Nucleation and Growth Processes During the Chemical Vapor Deposition of Diamond
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Mat. Res. Soc. Symp. Proc. Vol. 363 01995 Materials Research Society
Input Gas
Figure 1. Hot-filament microbalance reactor. The reactor is an 80 liter stainless steel bell jar. The microbalance is a Cahn DTantalum Filament 200 with a practical sensitivity of 0.2 gg at reaction conditions. The Viewport filament was a hairpin shaped, 0.5 mm diameter fully carburized tantalum Sample wire. The filament to substrate distance was approximately 15 mm. Other details are given by Wang and Angus [19] and Evans [23].
•
Thermocouple Probe
Stainless Steel Chamber
?q
Pumpdown Line
1 .2
+ 1 st order reaction
"L.
mmethane. a
0.9C" 0.9 -%% C
E
/substrate go -
ca 4-0
¾
0 0.3
4
*
U
0. 1% 0, added 0.3% 0, added 0.5% 02 added
0.0 0.0
0.5
1.0
1.5
2.0
Methane (%)
128
2.5
3.0
Figure 2. Growth rate of diamond versus percent Filament temperature was approximately 2300C and temperature 80OC; the pressure was 20 torr. The reaction order shifts from first-order to zero-order at higher methane concentrations. Line indicates first-order growth kinetics.
1.0 0 7:
o%
E
I
L Figure 3. Growth rate of diamond versus methane shown in a log-log Splot. Note the first-order behavior
*-0
2-
and approach to zero order at Filament higher concentrations. 4) temperature was approximately 2600C and substrate temperature S1000C; the pressure was 30 torr.
0.000
.)
at concentrations below 1% CH 4
00 0.10
-
irTFI
11rJ 1.00
0.6 Slope ,
E 0
Figure 4. Growth of diamond versus percent ethane. Filament was temperature approximately 2600C and temperature 850C. The pressure was 20 torr. The slope of the line indicates a reaction order of 0.59. The fall-off at lower concentrations is believed to arise from mass transfer effects [19].
0.59
•substrate 0.1
0L,.
0.01 0.07 0.1
1
Ethane (%)
129
SIncreasing Deposition
Figure 5. Growth rate of diamond vs. percent acetylene. Conditions were the same as given in Fig. 4 except for filament temperature which was increased approximately 500C intervals. slope of the line is approximately 0.59. Fall off to higher slopes at low concentrations is believed to be a mass transfer effect [19].
T
X +
E
+in S
"+
,,The
"
+ 0
0.1
U
C 0.05 1 . 0.06
Slope = 0.59
.. 0.1
. .
.
1
Acetylene (%)
C *
0.52
Proportional to growth rate
Figure 6.
Growth rate Inmgs/hr
on a temary C/H/O diagram. Circle diameters are proportional to the diamond growth rate. The numbers refer to absolute growth
H2/CO Tie Line
- -
98.5
rates in mg/hr. For the substrate sizes used, 1 mg/hr corresponds to approximately 3gtm per hour. The dashed line corresponds to the H2/CO tie line.
99/
919.5
OS
'
'
4'
N
-
H2
OTie L
100H
H
99.5
99
Growth rates plotted
0
98.50
130
Rate data taken using two-carbon source gases are shown in Figs. 4 and 5. Note that at moderate concentrations, the growth rate is approximately half-order in source gas concentration. Half-order growth kinetics have been observed much earlier with ethylene in a purely thermal reactor [15] and with ethane, ethylene,
