Aozasa, Masao

Nitta, Atsushi

Tanaka, Kenji

Taniguchi, Akifumi

Osaka City University Repository

Mem. Fac. Eng., Osaka City Univ., Vol. 43, pp. 7 -11 (2002)
Diffusion of ZnS:Mn Active Layer to Plasma Polymerized p-xylene Thin Film
Akifumi TANIGUCHI *, Atushi NARA**, Kenji TANAKA***
and Masao AOZASA****
( Received October 15, 2002 )
Synopsis
As a preliminary work to fabricate an organic and inorganic compound EL device, we investigated
diffusion across two layers by annealing. p-xylene was plasma polymerized on ZnS:Mn film deposited
by the sputtering method. The diffusion is enhanced as the annealing time and temperature increases.
And the previous annealing effectively suppresses the diffusion of inorganic material afterward.
KEYWORDS: Plasma polymerization, p -xylene, ZnS:Mn
1. Introduction
Organic electroluminescent (EL) and inorganic EL devices, which are expected as new generation
flat display device, have many advantages such as high brightness, thinness and self emitting. However
inorganic EL device has high operating voltage and organic EL device has short life time. The organic
and inorganic compound EL is expected to resolve these disadvantages. We prepared an organic and
inorganic compound thin film. The organic layer is plasma polymerized p-xylene (PPPX) with high
durability and less pinholes. However it is easily deteriorated after deposition due to its active
radicals. Inorganic layer is ZnS:Mn layer which is often used as an active layer of inorganic EL
devices. We investigated depth profile of atomic composition with ESCA (Electron Spectroscopy for
Chemical Analysis, SHIMADZU INC. ESCA-750).
2. Experimental
ZnS:Mn thin film was prepared by RF magnetron sputtering method on the cleaned indium-tin
oxide (ITO) coated glass substrate (MATSUNAMI GLASS IND., LTD., Corning #7059 25 x 25 x
0.6 mm). Then plasma polymerized p-xylene thin film was deposited using p-xylene monomer. Fig.l
and Fig.2 show capacitively coupled glow discharge system for plasma polymerization (SAMCO
ENGINEERING INC. PD-2) and RF magnetron sputtering equipment (TOKKI INC. SPK-30l)
respectively. Deposition conditions are shown in Table 1, Table 2.
Table 1: ZnS:Mn sputtering conditions
Target
Base pressure
Gas pressure
RF power
Substrate temperature
Deposition time
Sputtering gas flow rate
ZnS:Mn (Mn == 0.5 wt.%)
1.2 -- 1.4 X 10-6 Torr
2 X 10-3 Torr
50 W
200°C
50 min
Ar:l0 ccm + He:l0 ccm
*Student, Master Course of Department of Physical Electronics and Information
**Stuff of Hosiden Corporation
*• *Research Associate, Department of Physical Electronics and Information
** **Professor, Department of Physical Electronics and Information
7
Table 2: Deposition conditions of PPPX
Base pressure
Discharge pressure
RF power
Substrate temperature
Deposition time
Bubbling gas (Ar) flow rate
0.02 Torr
0.3 Torr
19.6 W
40°C
15 min
50 ccm
Depth profile of Zn(2p 3/2) and S(2p) were investigated. Etching was performed under the
conditions of Ar pressure of 5x10-4 Torr, acceleration voltage of 2 kV and ion beam current of 10
J-lA. Etching speed of all PPPX layer was about 6 nm/min. Any PPPX thin films are about 150
nm in thickness. After deposition of PPPX, ·samples were annealed by heat-treatment equipment
(KaYO LINDBERG INC.) under several different conditions.
Reactor
RF power supply
Carl!!!:.9as Gas rer,ator
Ar
PC
t
1
Sputter gas
Exhaust
Fig. 1: Capacitively Coupled Glow Discharge
System for Plasma Polymerization
Fig. 2: RF Magnetron Sputtering Equipment
3. Experimental results and discussions
3.1 Temporal change after annealing and effect of annealing temperature
Fig.3 shows the effect of annealing on depth profile of Zn(2p 3/2) peak and S(2p) peak and
the temporal change after annealing. The time of annealing was 1 hour. As PPPX layer thickness
and etching speed are known, we can easily estimate that 25 min etching reaches the boundary
between the PPPX layer and the ZnS:Mn layer. Fig.3(a) and Fig.3(d) show that, when the sample
was not annealed, the peak of Zn(2p 3/2) of the sample one week after deposition is observed at
the shallower position than that in the as deposited sample. Concerning S atom, Fig.4(a) and
Fig.4(d) show the similar result. Therefore it is clear that the diffusion of Zn atoms and S atoms to
PPPX layer occur one week after deposition. Fig.3(a) through Fig.3(c) and Fig.4(a) through Fig.4(c)
show that the higher annealing temperature causes enhanced diffusion. Comparing between Fig.3(a)
and Fig.3(d), Fig.3(b) and Fig.3(e), Fig.3(c) and Fig.3(f), it is found that the annealing at higher
temperature brings less change in the depth profile after one week. It suggests that annealing at
higher temperature promotes more crosslinking reaction and the tightly crosslinked structure would
suppress diffusions of Zn and S atoms.
8
101010151025 1020
Bincing Energy(eV)
1030103510101015
lOmin etch
1025 1020
Bincing Energy(eV)
no etch
10301035101010151025 1020
Binding Energy(eV)
20min etch
10min etch
no etch
1030
30min etch
(max70,OOOcps)~:CP.)
----- 50min etch
(max160,OOOcps)
1035
~
C
:I
-e
i
·
c
.s
oS
(a) as deposited (b) soon after annealing at
100 t
(c) soon after annealing at 200 t
10101030 1025 1020 1015
Binding Energy(eV)
103510101030 1025 1020 1015
Bincing Energy(eV)
103510101030 1025 1020 1015
Binding Energy(eV)
1035
no etch no etch
10min etch IOmin etch
~
ic ~:I C
-e
,
:I
:I
·
.f
-e~ .
"S j
·
.:t:!C .
.s .! coS i.s
(d) one week after deposited (e) one week after annealing at
100 t
(f) one week after annealing at
200 t
Fig. 3: Effect of annealing on depth profile of Zn(2p 3/2) and temporal change after annealing
9
no etch no etch
no etch
10min etch 10min etch lPmin etch
,prom'mh
155175 170 165 160
Bindng Energy(eV)
180
~ 20minetch/\
§ (mM,14,OOOcps) ~ ~ --#j 30min etc~ /\ -
! (m;_~1;5~'OOOCPS) 1':L-J /\ '--- -~ 40mln etch
(m 8000cps)
155170 165 160
Bileing Energy(eV)
175
20min etch
40min etch
(max 15.000cps)
50min etch
(max17.OOOcps)
30min etch /)...
(~J\'----
180155170 165 160
Binding Energy(eV)
175
SOmin etch
(max14,OOOcps)
40min etch
(max 11 ,OOOcps)
30min etch /\
(~ '-----
180
(a) as deposited (b) soon after annealing at
100 OC
(c) soon after annealing at 200 OC
n9 etph no ,tgh no etch
20min etch
(
30minetch ~;1MOOcpI)
40min etch
(1MX16,OOOCPI)~
; etch
17,OOOcpa)
180
lOmjn etch
20min etch
30min etch
(max 12,OOOcps)
50min etch
(max 16,OOOcps)
175 170 165 160
Binding Energy(eV)
155 180
10min etch
175 170 165 160
Binding En,rgy(eV)
155 180 175 170 165 160
Binding Energy(eV)
155
(d) one week after deposited (e) one week after annealing at
100 OC
(f) one week after annealing at
200 OC
Fig. 4: Effect of annealing on depth profile of S(2p) and temporal change after annealing
10
3.2 Annealing time dependence of diffusion
Fig.5 and Fig.6 show depth profile of Zn(2p 3/2) and S(2p) peak of the samples annealed at 200
°C for 0--3 hour. These figures show that the boundary between ZnS:Mn and PPPX moves up to
the surface as the annealing time is increased.
no etch no etch
5min etch 5min etch
10min etch
15min etch
~ ~ ~o§ '§ ~~ i .d il ~ t lj 0.~ :s I
1030 1028 102.11 102.4 102.2 102.0 1018 lOll 1030 102.8 102.11 102.4 102.2. 102.0 1018 10111 1030 1028 102.11 102.4 102.2. 102.0 1018 10111 1030 102.8 102.11 102.4 102.2 102.0 1018 10111
Bindin, Enet'IY(eV) Blndin, Enet'IY(eV) Blndin, EnermeV) Bindin, EneriMeV)
(a) as deposited (b) soon after annealing
at 200 t for one hour
(c) soon after annealing
at 200 t for two hours
(d) soon after annealing
at 200 t for three hours
Fig. 5: Depth profile of Zn(2p 3/2) in the sample after annealing
45min etch
50min etch
40min etch
no etch
5min etch
10min etch
15min etch
20min etch ~
25min etch i
30min etch ~
..
35min etch ~
no etch
5nin etch
~ ...----~
---i.....---
------I fl---__-
__~ 11---__-
no etch
5min etch
10min etch
15min etch
20min etch ~
25min etch
of
30min etch t35min etch i
40Iftin etch
45min etch
50min etch
~t----------------t
~~----~~----t11-----
i 1-----
172. 170 1118 III 1114 1111 1110 158 172 170 1118 11111 1114 1112 1110 1 8 172. 170 1118 11111 1114 1112 1110 158 172 170 1118 III 1114 1111 1110 158
Bindnl EnermeV) Bindinl Enel'JY(eV) Bindinl EnerrY<eV) Bindnl EnerrY<eV)
(a) as deposited (b) soon after annealing
at 200 t for one hour
(c) soon after annealing
at 200 t for two hours
(d) soon after annealing
at 200 t for three hours
Fig. 6: Depth profile of S(2p) in the sample after annealing
4. Conclusion
The conclusions can be summarized as follows:
1. Annealing at higher temperture enhanced the diffusion of ZnS:Mn into the PPPX thin film.
2. Previous annealing of the sample suppresses diffusion of inorganic material into organic material
afterward.
3. Annealing temperture and annealing time have to be optimized for the effective elimination of
radicals and effective suppression of inorganic material diffusion.
Acknowledgement
The authors would like to thank Mr. Yasuhiro Akita for his technical support on data processing,
and professors Yoshiharu Maekawa and Minoru Kusabiraki for their encouragement and helpful
discussions.
11


Diffusion of ZnS:Mn Active Layer to Plasma Polymerized p-xylene Thin Film

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Diffusion of ZnS:Mn Active Layer to Plasma Polymerized p-xylene Thin Film

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