Ground State and Excited State H-Atom Temperatures
in a Microwave Plasma Diamond Deposition Reactor
A. Gicquel, M. Chenevier, Y. Breton, M. Petiau, J. Booth, K. Hassouni
To cite this version:
A. Gicquel, M. Chenevier, Y. Breton, M. Petiau, J. Booth, et al.. Ground State and Excited
State H-Atom Temperatures in a Microwave Plasma Diamond Deposition Reactor. Journal
de Physique III, EDP Sciences, 1996, 6 (9), pp.1167-1180. <10.1051/jp3:1996176>. <jpa00249515>
HAL Id: jpa-00249515
https://hal.archives-ouvertes.fr/jpa-00249515
Submitted on 1 Jan 1996
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Phys.
J.
III
France
(1996)
6
and
Ground
State
Microwave
Plasma
Gicquel (~,*),
A.
and
(~),
Breton
Y.
a
M.
Petiau
(~),
J.P.
Booth
(~)
(~)
d'Ing4ni4rie des Mat4riaux et des Hautes
C14ment,
Villetaneuse,
France
93430
avenue
de Spectrom4trie
Physique (***), Universit4
Laboratoire
(~)
Saint
d'Hbres
Cedex, France
B-P. 87, 38402
Martin
(~)
in
Deposition
(~),
Chenevier
l167
PAGE
H-Atom
Temperatures
Reactor
State
Excited
Diamond
M.
Hassouni
K.
SEPTEMBER1996,
l167-l180
Laboratoire
(**),
Pressions
Universit4
Paris-Nord,
J.B.
(Received
February1996,
22
PACS.52.70.-m
Plasma
PACS.52.70.Kz
Optical
Abstract.
Ground
plasma
microwave
a
introduced
the
in
obtained
the
from
Laser
transition
techniques
and
and
gas
and
excited
temperature
of
the
respectively
Grenoble,
1996)
H-atom
measured
in
temperatures
are
low
percentage of methane
density.
Ground
Hmicrowave
state
power
H-atom in the n
excited
3
(THm) are
state
function
a
of
a
=
the
of
(TALIF)
Fluorescence
June
de
measurements
state
deposition
reactor
as
the averaged input
measurements
Induced
and
state
24
Fourier
instrumentation
(ultraviolet, visible, infrared)
electronic
(TH)
accepted
June1996,
14
diagnostic
diamond
feed
temperature
atom
revised
Joseph
excitation
the H~
and
line
profile by Two-photon
broadening by Optical
Allowed
Emission
diffusive
Spectroscopy (DES). They are compared to gas temperatures
calculated
with a lD
rotational
equilibrium H2 plasma flow model and to ground
electronic
state
temperatures
molecular
hydrogen measured previously by Coherent
Anti-Stokes
Spectroscopy.
Raman
non
of
Introduction
1.
Spatially
resolved
acteristics
in
the
knowledge
Their
The
nomena.
the
since
spectroscopic analysis of the plasma provides
measurements
plasma and at the plasma/surface interface (temperatures,
allows
validation
of
control
industrial
by Optical
measurements
of
analysis
spectroscopic
models
leading
provides
a
reactors
Emission
to
increased
an
monitoring the
by laser spectroscopy is unrealistic,
Spectroscopy (DES), associated to their
also
mean
for
of
local
char-
concentrations).
understanding of the phereactors.
However,
development of
calibration by laser
the
diagnostics
techniques, is needed.
of ground state
Measurements
H-atom
by Two-photon Allowed
Laser
transition
reported in the
literature
[1-6]. As well,
of excited
H-atom
have been performed, in particular
states
temperature
measurements
some
of them, in plasma
used for diamond
deposition [7-9]. However, to our knowledge, no
reactors
performed under experimental
conditions
comparison between these
typical for
measurements
Fluorescence
Induced
(*
Author
©
for
CNRS-UPR
(**
(***
correspondence
1311
CNRS-URM
Les
iditions
(TALIF)
C5588
de
Physique
1996
have
been
temperature
already
deposition (pressure higher than
diamond
of
pressure
the
around
H-atom
hot
H
temperature
from
atoms
electrons.
and
plasmas
of
have
and
been
n
=
for the
considered
estimation
have
owing
collisions
temperatures,
(TH)
(TH«) by
state
of the
n
in
microwave
between
Doppler
by TALIF,
measured
is
DES.
Stark
excited
3
=
molecules
from
measured
of
H2
comparison
A
at
that
production
the
to
between
deposition.
addition,
In
demonstrated
performed
measurements
temperature
excited
3
discussed.
yet
at. [4]
et
involving
H-atom
H-atom
state
the
in
been
diamond
state
N°9
temperature
gas
process
excited
Ground
H-atom
have
spectroscopic
typical for
III
Rousseau
the
than
report
we
state
and
excitation
conditions
presented.
is
temperature
broadenings
and
H-atom
pressure
temperature
These have been also compared to gas
calculated
with
temperatures
equilibrium H2 Plasma flow model [lo, iii, and to rotational
temperatures of
measured
previously by Coherent
molecular hydrogen in its ground electronic
Anti-Stokes
state
Raman
Spectroscopy (equal to the gas temperature) [12,13]. Their
function of
variations
as
a
from
a
under
ground
of
broadening
paper,
Pa)
2 000
iii
at.
et
higher
much
is
this
operating
Amorim
dissociative
a
In
measurements
and
Pa,
100
PHYSIQUE
DE
JOURNAL
l168
DES
low
a
measurements.
diffusive
ID
of
percentage
averaged
The
a
few
percentage
generator.
textured
Set-Up
and
feed
5
cm
diamond
of
gas is
activated
diameter
film
been
methane
were
the
in
feed
(up
gas
to
SK)
and
as
a
function
is
working
of the
presented.
are
Diagnostics
diamond
has
It
pressure.
The
introduced
density
plasma
microwave
moderated
sition.
methane
power
microwave
Experimental
2.
of
non
deposition reactor,
already presented
(0-5%)
in
by either
hydrogen,
a
1200
(loo) single crystal
placed
inside
the
W
silicon
made
of
elsewhere
silica
[12].
bell
The
conventionally
as
or
a
a
6
in
covered
by
such
way
a
for
used
kW, 2.45 GHz
wafers
plasma ball,
jar
feed
is
gas
diamond
SAIREM
a
to
under
mixture
a
depo-
microwave
polycrystalline
keep constant
un-
the
interacting system (H2 + CH4 Plasma/diamond surface).
The averaged input
the
microwave
microwave
power density defined as the input
power
over
volume of the plasma
obtained
substrate
holder (plasma ball) (in W cm~3) was
in absence of
of the
and the
changed by a
simultaneous
microwave
By changing
variation
pressure
power.
only either the power or the pressure
makes the plasma volume varying which is not desirsurface of 5
able since
diamond
deposition has to be carried out on a constant
centimeter
in
diameter.
In addition,
increase
lead eventually to
in the
at a given
an
power
can
pressure,
the
formation
of a second plasma at the top inside of the bell jar, which is also not
desirable.
of'both
and
the
plasma
volume
By a
simultaneous
well
the
variation
pressure
power,
as
as
(PMW/n)
(where
the
PMW
the
injected
total
density
is
in
W
and
power
over
power
n, the
cm3
possible,
respectively
total density, in cm~~) were kept as
and
between
constant
at 65
as
made
the plasma
volume
has been
The
relative
6 to 7 x 10~~5 W cm~/molecules.
error
on
2%,
10%,
density
around
estimated
around
that
the
the
owing
uncertainty
at
to
at
on
power
(injected and reflected powers are measured only by the
the injected
constructor
on
power
power-meters). The absorbed power is not known, however, according to Grotjohn et at. [14],
Since the plasma volume is kept constant,
it should be close to the net injected
at a
power.
measured
always
given axial location in the plasma, the averaged line-of-sight intensities
are
with the
plasma volume. The power was varied from 400 W to 2 400 W, and the pressure
same
from 800 Pa to 14 000 Pa. The
density was varied from 4.5 W cm~~ to 37 W cm~~
power
density,
Depending on the plasma conditions, in particular the averaged microwave
power
used
the
substrate
heating or cooling of the substrate
holder
maintain
to
temperature
was
conmeasured by a
bichromatic
stant
at the chosen
temperature (900 C for this study), which was
°
pyrometer.
GROUND
N°9
STATE
AND
STATE
EXCITED
TEMPERATURES
H-ATOM
excimer
n=3
656
laser
rim
Balmer
r~=2
l169
a
dye laser
llh B
2
photons
205
nm
615
nm
doubler
KDP
307.5
615
nm
nm
BBO
mixer
205 nm
focalisation
window
filter
PM
boxcar
BaJmer
u
micro
computer
~~~~~~ave
Fig.
Two
I.
Two
2.I.
induced
with
photons
PHOTON
U.V.
two
obtain
to
The
axial
system
(Xecl) emitting
and
of
L.I.F.
an
frequency
Transition
Laser
Induced
(TALIF).
TECHNIQUE
(TALIF) [5, 6,13]
fluorescence
measurements
Fluorescence
Two
were
(TALIF)
photons
conducted
experimental
block.
transition
laser
allowed
in
the
reactor
equipped
of 205 nm light. The whole
windows allowing
transmission
reactor
vertically and horizontally with respect to the laser beam in order
radial profiles. The spatial
resolution is
estimated
at 0.5
mm.
of a pulsed
laser
consists
excimer
to
generate the light at about 205 nm
of
This
dye
laser
tunable
oscillator
308 nm.
excimer
composed
a
pumps
a
grade
accurately
was
Allowed
reactor
silica
translated
and
used
at
amplifier.
With
rhodamine
B
an
intense
beam
is
obtained
at
615
nm
which
is
crystal to give 307.5 nm.
Mixing with the residual
beam at
crystal, produces the 205 nm beam, with a repetition rate of10 Hz and a
615 nm in a BBC
pulse duration of about 25 ns, the energy by pulse and the linewidth
typically of 50 ~IJ and
are
respectively. The whole laser system is computer
controlled
0.0025
and allows wavelength
nm
In our
scanning over a few nm.
experiment a scan of 0.030 nm is sufficient to cover the
obtained
with a laser wavelength varying from
line profile with 90 steps.
The profile line is
fluorescence
light is collected at 90° to the laser beam by two
205.095
The
205.065
to
nm
nm.
filter centered
lenses and
detected directly by a photomultiplier in front of which an
interference
used
eliminate
scattered
light.
resulting
is
laser
The
signal is proceeded by a
to
at 656.5
nm
fluorescence
signal is averaged over
boxcar
The
integrator and sent to a personal computer.
for
laser
each
wavelength
thus
takes
about
A block diagram
shots
20
3 minutes.
step,
a
scan
experimental
of the
Under
the
experimental
conditions, the
set-up is presented in Figure 1.
doubled
in
a
KDP
JOURNAL
l170
PHYSIQUE
DE
f~~
1-o
,,'
III
N°9
~
,
~
/
0.8
,
~±
;
~
_
~
~~
£
~
iF
ji
0.4
j
_
+
+
H~
~4
>,
+
+
0.2
+
p
j
+~
~%
4%
o-O
205.085
Example
2.
of
Doppler
a
broadened
TALIF
two-photon line profile (Fig. 2)
related
is directly
to the
observed
is
half-maximum
their
to
205.095
wavelengfl~ (urn)
Lmer
Fig.
205.OW
signal.
Fluorescence
Doppler broadening
translational
dominated.
of the
temperature
full-width
Its
and
atoms,
its
at
area
concentration.
As atomic hydrogen is the lightest atom, the Doppler broadening
Temperature.
and
advantageous for temperature
particularly
large,
this is therefore
is
measurements
from line profiles. By measuring the Doppler
AID (full width at half maximum,
linewidth
FWHM) of the fluorescence
profile, the H-atom
be
determined
excitation
temperature
can
Width
and
line
using the
formula:
~~~
lo
where
c
is
the
We
in
estimate
doubled
the
air).
A
TALIF
and
have
the
12S
value
@=
c
m
speed of light, k the
of the
temperature
~
-
of
and
atom
been
mass
x
constant,
of the atom
0.0057
nm
is
obtained
Therefore,
the
for AID
varying
are
line
from
of the
profile
For
1400
order
is
~
10~~
(l)
M
m
is the
in
AMU.
magnitude of A~D by applying equation
325(2D) H atom transition, I-e- for lo
measurements,
pressure
collisional
broadening, which
neglected.
Boltzmann
M is the
I-e-
the
7.16
=
the
to 5
(I)
to
205.14
"
of the
mass
the H
nm
experimental
200
Pa, the
atom
in
atom,
at
vacuum
conditions
atomic
fine
of 0.000 IS nm for the
transition
considered
Gaussian.
as a
pure
T is the
1500
K for
(205.082
used
for
structure
involved,
By fitting
GROUND
N°9
experimental
the
AND
STATE
profile
with
obtained
we
four
directly
is
the
to
-41n
bexp
+
l171
~°
(2)
(~~ ~~
2
(a, b, lo, AIR), where AIR
Doppler broadening, AID,
parameters
related
a
=
TEMPERATURES
H-ATOM
STATE
profile,
Gaussian
a
f(I)
AIR
EXCITED
resulting
the
is
and
to
the
signal FWHM.
width, AIL, by the
LIF
laser
relation:
AlR2
We
obtain
then
can
(laser width)
and
Owing
ducibility
to
is
0.0025
1800
with
of AIL
determination
For the
temperature.
hydrogen source
atomic
temperature
a
room
obtained.
was
blazed
K,
+250
Jobin
A
the
cooling system
THR
Yvon
equipped with
and
nm
from
measurements
long-term
repro-
2 000 K.
at
(OES).
450
at
effect
Pelletier
in the
error
SPECTROSCOPY
grating,
a
(3)
AlL2
+
H-atom
measurements
EmissioN
groves per
mm
R 3896) and
matsu
nm
the
estimate
experimental difficulties, the
quite large, it is estimated at
OPTICAL
2.2.
a
we
of
value
a
AID and
performed
AlD2
=
1000
mounted
photomultiplier
a
with
(Hama-
(with spectrometer slits of
(0.005 nm), making possible mea-
allowed
us
(1.5 ~lm)) to reach a resolution of around 5 pm
of Doppler broadening on H atoms
during the radiative decay from the n
3 to
fluorescence
from the plasma was
collected by a one
line (H~).
The light emitted
2
n
millimeter
optical collimator and transported via an optical fiber to the
slit of the
entrance
cylinder of
monochromator.
This
device
enables a spatial
resolution
in the plasma
emissive
mounted
controlled
approximately 2 mm in diameter.
The optical system
computer
on
was
a
profiles, averaged
moving table, allowing axial and radial
Emission
intensities
measurements.
the line-of-sight, were
measured
reactor.
at 90° to the axis of the
on
The Doppler
broadened
peak is a Gaussian and its FWHM is given by equation (1). Owing
500
1
nm
surements
=
=
the
to
finite
resolution
spectrometer
and
determined
was
found
We
using
laser.
the
using
Al~p~,sys~_
He-Ne
a
of
a
6.5
=
This
low
pm
Owing
the
spectrometer,
function.
response
to
latter
has
fine
which
structure
According
is
a
was
of
convolution
approximated
lamp (the natural
mercury
pressure
(0.0065 nm),
the
peak
been
confirmed
of the Ha line,
a
to
a
the
line
Gaussian
with
the
function,
broadening is known).
by a
measurement
systematic decomposition
later
R0pcke et at. [7], Vetterh0ffer
et at. [8] and
Condon et at. [15], the
has been decomposed in 7 Gaussian
functions.
For each of
spectrum
the FiVHM
obtained
after
the
substracting the optical system broadening.
components,
was
The range of experimental
studied by DES is relatively large, in particular the
conditions
Stark
and
broadening have
from 800 Pa to 14 000 Pa, and
both
varies
pressure
pressure
of
the
result
of the
been taken into
Then, the FWHM
each
Gaussian
account.
component is
Stark
broadening.
Doppler broadening, the Lorentzian
broadening
and
the
Lorentzian
pressure
According to ill,16,17], in hydrogen plasma, the pressure broadening is given by:
of
the
spectrum
be
must
Alp
done.
to
~~"/~~j~~~~/~~
=
=
l.54
x
10~~l(naH«/H~
(~)
~~~
(4a)
/t
where
n
is
aH~ /u~ the
and H2 (in
molecular
density (in m~3), vu~
velocity between H and H2,
mean
/u~ the relative
quenching cross section of H~ by H2 molecules (in m2), /t the reduced
of H
mass
g), and Tg the gas temperature. Alp is given in m. Owing to the dissociation of
hydrogen, the quenching term due to the collisions of H~ atoms with ground state
the
total
JOURNAL
1172
656.22
656.24
656.26
656.28
656.3
Experimental
H
in 7
atoms
is
shown.
also
be
taken
must
~~P
Doppler
features
~.~~
~
~°
=
estimated
literature
less
than
The
Wiese
into
section
xH,
(4)
relation
The
of H
mass
the
and
mole
H-atom
by H2
656.34
transition
XH)?Ha/H2(/~H/H2)
reduced
of Ho
ii 9].
(~
N°9
656.32
of H«
spectrum
account.
~~("(~g)~~~
where /tu /u~
represents the
I), and
of H and H (/tu /u
quenching cross
and
Prepperneau
broadened
III
656.36
656.38
Wavelengfl~ (mn)
Enfission
Fig. 3.
position
PHYSIQUE
DE
The
decom-
becomes:
~~~
+
XH?H~/H(/~H/H)
~~j
2/3), /tu /u the reduced
H2 (ILH/H~
fraction
determined
experimentally [13].
"
(au~
molecules
by OES.
obtained
has
/u~
been
taken
from
Bittner
et al.
(4b)
mass
The
[18]
quenching cross section of H~ by H atoms (aH~ /H) have been
12
hard
sphere model and taking the diameter
from
the
using
section
at 18
cross
probably
value.
Alp
has
been
This
value
however
evaluated
is
[20, 21j.
at
upper
an
the operating
used here.
conditions
I pm (0.001 nm) over
from the expression given by
contribution
of the Stark
broadening has been
estimated
et at.
The
[15]:
AIS
"
5
X
10~~O[%j/~
density (in cm~3), at is depending
anj Als is given
for the H~ line) [22]
(5)
the principal quantum
number
Angstrom. Over the conditions
similar
relationship for
used here, ~hls has been
estimated
at up to 1.5 pm (0.0015 nm). A
10~~°on(/~)
(Als
with
Stark
coefficient,
A~s is given by Griem [23, 24]
2.507 x
equal
a, the
0.00969.
With this relationship, the Stark broadening is lowered by a factor 3.75 compared
to
provided by the Wiese relationship.
to that
broadened peak corresponding to the Ha emission is given in Figure 3,
An experimental
where
(we
n~ is
took
ai
the
=
electron
0.018
on
in
"
where
of the
were
decomposition of the spectrum
contribution
approximately
Gaussian
the
subtracted
in
order
Doppler broadening can
of the optical system,
to
also
and
determine
be
the
the
with
of the
the H~
determined
Lorentzian
seven
temperature
by
features
optical system,
the
from
subtraction
contributions
of
is
shown.
the
After
Lorentzian
subtraction
contributions
Doppler broadening [25].
of the
pressure
Gaussian
broadening
The
contribution
and
Stark
N°9
GROUND
Table I.
Catcutated
STATE
averaged injected
density
power
(~~/
(Pa)
power
(pm)
Astark
(after Wiese)
1.31
1.08
0.287
0.136
1.18
1.00
0.268
0.200
15.3
5
200
1 000
1.24
1.04
0.277
0.368
22.9
8 500
500
1.46
1.16
0.309
0.501
1
33.6
10
000
2 200
2.06
1.46
0.389
0.493
36.6
14
000
2 400
2.07
1.46
0.390
0.655
following approximated
the
each
For
and
of
has
been
value
mathematical
available
OF
width, A~L the
date.
to
calculations
indicate
that
made
DENSITY.
the
absorbed
the
methane, (it) the
methane
added
increased
was
considered
of the
3.
argon
Results
3.I.
to
(H~, Hp, H6
atoms
be
in
up
as
a
dients
are
axial
to
the
20
has
Pa),
mm
to
a
been
distribution
assuming
when
estimated
a
by
plasma,
the
Maxwellian.
for
the
as
made
error
is
Max~&>ell
flow
variation
The
absorbed
function
not
was
diffusive
density
substrate.
effectively
power
Maxwell
35%
H2 Plasma
electron
the
distribution
energy
assuming
calculated
from
density (ne)
electron
dimensional
would
temperature
width).
and
Recent
electron
energy,
distribution.
The
at 10$io.
constant,
at
variation
the
from
of the
least
in
emission
concluded
we
first
intensity depends only
of
ratios
observed, and
approximation.
on
the
the
As
electron
of
intensities
that
difserent
the
consequence,
a
lines
temperature
electron
of H
can
variation
density.
Discussion
and
distance
was
emission
(TH)
attributed
estimated
SK, no
H~)
and
a
VARIATIONS
peratures
and
broad-
of the
variation
electron
density as a function of
(I) the electron density calculated in absence of
of the argon
variation
emission
intensity as a function of the percentage of
the feed gas (Fig. 4). As a
of fact, as the
matter
percentage of methane
At 9 W
at
power
2 500
cm~~ (600 W and
methane
percentage was
gives the
I
20
by
of real
The
the 1
at
without
out
from
calculated
electron
the
overestimated
is
n~
on
that
carried
[27]
mainly
is
assumption
determination
The
ELECTRON
THE
density
power
density
electron
the
to
error
the
optical system
and
line-of-sight signals (amplitude
experimentally. It was
estimated
developed at the laboratory. Table
of
(Stark
contributions
(Doppler
Ha-atom
recorded (each in 3
9 spectra
temperature,
were
calculated.
The
the absolute
temperature
was
error
on
10% [26]. Note that only line-of-sight averaged
around
at
accessible
function
(6)
Lorentzian
contributions
Gaussian
of the
treatment
DETERMINATION
2
A~[)
+
for the
estimated
are
~
~
(~)~
+
measured
measurement
averaged
an
relationship ii?]
~~~
=
AIG the
and
temperature
a
the
represents
broadenings)
the
(pm)
600
measurement
and
Apressure
400
H~-atom
on
Astark (pm)
(after Griem)
500
enings).
minutes),
a
density.
power
1 400
A~m~s
model
l173
2
pressure
2.3.
averaged
the
(10~~ cm~~)
n
(W)
A~m~s
need
function of
a
TEMPERATURES
H-ATOM
9.2
broadening using
where
as
STATE
injected
pressure
6
density
etectron
~-3)
~
EXCITED
AND
As
were
of 20 to
FUNCTION
A
measured
25
mm
as
a
from
negligible [6,10,12,13].
OF
THE
function
the
This
METHANE
of the CH4
substrate,
diamond
region
is
defined
The
PERCENTAGE.
introduced
Percentage
as
in
the
a
region
bulk
where
of the
H-atom
in the
the
feed
axial
tem-
gas
gra-
plasma (plasma
JOURNAL
1174
DE
PHYSIQUE
III
N°9
I
o
,
o
,
o,9
~
~
i
0,8
j
0,7
I
i~
(
0,6
$ O,5
0,4
0
2
3
5
4
6
pementogeofmethane(%)
Fig.
Variation
4.
of
function
a
W, 2500
600
substrate
volume)
of the
low
of
Pa,
9 W
(in
the
bulk
in
contrast
of CH4
cm~~,
300
intensity of argon (~
containing I$lo argon.
line-of-sight emission
hydrogen plasma
a
Ts
sccm,
=
plasma/surface
the
to
in
900
°C.
Measurements
made
are
nm)
750.3
=
Plasma
20
at
a
as
conditions:
mm
from
the
plasma).
of the
boundary layers.
thermal
temperatures
averaged
the
percentage
(TRH2(X))
The
interface
temperatures
are
previously by CARS
measured
at
location [12,13].
Whatever
(9 W cm~~) and at the same
equal to TRH2(X), that is to the gas kinetic
temperature.
around 2 150 K (Fig. 5).
remains
constant
to 5%, it
at
measured by TALIF
scattered
than TRH2(X).
are
more
gradients are
characteristics
compared to the H2(X) rotational
the
averaged power density
same
the
percentage of methane, TH is
strong
where
TH
As the
Note
that
the
from 0
increases
percentage
H-atom
temperatures
"line-of-sight averaged Ha-atom temperature", can be deduced from the experimental
(measured by DES) assuming first that the broadening is only Doppler
FWHM
dominated.
In the bulk of the plasma (at 20
far from the
substrate
holder), it (Tu~
mm
without corrections) is rather
function of the percentage of methane
introduced
constant
as a
in the feed gas (Fig. 6). It is around
150 K to 200 K higher than the gas
Using
temperature.
relations (4b) and (5), we can
contributions
the
of the
and Stark broadenings
estimate
pressure
H~-FWHM. The corrected
to the
temperatures (Tu~ pressure and Stark effects corrected) are
The
Ha
peak
reported
the
as
in
Gas
taking
into
conditions.
the
Figure
percentage
temperature
pressure
account
Note
Tu~
6.
of
is
equal
methane
then
can
for
that,
contribution.
be
the
at
to
the
and
temperature
gas
is varying up to 5$io
introduced
pressure
this
from
deduced
pressure
and
(2
Stark
500
measurement
effect
Pa),
the
remains
at
(within
the
the
of the H~ line
broadenings,
Stark
under
contribution
value
of 2 200 K
error).
experimental
broadening,
these
is
when
experimental
almost
10
times
GROUND
N°9
STATE
STATE
EXCITED
AND
TEMPERATURES
H-ATOM
l175
3000
TH(K) (TALIF)
TRH2(X) (CARS)
D
.
~~~~
~
2500
~
~s
~i
~
~
2250
ii
e
D
~
~
~
D
2°°°
nz
D
D
.
.
D
D
D
n~
j~~~
isoo
0
percentage of
Fig.
as
from
substrate,
the
function
a
cm~~,
9 W
300
of TH,
As
at
a
=
rotational
900
volume
mm
of
in
the
and
feed
plasma).
the
gas
gas,
Plasma
H-atom
measured
temperature
20
at
conditions:
600
to
W,
25
2500
TH
mm
Pa,
°C.
from
density are
power density
(bulk
feed
(CARS) [2,3]
methane
of
5
4
in the
methane
temperature
percentage
FUNCTION
A
25
IX)
low
plasma
the
Ts
sccm,
measured
of
in
VARIATIONS
3.2.
of the H2
Variations
5.
(TALIF)
3
2
the
OF
MICROWAVE
THE
(bulk
substrate
presented
Figure
of the
POWER
DENSITY.
plasma),
as
The
function
a
variations
of the
averaged
TH increases from 1550 +180 K to 2600 +
from 6 to 15 W cm~~. The
of TH is compared
300 K as the
increases
variation
calculated
kinetic
using the ID diffusive non equilibrium H2
to that of the gas
temperature,
plasma model [10,11), which is reported in Figure 7. There is a very good agreement between
the
measured
and the
calculated
densities
where TH
temperatures, for the range of power
gas
microwave
power
(<
measured
was
plasma
the
15 W
cm~~).
only Doppler
is
At 30 W
cm~~,
7.
the
calculated
gas
temperature
in
the
bulk
of
3 100 K.
"line-of-sight averaged
The
ening
reaches
in
temperature",
Ha-atom
dominated
(TH~
deduced
corrections)
without
assuming first
varies
from
that
1680
the
+170
broadK
to
density varies from 4.5 to almost 37 W cm~3 (Fig. 8) (meaas
power
far from the
holder). The higher the
sured in the bulk of the plasma at 20 mm
substrate
density, the higher the difference
corrections"
and the calcubetween
TH~ without
power
lated gas
Taking into account for the pressure and Stark effects, TH~ varies
temperature.
from 1610 K +150 K to around 3 600 K + 350 K as the power density
from 4.5 to
increases
3
900 +
400
K
the
"
(Fig. 8). TH~ is almost
cm~~, while it seems
density. At 37 W cm~~, the
37 W cm~~
identical
to
the
gas
temperature
for
power
densities
up
to
Tg for higher values of the
value of measured TH~ (taking
for the
lower limit
account
power
bar) is 100 K higher than the calculated Tg. However, owing to the 10% error made on
error
the power density, when considering the
bars, we can conclude that Tg is still within the
error
around
TH~
25
error
W
bar.
to
increase
slightly
faster
than
JOURNAL
1176
PHYSIQUE
DE
III
N°9
g
i
.
,
.
a
t
~
19oo
(CARS)
o-S
-0.5
I-S
2.5
percentage
Fig.
Variations
6.
measured
feed
from
H2(X)
of
Measurements
gas.
rotational
IDES)
broadening
line
as
carried
are
out
of
3.5
methane
of
distances
at
by
measured
temperature
function
a
percentage
the
of
S-S
4.5
(%)
20
25
to
CARS
and
methane
of
from
mm
the
fine-of-sight TH~
introduced
in
the
substrate,
in
the
the
deduced
assuming that the line
plasma volume.
temperature
TH~ (without corr.)
represents
dominated.
broadening is only Doppler
the
TH~ (with Press & Stark corr.)
represents
temperature
and Stark
Plasma
deduced
when, beyond Doppler broadening,
broadenings are
considered.
pressure
conditions:
9 W
According
elsect.
Stark
the
electrons
pm
cm~~,
pm
broadening
density
power
the
as
by
then
represent
The
values
300
sccm,
Ts
=
900
Pressure
ing
was
less
than
taken
Elsect.
seen
the
to
for
35%
when
to
upper
as
Stark
limits
of
leads
to
lower
°C.
limits
"
TH~
assuming
out
from
estimated
the
increases
from
without
corrections"
of
range
the
electron
conditions
energy
6 to
a
Maxwell
37 W
studied
indicates
by
100
here.
that
K
to
almost
Calculations
the
for
distribution
relationship
cm~~ (Tab. I).
Wiese
electron
varies
from
The
effect
200
K
as
assuming
density is
considering a Maxwellian
distribution.
100 K to
the Stark broadening effect on TH~
measurements.
lower Stark broadening effects on TH~ (50 K to 60 K).
of the Stark broadening effect on TH~
measurements.
200
K
These
plasma diamond deposition conditions,
broadenmicrowave
pressure
determination
negligible for the
of the Ha-atom
although
temperature,
broadening (using the Wiese's relationship). As the power density increased
Under
be
the
distribution
20
relationship
be
density
the
in
carried
calculations
broadening
power
lower
increases
the
Griem
can
the
is to
non-Maxwellian
overestimated
the
to
Stark
the
energy,
1.46
to
up
of this
a
Pa,
2500
DIscussIoN
3.3.
I
W,
600
non
GROUND
N°9
STATE
EXCITED
AND
STATE
H-ATOM
TEMPERATURES
1177
35~U
a
3~XY~
a
~
.
25~u
i
f
,
~
[
5~U
acalculatedTg-20mm/subst.
1Yu
O
emi~y
r+3)
ower
Fig.
Variations
7.
of
H-atom
performed
all
are
in
plasma
the
(the
from 9 to 34 W cm~~
ening
a
to
seen
was
lowering of
the
vary
"
TH~
0.14
without
kinetic
gas
function
a
(bulk)
volume
pressure
from
TH (measured by TALIF), H2 IX)
temperature
(measured by CARS), and
calculated
model), in a pure hydrogen plasma, as
20
a1D
averaged injected
of the
at
(with
temperature
to
25
mm
from
the
rotational
H2
diffusive
density.
power
temperature
plasma
flow
Measurements
substrate.
from 2 500 Pa to 12 000 Pa), the
broadpressure
of
the
broadening
is
The
consequence
pressure
pm.
by 20 K to 60 K, according to the experimental
corrections"
increased
to
0.65
conditions.
Comparison
of
range
Between
Experimental
densities
power
studied
Values
here
Pa), owing
(4.5
and
W
Calculated
cm~~
to
37
Temperatures.
Over
cm~3,
pressure
W
with
the
whole
ranging
the large uncertainties,
Ha-atom
be
temperature
can
ground state H-atom
temperature and gas
temperature.
As the
and the power
density increases), all the
increase (the power
temperatures,
pressure
electronic
excited G state of hydrogen
molecules
I-e- the gas
temperature, TH~, and also the
rotational
towards a plateau.
of the
The
temperature (as shown in Ref. [6j), tend
presence
plateau is attributed to the strong thermal
which
dissociation
at
temperatures
processes
occur
of the
ranging from 3 000 K to 3 500 K, and
microwave
consume
a large part
power.
The fact that the excited
H-atoms
temperature is equal to ground state H-atom
temperature,
this range of
conditions
of the
is the
occurring under these experiover
consequence
processes
which strongly differ from the one occurring in low pressure
plasmas. Owing
mental
conditions
from
1
400
considered
Pa
as
to
in
14
000
equilibrium
with
both
to
JOURNAL
1178
PHYSIQUE
DE
III
N°9
4tx~
35~U
a
31XYl
#
~
)i~
21XYl
TH«withoutconecfion
TH«with
15tXl
Tgcalculawd
11XYl
5
0
Averaged
Fig.
calculated
of
Variations
8.
fine-of-sight TH~
density. The
power
kinetic
gas
40
35
30
25
20
15
10
density (W cm-3)
power
(with
temperature
broadening by OES
a
diffusive
ID
H2 plasma flow model),
the averaged injected
(bulk).
volume
plasma
TH~ (without corr.)
are
deduced assuming that the line broadening is only Doppler
dominated.
represents the temperature
TH~
(with Press & Stark corr.)
the
deduced
when, beyond Doppler broadening,
temperature
represents
and
pressure
to
the
and
rather
Stark
low
measured
from
line
carried
measurements
broadenings
ii
to 2
terizing diamond deposition conditions, the
produced by thermal
of molecular
dissociation
around 100 Pa, it
through
electron
at
occurs
reactor,
the
the
ground
consequence
H atoms
state
high
energy
the
atoms
is that
by
in
function
a
of
the
considered.
are
temperature
electron
out
as
~he
n
collisions
=
3
with
eV)
main
and
part
to
of H
the
atoms
hydrogen while,
collisions
excited
H
electrons.
high
in
with H2
charactemperatures
gas
formed in these
is
reactors
microwave
molecules
plasma operating
[1,4].
In
diamond
mainly populated directly from
are
addition, the high collisional frequency
atoms
In
and atoms, and to a thermal
equilibrium
Also the production
ground electronic
states.
of some
hot H~
by strongly energetic repulsive
dissociative
excitation
atonls
very
processes
(threshold at around 27 eV) [28, 29] is unrealistic in these plasmas. In addition, the higher the
the less the
of both direct
contributions
electron
dissociation
and
dissociative
impact
pressure,
(calculations [10, Ill ).
mechanism, owing to the decrease in the electron
excitation
temperature
lead to
between
transfer
and
the
rates
between
molecules
in
molecules
their
Although, over the whole range of experimental
conditions
studied here, TH~ can
densities higher than 25 W cm~~, TH~ was
to
as equal to Tg, for
power
seen
slightly faster than the calculated Tg.
Uncertainties
calculated
in the
temperatures
gas
sidered
be
con-
increase
might
GROUND
N°9
STATE
STATE
EXCITED
AND
TEMPERATURES
H-ATOM
1179
models.
made for building the
assumptions
diffusive flow to
to couple the H2 plasma
ii) the Boltzmann equation for the electrons, iii) the Maxwell equations for knowing the exact
of the electromagnetic field, (iii) the
Navier-Stokes
distribution
equations for taking into acbe
also
models
for the
count
They can be attributed
being improved today
are
invoked.
Plasma
Further
might
which
convection
temperatures
measurements
to
the
in
order
be
important
are
also
still
power density (natural
in the laboratory.
progress
high
at
in
convection).
Conclusion
4.
typical
Under
ground
in
and
of
used for
conditions
and in the
state
=
state
(Ha
respectively. They have been compared
molecular
hydrogen measured by CARS under
calculated
with
Line-of-sight averaged
deposition
diamond
diffusive
Ha-atom
conditions,
Although
FWHM.
ID
a
temperatures
Doppler,
contribution
the
model
have
we
from
DES
temperature
the
n
deposition,
diamond
excited
3
the
to
measured
H-atom
temperature
Doppler broadening, using TALIF
ground state
rotational
temperature
the
conditions, and to the gas kinetic
same
developed for a non-equilibrium H2 plasma.
(TH~), measured by DES, showed that, under
the
Stark broadenings
broadening on TH~
and
pressure
of the
Stark
are
is
contributing
higher than
to
the
contribution, its importance differs from an author to another.
Owing to the uncertainties,
the
Ha-atom
rather in
thermal
temperature
to be
seen
was
equilibrium with the ground state H-atom
and with the ground
electronic
state
temperature
molecules
be
rotational
strongly
temperature (gas temperature). The temperatures
to
were
seen
density and to increase from
sensitive
550 K to almost 3 200 II as the
to the
power
power
density is increased from 4.5 to 37 W cm~~ A plateau was observed after 25 W cm~~, which
pressure
has
been
attributed
of 3
ature
2150
K,
2 200
a
thermal
power
percentage
dissociation
density
of
of 9
methane
which
processes
W
up
cm~~,
to
the
5% is
efficient
very
are
temperatures
introduced
in
remain
the
feed
at
temper-
constant
as
well
necessary,
in
surements
at
gas.
probably today one of the best way for approaching
diamond
deposition
Nevertheless, further
reactors.
calculations
using more sophisticated models of Ha-atom
temperature
as
particular at high power
densities.
of TH~
constitutes
temperature by DES in
kinetic
still
a
as
Measurements
gas
the
to
At
K.
100
the
meaare
Acknowledgments
This
work
thanked
was
the
for
TALIF
financially
CARS
measurements
partially by
supported
measurements,
and
Antoine
DRET.
Jean-Christophe
Rousseau
Michel
CNRS-ORSAY
from
Lefebvre
Cubertafon
for
for
from
its
helpful
ONERA
contribution
is
to
discussions.
References
iii
de
Amorim
Filho
[2)
de
Amorim
Filho
J., J. Appl. Phys. 76 (1994) 1487-1493.
d'orsay (Paris XI, 1994).
J., PhD thesis, Universit4
Chem.
[3) Dunlop J-R-, Tserepi A-D-, Preppemeau B-L-, Cerny T-M- and Miller T-A-, Plasma
Plasma
Process.
Prepperneau B-L-, Optical diagnostics in a diamond
12 (1992) 89-101;
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Tomasini L., Rousseau A., Gousset G. and Leprince P., J. Phys. D: Appl. Phys. 29 (1996)
[4)
1-8.
[5)
Chenevier
(1994)
M.,
587-592.
Cubertafon
J-C-,
Campargue
A.
and
Booth
J-P-,
Diam.
Ret.
Mater.
3
JOURNAL
1180
[6)
PHYSIQUE
DE
N°9
III
Gicquel A., Chenevier M., Hassouni K., Breton Y. and Cubertafon J.C., Dram. Ret. Mater.
(1996) 366-372.
Plasma Physics 34 (1994) 575-586; Ito K., Oda N.,
R6pcke J. and Ohl A., Contributed
Hatano Y. and
Tsuboi T., Chem. Phys. 17 (1976) 35-43.
Vetterh6ffer
J., Campargue A., Stoeckel F. and Chenevier M., Dram. Ret. Mater. 2 (1993)
5
[7)
[8)
481-485.
Stiegler J.,
[9j Lang T.,
lished.
Kaenel
Von
Y.
E.,
Blank
and
Dram.
Ret.
Mater.
(1996)
to
be
pub-
S., Scott C. and Gicquel A., J. Phys. III France 6 (1996) 1229.
C. and
Farhat
S., Chapter "Modelling and diagnostics in plasfor
mas"
Section
Handbook
Industrial
Diamonds
and
Films, M. Prelas,
7.IDiamond
G. Popovicci and K. Bigelow Eds., to be published (1996).
[12j Gicquel A., Hassouni K., Farhat S., Breton Y., Scott C-D-, Lefebvre M. and Pealat M.,
[10j
Hassouni
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