op o con inuous wa e (CW)
and pulsed plasma. RF, adio equency.
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FIGURE 2 Mass spec a o he neu al species in TVS plasma
co esponding o 10–70 W ope a ed in con inuous wa e mode and
ze o powe (plasma o ).
FIGURE 3 (a) Cumula i e powe dependence o ca bon species (m/z25–28) and silicon‐con aining species (m/z53–57, 80–83, and 105–
109) o con inuous wa e (solid line) and pulsed (dashed line) plasma. (b) Powe dependence o indi idual ca bon species (m/z25–28) o
con inuous wa e (CW) (solid line) and pulsed (dashed line) plasma. RF, adio equency
plo ed in Figu e 2. No oxides we e caused by esidual
wa e molecules in he deposi ion chambe and no
oligome s we e de ec ed by mass spec ome y.
Mass spec a can be quan i a i ely analyzed analo-
gously o TVS pulsed plasma.
[15]
This analysis is based on
he idea ha changes in plasma chemis y occu ing in
he deposi ion chambe a e e lec ed in co esponding
changes in he mass spec ome e due o simila
agmen a ion pa e ns o elec on impac dissocia ion
and dissocia i e elec on impac ioniza ion, which was
demons a ed by s ong co ela ions be ween he mos
p oduced ca ions eco ded by he mass spec ome e and
he ilm chemis y.
[15]
The pa ial p essu e o a gi en
ca ion is ela ed o i s concen a ion as desc ibed in
Equa ion (1). The mos p oduced ca ions include ca bon
species (m/z25–28), silicon‐con aining species (m/z
53–57 wi h one inyl g oup, 80–83 wi h wo inyl
g oups, 105–109 wi h h ee inyl g oups), which a e
he building blocks o he g owing ilm and de e mine i s
elemen al composi ion and chemical s uc u e,
[15]
and
also include a hyd ogen molecule (m/z2) as a by‐
p oduc ; m/zmeans he a io o ion mass (m) o cha ge
alence (z). The powe dependence o he abo e species
o he CW plasma (solid line) is compa ed wi h he
dis ibu ion o he pulsed plasma (dashed line) in
Figu e 3a. The ca bon species domina e o e he
silicon‐con aining species o all powe s in he 10–70 W
ange and include e hynyl ion (m/z25), ace ylene ion (m/
z26), inyl ion (m/z27), and e hylene ion (m/z28) and
hei powe dependences a e shown in Figu e 3b again
o CW and pulsed plasma. I is ypical o all powe
dependences ha he concen a ion o ca ions is lowe in
CW plasma han in pulsed plasma.
3.3 |S icking coe icien
The g ow h a e o he ilm is signi ican ly in luenced
by he densi y o ee‐binding si es on he su ace o
he g owing ilm. As explained in de ail in a p e ious
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s udy,
[15]
he concen a ion o ee adicals (H, CH
3
,
C
2
H, and C
2
H
3
) in he plasma is su icien o e y
e icien hyd ogen emo al (hyd ogen abs ac ion)
[16]
om he ilm su ace, allowing he o ma ion o ee
binding si es. F ee adicals and mul iple bond in e -
media es hen bind o hese binding si es and
con ibu e o he g ow h o he ilm. The deposi ion
a e o a‐SiC:H ilms p epa ed om he TVS p ecu so
using CW plasma is lowe han ha o pulsed plasma
o a gi en powe , as seen in Figu e 4a.Themaximum
deposi ion a e o CW plasma is 210 nm min
−1
(20 W)
bu 319 nm min
−1
(25 W) o pulsed plasma. A lowe
deposi ion a e was also con i med o a‐SiC:H ilms
deposi ed om he SiH
4
/CH
4
mix u e using CW
plasma compa ed o pulsed plasma.
[17]
The deposi ion a e is ela ed o he numbe o
plasma species ha impinge on a uni su ace pe uni
ime (molecula incidence a e). Howe e , no e e y
adical o in e media e is co alen ly bound o he su ace
o he g owing ilm due o s e ic and collision o ien a ion
e ec s.
[18,19]
The p obabili y ha an a om o molecule is
chemiso bed can be exp essed using he s icking
coe icien ,
[20]
which anges om 0 o 1. The g ow h o
he ilm also depends on he size o he a ached
agmen s. The deposi ion a e (R) can he e o e be
exp essed as he sum o he con ibu ions o indi idual
ypes o eac i e plasma species

RγV=Φ
,
i
N
iii
=1
(7)
whe e γ
i
is he s icking coe icien , Φ
i
is he molecula
incidence a e, and V
i
is he olume co esponding o he
i h agmen ype. The molecula incidence a e o a
gi en agmen o mass (m
i
) is de e mined by i s pa ial
p essu e (p
i
)
[21]
p
πmk T
Φ=2
,
ii
iB (8)
and he co esponding olume o he bound agmen is
gi en by
FIGURE 4 (a) Deposi ion a e as a unc ion o adio equency (RF) powe . (b) Molecula incidence a e o ca bon species and silicon‐
con aining species depending on RF powe . (c) Powe dependence o he s icking coe icien o ca bon species in he case o con inuous
wa e (CW) (solid line) and pulsed (dashed line) plasma.
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V
M
Nρ
=
,
ii
A(9)
whe e M
i
is he mola mass o he agmen , N
A
is he
A ogad o's cons an , and ρis he ilm densi y.
Hyd ogen abs ac ion is mos e icien due o hyd o-
gen a oms, leading o he elease o hyd ogen mole-
cules.
[16]
In he case o pulsed plasma,
[15]
he pe iod
consis s o an RF powe ‐on pa (1 ms) and an RF powe ‐
o pa (1–7 ms), and since he li e ime o he ions is only
10
−6
s,
[22]
sho ly a e he powe is u ned o , he e a e
no mo e elec ons a ailable o dissocia e he neu al
plasma species. This means ha H
2
p oduc ion inc eases
due o hyd ogen abs ac ion du ing he ime when he
powe is u ned o , as he li e ime o he adicals can be
longe han 1 h.
[8]
Howe e , he H
2
p oduc ion and as
well as he p oduc ion o o he plasma species a e
dissocia ed con inuously in ime in CW plasma, leading
o hei lowe concen a ions han in he case o pulsed
plasma (Figu e 3). Thus, hyd ogen abs ac ion may be
mo e e ec i e in CW plasma han in pulsed plasma and
may hus a ec he magni ude o he s ickiness
coe icien .
Cumula i e molecula incidence a es in Figu e 4b
we e calcula ed (Equa ion 8) o ca bon and silicon‐
con aining species based on he pa ial p essu es om
Figu e 3a o CW (solid line) and pulsed (dashed line)
plasma. The molecula incidence a e o ca bon species
domina es (10–70 W) and u he mo e, he s icking
coe icien o silicon‐con aining species is a leas 10
imes lowe han ha o ca bon species, as ound in a
p e ious s udy,
[15]
and hus he con ibu ion o silicon‐
con aining species o he deposi ion a e can be neglec-
ed. The simpli ied Equa ion (7) can be used o es ima e
he s icking coe icien o he ca bon species ep esen ed
mainly by he ace ylene molecule (Figu e 3b) wi h a
mola mass o 26.04 g mol
−1
. The ilm densi y as assessed
by X‐ ay e lec ome y inc eased om 1.35 g cm
−3
(10 W)
o 1.84 g cm
−3
(70 W), educing he olume pe agmen
(Equa ion 9). The molecula incidence a e o he ca bon
species in he deposi ion chambe , which was used in
Equa ion (7), was de e mined om he pa ial p essu e
p opo ional o he p ocess p essu e (Figu e 1). The
es ima ed s icking coe icien as a unc ion o powe o
CW (solid line) and pulsed (dashed line) plasma is gi en
in Figu e 4c. The s icking coe icien o he CW plasma
inc eased om 3 × 10
−5
(10 W) o 6 × 10
−5
(70 W),
indica ing an inc eased e ec i i y o hyd ogen abs ac-
ion wi h enhanced powe . The s icking coe icien o
pulsed plasma anges be ween alues (3–4) × 10
−5
and is
like he alues o CW plasma a lowe powe s
(10–25 W). These alues o he s icking coe icien
co espond o he alues published o he CH
3
adical
in he case o a‐C:H ilm g ow h.
[23]
The maximum
deposi ion a e o he CW plasma is lowe han o he
pulsed plasma (Figu e 4a) due o he lowe molecula
incidence a e, as he s icking coe icien and agmen
olume a e e y simila o bo h ypes o plasma.
The gene a ion and ecombina ion o plasma species
in bo h ypes o plasma di e s due o he di e en
kine ics o plasmachemical p ocesses du ing he on and
o egime o he pulsed plasma. P ecu so molecules a e
dissocia ed con inuously in ime in CW plasma, in
con as o pulsed plasma, whe e dissocia ion occu s
only when he plasma is u ned on o 1 ms, esul ing in a
highe deg ee o dissocia ion and highe consump ion o
p ecu so molecules in CW plasma, which is indica ed by
a highe dec ease in he p ocess p essu e. When he
plasma is swi ched o wi hin 1–7 ms, he concen a ion
o plasma species (H
2
,CH
4
,C
2
H
2
, and C
2
H
4
) due o
hyd ogen abs ac ion and no ongoing dissocia ion
inc eases and, oge he wi h he concen a ion o he
main adicals (C
2
H, C
2
H
3
), a e hus highe on a e age
o e he pe iod o he pulsed plasma han o he CW
plasma, esul ing in highe deposi ion a e.
3.4 |Chemical p ope ies
The elemen al composi ion o a‐SiC:H ilms, which is
con olled by he powe o CW (solid line) and pulsed
(dashed line) plasma, is shown in Figu e 5a. The
concen a ion o silicon a oms is simila o bo h ypes
o plasma and app oxima ely independen o powe . The
concen a ion o ca bon inc eases wi h enhanced powe
a he expense o hyd ogen also in bo h ypes o plasma,
bu in he case o CW plasma he concen a ion o
hyd ogen a oms is highe a lowe powe s (10–25 W)
han in pulsed plasma. As‐deposi ed ilms a e oxygen‐
ee ma e ials, which is consis en wi h he esul s o he
mass spec a analysis. McCu dy e al.
[24]
also ound ha
when CW plasma was used, he e was g ea e inco po a-
ion o hyd ogen in o a‐SiC:H ilms deposi ed om a
SiH
4
/CH
4
mix u e han when pulsed plasma was used.
The FTIR spec a shown in Figu e 5b p o ide insigh
in o he chemical s uc u e o he oxygen‐ ee a‐CSi:H
ilms modi ied by he applied powe used o he CW
plasma. The igu e also includes he assignmen o he
main abso p ion peaks o he ib a ions o speci ic
chemical g oups.
[25,26]
The concen a ion o inyl g oups
(1404, 1007, and 953 cm
−1
) bound o he ca bon‐silicon
ne wo k dec eases wi h enhanced powe , as al eady
known in he case o pulsed plasma.
[7]
Also, he a ea o
he abso p ion bands o he CH
x
(2905–2895 cm
−1
) and
SiH
x
(2116–2122 cm
−1
) ib a ions dec eases as hyd ogen
is elimina ed om he a‐CSi:H ilms a highe powe s.
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This means ha educing he hyd ogen concen a ion in
he ca bon‐silicon ne wo k esul s in a mo e c osslinked
and dense ma e ial,
[7]
see he inc ease in ilm densi y
wi h powe in he p e ious chap e . In addi ion, he
dense ca bon–silicon ne wo k con ains a highe con-
cen a ion o ca bon wi h a double bond
(1350–1650 cm
−1
), also obse ed in he case o pulsed
plasma.
[7]
The hyd ogen o highe concen a ion in ilms
deposi ed in CW plasma a lowe powe o 10 W appea s
o be bound in he inyl g oups (1404 cm
−1
) as well as in
he ca bon‐silicon ne wo k (CH
2
in sp
3
con igu a ion,
1454 cm
−1
) as shown in he inse g aph (Figu e 5b).
3.5 |Physical p ope ies
The mechanical p ope ies o a‐CSi:H ilms, Young's
modulus (black symbol), and ha dness ( ed symbol),
deposi ed in CW plasma (solid line) a e compa ed wi h
hose ob ained o pulsed plasma (dashed line) in
Figu e 6a. Bo h pa ame e s inc ease signi ican ly wi h
enhanced powe o he CW plasma, namely, Young's
modulus om 12 GPa (10 W) o 81 GPa (70 W) and he
ha dness om 0.8 GPa (10 W) o 8.8 GPa (70 W). Fo
pulsed plasma, he mechanical p ope ies we e ound o
inc ease due o inc eased c osslinking o he ca bon‐
silicon ne wo k cha ac e ized by an inc eased ilm
densi y o 1.5–1.9 g cm
−3
.
[7]
The mechanical p ope ies
co esponding o he CW plasma a e simila o hose o
he pulsed plasma (Figu e 6a), p obably due o he
simila deg ee o ne wo k c osslinking a a gi en powe .
Powe ‐dependen dispe sion cu es o he e ac i e
index and he ex inc ion coe icien (op ical p ope ies) in
he case o CW plasma a e e y simila o hose ob ained
o a‐CSi:H ilms deposi ed in pulsed plasma.
[7]
Thus, he
op ical p ope ies o a‐CSi:H ilms deposi ed using CW
(solid line) and pulsed (dashed line) plasma we e
compa ed only o a speci ic wa eleng h o 633 nm
(He–Ne lase ) in Figu e 6b. The powe dependences o
he e ac i e index (black symbol) and he ex inc ion
coe icien ( ed symbol) a e again simila o bo h ypes
o plasma. The e ac i e index inc eases wi h enhanced
powe o CW plasma om 1.7 o 2.1 depending on he
op ical densi y o he ma e ial desc ibed by he
Clausius–Mosso i ela ion.
[27]
The s ong co ela ion
be ween he e ac i e index and Young's modulus
demons a ed in Figu e 6c p o es ha bo h pa ame e s
a e con olled by he deg ee o ne wo k c osslinking o
bo h ypes o plasma. The powe dependence o he
ex inc ion coe icien in Figu e 6b shows ha he a‐CSi:H
ilms deposi ed a 10 and 20 W a e anspa en o a
wa eleng h o 633 nm, co esponding o he powe ‐
dependen band gap in Figu e 6d. The band gap
dec eased om 2.0 o 1.2 wi h enhanced powe o he
CW plasma consis en wi h he da a o he pulsed
plasma. This educ ion was co ela ed wi h a educed
concen a ion o nano oids ( inyl g oups) in he ma e ial
and an inc eased sp
2
con en in he ca bon‐silicon
ne wo k, which a e esponsible o band gap
modi ica ion.
[7]
3.6 |Sel ‐bias ol age
In asymme ic capaci i ely coupled RF plasma sys ems
wi h a smalle powe ed elec ode and a la ge g ounded
elec ode, a nega i e DC sel ‐bias ol age occu s on he
powe ed elec ode due o he highe mobili y o elec ons
han ions.
[28]
This nega i e shea h ol age accele a es he
posi i e ions ha bomba d he powe ed elec ode wi h a
FIGURE 5 (a) Powe ‐dependen elemen al composi ion o a‐CSi:H ilms deposi ed using con inuous wa e (CW) (solid line) and pulsed
(dashed line) plasma. (b) In a ed spec a o a‐CSi:H ilms deposi ed using CW plasma a 10–70 W, oge he wi h a de ail o he di e ence
spec a be ween CW and pulsed plasma o 10 W in he inse g aph. RF, adio equency.
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loaded subs a e, which in p inciple can a ec he g ow h
o he ilm. Howe e , he spu e ing e ec is moni o ed
wi h coppe ca ions (m/z63.5) due o he spu e ing o
coppe a oms om he powe ed elec ode, and no such
ca ions we e obse ed in CW (10–70 W) and pulsed
(2–150 W) plasma. As analyzed and discussed in he
p e ious s udy,
[15]
he neu al plasma species domina e
he g ow h o he ilm and no e ec o ions on he
chemical and physical p ope ies o he deposi ed ilms
was demons a ed. Ca he ine and Coude c
[29]
ound ha
he sel ‐bias ol age (V
B
) is p opo ional o he powe (W)
and he p ocess p essu e (p
on
)as
≈
V
W
p
.
B
on
(10)
This dependence is plo ed in Figu e 7 o CW and
pulsed plasma. The mean alue o he sel ‐bias ol age
was used o he pulsed plasma because he bias
oscilla es. Indi idual powe alues a e shown di ec ly
o he gi en dependency, o CW plasma in blue and o
pulsed plasma in ed. The sel ‐bias ol age o a gi en
powe is highe o CW plasma han o pulsed plasma
excep o 10 W (Figu e 7), o example, 929 V (70 W) o
CW plasma and 555 V (75 W) o pulsed plasma. F om
FIGURE 6 (a) Powe dependence o Young's modulus and ha dness o a‐CSi:H ilms deposi ed in con inuous wa e (CW) (solid line)
and pulsed (dashed line) plasma. (b) Compa ison o e ac i e index and ex inc ion coe icien a 633 nm o CW and pulsed plasma. (c)
Co ela ion o e ac i e index wi h Young's modulus o CW and pulsed plasma. (d) Powe ‐dependen band gap o CW and pulsed plasma.
RF, adio equency.
FIGURE 7 Sel ‐bias ol age co esponding o ma ked powe
e sus (W/p
on
)
1/2
o con inuous wa e (CW) (solid line) and pulsed
(dashed line) plasma.
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